postmaster.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * postmaster.c
 *    This program acts as a clearing house for requests to the
 *    POSTGRES system.  Frontend programs send a startup message
 *    to the Postmaster and the postmaster uses the info in the
 *    message to setup a backend process.
 *
 *    The postmaster also manages system-wide operations such as
 *    startup and shutdown. The postmaster itself doesn't do those
 *    operations, mind you --- it just forks off a subprocess to do them
 *    at the right times.  It also takes care of resetting the system
 *    if a backend crashes.
 *
 *    The postmaster process creates the shared memory and semaphore
 *    pools during startup, but as a rule does not touch them itself.
 *    In particular, it is not a member of the PGPROC array of backends
 *    and so it cannot participate in lock-manager operations.  Keeping
 *    the postmaster away from shared memory operations makes it simpler
 *    and more reliable.  The postmaster is almost always able to recover
 *    from crashes of individual backends by resetting shared memory;
 *    if it did much with shared memory then it would be prone to crashing
 *    along with the backends.
 *
 *    When a request message is received, we now fork() immediately.
 *    The child process performs authentication of the request, and
 *    then becomes a backend if successful.  This allows the auth code
 *    to be written in a simple single-threaded style (as opposed to the
 *    crufty "poor man's multitasking" code that used to be needed).
 *    More importantly, it ensures that blockages in non-multithreaded
 *    libraries like SSL or PAM cannot cause denial of service to other
 *    clients.
 *
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/postmaster/postmaster.c
 *
 * NOTES
 *
 * Initialization:
 *      The Postmaster sets up shared memory data structures
 *      for the backends.
 *
 * Synchronization:
 *      The Postmaster shares memory with the backends but should avoid
 *      touching shared memory, so as not to become stuck if a crashing
 *      backend screws up locks or shared memory.  Likewise, the Postmaster
 *      should never block on messages from frontend clients.
 *
 * Garbage Collection:
 *      The Postmaster cleans up after backends if they have an emergency
 *      exit and/or core dump.
 *
 * Error Reporting:
 *      Use write_stderr() only for reporting "interactive" errors
 *      (essentially, bogus arguments on the command line).  Once the
 *      postmaster is launched, use ereport().
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <unistd.h>
#include <signal.h>
#include <time.h>
#include <sys/wait.h>
#include <ctype.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <fcntl.h>
#include <sys/param.h>
#include <netdb.h>
#include <limits.h>

#ifdef HAVE_SYS_SELECT_H
#include <sys/select.h>
#endif

#ifdef USE_BONJOUR
#include <dns_sd.h>
#endif

#ifdef USE_SYSTEMD
#include <systemd/sd-daemon.h>
#endif

#ifdef HAVE_PTHREAD_IS_THREADED_NP
#include <pthread.h>
#endif

#include "access/transam.h"
#include "access/xlog.h"
#include "bootstrap/bootstrap.h"
#include "catalog/pg_control.h"
#include "common/file_perm.h"
#include "common/ip.h"
#include "common/string.h"
#include "lib/ilist.h"
#include "libpq/auth.h"
#include "libpq/libpq.h"
#include "libpq/pqformat.h"
#include "libpq/pqsignal.h"
#include "miscadmin.h"
#include "pg_getopt.h"
#include "pgstat.h"
#include "port/pg_bswap.h"
#include "postmaster/autovacuum.h"
#include "postmaster/bgworker_internals.h"
#include "postmaster/fork_process.h"
#include "postmaster/interrupt.h"
#include "postmaster/pgarch.h"
#include "postmaster/postmaster.h"
#include "postmaster/syslogger.h"
#include "replication/logicallauncher.h"
#include "replication/walsender.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/pg_shmem.h"
#include "storage/pmsignal.h"
#include "storage/proc.h"
#include "tcop/tcopprot.h"
#include "utils/builtins.h"
#include "utils/datetime.h"
#include "utils/memutils.h"
#include "utils/pidfile.h"
#include "utils/ps_status.h"
#include "utils/timeout.h"
#include "utils/timestamp.h"
#include "utils/varlena.h"

#ifdef EXEC_BACKEND
#include "storage/spin.h"
#endif


/*
 * Possible types of a backend. Beyond being the possible bkend_type values in
 * struct bkend, these are OR-able request flag bits for SignalSomeChildren()
 * and CountChildren().
 */
#define BACKEND_TYPE_NORMAL     0x0001  /* normal backend */
#define BACKEND_TYPE_AUTOVAC    0x0002  /* autovacuum worker process */
#define BACKEND_TYPE_WALSND     0x0004  /* walsender process */
#define BACKEND_TYPE_BGWORKER   0x0008  /* bgworker process */
#define BACKEND_TYPE_ALL        0x000F  /* OR of all the above */

/*
 * List of active backends (or child processes anyway; we don't actually
 * know whether a given child has become a backend or is still in the
 * authorization phase).  This is used mainly to keep track of how many
 * children we have and send them appropriate signals when necessary.
 *
 * As shown in the above set of backend types, this list includes not only
 * "normal" client sessions, but also autovacuum workers, walsenders, and
 * background workers.  (Note that at the time of launch, walsenders are
 * labeled BACKEND_TYPE_NORMAL; we relabel them to BACKEND_TYPE_WALSND
 * upon noticing they've changed their PMChildFlags entry.  Hence that check
 * must be done before any operation that needs to distinguish walsenders
 * from normal backends.)
 *
 * Also, "dead_end" children are in it: these are children launched just for
 * the purpose of sending a friendly rejection message to a would-be client.
 * We must track them because they are attached to shared memory, but we know
 * they will never become live backends.  dead_end children are not assigned a
 * PMChildSlot.  dead_end children have bkend_type NORMAL.
 *
 * "Special" children such as the startup, bgwriter and autovacuum launcher
 * tasks are not in this list.  They are tracked via StartupPID and other
 * pid_t variables below.  (Thus, there can't be more than one of any given
 * "special" child process type.  We use BackendList entries for any child
 * process there can be more than one of.)
 */
typedef struct bkend
{
    pid_t       pid;            /* process id of backend */
    int32       cancel_key;     /* cancel key for cancels for this backend */
    int         child_slot;     /* PMChildSlot for this backend, if any */
    int         bkend_type;     /* child process flavor, see above */
    bool        dead_end;       /* is it going to send an error and quit? */
    bool        bgworker_notify;    /* gets bgworker start/stop notifications */
    dlist_node  elem;           /* list link in BackendList */
} Backend;

static dlist_head BackendList = DLIST_STATIC_INIT(BackendList);

#ifdef EXEC_BACKEND
static Backend *ShmemBackendArray;
#endif

BackgroundWorker *MyBgworkerEntry = NULL;



/* The socket number we are listening for connections on */
int         PostPortNumber;

/* The directory names for Unix socket(s) */
char       *Unix_socket_directories;

/* The TCP listen address(es) */
char       *ListenAddresses;

/*
 * ReservedBackends is the number of backends reserved for superuser use.
 * This number is taken out of the pool size given by MaxConnections so
 * number of backend slots available to non-superusers is
 * (MaxConnections - ReservedBackends).  Note what this really means is
 * "if there are <= ReservedBackends connections available, only superusers
 * can make new connections" --- pre-existing superuser connections don't
 * count against the limit.
 */
int         ReservedBackends;

/* The socket(s) we're listening to. */
#define MAXLISTEN   64
static pgsocket ListenSocket[MAXLISTEN];

/*
 * Set by the -o option
 */
static char ExtraOptions[MAXPGPATH];

/*
 * These globals control the behavior of the postmaster in case some
 * backend dumps core.  Normally, it kills all peers of the dead backend
 * and reinitializes shared memory.  By specifying -s or -n, we can have
 * the postmaster stop (rather than kill) peers and not reinitialize
 * shared data structures.  (Reinit is currently dead code, though.)
 */
static bool Reinit = true;
static int  SendStop = false;

/* still more option variables */
bool        EnableSSL = false;

int         PreAuthDelay = 0;
int         AuthenticationTimeout = 60;

bool        log_hostname;       /* for ps display and logging */
bool        Log_connections = false;
bool        Db_user_namespace = false;

bool        enable_bonjour = false;
char       *bonjour_name;
bool        restart_after_crash = true;

/* PIDs of special child processes; 0 when not running */
static pid_t StartupPID = 0,
            BgWriterPID = 0,
            CheckpointerPID = 0,
            WalWriterPID = 0,
            WalReceiverPID = 0,
            AutoVacPID = 0,
            PgArchPID = 0,
            PgStatPID = 0,
            SysLoggerPID = 0;

/* Startup process's status */
typedef enum
{
    STARTUP_NOT_RUNNING,
    STARTUP_RUNNING,
    STARTUP_SIGNALED,           /* we sent it a SIGQUIT or SIGKILL */
    STARTUP_CRASHED
} StartupStatusEnum;

static StartupStatusEnum StartupStatus = STARTUP_NOT_RUNNING;

/* Startup/shutdown state */
#define         NoShutdown      0
#define         SmartShutdown   1
#define         FastShutdown    2
#define         ImmediateShutdown   3

static int  Shutdown = NoShutdown;

static bool FatalError = false; /* T if recovering from backend crash */

/*
 * We use a simple state machine to control startup, shutdown, and
 * crash recovery (which is rather like shutdown followed by startup).
 *
 * After doing all the postmaster initialization work, we enter PM_STARTUP
 * state and the startup process is launched. The startup process begins by
 * reading the control file and other preliminary initialization steps.
 * In a normal startup, or after crash recovery, the startup process exits
 * with exit code 0 and we switch to PM_RUN state.  However, archive recovery
 * is handled specially since it takes much longer and we would like to support
 * hot standby during archive recovery.
 *
 * When the startup process is ready to start archive recovery, it signals the
 * postmaster, and we switch to PM_RECOVERY state. The background writer and
 * checkpointer are launched, while the startup process continues applying WAL.
 * If Hot Standby is enabled, then, after reaching a consistent point in WAL
 * redo, startup process signals us again, and we switch to PM_HOT_STANDBY
 * state and begin accepting connections to perform read-only queries.  When
 * archive recovery is finished, the startup process exits with exit code 0
 * and we switch to PM_RUN state.
 *
 * Normal child backends can only be launched when we are in PM_RUN or
 * PM_HOT_STANDBY state.  (connsAllowed can also restrict launching.)
 * In other states we handle connection requests by launching "dead_end"
 * child processes, which will simply send the client an error message and
 * quit.  (We track these in the BackendList so that we can know when they
 * are all gone; this is important because they're still connected to shared
 * memory, and would interfere with an attempt to destroy the shmem segment,
 * possibly leading to SHMALL failure when we try to make a new one.)
 * In PM_WAIT_DEAD_END state we are waiting for all the dead_end children
 * to drain out of the system, and therefore stop accepting connection
 * requests at all until the last existing child has quit (which hopefully
 * will not be very long).
 *
 * Notice that this state variable does not distinguish *why* we entered
 * states later than PM_RUN --- Shutdown and FatalError must be consulted
 * to find that out.  FatalError is never true in PM_RECOVERY, PM_HOT_STANDBY,
 * or PM_RUN states, nor in PM_SHUTDOWN states (because we don't enter those
 * states when trying to recover from a crash).  It can be true in PM_STARTUP
 * state, because we don't clear it until we've successfully started WAL redo.
 */
typedef enum
{
    PM_INIT,                    /* postmaster starting */
    PM_STARTUP,                 /* waiting for startup subprocess */
    PM_RECOVERY,                /* in archive recovery mode */
    PM_HOT_STANDBY,             /* in hot standby mode */
    PM_RUN,                     /* normal "database is alive" state */
    PM_STOP_BACKENDS,           /* need to stop remaining backends */
    PM_WAIT_BACKENDS,           /* waiting for live backends to exit */
    PM_SHUTDOWN,                /* waiting for checkpointer to do shutdown
                                 * ckpt */
    PM_SHUTDOWN_2,              /* waiting for archiver and walsenders to
                                 * finish */
    PM_WAIT_DEAD_END,           /* waiting for dead_end children to exit */
    PM_NO_CHILDREN              /* all important children have exited */
} PMState;

static PMState pmState = PM_INIT;

/*
 * While performing a "smart shutdown", we restrict new connections but stay
 * in PM_RUN or PM_HOT_STANDBY state until all the client backends are gone.
 * connsAllowed is a sub-state indicator showing the active restriction.
 * It is of no interest unless pmState is PM_RUN or PM_HOT_STANDBY.
 */
typedef enum
{
    ALLOW_ALL_CONNS,            /* normal not-shutting-down state */
    ALLOW_SUPERUSER_CONNS,      /* only superusers can connect */
    ALLOW_NO_CONNS              /* no new connections allowed, period */
} ConnsAllowedState;

static ConnsAllowedState connsAllowed = ALLOW_ALL_CONNS;

/* Start time of SIGKILL timeout during immediate shutdown or child crash */
/* Zero means timeout is not running */
static time_t AbortStartTime = 0;

/* Length of said timeout */
#define SIGKILL_CHILDREN_AFTER_SECS     5

static bool ReachedNormalRunning = false;   /* T if we've reached PM_RUN */

bool        ClientAuthInProgress = false;   /* T during new-client
                                             * authentication */

bool        redirection_done = false;   /* stderr redirected for syslogger? */

/* received START_AUTOVAC_LAUNCHER signal */
static volatile sig_atomic_t start_autovac_launcher = false;

/* the launcher needs to be signaled to communicate some condition */
static volatile bool avlauncher_needs_signal = false;

/* received START_WALRECEIVER signal */
static volatile sig_atomic_t WalReceiverRequested = false;

/* set when there's a worker that needs to be started up */
static volatile bool StartWorkerNeeded = true;
static volatile bool HaveCrashedWorker = false;

#ifdef USE_SSL
/* Set when and if SSL has been initialized properly */
static bool LoadedSSL = false;
#endif

#ifdef USE_BONJOUR
static DNSServiceRef bonjour_sdref = NULL;
#endif

/*
 * postmaster.c - function prototypes
 */
static void CloseServerPorts(int status, Datum arg);
static void unlink_external_pid_file(int status, Datum arg);
static void getInstallationPaths(const char *argv0);
static void checkControlFile(void);
static Port *ConnCreate(int serverFd);
static void ConnFree(Port *port);
static void reset_shared(void);
static void SIGHUP_handler(SIGNAL_ARGS);
static void pmdie(SIGNAL_ARGS);
static void reaper(SIGNAL_ARGS);
static void sigusr1_handler(SIGNAL_ARGS);
static void process_startup_packet_die(SIGNAL_ARGS);
static void dummy_handler(SIGNAL_ARGS);
static void StartupPacketTimeoutHandler(void);
static void CleanupBackend(int pid, int exitstatus);
static bool CleanupBackgroundWorker(int pid, int exitstatus);
static void HandleChildCrash(int pid, int exitstatus, const char *procname);
static void LogChildExit(int lev, const char *procname,
                         int pid, int exitstatus);
static void PostmasterStateMachine(void);
static void BackendInitialize(Port *port);
static void BackendRun(Port *port) pg_attribute_noreturn();
static void ExitPostmaster(int status) pg_attribute_noreturn();
static int  ServerLoop(void);
static int  BackendStartup(Port *port);
static int  ProcessStartupPacket(Port *port, bool ssl_done, bool gss_done);
static void SendNegotiateProtocolVersion(List *unrecognized_protocol_options);
static void processCancelRequest(Port *port, void *pkt);
static int  initMasks(fd_set *rmask);
static void report_fork_failure_to_client(Port *port, int errnum);
static CAC_state canAcceptConnections(int backend_type);
static bool RandomCancelKey(int32 *cancel_key);
static void signal_child(pid_t pid, int signal);
static bool SignalSomeChildren(int signal, int targets);
static void TerminateChildren(int signal);

#define SignalChildren(sig)            SignalSomeChildren(sig, BACKEND_TYPE_ALL)

static int  CountChildren(int target);
static bool assign_backendlist_entry(RegisteredBgWorker *rw);
static void maybe_start_bgworkers(void);
static bool CreateOptsFile(int argc, char *argv[], char *fullprogname);
static pid_t StartChildProcess(AuxProcType type);
static void StartAutovacuumWorker(void);
static void MaybeStartWalReceiver(void);
static void InitPostmasterDeathWatchHandle(void);

/*
 * Archiver is allowed to start up at the current postmaster state?
 *
 * If WAL archiving is enabled always, we are allowed to start archiver
 * even during recovery.
 */
#define PgArchStartupAllowed()  \
    ((XLogArchivingActive() && pmState == PM_RUN) ||    \
     (XLogArchivingAlways() &&  \
      (pmState == PM_RECOVERY || pmState == PM_HOT_STANDBY)))

#ifdef EXEC_BACKEND

#ifdef WIN32
#define WNOHANG 0               /* ignored, so any integer value will do */

static pid_t waitpid(pid_t pid, int *exitstatus, int options);
static void WINAPI pgwin32_deadchild_callback(PVOID lpParameter, BOOLEAN TimerOrWaitFired);

static HANDLE win32ChildQueue;

typedef struct
{
    HANDLE      waitHandle;
    HANDLE      procHandle;
    DWORD       procId;
} win32_deadchild_waitinfo;
#endif                          /* WIN32 */

static pid_t backend_forkexec(Port *port);
static pid_t internal_forkexec(int argc, char *argv[], Port *port);

/* Type for a socket that can be inherited to a client process */
#ifdef WIN32
typedef struct
{
    SOCKET      origsocket;     /* Original socket value, or PGINVALID_SOCKET
                                 * if not a socket */
    WSAPROTOCOL_INFO wsainfo;
} InheritableSocket;
#else
typedef int InheritableSocket;
#endif

/*
 * Structure contains all variables passed to exec:ed backends
 */
typedef struct
{
    Port        port;
    InheritableSocket portsocket;
    char        DataDir[MAXPGPATH];
    pgsocket    ListenSocket[MAXLISTEN];
    int32       MyCancelKey;
    int         MyPMChildSlot;
#ifndef WIN32
    unsigned long UsedShmemSegID;
#else
    void       *ShmemProtectiveRegion;
    HANDLE      UsedShmemSegID;
#endif
    void       *UsedShmemSegAddr;
    slock_t    *ShmemLock;
    VariableCache ShmemVariableCache;
    Backend    *ShmemBackendArray;
#ifndef HAVE_SPINLOCKS
    PGSemaphore *SpinlockSemaArray;
#endif
    int         NamedLWLockTrancheRequests;
    NamedLWLockTranche *NamedLWLockTrancheArray;
    LWLockPadded *MainLWLockArray;
    slock_t    *ProcStructLock;
    PROC_HDR   *ProcGlobal;
    PGPROC     *AuxiliaryProcs;
    PGPROC     *PreparedXactProcs;
    PMSignalData *PMSignalState;
    InheritableSocket pgStatSock;
    pid_t       PostmasterPid;
    TimestampTz PgStartTime;
    TimestampTz PgReloadTime;
    pg_time_t   first_syslogger_file_time;
    bool        redirection_done;
    bool        IsBinaryUpgrade;
    int         max_safe_fds;
    int         MaxBackends;
#ifdef WIN32
    HANDLE      PostmasterHandle;
    HANDLE      initial_signal_pipe;
    HANDLE      syslogPipe[2];
#else
    int         postmaster_alive_fds[2];
    int         syslogPipe[2];
#endif
    char        my_exec_path[MAXPGPATH];
    char        pkglib_path[MAXPGPATH];
    char        ExtraOptions[MAXPGPATH];
} BackendParameters;

static void read_backend_variables(char *id, Port *port);
static void restore_backend_variables(BackendParameters *param, Port *port);

#ifndef WIN32
static bool save_backend_variables(BackendParameters *param, Port *port);
#else
static bool save_backend_variables(BackendParameters *param, Port *port,
                                   HANDLE childProcess, pid_t childPid);
#endif

static void ShmemBackendArrayAdd(Backend *bn);
static void ShmemBackendArrayRemove(Backend *bn);
#endif                          /* EXEC_BACKEND */

#define StartupDataBase()       StartChildProcess(StartupProcess)
#define StartBackgroundWriter() StartChildProcess(BgWriterProcess)
#define StartCheckpointer()     StartChildProcess(CheckpointerProcess)
#define StartWalWriter()        StartChildProcess(WalWriterProcess)
#define StartWalReceiver()      StartChildProcess(WalReceiverProcess)

/* Macros to check exit status of a child process */
#define EXIT_STATUS_0(st)  ((st) == 0)
#define EXIT_STATUS_1(st)  (WIFEXITED(st) && WEXITSTATUS(st) == 1)
#define EXIT_STATUS_3(st)  (WIFEXITED(st) && WEXITSTATUS(st) == 3)

#ifndef WIN32
/*
 * File descriptors for pipe used to monitor if postmaster is alive.
 * First is POSTMASTER_FD_WATCH, second is POSTMASTER_FD_OWN.
 */
int         postmaster_alive_fds[2] = {-1, -1};
#else
/* Process handle of postmaster used for the same purpose on Windows */
HANDLE      PostmasterHandle;
#endif

/*
 * Postmaster main entry point
 */
void
PostmasterMain(int argc, char *argv[])
{
    int         opt;
    int         status;
    char       *userDoption = NULL;
    bool        listen_addr_saved = false;
    int         i;
    char       *output_config_variable = NULL;

    InitProcessGlobals();

    PostmasterPid = MyProcPid;

    IsPostmasterEnvironment = true;

    /*
     * We should not be creating any files or directories before we check the
     * data directory (see checkDataDir()), but just in case set the umask to
     * the most restrictive (owner-only) permissions.
     *
     * checkDataDir() will reset the umask based on the data directory
     * permissions.
     */
    umask(PG_MODE_MASK_OWNER);

    /*
     * By default, palloc() requests in the postmaster will be allocated in
     * the PostmasterContext, which is space that can be recycled by backends.
     * Allocated data that needs to be available to backends should be
     * allocated in TopMemoryContext.
     */
    PostmasterContext = AllocSetContextCreate(TopMemoryContext,
                                              "Postmaster",
                                              ALLOCSET_DEFAULT_SIZES);
    MemoryContextSwitchTo(PostmasterContext);

    /* Initialize paths to installation files */
    getInstallationPaths(argv[0]);

    /*
     * Set up signal handlers for the postmaster process.
     *
     * In the postmaster, we use pqsignal_pm() rather than pqsignal() (which
     * is used by all child processes and client processes).  That has a
     * couple of special behaviors:
     *
     * 1. Except on Windows, we tell sigaction() to block all signals for the
     * duration of the signal handler.  This is faster than our old approach
     * of blocking/unblocking explicitly in the signal handler, and it should
     * also prevent excessive stack consumption if signals arrive quickly.
     *
     * 2. We do not set the SA_RESTART flag.  This is because signals will be
     * blocked at all times except when ServerLoop is waiting for something to
     * happen, and during that window, we want signals to exit the select(2)
     * wait so that ServerLoop can respond if anything interesting happened.
     * On some platforms, signals marked SA_RESTART would not cause the
     * select() wait to end.
     *
     * Child processes will generally want SA_RESTART, so pqsignal() sets that
     * flag.  We expect children to set up their own handlers before
     * unblocking signals.
     *
     * CAUTION: when changing this list, check for side-effects on the signal
     * handling setup of child processes.  See tcop/postgres.c,
     * bootstrap/bootstrap.c, postmaster/bgwriter.c, postmaster/walwriter.c,
     * postmaster/autovacuum.c, postmaster/pgarch.c, postmaster/pgstat.c,
     * postmaster/syslogger.c, postmaster/bgworker.c and
     * postmaster/checkpointer.c.
     */
    pqinitmask();
    PG_SETMASK(&BlockSig);

    pqsignal_pm(SIGHUP, SIGHUP_handler);    /* reread config file and have
                                             * children do same */
    pqsignal_pm(SIGINT, pmdie); /* send SIGTERM and shut down */
    pqsignal_pm(SIGQUIT, pmdie);    /* send SIGQUIT and die */
    pqsignal_pm(SIGTERM, pmdie);    /* wait for children and shut down */
    pqsignal_pm(SIGALRM, SIG_IGN);  /* ignored */
    pqsignal_pm(SIGPIPE, SIG_IGN);  /* ignored */
    pqsignal_pm(SIGUSR1, sigusr1_handler);  /* message from child process */
    pqsignal_pm(SIGUSR2, dummy_handler);    /* unused, reserve for children */
    pqsignal_pm(SIGCHLD, reaper);   /* handle child termination */

    /*
     * No other place in Postgres should touch SIGTTIN/SIGTTOU handling.  We
     * ignore those signals in a postmaster environment, so that there is no
     * risk of a child process freezing up due to writing to stderr.  But for
     * a standalone backend, their default handling is reasonable.  Hence, all
     * child processes should just allow the inherited settings to stand.
     */
#ifdef SIGTTIN
    pqsignal_pm(SIGTTIN, SIG_IGN);  /* ignored */
#endif
#ifdef SIGTTOU
    pqsignal_pm(SIGTTOU, SIG_IGN);  /* ignored */
#endif

    /* ignore SIGXFSZ, so that ulimit violations work like disk full */
#ifdef SIGXFSZ
    pqsignal_pm(SIGXFSZ, SIG_IGN);  /* ignored */
#endif

    /*
     * Options setup
     */
    InitializeGUCOptions();

    opterr = 1;

    /*
     * Parse command-line options.  CAUTION: keep this in sync with
     * tcop/postgres.c (the option sets should not conflict) and with the
     * common help() function in main/main.c.
     */
    while ((opt = getopt(argc, argv, "B:bc:C:D:d:EeFf:h:ijk:lN:nOo:Pp:r:S:sTt:W:-:")) != -1)
    {
        switch (opt)
        {
            case 'B':
                SetConfigOption("shared_buffers", optarg, PGC_POSTMASTER, PGC_S_ARGV);
                break;

            case 'b':
                /* Undocumented flag used for binary upgrades */
                IsBinaryUpgrade = true;
                break;

            case 'C':
                output_config_variable = strdup(optarg);
                break;

            case 'D':
                userDoption = strdup(optarg);
                break;

            case 'd':
                set_debug_options(atoi(optarg), PGC_POSTMASTER, PGC_S_ARGV);
                break;

            case 'E':
                SetConfigOption("log_statement", "all", PGC_POSTMASTER, PGC_S_ARGV);
                break;

            case 'e':
                SetConfigOption("datestyle", "euro", PGC_POSTMASTER, PGC_S_ARGV);
                break;

            case 'F':
                SetConfigOption("fsync", "false", PGC_POSTMASTER, PGC_S_ARGV);
                break;

            case 'f':
                if (!set_plan_disabling_options(optarg, PGC_POSTMASTER, PGC_S_ARGV))
                {
                    write_stderr("%s: invalid argument for option -f: \"%s\"\n",
                                 progname, optarg);
                    ExitPostmaster(1);
                }
                break;

            case 'h':
                SetConfigOption("listen_addresses", optarg, PGC_POSTMASTER, PGC_S_ARGV);
                break;

            case 'i':
                SetConfigOption("listen_addresses", "*", PGC_POSTMASTER, PGC_S_ARGV);
                break;

            case 'j':
                /* only used by interactive backend */
                break;

            case 'k':
                SetConfigOption("unix_socket_directories", optarg, PGC_POSTMASTER, PGC_S_ARGV);
                break;

            case 'l':
                SetConfigOption("ssl", "true", PGC_POSTMASTER, PGC_S_ARGV);
                break;

            case 'N':
                SetConfigOption("max_connections", optarg, PGC_POSTMASTER, PGC_S_ARGV);
                break;

            case 'n':
                /* Don't reinit shared mem after abnormal exit */
                Reinit = false;
                break;

            case 'O':
                SetConfigOption("allow_system_table_mods", "true", PGC_POSTMASTER, PGC_S_ARGV);
                break;

            case 'o':
                /* Other options to pass to the backend on the command line */
                snprintf(ExtraOptions + strlen(ExtraOptions),
                         sizeof(ExtraOptions) - strlen(ExtraOptions),
                         " %s", optarg);
                break;

            case 'P':
                SetConfigOption("ignore_system_indexes", "true", PGC_POSTMASTER, PGC_S_ARGV);
                break;

            case 'p':
                SetConfigOption("port", optarg, PGC_POSTMASTER, PGC_S_ARGV);
                break;

            case 'r':
                /* only used by single-user backend */
                break;

            case 'S':
                SetConfigOption("work_mem", optarg, PGC_POSTMASTER, PGC_S_ARGV);
                break;

            case 's':
                SetConfigOption("log_statement_stats", "true", PGC_POSTMASTER, PGC_S_ARGV);
                break;

            case 'T':

                /*
                 * In the event that some backend dumps core, send SIGSTOP,
                 * rather than SIGQUIT, to all its peers.  This lets the wily
                 * post_hacker collect core dumps from everyone.
                 */
                SendStop = true;
                break;

            case 't':
                {
                    const char *tmp = get_stats_option_name(optarg);

                    if (tmp)
                    {
                        SetConfigOption(tmp, "true", PGC_POSTMASTER, PGC_S_ARGV);
                    }
                    else
                    {
                        write_stderr("%s: invalid argument for option -t: \"%s\"\n",
                                     progname, optarg);
                        ExitPostmaster(1);
                    }
                    break;
                }

            case 'W':
                SetConfigOption("post_auth_delay", optarg, PGC_POSTMASTER, PGC_S_ARGV);
                break;

            case 'c':
            case '-':
                {
                    char       *name,
                               *value;

                    ParseLongOption(optarg, &name, &value);
                    if (!value)
                    {
                        if (opt == '-')
                            ereport(ERROR,
                                    (errcode(ERRCODE_SYNTAX_ERROR),
                                     errmsg("--%s requires a value",
                                            optarg)));
                        else
                            ereport(ERROR,
                                    (errcode(ERRCODE_SYNTAX_ERROR),
                                     errmsg("-c %s requires a value",
                                            optarg)));
                    }

                    SetConfigOption(name, value, PGC_POSTMASTER, PGC_S_ARGV);
                    free(name);
                    if (value)
                        free(value);
                    break;
                }

            default:
                write_stderr("Try \"%s --help\" for more information.\n",
                             progname);
                ExitPostmaster(1);
        }
    }

    /*
     * Postmaster accepts no non-option switch arguments.
     */
    if (optind < argc)
    {
        write_stderr("%s: invalid argument: \"%s\"\n",
                     progname, argv[optind]);
        write_stderr("Try \"%s --help\" for more information.\n",
                     progname);
        ExitPostmaster(1);
    }

    /*
     * Locate the proper configuration files and data directory, and read
     * postgresql.conf for the first time.
     */
    if (!SelectConfigFiles(userDoption, progname))
        ExitPostmaster(2);

    if (output_config_variable != NULL)
    {
        /*
         * "-C guc" was specified, so print GUC's value and exit.  No extra
         * permission check is needed because the user is reading inside the
         * data dir.
         */
        const char *config_val = GetConfigOption(output_config_variable,
                                                 false, false);

        puts(config_val ? config_val : "");
        ExitPostmaster(0);
    }

    /* Verify that DataDir looks reasonable */
    checkDataDir();

    /* Check that pg_control exists */
    checkControlFile();

    /* And switch working directory into it */
    ChangeToDataDir();

    /*
     * Check for invalid combinations of GUC settings.
     */
    if (ReservedBackends >= MaxConnections)
    {
        write_stderr("%s: superuser_reserved_connections (%d) must be less than max_connections (%d)\n",
                     progname,
                     ReservedBackends, MaxConnections);
        ExitPostmaster(1);
    }
    if (XLogArchiveMode > ARCHIVE_MODE_OFF && wal_level == WAL_LEVEL_MINIMAL)
        ereport(ERROR,
                (errmsg("WAL archival cannot be enabled when wal_level is \"minimal\"")));
    if (max_wal_senders > 0 && wal_level == WAL_LEVEL_MINIMAL)
        ereport(ERROR,
                (errmsg("WAL streaming (max_wal_senders > 0) requires wal_level \"replica\" or \"logical\"")));

    /*
     * Other one-time internal sanity checks can go here, if they are fast.
     * (Put any slow processing further down, after postmaster.pid creation.)
     */
    if (!CheckDateTokenTables())
    {
        write_stderr("%s: invalid datetoken tables, please fix\n", progname);
        ExitPostmaster(1);
    }

    /*
     * Now that we are done processing the postmaster arguments, reset
     * getopt(3) library so that it will work correctly in subprocesses.
     */
    optind = 1;
#ifdef HAVE_INT_OPTRESET
    optreset = 1;               /* some systems need this too */
#endif

    /* For debugging: display postmaster environment */
    {
        extern char **environ;
        char      **p;

        ereport(DEBUG3,
                (errmsg_internal("%s: PostmasterMain: initial environment dump:",
                                 progname)));
        ereport(DEBUG3,
                (errmsg_internal("-----------------------------------------")));
        for (p = environ; *p; ++p)
            ereport(DEBUG3,
                    (errmsg_internal("\t%s", *p)));
        ereport(DEBUG3,
                (errmsg_internal("-----------------------------------------")));
    }

    /*
     * Create lockfile for data directory.
     *
     * We want to do this before we try to grab the input sockets, because the
     * data directory interlock is more reliable than the socket-file
     * interlock (thanks to whoever decided to put socket files in /tmp :-().
     * For the same reason, it's best to grab the TCP socket(s) before the
     * Unix socket(s).
     *
     * Also note that this internally sets up the on_proc_exit function that
     * is responsible for removing both data directory and socket lockfiles;
     * so it must happen before opening sockets so that at exit, the socket
     * lockfiles go away after CloseServerPorts runs.
     */
    CreateDataDirLockFile(true);

    /*
     * Read the control file (for error checking and config info).
     *
     * Since we verify the control file's CRC, this has a useful side effect
     * on machines where we need a run-time test for CRC support instructions.
     * The postmaster will do the test once at startup, and then its child
     * processes will inherit the correct function pointer and not need to
     * repeat the test.
     */
    LocalProcessControlFile(false);

    /*
     * Register the apply launcher.  Since it registers a background worker,
     * it needs to be called before InitializeMaxBackends(), and it's probably
     * a good idea to call it before any modules had chance to take the
     * background worker slots.
     */
    ApplyLauncherRegister();

    /*
     * process any libraries that should be preloaded at postmaster start
     */
    process_shared_preload_libraries();

    /*
     * Initialize SSL library, if specified.
     */
#ifdef USE_SSL
    if (EnableSSL)
    {
        (void) secure_initialize(true);
        LoadedSSL = true;
    }
#endif

    /*
     * Now that loadable modules have had their chance to register background
     * workers, calculate MaxBackends.
     */
    InitializeMaxBackends();

    /*
     * Set up shared memory and semaphores.
     */
    reset_shared();

    /*
     * Estimate number of openable files.  This must happen after setting up
     * semaphores, because on some platforms semaphores count as open files.
     */
    set_max_safe_fds();

    /*
     * Set reference point for stack-depth checking.
     */
    set_stack_base();

    /*
     * Initialize pipe (or process handle on Windows) that allows children to
     * wake up from sleep on postmaster death.
     */
    InitPostmasterDeathWatchHandle();

#ifdef WIN32

    /*
     * Initialize I/O completion port used to deliver list of dead children.
     */
    win32ChildQueue = CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, 0, 1);
    if (win32ChildQueue == NULL)
        ereport(FATAL,
                (errmsg("could not create I/O completion port for child queue")));
#endif

#ifdef EXEC_BACKEND
    /* Write out nondefault GUC settings for child processes to use */
    write_nondefault_variables(PGC_POSTMASTER);

    /*
     * Clean out the temp directory used to transmit parameters to child
     * processes (see internal_forkexec, below).  We must do this before
     * launching any child processes, else we have a race condition: we could
     * remove a parameter file before the child can read it.  It should be
     * safe to do so now, because we verified earlier that there are no
     * conflicting Postgres processes in this data directory.
     */
    RemovePgTempFilesInDir(PG_TEMP_FILES_DIR, true, false);
#endif

    /*
     * Forcibly remove the files signaling a standby promotion request.
     * Otherwise, the existence of those files triggers a promotion too early,
     * whether a user wants that or not.
     *
     * This removal of files is usually unnecessary because they can exist
     * only during a few moments during a standby promotion. However there is
     * a race condition: if pg_ctl promote is executed and creates the files
     * during a promotion, the files can stay around even after the server is
     * brought up to be the primary.  Then, if a new standby starts by using
     * the backup taken from the new primary, the files can exist at server
     * startup and must be removed in order to avoid an unexpected promotion.
     *
     * Note that promotion signal files need to be removed before the startup
     * process is invoked. Because, after that, they can be used by
     * postmaster's SIGUSR1 signal handler.
     */
    RemovePromoteSignalFiles();

    /* Do the same for logrotate signal file */
    RemoveLogrotateSignalFiles();

    /* Remove any outdated file holding the current log filenames. */
    if (unlink(LOG_METAINFO_DATAFILE) < 0 && errno != ENOENT)
        ereport(LOG,
                (errcode_for_file_access(),
                 errmsg("could not remove file \"%s\": %m",
                        LOG_METAINFO_DATAFILE)));

    /*
     * If enabled, start up syslogger collection subprocess
     */
    SysLoggerPID = SysLogger_Start();

    /*
     * Reset whereToSendOutput from DestDebug (its starting state) to
     * DestNone. This stops ereport from sending log messages to stderr unless
     * Log_destination permits.  We don't do this until the postmaster is
     * fully launched, since startup failures may as well be reported to
     * stderr.
     *
     * If we are in fact disabling logging to stderr, first emit a log message
     * saying so, to provide a breadcrumb trail for users who may not remember
     * that their logging is configured to go somewhere else.
     */
    if (!(Log_destination & LOG_DESTINATION_STDERR))
        ereport(LOG,
                (errmsg("ending log output to stderr"),
                 errhint("Future log output will go to log destination \"%s\".",
                         Log_destination_string)));

    whereToSendOutput = DestNone;

    /*
     * Report server startup in log.  While we could emit this much earlier,
     * it seems best to do so after starting the log collector, if we intend
     * to use one.
     */
    ereport(LOG,
            (errmsg("starting %s", PG_VERSION_STR)));

    /*
     * Establish input sockets.
     *
     * First, mark them all closed, and set up an on_proc_exit function that's
     * charged with closing the sockets again at postmaster shutdown.
     */
    for (i = 0; i < MAXLISTEN; i++)
        ListenSocket[i] = PGINVALID_SOCKET;

    on_proc_exit(CloseServerPorts, 0);

    if (ListenAddresses)
    {
        char       *rawstring;
        List       *elemlist;
        ListCell   *l;
        int         success = 0;

        /* Need a modifiable copy of ListenAddresses */
        rawstring = pstrdup(ListenAddresses);

        /* Parse string into list of hostnames */
        if (!SplitGUCList(rawstring, ',', &elemlist))
        {
            /* syntax error in list */
            ereport(FATAL,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("invalid list syntax in parameter \"%s\"",
                            "listen_addresses")));
        }

        foreach(l, elemlist)
        {
            char       *curhost = (char *) lfirst(l);

            if (strcmp(curhost, "*") == 0)
                status = StreamServerPort(AF_UNSPEC, NULL,
                                          (unsigned short) PostPortNumber,
                                          NULL,
                                          ListenSocket, MAXLISTEN);
            else
                status = StreamServerPort(AF_UNSPEC, curhost,
                                          (unsigned short) PostPortNumber,
                                          NULL,
                                          ListenSocket, MAXLISTEN);

            if (status == STATUS_OK)
            {
                success++;
                /* record the first successful host addr in lockfile */
                if (!listen_addr_saved)
                {
                    AddToDataDirLockFile(LOCK_FILE_LINE_LISTEN_ADDR, curhost);
                    listen_addr_saved = true;
                }
            }
            else
                ereport(WARNING,
                        (errmsg("could not create listen socket for \"%s\"",
                                curhost)));
        }

        if (!success && elemlist != NIL)
            ereport(FATAL,
                    (errmsg("could not create any TCP/IP sockets")));

        list_free(elemlist);
        pfree(rawstring);
    }

#ifdef USE_BONJOUR
    /* Register for Bonjour only if we opened TCP socket(s) */
    if (enable_bonjour && ListenSocket[0] != PGINVALID_SOCKET)
    {
        DNSServiceErrorType err;

        /*
         * We pass 0 for interface_index, which will result in registering on
         * all "applicable" interfaces.  It's not entirely clear from the
         * DNS-SD docs whether this would be appropriate if we have bound to
         * just a subset of the available network interfaces.
         */
        err = DNSServiceRegister(&bonjour_sdref,
                                 0,
                                 0,
                                 bonjour_name,
                                 "_postgresql._tcp.",
                                 NULL,
                                 NULL,
                                 pg_hton16(PostPortNumber),
                                 0,
                                 NULL,
                                 NULL,
                                 NULL);
        if (err != kDNSServiceErr_NoError)
            elog(LOG, "DNSServiceRegister() failed: error code %ld",
                 (long) err);

        /*
         * We don't bother to read the mDNS daemon's reply, and we expect that
         * it will automatically terminate our registration when the socket is
         * closed at postmaster termination.  So there's nothing more to be
         * done here.  However, the bonjour_sdref is kept around so that
         * forked children can close their copies of the socket.
         */
    }
#endif

#ifdef HAVE_UNIX_SOCKETS
    if (Unix_socket_directories)
    {
        char       *rawstring;
        List       *elemlist;
        ListCell   *l;
        int         success = 0;

        /* Need a modifiable copy of Unix_socket_directories */
        rawstring = pstrdup(Unix_socket_directories);

        /* Parse string into list of directories */
        if (!SplitDirectoriesString(rawstring, ',', &elemlist))
        {
            /* syntax error in list */
            ereport(FATAL,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("invalid list syntax in parameter \"%s\"",
                            "unix_socket_directories")));
        }

        foreach(l, elemlist)
        {
            char       *socketdir = (char *) lfirst(l);

            status = StreamServerPort(AF_UNIX, NULL,
                                      (unsigned short) PostPortNumber,
                                      socketdir,
                                      ListenSocket, MAXLISTEN);

            if (status == STATUS_OK)
            {
                success++;
                /* record the first successful Unix socket in lockfile */
                if (success == 1)
                    AddToDataDirLockFile(LOCK_FILE_LINE_SOCKET_DIR, socketdir);
            }
            else
                ereport(WARNING,
                        (errmsg("could not create Unix-domain socket in directory \"%s\"",
                                socketdir)));
        }

        if (!success && elemlist != NIL)
            ereport(FATAL,
                    (errmsg("could not create any Unix-domain sockets")));

        list_free_deep(elemlist);
        pfree(rawstring);
    }
#endif

    /*
     * check that we have some socket to listen on
     */
    if (ListenSocket[0] == PGINVALID_SOCKET)
        ereport(FATAL,
                (errmsg("no socket created for listening")));

    /*
     * If no valid TCP ports, write an empty line for listen address,
     * indicating the Unix socket must be used.  Note that this line is not
     * added to the lock file until there is a socket backing it.
     */
    if (!listen_addr_saved)
        AddToDataDirLockFile(LOCK_FILE_LINE_LISTEN_ADDR, "");

    /*
     * Record postmaster options.  We delay this till now to avoid recording
     * bogus options (eg, unusable port number).
     */
    if (!CreateOptsFile(argc, argv, my_exec_path))
        ExitPostmaster(1);

    /*
     * Write the external PID file if requested
     */
    if (external_pid_file)
    {
        FILE       *fpidfile = fopen(external_pid_file, "w");

        if (fpidfile)
        {
            fprintf(fpidfile, "%d\n", MyProcPid);
            fclose(fpidfile);

            /* Make PID file world readable */
            if (chmod(external_pid_file, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH) != 0)
                write_stderr("%s: could not change permissions of external PID file \"%s\": %s\n",
                             progname, external_pid_file, strerror(errno));
        }
        else
            write_stderr("%s: could not write external PID file \"%s\": %s\n",
                         progname, external_pid_file, strerror(errno));

        on_proc_exit(unlink_external_pid_file, 0);
    }

    /*
     * Remove old temporary files.  At this point there can be no other
     * Postgres processes running in this directory, so this should be safe.
     */
    RemovePgTempFiles();

    /*
     * Initialize stats collection subsystem (this does NOT start the
     * collector process!)
     */
    pgstat_init();

    /*
     * Initialize the autovacuum subsystem (again, no process start yet)
     */
    autovac_init();

    /*
     * Load configuration files for client authentication.
     */
    if (!load_hba())
    {
        /*
         * It makes no sense to continue if we fail to load the HBA file,
         * since there is no way to connect to the database in this case.
         */
        ereport(FATAL,
                (errmsg("could not load pg_hba.conf")));
    }
    if (!load_ident())
    {
        /*
         * We can start up without the IDENT file, although it means that you
         * cannot log in using any of the authentication methods that need a
         * user name mapping. load_ident() already logged the details of error
         * to the log.
         */
    }

#ifdef HAVE_PTHREAD_IS_THREADED_NP

    /*
     * On macOS, libintl replaces setlocale() with a version that calls
     * CFLocaleCopyCurrent() when its second argument is "" and every relevant
     * environment variable is unset or empty.  CFLocaleCopyCurrent() makes
     * the process multithreaded.  The postmaster calls sigprocmask() and
     * calls fork() without an immediate exec(), both of which have undefined
     * behavior in a multithreaded program.  A multithreaded postmaster is the
     * normal case on Windows, which offers neither fork() nor sigprocmask().
     */
    if (pthread_is_threaded_np() != 0)
        ereport(FATAL,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("postmaster became multithreaded during startup"),
                 errhint("Set the LC_ALL environment variable to a valid locale.")));
#endif

    /*
     * Remember postmaster startup time
     */
    PgStartTime = GetCurrentTimestamp();

    /*
     * Report postmaster status in the postmaster.pid file, to allow pg_ctl to
     * see what's happening.
     */
    AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_STARTING);

    /*
     * We're ready to rock and roll...
     */
    StartupPID = StartupDataBase();
    Assert(StartupPID != 0);
    StartupStatus = STARTUP_RUNNING;
    pmState = PM_STARTUP;

    /* Some workers may be scheduled to start now */
    maybe_start_bgworkers();

    status = ServerLoop();

    /*
     * ServerLoop probably shouldn't ever return, but if it does, close down.
     */
    ExitPostmaster(status != STATUS_OK);

    abort();                    /* not reached */
}


/*
 * on_proc_exit callback to close server's listen sockets
 */
static void
CloseServerPorts(int status, Datum arg)
{
    int         i;

    /*
     * First, explicitly close all the socket FDs.  We used to just let this
     * happen implicitly at postmaster exit, but it's better to close them
     * before we remove the postmaster.pid lockfile; otherwise there's a race
     * condition if a new postmaster wants to re-use the TCP port number.
     */
    for (i = 0; i < MAXLISTEN; i++)
    {
        if (ListenSocket[i] != PGINVALID_SOCKET)
        {
            StreamClose(ListenSocket[i]);
            ListenSocket[i] = PGINVALID_SOCKET;
        }
    }

    /*
     * Next, remove any filesystem entries for Unix sockets.  To avoid race
     * conditions against incoming postmasters, this must happen after closing
     * the sockets and before removing lock files.
     */
    RemoveSocketFiles();

    /*
     * We don't do anything about socket lock files here; those will be
     * removed in a later on_proc_exit callback.
     */
}

/*
 * on_proc_exit callback to delete external_pid_file
 */
static void
unlink_external_pid_file(int status, Datum arg)
{
    if (external_pid_file)
        unlink(external_pid_file);
}


/*
 * Compute and check the directory paths to files that are part of the
 * installation (as deduced from the postgres executable's own location)
 */
static void
getInstallationPaths(const char *argv0)
{
    DIR        *pdir;

    /* Locate the postgres executable itself */
    if (find_my_exec(argv0, my_exec_path) < 0)
        elog(FATAL, "%s: could not locate my own executable path", argv0);

#ifdef EXEC_BACKEND
    /* Locate executable backend before we change working directory */
    if (find_other_exec(argv0, "postgres", PG_BACKEND_VERSIONSTR,
                        postgres_exec_path) < 0)
        ereport(FATAL,
                (errmsg("%s: could not locate matching postgres executable",
                        argv0)));
#endif

    /*
     * Locate the pkglib directory --- this has to be set early in case we try
     * to load any modules from it in response to postgresql.conf entries.
     */
    get_pkglib_path(my_exec_path, pkglib_path);

    /*
     * Verify that there's a readable directory there; otherwise the Postgres
     * installation is incomplete or corrupt.  (A typical cause of this
     * failure is that the postgres executable has been moved or hardlinked to
     * some directory that's not a sibling of the installation lib/
     * directory.)
     */
    pdir = AllocateDir(pkglib_path);
    if (pdir == NULL)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not open directory \"%s\": %m",
                        pkglib_path),
                 errhint("This may indicate an incomplete PostgreSQL installation, or that the file \"%s\" has been moved away from its proper location.",
                         my_exec_path)));
    FreeDir(pdir);

    /*
     * XXX is it worth similarly checking the share/ directory?  If the lib/
     * directory is there, then share/ probably is too.
     */
}

/*
 * Check that pg_control exists in the correct location in the data directory.
 *
 * No attempt is made to validate the contents of pg_control here.  This is
 * just a sanity check to see if we are looking at a real data directory.
 */
static void
checkControlFile(void)
{
    char        path[MAXPGPATH];
    FILE       *fp;

    snprintf(path, sizeof(path), "%s/global/pg_control", DataDir);

    fp = AllocateFile(path, PG_BINARY_R);
    if (fp == NULL)
    {
        write_stderr("%s: could not find the database system\n"
                     "Expected to find it in the directory \"%s\",\n"
                     "but could not open file \"%s\": %s\n",
                     progname, DataDir, path, strerror(errno));
        ExitPostmaster(2);
    }
    FreeFile(fp);
}

/*
 * Determine how long should we let ServerLoop sleep.
 *
 * In normal conditions we wait at most one minute, to ensure that the other
 * background tasks handled by ServerLoop get done even when no requests are
 * arriving.  However, if there are background workers waiting to be started,
 * we don't actually sleep so that they are quickly serviced.  Other exception
 * cases are as shown in the code.
 */
static void
DetermineSleepTime(struct timeval *timeout)
{
    TimestampTz next_wakeup = 0;

    /*
     * Normal case: either there are no background workers at all, or we're in
     * a shutdown sequence (during which we ignore bgworkers altogether).
     */
    if (Shutdown > NoShutdown ||
        (!StartWorkerNeeded && !HaveCrashedWorker))
    {
        if (AbortStartTime != 0)
        {
            /* time left to abort; clamp to 0 in case it already expired */
            timeout->tv_sec = SIGKILL_CHILDREN_AFTER_SECS -
                (time(NULL) - AbortStartTime);
            timeout->tv_sec = Max(timeout->tv_sec, 0);
            timeout->tv_usec = 0;
        }
        else
        {
            timeout->tv_sec = 60;
            timeout->tv_usec = 0;
        }
        return;
    }

    if (StartWorkerNeeded)
    {
        timeout->tv_sec = 0;
        timeout->tv_usec = 0;
        return;
    }

    if (HaveCrashedWorker)
    {
        slist_mutable_iter siter;

        /*
         * When there are crashed bgworkers, we sleep just long enough that
         * they are restarted when they request to be.  Scan the list to
         * determine the minimum of all wakeup times according to most recent
         * crash time and requested restart interval.
         */
        slist_foreach_modify(siter, &BackgroundWorkerList)
        {
            RegisteredBgWorker *rw;
            TimestampTz this_wakeup;

            rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur);

            if (rw->rw_crashed_at == 0)
                continue;

            if (rw->rw_worker.bgw_restart_time == BGW_NEVER_RESTART
                || rw->rw_terminate)
            {
                ForgetBackgroundWorker(&siter);
                continue;
            }

            this_wakeup = TimestampTzPlusMilliseconds(rw->rw_crashed_at,
                                                      1000L * rw->rw_worker.bgw_restart_time);
            if (next_wakeup == 0 || this_wakeup < next_wakeup)
                next_wakeup = this_wakeup;
        }
    }

    if (next_wakeup != 0)
    {
        long        secs;
        int         microsecs;

        TimestampDifference(GetCurrentTimestamp(), next_wakeup,
                            &secs, &microsecs);
        timeout->tv_sec = secs;
        timeout->tv_usec = microsecs;

        /* Ensure we don't exceed one minute */
        if (timeout->tv_sec > 60)
        {
            timeout->tv_sec = 60;
            timeout->tv_usec = 0;
        }
    }
    else
    {
        timeout->tv_sec = 60;
        timeout->tv_usec = 0;
    }
}

/*
 * Main idle loop of postmaster
 *
 * NB: Needs to be called with signals blocked
 */
static int
ServerLoop(void)
{
    fd_set      readmask;
    int         nSockets;
    time_t      last_lockfile_recheck_time,
                last_touch_time;

    last_lockfile_recheck_time = last_touch_time = time(NULL);

    nSockets = initMasks(&readmask);

    for (;;)
    {
        fd_set      rmask;
        int         selres;
        time_t      now;

        /*
         * Wait for a connection request to arrive.
         *
         * We block all signals except while sleeping. That makes it safe for
         * signal handlers, which again block all signals while executing, to
         * do nontrivial work.
         *
         * If we are in PM_WAIT_DEAD_END state, then we don't want to accept
         * any new connections, so we don't call select(), and just sleep.
         */
        memcpy((char *) &rmask, (char *) &readmask, sizeof(fd_set));

        if (pmState == PM_WAIT_DEAD_END)
        {
            PG_SETMASK(&UnBlockSig);

            pg_usleep(100000L); /* 100 msec seems reasonable */
            selres = 0;

            PG_SETMASK(&BlockSig);
        }
        else
        {
            /* must set timeout each time; some OSes change it! */
            struct timeval timeout;

            /* Needs to run with blocked signals! */
            DetermineSleepTime(&timeout);

            PG_SETMASK(&UnBlockSig);

            selres = select(nSockets, &rmask, NULL, NULL, &timeout);

            PG_SETMASK(&BlockSig);
        }

        /* Now check the select() result */
        if (selres < 0)
        {
            if (errno != EINTR && errno != EWOULDBLOCK)
            {
                ereport(LOG,
                        (errcode_for_socket_access(),
                         errmsg("select() failed in postmaster: %m")));
                return STATUS_ERROR;
            }
        }

        /*
         * New connection pending on any of our sockets? If so, fork a child
         * process to deal with it.
         */
        if (selres > 0)
        {
            int         i;

            for (i = 0; i < MAXLISTEN; i++)
            {
                if (ListenSocket[i] == PGINVALID_SOCKET)
                    break;
                if (FD_ISSET(ListenSocket[i], &rmask))
                {
                    Port       *port;

                    port = ConnCreate(ListenSocket[i]);
                    if (port)
                    {
                        BackendStartup(port);

                        /*
                         * We no longer need the open socket or port structure
                         * in this process
                         */
                        StreamClose(port->sock);
                        ConnFree(port);
                    }
                }
            }
        }

        /* If we have lost the log collector, try to start a new one */
        if (SysLoggerPID == 0 && Logging_collector)
            SysLoggerPID = SysLogger_Start();

        /*
         * If no background writer process is running, and we are not in a
         * state that prevents it, start one.  It doesn't matter if this
         * fails, we'll just try again later.  Likewise for the checkpointer.
         */
        if (pmState == PM_RUN || pmState == PM_RECOVERY ||
            pmState == PM_HOT_STANDBY)
        {
            if (CheckpointerPID == 0)
                CheckpointerPID = StartCheckpointer();
            if (BgWriterPID == 0)
                BgWriterPID = StartBackgroundWriter();
        }

        /*
         * Likewise, if we have lost the walwriter process, try to start a new
         * one.  But this is needed only in normal operation (else we cannot
         * be writing any new WAL).
         */
        if (WalWriterPID == 0 && pmState == PM_RUN)
            WalWriterPID = StartWalWriter();

        /*
         * If we have lost the autovacuum launcher, try to start a new one. We
         * don't want autovacuum to run in binary upgrade mode because
         * autovacuum might update relfrozenxid for empty tables before the
         * physical files are put in place.
         */
        if (!IsBinaryUpgrade && AutoVacPID == 0 &&
            (AutoVacuumingActive() || start_autovac_launcher) &&
            pmState == PM_RUN)
        {
            AutoVacPID = StartAutoVacLauncher();
            if (AutoVacPID != 0)
                start_autovac_launcher = false; /* signal processed */
        }

        /* If we have lost the stats collector, try to start a new one */
        if (PgStatPID == 0 &&
            (pmState == PM_RUN || pmState == PM_HOT_STANDBY))
            PgStatPID = pgstat_start();

        /* If we have lost the archiver, try to start a new one. */
        if (PgArchPID == 0 && PgArchStartupAllowed())
            PgArchPID = pgarch_start();

        /* If we need to signal the autovacuum launcher, do so now */
        if (avlauncher_needs_signal)
        {
            avlauncher_needs_signal = false;
            if (AutoVacPID != 0)
                kill(AutoVacPID, SIGUSR2);
        }

        /* If we need to start a WAL receiver, try to do that now */
        if (WalReceiverRequested)
            MaybeStartWalReceiver();

        /* Get other worker processes running, if needed */
        if (StartWorkerNeeded || HaveCrashedWorker)
            maybe_start_bgworkers();

#ifdef HAVE_PTHREAD_IS_THREADED_NP

        /*
         * With assertions enabled, check regularly for appearance of
         * additional threads.  All builds check at start and exit.
         */
        Assert(pthread_is_threaded_np() == 0);
#endif

        /*
         * Lastly, check to see if it's time to do some things that we don't
         * want to do every single time through the loop, because they're a
         * bit expensive.  Note that there's up to a minute of slop in when
         * these tasks will be performed, since DetermineSleepTime() will let
         * us sleep at most that long; except for SIGKILL timeout which has
         * special-case logic there.
         */
        now = time(NULL);

        /*
         * If we already sent SIGQUIT to children and they are slow to shut
         * down, it's time to send them SIGKILL.  This doesn't happen
         * normally, but under certain conditions backends can get stuck while
         * shutting down.  This is a last measure to get them unwedged.
         *
         * Note we also do this during recovery from a process crash.
         */
        if ((Shutdown >= ImmediateShutdown || (FatalError && !SendStop)) &&
            AbortStartTime != 0 &&
            (now - AbortStartTime) >= SIGKILL_CHILDREN_AFTER_SECS)
        {
            /* We were gentle with them before. Not anymore */
            ereport(LOG,
                    (errmsg("issuing SIGKILL to recalcitrant children")));
            TerminateChildren(SIGKILL);
            /* reset flag so we don't SIGKILL again */
            AbortStartTime = 0;
        }

        /*
         * Once a minute, verify that postmaster.pid hasn't been removed or
         * overwritten.  If it has, we force a shutdown.  This avoids having
         * postmasters and child processes hanging around after their database
         * is gone, and maybe causing problems if a new database cluster is
         * created in the same place.  It also provides some protection
         * against a DBA foolishly removing postmaster.pid and manually
         * starting a new postmaster.  Data corruption is likely to ensue from
         * that anyway, but we can minimize the damage by aborting ASAP.
         */
        if (now - last_lockfile_recheck_time >= 1 * SECS_PER_MINUTE)
        {
            if (!RecheckDataDirLockFile())
            {
                ereport(LOG,
                        (errmsg("performing immediate shutdown because data directory lock file is invalid")));
                kill(MyProcPid, SIGQUIT);
            }
            last_lockfile_recheck_time = now;
        }

        /*
         * Touch Unix socket and lock files every 58 minutes, to ensure that
         * they are not removed by overzealous /tmp-cleaning tasks.  We assume
         * no one runs cleaners with cutoff times of less than an hour ...
         */
        if (now - last_touch_time >= 58 * SECS_PER_MINUTE)
        {
            TouchSocketFiles();
            TouchSocketLockFiles();
            last_touch_time = now;
        }
    }
}

/*
 * Initialise the masks for select() for the ports we are listening on.
 * Return the number of sockets to listen on.
 */
static int
initMasks(fd_set *rmask)
{
    int         maxsock = -1;
    int         i;

    FD_ZERO(rmask);

    for (i = 0; i < MAXLISTEN; i++)
    {
        int         fd = ListenSocket[i];

        if (fd == PGINVALID_SOCKET)
            break;
        FD_SET(fd, rmask);

        if (fd > maxsock)
            maxsock = fd;
    }

    return maxsock + 1;
}


/*
 * Read a client's startup packet and do something according to it.
 *
 * Returns STATUS_OK or STATUS_ERROR, or might call ereport(FATAL) and
 * not return at all.
 *
 * (Note that ereport(FATAL) stuff is sent to the client, so only use it
 * if that's what you want.  Return STATUS_ERROR if you don't want to
 * send anything to the client, which would typically be appropriate
 * if we detect a communications failure.)
 *
 * Set ssl_done and/or gss_done when negotiation of an encrypted layer
 * (currently, TLS or GSSAPI) is completed. A successful negotiation of either
 * encryption layer sets both flags, but a rejected negotiation sets only the
 * flag for that layer, since the client may wish to try the other one. We
 * should make no assumption here about the order in which the client may make
 * requests.
 */
static int
ProcessStartupPacket(Port *port, bool ssl_done, bool gss_done)
{
    int32       len;
    void       *buf;
    ProtocolVersion proto;
    MemoryContext oldcontext;

    pq_startmsgread();

    /*
     * Grab the first byte of the length word separately, so that we can tell
     * whether we have no data at all or an incomplete packet.  (This might
     * sound inefficient, but it's not really, because of buffering in
     * pqcomm.c.)
     */
    if (pq_getbytes((char *) &len, 1) == EOF)
    {
        /*
         * If we get no data at all, don't clutter the log with a complaint;
         * such cases often occur for legitimate reasons.  An example is that
         * we might be here after responding to NEGOTIATE_SSL_CODE, and if the
         * client didn't like our response, it'll probably just drop the
         * connection.  Service-monitoring software also often just opens and
         * closes a connection without sending anything.  (So do port
         * scanners, which may be less benign, but it's not really our job to
         * notice those.)
         */
        return STATUS_ERROR;
    }

    if (pq_getbytes(((char *) &len) + 1, 3) == EOF)
    {
        /* Got a partial length word, so bleat about that */
        if (!ssl_done && !gss_done)
            ereport(COMMERROR,
                    (errcode(ERRCODE_PROTOCOL_VIOLATION),
                     errmsg("incomplete startup packet")));
        return STATUS_ERROR;
    }

    len = pg_ntoh32(len);
    len -= 4;

    if (len < (int32) sizeof(ProtocolVersion) ||
        len > MAX_STARTUP_PACKET_LENGTH)
    {
        ereport(COMMERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg("invalid length of startup packet")));
        return STATUS_ERROR;
    }

    /*
     * Allocate at least the size of an old-style startup packet, plus one
     * extra byte, and make sure all are zeroes.  This ensures we will have
     * null termination of all strings, in both fixed- and variable-length
     * packet layouts.
     */
    if (len <= (int32) sizeof(StartupPacket))
        buf = palloc0(sizeof(StartupPacket) + 1);
    else
        buf = palloc0(len + 1);

    if (pq_getbytes(buf, len) == EOF)
    {
        ereport(COMMERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg("incomplete startup packet")));
        return STATUS_ERROR;
    }
    pq_endmsgread();

    /*
     * The first field is either a protocol version number or a special
     * request code.
     */
    port->proto = proto = pg_ntoh32(*((ProtocolVersion *) buf));

    if (proto == CANCEL_REQUEST_CODE)
    {
        processCancelRequest(port, buf);
        /* Not really an error, but we don't want to proceed further */
        return STATUS_ERROR;
    }

    if (proto == NEGOTIATE_SSL_CODE && !ssl_done)
    {
        char        SSLok;

#ifdef USE_SSL
        /* No SSL when disabled or on Unix sockets */
        if (!LoadedSSL || IS_AF_UNIX(port->laddr.addr.ss_family))
            SSLok = 'N';
        else
            SSLok = 'S';        /* Support for SSL */
#else
        SSLok = 'N';            /* No support for SSL */
#endif

retry1:
        if (send(port->sock, &SSLok, 1, 0) != 1)
        {
            if (errno == EINTR)
                goto retry1;    /* if interrupted, just retry */
            ereport(COMMERROR,
                    (errcode_for_socket_access(),
                     errmsg("failed to send SSL negotiation response: %m")));
            return STATUS_ERROR;    /* close the connection */
        }

#ifdef USE_SSL
        if (SSLok == 'S' && secure_open_server(port) == -1)
            return STATUS_ERROR;
#endif

        /*
         * regular startup packet, cancel, etc packet should follow, but not
         * another SSL negotiation request, and a GSS request should only
         * follow if SSL was rejected (client may negotiate in either order)
         */
        return ProcessStartupPacket(port, true, SSLok == 'S');
    }
    else if (proto == NEGOTIATE_GSS_CODE && !gss_done)
    {
        char        GSSok = 'N';
#ifdef ENABLE_GSS
        /* No GSSAPI encryption when on Unix socket */
        if (!IS_AF_UNIX(port->laddr.addr.ss_family))
            GSSok = 'G';
#endif

        while (send(port->sock, &GSSok, 1, 0) != 1)
        {
            if (errno == EINTR)
                continue;
            ereport(COMMERROR,
                    (errcode_for_socket_access(),
                     errmsg("failed to send GSSAPI negotiation response: %m")));
            return STATUS_ERROR;    /* close the connection */
        }

#ifdef ENABLE_GSS
        if (GSSok == 'G' && secure_open_gssapi(port) == -1)
            return STATUS_ERROR;
#endif

        /*
         * regular startup packet, cancel, etc packet should follow, but not
         * another GSS negotiation request, and an SSL request should only
         * follow if GSS was rejected (client may negotiate in either order)
         */
        return ProcessStartupPacket(port, GSSok == 'G', true);
    }

    /* Could add additional special packet types here */

    /*
     * Set FrontendProtocol now so that ereport() knows what format to send if
     * we fail during startup.
     */
    FrontendProtocol = proto;

    /* Check that the major protocol version is in range. */
    if (PG_PROTOCOL_MAJOR(proto) < PG_PROTOCOL_MAJOR(PG_PROTOCOL_EARLIEST) ||
        PG_PROTOCOL_MAJOR(proto) > PG_PROTOCOL_MAJOR(PG_PROTOCOL_LATEST))
        ereport(FATAL,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("unsupported frontend protocol %u.%u: server supports %u.0 to %u.%u",
                        PG_PROTOCOL_MAJOR(proto), PG_PROTOCOL_MINOR(proto),
                        PG_PROTOCOL_MAJOR(PG_PROTOCOL_EARLIEST),
                        PG_PROTOCOL_MAJOR(PG_PROTOCOL_LATEST),
                        PG_PROTOCOL_MINOR(PG_PROTOCOL_LATEST))));

    /*
     * Now fetch parameters out of startup packet and save them into the Port
     * structure.  All data structures attached to the Port struct must be
     * allocated in TopMemoryContext so that they will remain available in a
     * running backend (even after PostmasterContext is destroyed).  We need
     * not worry about leaking this storage on failure, since we aren't in the
     * postmaster process anymore.
     */
    oldcontext = MemoryContextSwitchTo(TopMemoryContext);

    if (PG_PROTOCOL_MAJOR(proto) >= 3)
    {
        int32       offset = sizeof(ProtocolVersion);
        List       *unrecognized_protocol_options = NIL;

        /*
         * Scan packet body for name/option pairs.  We can assume any string
         * beginning within the packet body is null-terminated, thanks to
         * zeroing extra byte above.
         */
        port->guc_options = NIL;

        while (offset < len)
        {
            char       *nameptr = ((char *) buf) + offset;
            int32       valoffset;
            char       *valptr;

            if (*nameptr == '\0')
                break;          /* found packet terminator */
            valoffset = offset + strlen(nameptr) + 1;
            if (valoffset >= len)
                break;          /* missing value, will complain below */
            valptr = ((char *) buf) + valoffset;

            if (strcmp(nameptr, "database") == 0)
                port->database_name = pstrdup(valptr);
            else if (strcmp(nameptr, "user") == 0)
                port->user_name = pstrdup(valptr);
            else if (strcmp(nameptr, "options") == 0)
                port->cmdline_options = pstrdup(valptr);
            else if (strcmp(nameptr, "replication") == 0)
            {
                /*
                 * Due to backward compatibility concerns the replication
                 * parameter is a hybrid beast which allows the value to be
                 * either boolean or the string 'database'. The latter
                 * connects to a specific database which is e.g. required for
                 * logical decoding while.
                 */
                if (strcmp(valptr, "database") == 0)
                {
                    am_walsender = true;
                    am_db_walsender = true;
                }
                else if (!parse_bool(valptr, &am_walsender))
                    ereport(FATAL,
                            (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                             errmsg("invalid value for parameter \"%s\": \"%s\"",
                                    "replication",
                                    valptr),
                             errhint("Valid values are: \"false\", 0, \"true\", 1, \"database\".")));
            }
            else if (strncmp(nameptr, "_pq_.", 5) == 0)
            {
                /*
                 * Any option beginning with _pq_. is reserved for use as a
                 * protocol-level option, but at present no such options are
                 * defined.
                 */
                unrecognized_protocol_options =
                    lappend(unrecognized_protocol_options, pstrdup(nameptr));
            }
            else
            {
                /* Assume it's a generic GUC option */
                port->guc_options = lappend(port->guc_options,
                                            pstrdup(nameptr));
                port->guc_options = lappend(port->guc_options,
                                            pstrdup(valptr));

                /*
                 * Copy application_name to port if we come across it.  This
                 * is done so we can log the application_name in the
                 * connection authorization message.  Note that the GUC would
                 * be used but we haven't gone through GUC setup yet.
                 */
                if (strcmp(nameptr, "application_name") == 0)
                {
                    char       *tmp_app_name = pstrdup(valptr);

                    pg_clean_ascii(tmp_app_name);

                    port->application_name = tmp_app_name;
                }
            }
            offset = valoffset + strlen(valptr) + 1;
        }

        /*
         * If we didn't find a packet terminator exactly at the end of the
         * given packet length, complain.
         */
        if (offset != len - 1)
            ereport(FATAL,
                    (errcode(ERRCODE_PROTOCOL_VIOLATION),
                     errmsg("invalid startup packet layout: expected terminator as last byte")));

        /*
         * If the client requested a newer protocol version or if the client
         * requested any protocol options we didn't recognize, let them know
         * the newest minor protocol version we do support and the names of
         * any unrecognized options.
         */
        if (PG_PROTOCOL_MINOR(proto) > PG_PROTOCOL_MINOR(PG_PROTOCOL_LATEST) ||
            unrecognized_protocol_options != NIL)
            SendNegotiateProtocolVersion(unrecognized_protocol_options);
    }
    else
    {
        /*
         * Get the parameters from the old-style, fixed-width-fields startup
         * packet as C strings.  The packet destination was cleared first so a
         * short packet has zeros silently added.  We have to be prepared to
         * truncate the pstrdup result for oversize fields, though.
         */
        StartupPacket *packet = (StartupPacket *) buf;

        port->database_name = pstrdup(packet->database);
        if (strlen(port->database_name) > sizeof(packet->database))
            port->database_name[sizeof(packet->database)] = '\0';
        port->user_name = pstrdup(packet->user);
        if (strlen(port->user_name) > sizeof(packet->user))
            port->user_name[sizeof(packet->user)] = '\0';
        port->cmdline_options = pstrdup(packet->options);
        if (strlen(port->cmdline_options) > sizeof(packet->options))
            port->cmdline_options[sizeof(packet->options)] = '\0';
        port->guc_options = NIL;
    }

    /* Check a user name was given. */
    if (port->user_name == NULL || port->user_name[0] == '\0')
        ereport(FATAL,
                (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
                 errmsg("no PostgreSQL user name specified in startup packet")));

    /* The database defaults to the user name. */
    if (port->database_name == NULL || port->database_name[0] == '\0')
        port->database_name = pstrdup(port->user_name);

    if (Db_user_namespace)
    {
        /*
         * If user@, it is a global user, remove '@'. We only want to do this
         * if there is an '@' at the end and no earlier in the user string or
         * they may fake as a local user of another database attaching to this
         * database.
         */
        if (strchr(port->user_name, '@') ==
            port->user_name + strlen(port->user_name) - 1)
            *strchr(port->user_name, '@') = '\0';
        else
        {
            /* Append '@' and dbname */
            port->user_name = psprintf("%s@%s", port->user_name, port->database_name);
        }
    }

    /*
     * Truncate given database and user names to length of a Postgres name.
     * This avoids lookup failures when overlength names are given.
     */
    if (strlen(port->database_name) >= NAMEDATALEN)
        port->database_name[NAMEDATALEN - 1] = '\0';
    if (strlen(port->user_name) >= NAMEDATALEN)
        port->user_name[NAMEDATALEN - 1] = '\0';

    if (am_walsender)
        MyBackendType = B_WAL_SENDER;
    else
        MyBackendType = B_BACKEND;

    /*
     * Normal walsender backends, e.g. for streaming replication, are not
     * connected to a particular database. But walsenders used for logical
     * replication need to connect to a specific database. We allow streaming
     * replication commands to be issued even if connected to a database as it
     * can make sense to first make a basebackup and then stream changes
     * starting from that.
     */
    if (am_walsender && !am_db_walsender)
        port->database_name[0] = '\0';

    /*
     * Done putting stuff in TopMemoryContext.
     */
    MemoryContextSwitchTo(oldcontext);

    /*
     * If we're going to reject the connection due to database state, say so
     * now instead of wasting cycles on an authentication exchange. (This also
     * allows a pg_ping utility to be written.)
     */
    switch (port->canAcceptConnections)
    {
        case CAC_STARTUP:
            ereport(FATAL,
                    (errcode(ERRCODE_CANNOT_CONNECT_NOW),
                     errmsg("the database system is starting up")));
            break;
        case CAC_SHUTDOWN:
            ereport(FATAL,
                    (errcode(ERRCODE_CANNOT_CONNECT_NOW),
                     errmsg("the database system is shutting down")));
            break;
        case CAC_RECOVERY:
            ereport(FATAL,
                    (errcode(ERRCODE_CANNOT_CONNECT_NOW),
                     errmsg("the database system is in recovery mode")));
            break;
        case CAC_TOOMANY:
            ereport(FATAL,
                    (errcode(ERRCODE_TOO_MANY_CONNECTIONS),
                     errmsg("sorry, too many clients already")));
            break;
        case CAC_SUPERUSER:
            /* OK for now, will check in InitPostgres */
            break;
        case CAC_OK:
            break;
    }

    return STATUS_OK;
}

/*
 * Send a NegotiateProtocolVersion to the client.  This lets the client know
 * that they have requested a newer minor protocol version than we are able
 * to speak.  We'll speak the highest version we know about; the client can,
 * of course, abandon the connection if that's a problem.
 *
 * We also include in the response a list of protocol options we didn't
 * understand.  This allows clients to include optional parameters that might
 * be present either in newer protocol versions or third-party protocol
 * extensions without fear of having to reconnect if those options are not
 * understood, while at the same time making certain that the client is aware
 * of which options were actually accepted.
 */
static void
SendNegotiateProtocolVersion(List *unrecognized_protocol_options)
{
    StringInfoData buf;
    ListCell   *lc;

    pq_beginmessage(&buf, 'v'); /* NegotiateProtocolVersion */
    pq_sendint32(&buf, PG_PROTOCOL_LATEST);
    pq_sendint32(&buf, list_length(unrecognized_protocol_options));
    foreach(lc, unrecognized_protocol_options)
        pq_sendstring(&buf, lfirst(lc));
    pq_endmessage(&buf);

    /* no need to flush, some other message will follow */
}

/*
 * The client has sent a cancel request packet, not a normal
 * start-a-new-connection packet.  Perform the necessary processing.
 * Nothing is sent back to the client.
 */
static void
processCancelRequest(Port *port, void *pkt)
{
    CancelRequestPacket *canc = (CancelRequestPacket *) pkt;
    int         backendPID;
    int32       cancelAuthCode;
    Backend    *bp;

#ifndef EXEC_BACKEND
    dlist_iter  iter;
#else
    int         i;
#endif

    backendPID = (int) pg_ntoh32(canc->backendPID);
    cancelAuthCode = (int32) pg_ntoh32(canc->cancelAuthCode);

    /*
     * See if we have a matching backend.  In the EXEC_BACKEND case, we can no
     * longer access the postmaster's own backend list, and must rely on the
     * duplicate array in shared memory.
     */
#ifndef EXEC_BACKEND
    dlist_foreach(iter, &BackendList)
    {
        bp = dlist_container(Backend, elem, iter.cur);
#else
    for (i = MaxLivePostmasterChildren() - 1; i >= 0; i--)
    {
        bp = (Backend *) &ShmemBackendArray[i];
#endif
        if (bp->pid == backendPID)
        {
            if (bp->cancel_key == cancelAuthCode)
            {
                /* Found a match; signal that backend to cancel current op */
                ereport(DEBUG2,
                        (errmsg_internal("processing cancel request: sending SIGINT to process %d",
                                         backendPID)));
                signal_child(bp->pid, SIGINT);
            }
            else
                /* Right PID, wrong key: no way, Jose */
                ereport(LOG,
                        (errmsg("wrong key in cancel request for process %d",
                                backendPID)));
            return;
        }
#ifndef EXEC_BACKEND            /* make GNU Emacs 26.1 see brace balance */
    }
#else
    }
#endif

    /* No matching backend */
    ereport(LOG,
            (errmsg("PID %d in cancel request did not match any process",
                    backendPID)));
}

/*
 * canAcceptConnections --- check to see if database state allows connections
 * of the specified type.  backend_type can be BACKEND_TYPE_NORMAL,
 * BACKEND_TYPE_AUTOVAC, or BACKEND_TYPE_BGWORKER.  (Note that we don't yet
 * know whether a NORMAL connection might turn into a walsender.)
 */
static CAC_state
canAcceptConnections(int backend_type)
{
    CAC_state   result = CAC_OK;

    /*
     * Can't start backends when in startup/shutdown/inconsistent recovery
     * state.  We treat autovac workers the same as user backends for this
     * purpose.  However, bgworkers are excluded from this test; we expect
     * bgworker_should_start_now() decided whether the DB state allows them.
     */
    if (pmState != PM_RUN && pmState != PM_HOT_STANDBY &&
        backend_type != BACKEND_TYPE_BGWORKER)
    {
        if (Shutdown > NoShutdown)
            return CAC_SHUTDOWN;    /* shutdown is pending */
        else if (!FatalError &&
                 (pmState == PM_STARTUP ||
                  pmState == PM_RECOVERY))
            return CAC_STARTUP; /* normal startup */
        else
            return CAC_RECOVERY;    /* else must be crash recovery */
    }

    /*
     * "Smart shutdown" restrictions are applied only to normal connections,
     * not to autovac workers or bgworkers.  When only superusers can connect,
     * we return CAC_SUPERUSER to indicate that superuserness must be checked
     * later.  Note that neither CAC_OK nor CAC_SUPERUSER can safely be
     * returned until we have checked for too many children.
     */
    if (connsAllowed != ALLOW_ALL_CONNS &&
        backend_type == BACKEND_TYPE_NORMAL)
    {
        if (connsAllowed == ALLOW_SUPERUSER_CONNS)
            result = CAC_SUPERUSER; /* allow superusers only */
        else
            return CAC_SHUTDOWN;    /* shutdown is pending */
    }

    /*
     * Don't start too many children.
     *
     * We allow more connections here than we can have backends because some
     * might still be authenticating; they might fail auth, or some existing
     * backend might exit before the auth cycle is completed.  The exact
     * MaxBackends limit is enforced when a new backend tries to join the
     * shared-inval backend array.
     *
     * The limit here must match the sizes of the per-child-process arrays;
     * see comments for MaxLivePostmasterChildren().
     */
    if (CountChildren(BACKEND_TYPE_ALL) >= MaxLivePostmasterChildren())
        result = CAC_TOOMANY;

    return result;
}


/*
 * ConnCreate -- create a local connection data structure
 *
 * Returns NULL on failure, other than out-of-memory which is fatal.
 */
static Port *
ConnCreate(int serverFd)
{
    Port       *port;

    if (!(port = (Port *) calloc(1, sizeof(Port))))
    {
        ereport(LOG,
                (errcode(ERRCODE_OUT_OF_MEMORY),
                 errmsg("out of memory")));
        ExitPostmaster(1);
    }

    if (StreamConnection(serverFd, port) != STATUS_OK)
    {
        if (port->sock != PGINVALID_SOCKET)
            StreamClose(port->sock);
        ConnFree(port);
        return NULL;
    }

    /*
     * Allocate GSSAPI specific state struct
     */
#ifndef EXEC_BACKEND
#if defined(ENABLE_GSS) || defined(ENABLE_SSPI)
    port->gss = (pg_gssinfo *) calloc(1, sizeof(pg_gssinfo));
    if (!port->gss)
    {
        ereport(LOG,
                (errcode(ERRCODE_OUT_OF_MEMORY),
                 errmsg("out of memory")));
        ExitPostmaster(1);
    }
#endif
#endif

    return port;
}


/*
 * ConnFree -- free a local connection data structure
 */
static void
ConnFree(Port *conn)
{
#ifdef USE_SSL
    secure_close(conn);
#endif
    if (conn->gss)
        free(conn->gss);
    free(conn);
}


/*
 * ClosePostmasterPorts -- close all the postmaster's open sockets
 *
 * This is called during child process startup to release file descriptors
 * that are not needed by that child process.  The postmaster still has
 * them open, of course.
 *
 * Note: we pass am_syslogger as a boolean because we don't want to set
 * the global variable yet when this is called.
 */
void
ClosePostmasterPorts(bool am_syslogger)
{
    int         i;

#ifndef WIN32

    /*
     * Close the write end of postmaster death watch pipe. It's important to
     * do this as early as possible, so that if postmaster dies, others won't
     * think that it's still running because we're holding the pipe open.
     */
    if (close(postmaster_alive_fds[POSTMASTER_FD_OWN]) != 0)
        ereport(FATAL,
                (errcode_for_file_access(),
                 errmsg_internal("could not close postmaster death monitoring pipe in child process: %m")));
    postmaster_alive_fds[POSTMASTER_FD_OWN] = -1;
    /* Notify fd.c that we released one pipe FD. */
    ReleaseExternalFD();
#endif

    /*
     * Close the postmaster's listen sockets.  These aren't tracked by fd.c,
     * so we don't call ReleaseExternalFD() here.
     */
    for (i = 0; i < MAXLISTEN; i++)
    {
        if (ListenSocket[i] != PGINVALID_SOCKET)
        {
            StreamClose(ListenSocket[i]);
            ListenSocket[i] = PGINVALID_SOCKET;
        }
    }

    /*
     * If using syslogger, close the read side of the pipe.  We don't bother
     * tracking this in fd.c, either.
     */
    if (!am_syslogger)
    {
#ifndef WIN32
        if (syslogPipe[0] >= 0)
            close(syslogPipe[0]);
        syslogPipe[0] = -1;
#else
        if (syslogPipe[0])
            CloseHandle(syslogPipe[0]);
        syslogPipe[0] = 0;
#endif
    }

#ifdef USE_BONJOUR
    /* If using Bonjour, close the connection to the mDNS daemon */
    if (bonjour_sdref)
        close(DNSServiceRefSockFD(bonjour_sdref));
#endif
}


/*
 * InitProcessGlobals -- set MyProcPid, MyStartTime[stamp], random seeds
 *
 * Called early in the postmaster and every backend.
 */
void
InitProcessGlobals(void)
{
    unsigned int rseed;

    MyProcPid = getpid();
    MyStartTimestamp = GetCurrentTimestamp();
    MyStartTime = timestamptz_to_time_t(MyStartTimestamp);

    /*
     * Set a different seed for random() in every process.  We want something
     * unpredictable, so if possible, use high-quality random bits for the
     * seed.  Otherwise, fall back to a seed based on timestamp and PID.
     */
    if (!pg_strong_random(&rseed, sizeof(rseed)))
    {
        /*
         * Since PIDs and timestamps tend to change more frequently in their
         * least significant bits, shift the timestamp left to allow a larger
         * total number of seeds in a given time period.  Since that would
         * leave only 20 bits of the timestamp that cycle every ~1 second,
         * also mix in some higher bits.
         */
        rseed = ((uint64) MyProcPid) ^
            ((uint64) MyStartTimestamp << 12) ^
            ((uint64) MyStartTimestamp >> 20);
    }
    srandom(rseed);
}


/*
 * reset_shared -- reset shared memory and semaphores
 */
static void
reset_shared(void)
{
    /*
     * Create or re-create shared memory and semaphores.
     *
     * Note: in each "cycle of life" we will normally assign the same IPC keys
     * (if using SysV shmem and/or semas).  This helps ensure that we will
     * clean up dead IPC objects if the postmaster crashes and is restarted.
     */
    CreateSharedMemoryAndSemaphores();
}


/*
 * SIGHUP -- reread config files, and tell children to do same
 */
static void
SIGHUP_handler(SIGNAL_ARGS)
{
    int         save_errno = errno;

    /*
     * We rely on the signal mechanism to have blocked all signals ... except
     * on Windows, which lacks sigaction(), so we have to do it manually.
     */
#ifdef WIN32
    PG_SETMASK(&BlockSig);
#endif

    if (Shutdown <= SmartShutdown)
    {
        ereport(LOG,
                (errmsg("received SIGHUP, reloading configuration files")));
        ProcessConfigFile(PGC_SIGHUP);
        SignalChildren(SIGHUP);
        if (StartupPID != 0)
            signal_child(StartupPID, SIGHUP);
        if (BgWriterPID != 0)
            signal_child(BgWriterPID, SIGHUP);
        if (CheckpointerPID != 0)
            signal_child(CheckpointerPID, SIGHUP);
        if (WalWriterPID != 0)
            signal_child(WalWriterPID, SIGHUP);
        if (WalReceiverPID != 0)
            signal_child(WalReceiverPID, SIGHUP);
        if (AutoVacPID != 0)
            signal_child(AutoVacPID, SIGHUP);
        if (PgArchPID != 0)
            signal_child(PgArchPID, SIGHUP);
        if (SysLoggerPID != 0)
            signal_child(SysLoggerPID, SIGHUP);
        if (PgStatPID != 0)
            signal_child(PgStatPID, SIGHUP);

        /* Reload authentication config files too */
        if (!load_hba())
            ereport(LOG,
            /* translator: %s is a configuration file */
                    (errmsg("%s was not reloaded", "pg_hba.conf")));

        if (!load_ident())
            ereport(LOG,
                    (errmsg("%s was not reloaded", "pg_ident.conf")));

#ifdef USE_SSL
        /* Reload SSL configuration as well */
        if (EnableSSL)
        {
            if (secure_initialize(false) == 0)
                LoadedSSL = true;
            else
                ereport(LOG,
                        (errmsg("SSL configuration was not reloaded")));
        }
        else
        {
            secure_destroy();
            LoadedSSL = false;
        }
#endif

#ifdef EXEC_BACKEND
        /* Update the starting-point file for future children */
        write_nondefault_variables(PGC_SIGHUP);
#endif
    }

#ifdef WIN32
    PG_SETMASK(&UnBlockSig);
#endif

    errno = save_errno;
}


/*
 * pmdie -- signal handler for processing various postmaster signals.
 */
static void
pmdie(SIGNAL_ARGS)
{
    int         save_errno = errno;

    /*
     * We rely on the signal mechanism to have blocked all signals ... except
     * on Windows, which lacks sigaction(), so we have to do it manually.
     */
#ifdef WIN32
    PG_SETMASK(&BlockSig);
#endif

    ereport(DEBUG2,
            (errmsg_internal("postmaster received signal %d",
                             postgres_signal_arg)));

    switch (postgres_signal_arg)
    {
        case SIGTERM:

            /*
             * Smart Shutdown:
             *
             * Wait for children to end their work, then shut down.
             */
            if (Shutdown >= SmartShutdown)
                break;
            Shutdown = SmartShutdown;
            ereport(LOG,
                    (errmsg("received smart shutdown request")));

            /* Report status */
            AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_STOPPING);
#ifdef USE_SYSTEMD
            sd_notify(0, "STOPPING=1");
#endif

            /*
             * If we reached normal running, we have to wait for any online
             * backup mode to end; otherwise go straight to waiting for client
             * backends to exit.  (The difference is that in the former state,
             * we'll still let in new superuser clients, so that somebody can
             * end the online backup mode.)  If already in PM_STOP_BACKENDS or
             * a later state, do not change it.
             */
            if (pmState == PM_RUN)
                connsAllowed = ALLOW_SUPERUSER_CONNS;
            else if (pmState == PM_HOT_STANDBY)
                connsAllowed = ALLOW_NO_CONNS;
            else if (pmState == PM_STARTUP || pmState == PM_RECOVERY)
            {
                /* There should be no clients, so proceed to stop children */
                pmState = PM_STOP_BACKENDS;
            }

            /*
             * Now wait for online backup mode to end and backends to exit. If
             * that is already the case, PostmasterStateMachine will take the
             * next step.
             */
            PostmasterStateMachine();
            break;

        case SIGINT:

            /*
             * Fast Shutdown:
             *
             * Abort all children with SIGTERM (rollback active transactions
             * and exit) and shut down when they are gone.
             */
            if (Shutdown >= FastShutdown)
                break;
            Shutdown = FastShutdown;
            ereport(LOG,
                    (errmsg("received fast shutdown request")));

            /* Report status */
            AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_STOPPING);
#ifdef USE_SYSTEMD
            sd_notify(0, "STOPPING=1");
#endif

            if (pmState == PM_STARTUP || pmState == PM_RECOVERY)
            {
                /* Just shut down background processes silently */
                pmState = PM_STOP_BACKENDS;
            }
            else if (pmState == PM_RUN ||
                     pmState == PM_HOT_STANDBY)
            {
                /* Report that we're about to zap live client sessions */
                ereport(LOG,
                        (errmsg("aborting any active transactions")));
                pmState = PM_STOP_BACKENDS;
            }

            /*
             * PostmasterStateMachine will issue any necessary signals, or
             * take the next step if no child processes need to be killed.
             */
            PostmasterStateMachine();
            break;

        case SIGQUIT:

            /*
             * Immediate Shutdown:
             *
             * abort all children with SIGQUIT, wait for them to exit,
             * terminate remaining ones with SIGKILL, then exit without
             * attempt to properly shut down the data base system.
             */
            if (Shutdown >= ImmediateShutdown)
                break;
            Shutdown = ImmediateShutdown;
            ereport(LOG,
                    (errmsg("received immediate shutdown request")));

            /* Report status */
            AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_STOPPING);
#ifdef USE_SYSTEMD
            sd_notify(0, "STOPPING=1");
#endif

            TerminateChildren(SIGQUIT);
            pmState = PM_WAIT_BACKENDS;

            /* set stopwatch for them to die */
            AbortStartTime = time(NULL);

            /*
             * Now wait for backends to exit.  If there are none,
             * PostmasterStateMachine will take the next step.
             */
            PostmasterStateMachine();
            break;
    }

#ifdef WIN32
    PG_SETMASK(&UnBlockSig);
#endif

    errno = save_errno;
}

/*
 * Reaper -- signal handler to cleanup after a child process dies.
 */
static void
reaper(SIGNAL_ARGS)
{
    int         save_errno = errno;
    int         pid;            /* process id of dead child process */
    int         exitstatus;     /* its exit status */

    /*
     * We rely on the signal mechanism to have blocked all signals ... except
     * on Windows, which lacks sigaction(), so we have to do it manually.
     */
#ifdef WIN32
    PG_SETMASK(&BlockSig);
#endif

    ereport(DEBUG4,
            (errmsg_internal("reaping dead processes")));

    while ((pid = waitpid(-1, &exitstatus, WNOHANG)) > 0)
    {
        /*
         * Check if this child was a startup process.
         */
        if (pid == StartupPID)
        {
            StartupPID = 0;

            /*
             * Startup process exited in response to a shutdown request (or it
             * completed normally regardless of the shutdown request).
             */
            if (Shutdown > NoShutdown &&
                (EXIT_STATUS_0(exitstatus) || EXIT_STATUS_1(exitstatus)))
            {
                StartupStatus = STARTUP_NOT_RUNNING;
                pmState = PM_WAIT_BACKENDS;
                /* PostmasterStateMachine logic does the rest */
                continue;
            }

            if (EXIT_STATUS_3(exitstatus))
            {
                ereport(LOG,
                        (errmsg("shutdown at recovery target")));
                StartupStatus = STARTUP_NOT_RUNNING;
                Shutdown = Max(Shutdown, SmartShutdown);
                TerminateChildren(SIGTERM);
                pmState = PM_WAIT_BACKENDS;
                /* PostmasterStateMachine logic does the rest */
                continue;
            }

            /*
             * Unexpected exit of startup process (including FATAL exit)
             * during PM_STARTUP is treated as catastrophic. There are no
             * other processes running yet, so we can just exit.
             */
            if (pmState == PM_STARTUP &&
                StartupStatus != STARTUP_SIGNALED &&
                !EXIT_STATUS_0(exitstatus))
            {
                LogChildExit(LOG, _("startup process"),
                             pid, exitstatus);
                ereport(LOG,
                        (errmsg("aborting startup due to startup process failure")));
                ExitPostmaster(1);
            }

            /*
             * After PM_STARTUP, any unexpected exit (including FATAL exit) of
             * the startup process is catastrophic, so kill other children,
             * and set StartupStatus so we don't try to reinitialize after
             * they're gone.  Exception: if StartupStatus is STARTUP_SIGNALED,
             * then we previously sent the startup process a SIGQUIT; so
             * that's probably the reason it died, and we do want to try to
             * restart in that case.
             *
             * This stanza also handles the case where we sent a SIGQUIT
             * during PM_STARTUP due to some dead_end child crashing: in that
             * situation, if the startup process dies on the SIGQUIT, we need
             * to transition to PM_WAIT_BACKENDS state which will allow
             * PostmasterStateMachine to restart the startup process.  (On the
             * other hand, the startup process might complete normally, if we
             * were too late with the SIGQUIT.  In that case we'll fall
             * through and commence normal operations.)
             */
            if (!EXIT_STATUS_0(exitstatus))
            {
                if (StartupStatus == STARTUP_SIGNALED)
                {
                    StartupStatus = STARTUP_NOT_RUNNING;
                    if (pmState == PM_STARTUP)
                        pmState = PM_WAIT_BACKENDS;
                }
                else
                    StartupStatus = STARTUP_CRASHED;
                HandleChildCrash(pid, exitstatus,
                                 _("startup process"));
                continue;
            }

            /*
             * Startup succeeded, commence normal operations
             */
            StartupStatus = STARTUP_NOT_RUNNING;
            FatalError = false;
            AbortStartTime = 0;
            ReachedNormalRunning = true;
            pmState = PM_RUN;
            connsAllowed = ALLOW_ALL_CONNS;

            /*
             * Crank up the background tasks, if we didn't do that already
             * when we entered consistent recovery state.  It doesn't matter
             * if this fails, we'll just try again later.
             */
            if (CheckpointerPID == 0)
                CheckpointerPID = StartCheckpointer();
            if (BgWriterPID == 0)
                BgWriterPID = StartBackgroundWriter();
            if (WalWriterPID == 0)
                WalWriterPID = StartWalWriter();

            /*
             * Likewise, start other special children as needed.  In a restart
             * situation, some of them may be alive already.
             */
            if (!IsBinaryUpgrade && AutoVacuumingActive() && AutoVacPID == 0)
                AutoVacPID = StartAutoVacLauncher();
            if (PgArchStartupAllowed() && PgArchPID == 0)
                PgArchPID = pgarch_start();
            if (PgStatPID == 0)
                PgStatPID = pgstat_start();

            /* workers may be scheduled to start now */
            maybe_start_bgworkers();

            /* at this point we are really open for business */
            ereport(LOG,
                    (errmsg("database system is ready to accept connections")));

            /* Report status */
            AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_READY);
#ifdef USE_SYSTEMD
            sd_notify(0, "READY=1");
#endif

            continue;
        }

        /*
         * Was it the bgwriter?  Normal exit can be ignored; we'll start a new
         * one at the next iteration of the postmaster's main loop, if
         * necessary.  Any other exit condition is treated as a crash.
         */
        if (pid == BgWriterPID)
        {
            BgWriterPID = 0;
            if (!EXIT_STATUS_0(exitstatus))
                HandleChildCrash(pid, exitstatus,
                                 _("background writer process"));
            continue;
        }

        /*
         * Was it the checkpointer?
         */
        if (pid == CheckpointerPID)
        {
            CheckpointerPID = 0;
            if (EXIT_STATUS_0(exitstatus) && pmState == PM_SHUTDOWN)
            {
                /*
                 * OK, we saw normal exit of the checkpointer after it's been
                 * told to shut down.  We expect that it wrote a shutdown
                 * checkpoint.  (If for some reason it didn't, recovery will
                 * occur on next postmaster start.)
                 *
                 * At this point we should have no normal backend children
                 * left (else we'd not be in PM_SHUTDOWN state) but we might
                 * have dead_end children to wait for.
                 *
                 * If we have an archiver subprocess, tell it to do a last
                 * archive cycle and quit. Likewise, if we have walsender
                 * processes, tell them to send any remaining WAL and quit.
                 */
                Assert(Shutdown > NoShutdown);

                /* Waken archiver for the last time */
                if (PgArchPID != 0)
                    signal_child(PgArchPID, SIGUSR2);

                /*
                 * Waken walsenders for the last time. No regular backends
                 * should be around anymore.
                 */
                SignalChildren(SIGUSR2);

                pmState = PM_SHUTDOWN_2;

                /*
                 * We can also shut down the stats collector now; there's
                 * nothing left for it to do.
                 */
                if (PgStatPID != 0)
                    signal_child(PgStatPID, SIGQUIT);
            }
            else
            {
                /*
                 * Any unexpected exit of the checkpointer (including FATAL
                 * exit) is treated as a crash.
                 */
                HandleChildCrash(pid, exitstatus,
                                 _("checkpointer process"));
            }

            continue;
        }

        /*
         * Was it the wal writer?  Normal exit can be ignored; we'll start a
         * new one at the next iteration of the postmaster's main loop, if
         * necessary.  Any other exit condition is treated as a crash.
         */
        if (pid == WalWriterPID)
        {
            WalWriterPID = 0;
            if (!EXIT_STATUS_0(exitstatus))
                HandleChildCrash(pid, exitstatus,
                                 _("WAL writer process"));
            continue;
        }

        /*
         * Was it the wal receiver?  If exit status is zero (normal) or one
         * (FATAL exit), we assume everything is all right just like normal
         * backends.  (If we need a new wal receiver, we'll start one at the
         * next iteration of the postmaster's main loop.)
         */
        if (pid == WalReceiverPID)
        {
            WalReceiverPID = 0;
            if (!EXIT_STATUS_0(exitstatus) && !EXIT_STATUS_1(exitstatus))
                HandleChildCrash(pid, exitstatus,
                                 _("WAL receiver process"));
            continue;
        }

        /*
         * Was it the autovacuum launcher?  Normal exit can be ignored; we'll
         * start a new one at the next iteration of the postmaster's main
         * loop, if necessary.  Any other exit condition is treated as a
         * crash.
         */
        if (pid == AutoVacPID)
        {
            AutoVacPID = 0;
            if (!EXIT_STATUS_0(exitstatus))
                HandleChildCrash(pid, exitstatus,
                                 _("autovacuum launcher process"));
            continue;
        }

        /*
         * Was it the archiver?  If so, just try to start a new one; no need
         * to force reset of the rest of the system.  (If fail, we'll try
         * again in future cycles of the main loop.).  Unless we were waiting
         * for it to shut down; don't restart it in that case, and
         * PostmasterStateMachine() will advance to the next shutdown step.
         */
        if (pid == PgArchPID)
        {
            PgArchPID = 0;
            if (!EXIT_STATUS_0(exitstatus))
                LogChildExit(LOG, _("archiver process"),
                             pid, exitstatus);
            if (PgArchStartupAllowed())
                PgArchPID = pgarch_start();
            continue;
        }

        /*
         * Was it the statistics collector?  If so, just try to start a new
         * one; no need to force reset of the rest of the system.  (If fail,
         * we'll try again in future cycles of the main loop.)
         */
        if (pid == PgStatPID)
        {
            PgStatPID = 0;
            if (!EXIT_STATUS_0(exitstatus))
                LogChildExit(LOG, _("statistics collector process"),
                             pid, exitstatus);
            if (pmState == PM_RUN || pmState == PM_HOT_STANDBY)
                PgStatPID = pgstat_start();
            continue;
        }

        /* Was it the system logger?  If so, try to start a new one */
        if (pid == SysLoggerPID)
        {
            SysLoggerPID = 0;
            /* for safety's sake, launch new logger *first* */
            SysLoggerPID = SysLogger_Start();
            if (!EXIT_STATUS_0(exitstatus))
                LogChildExit(LOG, _("system logger process"),
                             pid, exitstatus);
            continue;
        }

        /* Was it one of our background workers? */
        if (CleanupBackgroundWorker(pid, exitstatus))
        {
            /* have it be restarted */
            HaveCrashedWorker = true;
            continue;
        }

        /*
         * Else do standard backend child cleanup.
         */
        CleanupBackend(pid, exitstatus);
    }                           /* loop over pending child-death reports */

    /*
     * After cleaning out the SIGCHLD queue, see if we have any state changes
     * or actions to make.
     */
    PostmasterStateMachine();

    /* Done with signal handler */
#ifdef WIN32
    PG_SETMASK(&UnBlockSig);
#endif

    errno = save_errno;
}

/*
 * Scan the bgworkers list and see if the given PID (which has just stopped
 * or crashed) is in it.  Handle its shutdown if so, and return true.  If not a
 * bgworker, return false.
 *
 * This is heavily based on CleanupBackend.  One important difference is that
 * we don't know yet that the dying process is a bgworker, so we must be silent
 * until we're sure it is.
 */
static bool
CleanupBackgroundWorker(int pid,
                        int exitstatus) /* child's exit status */
{
    char        namebuf[MAXPGPATH];
    slist_mutable_iter iter;

    slist_foreach_modify(iter, &BackgroundWorkerList)
    {
        RegisteredBgWorker *rw;

        rw = slist_container(RegisteredBgWorker, rw_lnode, iter.cur);

        if (rw->rw_pid != pid)
            continue;

#ifdef WIN32
        /* see CleanupBackend */
        if (exitstatus == ERROR_WAIT_NO_CHILDREN)
            exitstatus = 0;
#endif

        snprintf(namebuf, MAXPGPATH, _("background worker \"%s\""),
                 rw->rw_worker.bgw_type);


        if (!EXIT_STATUS_0(exitstatus))
        {
            /* Record timestamp, so we know when to restart the worker. */
            rw->rw_crashed_at = GetCurrentTimestamp();
        }
        else
        {
            /* Zero exit status means terminate */
            rw->rw_crashed_at = 0;
            rw->rw_terminate = true;
        }

        /*
         * Additionally, for shared-memory-connected workers, just like a
         * backend, any exit status other than 0 or 1 is considered a crash
         * and causes a system-wide restart.
         */
        if ((rw->rw_worker.bgw_flags & BGWORKER_SHMEM_ACCESS) != 0)
        {
            if (!EXIT_STATUS_0(exitstatus) && !EXIT_STATUS_1(exitstatus))
            {
                HandleChildCrash(pid, exitstatus, namebuf);
                return true;
            }
        }

        /*
         * We must release the postmaster child slot whether this worker is
         * connected to shared memory or not, but we only treat it as a crash
         * if it is in fact connected.
         */
        if (!ReleasePostmasterChildSlot(rw->rw_child_slot) &&
            (rw->rw_worker.bgw_flags & BGWORKER_SHMEM_ACCESS) != 0)
        {
            HandleChildCrash(pid, exitstatus, namebuf);
            return true;
        }

        /* Get it out of the BackendList and clear out remaining data */
        dlist_delete(&rw->rw_backend->elem);
#ifdef EXEC_BACKEND
        ShmemBackendArrayRemove(rw->rw_backend);
#endif

        /*
         * It's possible that this background worker started some OTHER
         * background worker and asked to be notified when that worker started
         * or stopped.  If so, cancel any notifications destined for the
         * now-dead backend.
         */
        if (rw->rw_backend->bgworker_notify)
            BackgroundWorkerStopNotifications(rw->rw_pid);
        free(rw->rw_backend);
        rw->rw_backend = NULL;
        rw->rw_pid = 0;
        rw->rw_child_slot = 0;
        ReportBackgroundWorkerExit(&iter);  /* report child death */

        LogChildExit(EXIT_STATUS_0(exitstatus) ? DEBUG1 : LOG,
                     namebuf, pid, exitstatus);

        return true;
    }

    return false;
}

/*
 * CleanupBackend -- cleanup after terminated backend.
 *
 * Remove all local state associated with backend.
 *
 * If you change this, see also CleanupBackgroundWorker.
 */
static void
CleanupBackend(int pid,
               int exitstatus)  /* child's exit status. */
{
    dlist_mutable_iter iter;

    LogChildExit(DEBUG2, _("server process"), pid, exitstatus);

    /*
     * If a backend dies in an ugly way then we must signal all other backends
     * to quickdie.  If exit status is zero (normal) or one (FATAL exit), we
     * assume everything is all right and proceed to remove the backend from
     * the active backend list.
     */

#ifdef WIN32

    /*
     * On win32, also treat ERROR_WAIT_NO_CHILDREN (128) as nonfatal case,
     * since that sometimes happens under load when the process fails to start
     * properly (long before it starts using shared memory). Microsoft reports
     * it is related to mutex failure:
     * http://archives.postgresql.org/pgsql-hackers/2010-09/msg00790.php
     */
    if (exitstatus == ERROR_WAIT_NO_CHILDREN)
    {
        LogChildExit(LOG, _("server process"), pid, exitstatus);
        exitstatus = 0;
    }
#endif

    if (!EXIT_STATUS_0(exitstatus) && !EXIT_STATUS_1(exitstatus))
    {
        HandleChildCrash(pid, exitstatus, _("server process"));
        return;
    }

    dlist_foreach_modify(iter, &BackendList)
    {
        Backend    *bp = dlist_container(Backend, elem, iter.cur);

        if (bp->pid == pid)
        {
            if (!bp->dead_end)
            {
                if (!ReleasePostmasterChildSlot(bp->child_slot))
                {
                    /*
                     * Uh-oh, the child failed to clean itself up.  Treat as a
                     * crash after all.
                     */
                    HandleChildCrash(pid, exitstatus, _("server process"));
                    return;
                }
#ifdef EXEC_BACKEND
                ShmemBackendArrayRemove(bp);
#endif
            }
            if (bp->bgworker_notify)
            {
                /*
                 * This backend may have been slated to receive SIGUSR1 when
                 * some background worker started or stopped.  Cancel those
                 * notifications, as we don't want to signal PIDs that are not
                 * PostgreSQL backends.  This gets skipped in the (probably
                 * very common) case where the backend has never requested any
                 * such notifications.
                 */
                BackgroundWorkerStopNotifications(bp->pid);
            }
            dlist_delete(iter.cur);
            free(bp);
            break;
        }
    }
}

/*
 * HandleChildCrash -- cleanup after failed backend, bgwriter, checkpointer,
 * walwriter, autovacuum, or background worker.
 *
 * The objectives here are to clean up our local state about the child
 * process, and to signal all other remaining children to quickdie.
 */
static void
HandleChildCrash(int pid, int exitstatus, const char *procname)
{
    dlist_mutable_iter iter;
    slist_iter  siter;
    Backend    *bp;
    bool        take_action;

    /*
     * We only log messages and send signals if this is the first process
     * crash and we're not doing an immediate shutdown; otherwise, we're only
     * here to update postmaster's idea of live processes.  If we have already
     * signaled children, nonzero exit status is to be expected, so don't
     * clutter log.
     */
    take_action = !FatalError && Shutdown != ImmediateShutdown;

    if (take_action)
    {
        LogChildExit(LOG, procname, pid, exitstatus);
        ereport(LOG,
                (errmsg("terminating any other active server processes")));
    }

    /* Process background workers. */
    slist_foreach(siter, &BackgroundWorkerList)
    {
        RegisteredBgWorker *rw;

        rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur);
        if (rw->rw_pid == 0)
            continue;           /* not running */
        if (rw->rw_pid == pid)
        {
            /*
             * Found entry for freshly-dead worker, so remove it.
             */
            (void) ReleasePostmasterChildSlot(rw->rw_child_slot);
            dlist_delete(&rw->rw_backend->elem);
#ifdef EXEC_BACKEND
            ShmemBackendArrayRemove(rw->rw_backend);
#endif
            free(rw->rw_backend);
            rw->rw_backend = NULL;
            rw->rw_pid = 0;
            rw->rw_child_slot = 0;
            /* don't reset crashed_at */
            /* don't report child stop, either */
            /* Keep looping so we can signal remaining workers */
        }
        else
        {
            /*
             * This worker is still alive.  Unless we did so already, tell it
             * to commit hara-kiri.
             *
             * SIGQUIT is the special signal that says exit without proc_exit
             * and let the user know what's going on. But if SendStop is set
             * (-s on command line), then we send SIGSTOP instead, so that we
             * can get core dumps from all backends by hand.
             */
            if (take_action)
            {
                ereport(DEBUG2,
                        (errmsg_internal("sending %s to process %d",
                                         (SendStop ? "SIGSTOP" : "SIGQUIT"),
                                         (int) rw->rw_pid)));
                signal_child(rw->rw_pid, (SendStop ? SIGSTOP : SIGQUIT));
            }
        }
    }

    /* Process regular backends */
    dlist_foreach_modify(iter, &BackendList)
    {
        bp = dlist_container(Backend, elem, iter.cur);

        if (bp->pid == pid)
        {
            /*
             * Found entry for freshly-dead backend, so remove it.
             */
            if (!bp->dead_end)
            {
                (void) ReleasePostmasterChildSlot(bp->child_slot);
#ifdef EXEC_BACKEND
                ShmemBackendArrayRemove(bp);
#endif
            }
            dlist_delete(iter.cur);
            free(bp);
            /* Keep looping so we can signal remaining backends */
        }
        else
        {
            /*
             * This backend is still alive.  Unless we did so already, tell it
             * to commit hara-kiri.
             *
             * SIGQUIT is the special signal that says exit without proc_exit
             * and let the user know what's going on. But if SendStop is set
             * (-s on command line), then we send SIGSTOP instead, so that we
             * can get core dumps from all backends by hand.
             *
             * We could exclude dead_end children here, but at least in the
             * SIGSTOP case it seems better to include them.
             *
             * Background workers were already processed above; ignore them
             * here.
             */
            if (bp->bkend_type == BACKEND_TYPE_BGWORKER)
                continue;

            if (take_action)
            {
                ereport(DEBUG2,
                        (errmsg_internal("sending %s to process %d",
                                         (SendStop ? "SIGSTOP" : "SIGQUIT"),
                                         (int) bp->pid)));
                signal_child(bp->pid, (SendStop ? SIGSTOP : SIGQUIT));
            }
        }
    }

    /* Take care of the startup process too */
    if (pid == StartupPID)
    {
        StartupPID = 0;
        /* Caller adjusts StartupStatus, so don't touch it here */
    }
    else if (StartupPID != 0 && take_action)
    {
        ereport(DEBUG2,
                (errmsg_internal("sending %s to process %d",
                                 (SendStop ? "SIGSTOP" : "SIGQUIT"),
                                 (int) StartupPID)));
        signal_child(StartupPID, (SendStop ? SIGSTOP : SIGQUIT));
        StartupStatus = STARTUP_SIGNALED;
    }

    /* Take care of the bgwriter too */
    if (pid == BgWriterPID)
        BgWriterPID = 0;
    else if (BgWriterPID != 0 && take_action)
    {
        ereport(DEBUG2,
                (errmsg_internal("sending %s to process %d",
                                 (SendStop ? "SIGSTOP" : "SIGQUIT"),
                                 (int) BgWriterPID)));
        signal_child(BgWriterPID, (SendStop ? SIGSTOP : SIGQUIT));
    }

    /* Take care of the checkpointer too */
    if (pid == CheckpointerPID)
        CheckpointerPID = 0;
    else if (CheckpointerPID != 0 && take_action)
    {
        ereport(DEBUG2,
                (errmsg_internal("sending %s to process %d",
                                 (SendStop ? "SIGSTOP" : "SIGQUIT"),
                                 (int) CheckpointerPID)));
        signal_child(CheckpointerPID, (SendStop ? SIGSTOP : SIGQUIT));
    }

    /* Take care of the walwriter too */
    if (pid == WalWriterPID)
        WalWriterPID = 0;
    else if (WalWriterPID != 0 && take_action)
    {
        ereport(DEBUG2,
                (errmsg_internal("sending %s to process %d",
                                 (SendStop ? "SIGSTOP" : "SIGQUIT"),
                                 (int) WalWriterPID)));
        signal_child(WalWriterPID, (SendStop ? SIGSTOP : SIGQUIT));
    }

    /* Take care of the walreceiver too */
    if (pid == WalReceiverPID)
        WalReceiverPID = 0;
    else if (WalReceiverPID != 0 && take_action)
    {
        ereport(DEBUG2,
                (errmsg_internal("sending %s to process %d",
                                 (SendStop ? "SIGSTOP" : "SIGQUIT"),
                                 (int) WalReceiverPID)));
        signal_child(WalReceiverPID, (SendStop ? SIGSTOP : SIGQUIT));
    }

    /* Take care of the autovacuum launcher too */
    if (pid == AutoVacPID)
        AutoVacPID = 0;
    else if (AutoVacPID != 0 && take_action)
    {
        ereport(DEBUG2,
                (errmsg_internal("sending %s to process %d",
                                 (SendStop ? "SIGSTOP" : "SIGQUIT"),
                                 (int) AutoVacPID)));
        signal_child(AutoVacPID, (SendStop ? SIGSTOP : SIGQUIT));
    }

    /*
     * Force a power-cycle of the pgarch process too.  (This isn't absolutely
     * necessary, but it seems like a good idea for robustness, and it
     * simplifies the state-machine logic in the case where a shutdown request
     * arrives during crash processing.)
     */
    if (PgArchPID != 0 && take_action)
    {
        ereport(DEBUG2,
                (errmsg_internal("sending %s to process %d",
                                 "SIGQUIT",
                                 (int) PgArchPID)));
        signal_child(PgArchPID, SIGQUIT);
    }

    /*
     * Force a power-cycle of the pgstat process too.  (This isn't absolutely
     * necessary, but it seems like a good idea for robustness, and it
     * simplifies the state-machine logic in the case where a shutdown request
     * arrives during crash processing.)
     */
    if (PgStatPID != 0 && take_action)
    {
        ereport(DEBUG2,
                (errmsg_internal("sending %s to process %d",
                                 "SIGQUIT",
                                 (int) PgStatPID)));
        signal_child(PgStatPID, SIGQUIT);
        allow_immediate_pgstat_restart();
    }

    /* We do NOT restart the syslogger */

    if (Shutdown != ImmediateShutdown)
        FatalError = true;

    /* We now transit into a state of waiting for children to die */
    if (pmState == PM_RECOVERY ||
        pmState == PM_HOT_STANDBY ||
        pmState == PM_RUN ||
        pmState == PM_STOP_BACKENDS ||
        pmState == PM_SHUTDOWN)
        pmState = PM_WAIT_BACKENDS;

    /*
     * .. and if this doesn't happen quickly enough, now the clock is ticking
     * for us to kill them without mercy.
     */
    if (AbortStartTime == 0)
        AbortStartTime = time(NULL);
}

/*
 * Log the death of a child process.
 */
static void
LogChildExit(int lev, const char *procname, int pid, int exitstatus)
{
    /*
     * size of activity_buffer is arbitrary, but set equal to default
     * track_activity_query_size
     */
    char        activity_buffer[1024];
    const char *activity = NULL;

    if (!EXIT_STATUS_0(exitstatus))
        activity = pgstat_get_crashed_backend_activity(pid,
                                                       activity_buffer,
                                                       sizeof(activity_buffer));

    if (WIFEXITED(exitstatus))
        ereport(lev,

        /*------
          translator: %s is a noun phrase describing a child process, such as
          "server process" */
                (errmsg("%s (PID %d) exited with exit code %d",
                        procname, pid, WEXITSTATUS(exitstatus)),
                 activity ? errdetail("Failed process was running: %s", activity) : 0));
    else if (WIFSIGNALED(exitstatus))
    {
#if defined(WIN32)
        ereport(lev,

        /*------
          translator: %s is a noun phrase describing a child process, such as
          "server process" */
                (errmsg("%s (PID %d) was terminated by exception 0x%X",
                        procname, pid, WTERMSIG(exitstatus)),
                 errhint("See C include file \"ntstatus.h\" for a description of the hexadecimal value."),
                 activity ? errdetail("Failed process was running: %s", activity) : 0));
#else
        ereport(lev,

        /*------
          translator: %s is a noun phrase describing a child process, such as
          "server process" */
                (errmsg("%s (PID %d) was terminated by signal %d: %s",
                        procname, pid, WTERMSIG(exitstatus),
                        pg_strsignal(WTERMSIG(exitstatus))),
                 activity ? errdetail("Failed process was running: %s", activity) : 0));
#endif
    }
    else
        ereport(lev,

        /*------
          translator: %s is a noun phrase describing a child process, such as
          "server process" */
                (errmsg("%s (PID %d) exited with unrecognized status %d",
                        procname, pid, exitstatus),
                 activity ? errdetail("Failed process was running: %s", activity) : 0));
}

/*
 * Advance the postmaster's state machine and take actions as appropriate
 *
 * This is common code for pmdie(), reaper() and sigusr1_handler(), which
 * receive the signals that might mean we need to change state.
 */
static void
PostmasterStateMachine(void)
{
    /* If we're doing a smart shutdown, try to advance that state. */
    if (pmState == PM_RUN || pmState == PM_HOT_STANDBY)
    {
        if (connsAllowed == ALLOW_SUPERUSER_CONNS)
        {
            /*
             * ALLOW_SUPERUSER_CONNS state ends as soon as online backup mode
             * is not active.
             */
            if (!BackupInProgress())
                connsAllowed = ALLOW_NO_CONNS;
        }

        if (connsAllowed == ALLOW_NO_CONNS)
        {
            /*
             * ALLOW_NO_CONNS state ends when we have no normal client
             * backends running.  Then we're ready to stop other children.
             */
            if (CountChildren(BACKEND_TYPE_NORMAL) == 0)
                pmState = PM_STOP_BACKENDS;
        }
    }

    /*
     * If we're ready to do so, signal child processes to shut down.  (This
     * isn't a persistent state, but treating it as a distinct pmState allows
     * us to share this code across multiple shutdown code paths.)
     */
    if (pmState == PM_STOP_BACKENDS)
    {
        /* Signal all backend children except walsenders */
        SignalSomeChildren(SIGTERM,
                           BACKEND_TYPE_ALL - BACKEND_TYPE_WALSND);
        /* and the autovac launcher too */
        if (AutoVacPID != 0)
            signal_child(AutoVacPID, SIGTERM);
        /* and the bgwriter too */
        if (BgWriterPID != 0)
            signal_child(BgWriterPID, SIGTERM);
        /* and the walwriter too */
        if (WalWriterPID != 0)
            signal_child(WalWriterPID, SIGTERM);
        /* If we're in recovery, also stop startup and walreceiver procs */
        if (StartupPID != 0)
            signal_child(StartupPID, SIGTERM);
        if (WalReceiverPID != 0)
            signal_child(WalReceiverPID, SIGTERM);
        /* checkpointer, archiver, stats, and syslogger may continue for now */

        /* Now transition to PM_WAIT_BACKENDS state to wait for them to die */
        pmState = PM_WAIT_BACKENDS;
    }

    /*
     * If we are in a state-machine state that implies waiting for backends to
     * exit, see if they're all gone, and change state if so.
     */
    if (pmState == PM_WAIT_BACKENDS)
    {
        /*
         * PM_WAIT_BACKENDS state ends when we have no regular backends
         * (including autovac workers), no bgworkers (including unconnected
         * ones), and no walwriter, autovac launcher or bgwriter.  If we are
         * doing crash recovery or an immediate shutdown then we expect the
         * checkpointer to exit as well, otherwise not. The archiver, stats,
         * and syslogger processes are disregarded since they are not
         * connected to shared memory; we also disregard dead_end children
         * here. Walsenders are also disregarded, they will be terminated
         * later after writing the checkpoint record, like the archiver
         * process.
         */
        if (CountChildren(BACKEND_TYPE_ALL - BACKEND_TYPE_WALSND) == 0 &&
            StartupPID == 0 &&
            WalReceiverPID == 0 &&
            BgWriterPID == 0 &&
            (CheckpointerPID == 0 ||
             (!FatalError && Shutdown < ImmediateShutdown)) &&
            WalWriterPID == 0 &&
            AutoVacPID == 0)
        {
            if (Shutdown >= ImmediateShutdown || FatalError)
            {
                /*
                 * Start waiting for dead_end children to die.  This state
                 * change causes ServerLoop to stop creating new ones.
                 */
                pmState = PM_WAIT_DEAD_END;

                /*
                 * We already SIGQUIT'd the archiver and stats processes, if
                 * any, when we started immediate shutdown or entered
                 * FatalError state.
                 */
            }
            else
            {
                /*
                 * If we get here, we are proceeding with normal shutdown. All
                 * the regular children are gone, and it's time to tell the
                 * checkpointer to do a shutdown checkpoint.
                 */
                Assert(Shutdown > NoShutdown);
                /* Start the checkpointer if not running */
                if (CheckpointerPID == 0)
                    CheckpointerPID = StartCheckpointer();
                /* And tell it to shut down */
                if (CheckpointerPID != 0)
                {
                    signal_child(CheckpointerPID, SIGUSR2);
                    pmState = PM_SHUTDOWN;
                }
                else
                {
                    /*
                     * If we failed to fork a checkpointer, just shut down.
                     * Any required cleanup will happen at next restart. We
                     * set FatalError so that an "abnormal shutdown" message
                     * gets logged when we exit.
                     */
                    FatalError = true;
                    pmState = PM_WAIT_DEAD_END;

                    /* Kill the walsenders, archiver and stats collector too */
                    SignalChildren(SIGQUIT);
                    if (PgArchPID != 0)
                        signal_child(PgArchPID, SIGQUIT);
                    if (PgStatPID != 0)
                        signal_child(PgStatPID, SIGQUIT);
                }
            }
        }
    }

    if (pmState == PM_SHUTDOWN_2)
    {
        /*
         * PM_SHUTDOWN_2 state ends when there's no other children than
         * dead_end children left. There shouldn't be any regular backends
         * left by now anyway; what we're really waiting for is walsenders and
         * archiver.
         */
        if (PgArchPID == 0 && CountChildren(BACKEND_TYPE_ALL) == 0)
        {
            pmState = PM_WAIT_DEAD_END;
        }
    }

    if (pmState == PM_WAIT_DEAD_END)
    {
        /*
         * PM_WAIT_DEAD_END state ends when the BackendList is entirely empty
         * (ie, no dead_end children remain), and the archiver and stats
         * collector are gone too.
         *
         * The reason we wait for those two is to protect them against a new
         * postmaster starting conflicting subprocesses; this isn't an
         * ironclad protection, but it at least helps in the
         * shutdown-and-immediately-restart scenario.  Note that they have
         * already been sent appropriate shutdown signals, either during a
         * normal state transition leading up to PM_WAIT_DEAD_END, or during
         * FatalError processing.
         */
        if (dlist_is_empty(&BackendList) &&
            PgArchPID == 0 && PgStatPID == 0)
        {
            /* These other guys should be dead already */
            Assert(StartupPID == 0);
            Assert(WalReceiverPID == 0);
            Assert(BgWriterPID == 0);
            Assert(CheckpointerPID == 0);
            Assert(WalWriterPID == 0);
            Assert(AutoVacPID == 0);
            /* syslogger is not considered here */
            pmState = PM_NO_CHILDREN;
        }
    }

    /*
     * If we've been told to shut down, we exit as soon as there are no
     * remaining children.  If there was a crash, cleanup will occur at the
     * next startup.  (Before PostgreSQL 8.3, we tried to recover from the
     * crash before exiting, but that seems unwise if we are quitting because
     * we got SIGTERM from init --- there may well not be time for recovery
     * before init decides to SIGKILL us.)
     *
     * Note that the syslogger continues to run.  It will exit when it sees
     * EOF on its input pipe, which happens when there are no more upstream
     * processes.
     */
    if (Shutdown > NoShutdown && pmState == PM_NO_CHILDREN)
    {
        if (FatalError)
        {
            ereport(LOG, (errmsg("abnormal database system shutdown")));
            ExitPostmaster(1);
        }
        else
        {
            /*
             * Terminate exclusive backup mode to avoid recovery after a clean
             * fast shutdown.  Since an exclusive backup can only be taken
             * during normal running (and not, for example, while running
             * under Hot Standby) it only makes sense to do this if we reached
             * normal running. If we're still in recovery, the backup file is
             * one we're recovering *from*, and we must keep it around so that
             * recovery restarts from the right place.
             */
            if (ReachedNormalRunning)
                CancelBackup();

            /* Normal exit from the postmaster is here */
            ExitPostmaster(0);
        }
    }

    /*
     * If the startup process failed, or the user does not want an automatic
     * restart after backend crashes, wait for all non-syslogger children to
     * exit, and then exit postmaster.  We don't try to reinitialize when the
     * startup process fails, because more than likely it will just fail again
     * and we will keep trying forever.
     */
    if (pmState == PM_NO_CHILDREN &&
        (StartupStatus == STARTUP_CRASHED || !restart_after_crash))
        ExitPostmaster(1);

    /*
     * If we need to recover from a crash, wait for all non-syslogger children
     * to exit, then reset shmem and StartupDataBase.
     */
    if (FatalError && pmState == PM_NO_CHILDREN)
    {
        ereport(LOG,
                (errmsg("all server processes terminated; reinitializing")));

        /* allow background workers to immediately restart */
        ResetBackgroundWorkerCrashTimes();

        shmem_exit(1);

        /* re-read control file into local memory */
        LocalProcessControlFile(true);

        reset_shared();

        StartupPID = StartupDataBase();
        Assert(StartupPID != 0);
        StartupStatus = STARTUP_RUNNING;
        pmState = PM_STARTUP;
        /* crash recovery started, reset SIGKILL flag */
        AbortStartTime = 0;
    }
}


/*
 * Send a signal to a postmaster child process
 *
 * On systems that have setsid(), each child process sets itself up as a
 * process group leader.  For signals that are generally interpreted in the
 * appropriate fashion, we signal the entire process group not just the
 * direct child process.  This allows us to, for example, SIGQUIT a blocked
 * archive_recovery script, or SIGINT a script being run by a backend via
 * system().
 *
 * There is a race condition for recently-forked children: they might not
 * have executed setsid() yet.  So we signal the child directly as well as
 * the group.  We assume such a child will handle the signal before trying
 * to spawn any grandchild processes.  We also assume that signaling the
 * child twice will not cause any problems.
 */
static void
signal_child(pid_t pid, int signal)
{
    if (kill(pid, signal) < 0)
        elog(DEBUG3, "kill(%ld,%d) failed: %m", (long) pid, signal);
#ifdef HAVE_SETSID
    switch (signal)
    {
        case SIGINT:
        case SIGTERM:
        case SIGQUIT:
        case SIGSTOP:
        case SIGKILL:
            if (kill(-pid, signal) < 0)
                elog(DEBUG3, "kill(%ld,%d) failed: %m", (long) (-pid), signal);
            break;
        default:
            break;
    }
#endif
}

/*
 * Send a signal to the targeted children (but NOT special children;
 * dead_end children are never signaled, either).
 */
static bool
SignalSomeChildren(int signal, int target)
{
    dlist_iter  iter;
    bool        signaled = false;

    dlist_foreach(iter, &BackendList)
    {
        Backend    *bp = dlist_container(Backend, elem, iter.cur);

        if (bp->dead_end)
            continue;

        /*
         * Since target == BACKEND_TYPE_ALL is the most common case, we test
         * it first and avoid touching shared memory for every child.
         */
        if (target != BACKEND_TYPE_ALL)
        {
            /*
             * Assign bkend_type for any recently announced WAL Sender
             * processes.
             */
            if (bp->bkend_type == BACKEND_TYPE_NORMAL &&
                IsPostmasterChildWalSender(bp->child_slot))
                bp->bkend_type = BACKEND_TYPE_WALSND;

            if (!(target & bp->bkend_type))
                continue;
        }

        ereport(DEBUG4,
                (errmsg_internal("sending signal %d to process %d",
                                 signal, (int) bp->pid)));
        signal_child(bp->pid, signal);
        signaled = true;
    }
    return signaled;
}

/*
 * Send a termination signal to children.  This considers all of our children
 * processes, except syslogger and dead_end backends.
 */
static void
TerminateChildren(int signal)
{
    SignalChildren(signal);
    if (StartupPID != 0)
    {
        signal_child(StartupPID, signal);
        if (signal == SIGQUIT || signal == SIGKILL)
            StartupStatus = STARTUP_SIGNALED;
    }
    if (BgWriterPID != 0)
        signal_child(BgWriterPID, signal);
    if (CheckpointerPID != 0)
        signal_child(CheckpointerPID, signal);
    if (WalWriterPID != 0)
        signal_child(WalWriterPID, signal);
    if (WalReceiverPID != 0)
        signal_child(WalReceiverPID, signal);
    if (AutoVacPID != 0)
        signal_child(AutoVacPID, signal);
    if (PgArchPID != 0)
        signal_child(PgArchPID, signal);
    if (PgStatPID != 0)
        signal_child(PgStatPID, signal);
}

/*
 * BackendStartup -- start backend process
 *
 * returns: STATUS_ERROR if the fork failed, STATUS_OK otherwise.
 *
 * Note: if you change this code, also consider StartAutovacuumWorker.
 */
static int
BackendStartup(Port *port)
{
    Backend    *bn;             /* for backend cleanup */
    pid_t       pid;

    /*
     * Create backend data structure.  Better before the fork() so we can
     * handle failure cleanly.
     */
    bn = (Backend *) malloc(sizeof(Backend));
    if (!bn)
    {
        ereport(LOG,
                (errcode(ERRCODE_OUT_OF_MEMORY),
                 errmsg("out of memory")));
        return STATUS_ERROR;
    }

    /*
     * Compute the cancel key that will be assigned to this backend. The
     * backend will have its own copy in the forked-off process' value of
     * MyCancelKey, so that it can transmit the key to the frontend.
     */
    if (!RandomCancelKey(&MyCancelKey))
    {
        free(bn);
        ereport(LOG,
                (errcode(ERRCODE_INTERNAL_ERROR),
                 errmsg("could not generate random cancel key")));
        return STATUS_ERROR;
    }

    bn->cancel_key = MyCancelKey;

    /* Pass down canAcceptConnections state */
    port->canAcceptConnections = canAcceptConnections(BACKEND_TYPE_NORMAL);
    bn->dead_end = (port->canAcceptConnections != CAC_OK &&
                    port->canAcceptConnections != CAC_SUPERUSER);

    /*
     * Unless it's a dead_end child, assign it a child slot number
     */
    if (!bn->dead_end)
        bn->child_slot = MyPMChildSlot = AssignPostmasterChildSlot();
    else
        bn->child_slot = 0;

    /* Hasn't asked to be notified about any bgworkers yet */
    bn->bgworker_notify = false;

#ifdef EXEC_BACKEND
    pid = backend_forkexec(port);
#else                           /* !EXEC_BACKEND */
    pid = fork_process();
    if (pid == 0)               /* child */
    {
        free(bn);

        /* Detangle from postmaster */
        InitPostmasterChild();

        /* Close the postmaster's sockets */
        ClosePostmasterPorts(false);

        /* Perform additional initialization and collect startup packet */
        BackendInitialize(port);

        /* And run the backend */
        BackendRun(port);
    }
#endif                          /* EXEC_BACKEND */

    if (pid < 0)
    {
        /* in parent, fork failed */
        int         save_errno = errno;

        if (!bn->dead_end)
            (void) ReleasePostmasterChildSlot(bn->child_slot);
        free(bn);
        errno = save_errno;
        ereport(LOG,
                (errmsg("could not fork new process for connection: %m")));
        report_fork_failure_to_client(port, save_errno);
        return STATUS_ERROR;
    }

    /* in parent, successful fork */
    ereport(DEBUG2,
            (errmsg_internal("forked new backend, pid=%d socket=%d",
                             (int) pid, (int) port->sock)));

    /*
     * Everything's been successful, it's safe to add this backend to our list
     * of backends.
     */
    bn->pid = pid;
    bn->bkend_type = BACKEND_TYPE_NORMAL;   /* Can change later to WALSND */
    dlist_push_head(&BackendList, &bn->elem);

#ifdef EXEC_BACKEND
    if (!bn->dead_end)
        ShmemBackendArrayAdd(bn);
#endif

    return STATUS_OK;
}

/*
 * Try to report backend fork() failure to client before we close the
 * connection.  Since we do not care to risk blocking the postmaster on
 * this connection, we set the connection to non-blocking and try only once.
 *
 * This is grungy special-purpose code; we cannot use backend libpq since
 * it's not up and running.
 */
static void
report_fork_failure_to_client(Port *port, int errnum)
{
    char        buffer[1000];
    int         rc;

    /* Format the error message packet (always V2 protocol) */
    snprintf(buffer, sizeof(buffer), "E%s%s\n",
             _("could not fork new process for connection: "),
             strerror(errnum));

    /* Set port to non-blocking.  Don't do send() if this fails */
    if (!pg_set_noblock(port->sock))
        return;

    /* We'll retry after EINTR, but ignore all other failures */
    do
    {
        rc = send(port->sock, buffer, strlen(buffer) + 1, 0);
    } while (rc < 0 && errno == EINTR);
}


/*
 * BackendInitialize -- initialize an interactive (postmaster-child)
 *              backend process, and collect the client's startup packet.
 *
 * returns: nothing.  Will not return at all if there's any failure.
 *
 * Note: this code does not depend on having any access to shared memory.
 * Indeed, our approach to SIGTERM/timeout handling *requires* that
 * shared memory not have been touched yet; see comments within.
 * In the EXEC_BACKEND case, we are physically attached to shared memory
 * but have not yet set up most of our local pointers to shmem structures.
 */
static void
BackendInitialize(Port *port)
{
    int         status;
    int         ret;
    char        remote_host[NI_MAXHOST];
    char        remote_port[NI_MAXSERV];
    StringInfoData ps_data;

    /* Save port etc. for ps status */
    MyProcPort = port;

    /* Tell fd.c about the long-lived FD associated with the port */
    ReserveExternalFD();

    /*
     * PreAuthDelay is a debugging aid for investigating problems in the
     * authentication cycle: it can be set in postgresql.conf to allow time to
     * attach to the newly-forked backend with a debugger.  (See also
     * PostAuthDelay, which we allow clients to pass through PGOPTIONS, but it
     * is not honored until after authentication.)
     */
    if (PreAuthDelay > 0)
        pg_usleep(PreAuthDelay * 1000000L);

    /* This flag will remain set until InitPostgres finishes authentication */
    ClientAuthInProgress = true;    /* limit visibility of log messages */

    /* set these to empty in case they are needed before we set them up */
    port->remote_host = "";
    port->remote_port = "";

    /*
     * Initialize libpq and enable reporting of ereport errors to the client.
     * Must do this now because authentication uses libpq to send messages.
     */
    pq_init();                  /* initialize libpq to talk to client */
    whereToSendOutput = DestRemote; /* now safe to ereport to client */

    /*
     * We arrange to do _exit(1) if we receive SIGTERM or timeout while trying
     * to collect the startup packet; while SIGQUIT results in _exit(2).
     * Otherwise the postmaster cannot shutdown the database FAST or IMMED
     * cleanly if a buggy client fails to send the packet promptly.
     *
     * Exiting with _exit(1) is only possible because we have not yet touched
     * shared memory; therefore no outside-the-process state needs to get
     * cleaned up.
     */
    pqsignal(SIGTERM, process_startup_packet_die);
    /* SIGQUIT handler was already set up by InitPostmasterChild */
    InitializeTimeouts();       /* establishes SIGALRM handler */
    PG_SETMASK(&StartupBlockSig);

    /*
     * Get the remote host name and port for logging and status display.
     */
    remote_host[0] = '\0';
    remote_port[0] = '\0';
    if ((ret = pg_getnameinfo_all(&port->raddr.addr, port->raddr.salen,
                                  remote_host, sizeof(remote_host),
                                  remote_port, sizeof(remote_port),
                                  (log_hostname ? 0 : NI_NUMERICHOST) | NI_NUMERICSERV)) != 0)
        ereport(WARNING,
                (errmsg_internal("pg_getnameinfo_all() failed: %s",
                                 gai_strerror(ret))));

    /*
     * Save remote_host and remote_port in port structure (after this, they
     * will appear in log_line_prefix data for log messages).
     */
    port->remote_host = strdup(remote_host);
    port->remote_port = strdup(remote_port);

    /* And now we can issue the Log_connections message, if wanted */
    if (Log_connections)
    {
        if (remote_port[0])
            ereport(LOG,
                    (errmsg("connection received: host=%s port=%s",
                            remote_host,
                            remote_port)));
        else
            ereport(LOG,
                    (errmsg("connection received: host=%s",
                            remote_host)));
    }

    /*
     * If we did a reverse lookup to name, we might as well save the results
     * rather than possibly repeating the lookup during authentication.
     *
     * Note that we don't want to specify NI_NAMEREQD above, because then we'd
     * get nothing useful for a client without an rDNS entry.  Therefore, we
     * must check whether we got a numeric IPv4 or IPv6 address, and not save
     * it into remote_hostname if so.  (This test is conservative and might
     * sometimes classify a hostname as numeric, but an error in that
     * direction is safe; it only results in a possible extra lookup.)
     */
    if (log_hostname &&
        ret == 0 &&
        strspn(remote_host, "0123456789.") < strlen(remote_host) &&
        strspn(remote_host, "0123456789ABCDEFabcdef:") < strlen(remote_host))
        port->remote_hostname = strdup(remote_host);

    /*
     * Ready to begin client interaction.  We will give up and _exit(1) after
     * a time delay, so that a broken client can't hog a connection
     * indefinitely.  PreAuthDelay and any DNS interactions above don't count
     * against the time limit.
     *
     * Note: AuthenticationTimeout is applied here while waiting for the
     * startup packet, and then again in InitPostgres for the duration of any
     * authentication operations.  So a hostile client could tie up the
     * process for nearly twice AuthenticationTimeout before we kick him off.
     *
     * Note: because PostgresMain will call InitializeTimeouts again, the
     * registration of STARTUP_PACKET_TIMEOUT will be lost.  This is okay
     * since we never use it again after this function.
     */
    RegisterTimeout(STARTUP_PACKET_TIMEOUT, StartupPacketTimeoutHandler);
    enable_timeout_after(STARTUP_PACKET_TIMEOUT, AuthenticationTimeout * 1000);

    /*
     * Receive the startup packet (which might turn out to be a cancel request
     * packet).
     */
    status = ProcessStartupPacket(port, false, false);

    /*
     * Disable the timeout, and prevent SIGTERM again.
     */
    disable_timeout(STARTUP_PACKET_TIMEOUT, false);
    PG_SETMASK(&BlockSig);

    /*
     * As a safety check that nothing in startup has yet performed
     * shared-memory modifications that would need to be undone if we had
     * exited through SIGTERM or timeout above, check that no on_shmem_exit
     * handlers have been registered yet.  (This isn't terribly bulletproof,
     * since someone might misuse an on_proc_exit handler for shmem cleanup,
     * but it's a cheap and helpful check.  We cannot disallow on_proc_exit
     * handlers unfortunately, since pq_init() already registered one.)
     */
    check_on_shmem_exit_lists_are_empty();

    /*
     * Stop here if it was bad or a cancel packet.  ProcessStartupPacket
     * already did any appropriate error reporting.
     */
    if (status != STATUS_OK)
        proc_exit(0);

    /*
     * Now that we have the user and database name, we can set the process
     * title for ps.  It's good to do this as early as possible in startup.
     */
    initStringInfo(&ps_data);
    if (am_walsender)
        appendStringInfo(&ps_data, "%s ", GetBackendTypeDesc(B_WAL_SENDER));
    appendStringInfo(&ps_data, "%s ", port->user_name);
    if (!am_walsender)
        appendStringInfo(&ps_data, "%s ", port->database_name);
    appendStringInfo(&ps_data, "%s", port->remote_host);
    if (port->remote_port[0] != '\0')
        appendStringInfo(&ps_data, "(%s)", port->remote_port);

    init_ps_display(ps_data.data);
    pfree(ps_data.data);

    set_ps_display("initializing");
}


/*
 * BackendRun -- set up the backend's argument list and invoke PostgresMain()
 *
 * returns:
 *      Shouldn't return at all.
 *      If PostgresMain() fails, return status.
 */
static void
BackendRun(Port *port)
{
    char      **av;
    int         maxac;
    int         ac;
    int         i;

    /*
     * Now, build the argv vector that will be given to PostgresMain.
     *
     * The maximum possible number of commandline arguments that could come
     * from ExtraOptions is (strlen(ExtraOptions) + 1) / 2; see
     * pg_split_opts().
     */
    maxac = 2;                  /* for fixed args supplied below */
    maxac += (strlen(ExtraOptions) + 1) / 2;

    av = (char **) MemoryContextAlloc(TopMemoryContext,
                                      maxac * sizeof(char *));
    ac = 0;

    av[ac++] = "postgres";

    /*
     * Pass any backend switches specified with -o on the postmaster's own
     * command line.  We assume these are secure.
     */
    pg_split_opts(av, &ac, ExtraOptions);

    av[ac] = NULL;

    Assert(ac < maxac);

    /*
     * Debug: print arguments being passed to backend
     */
    ereport(DEBUG3,
            (errmsg_internal("%s child[%d]: starting with (",
                             progname, (int) getpid())));
    for (i = 0; i < ac; ++i)
        ereport(DEBUG3,
                (errmsg_internal("\t%s", av[i])));
    ereport(DEBUG3,
            (errmsg_internal(")")));

    /*
     * Make sure we aren't in PostmasterContext anymore.  (We can't delete it
     * just yet, though, because InitPostgres will need the HBA data.)
     */
    MemoryContextSwitchTo(TopMemoryContext);

    PostgresMain(ac, av, port->database_name, port->user_name);
}


#ifdef EXEC_BACKEND

/*
 * postmaster_forkexec -- fork and exec a postmaster subprocess
 *
 * The caller must have set up the argv array already, except for argv[2]
 * which will be filled with the name of the temp variable file.
 *
 * Returns the child process PID, or -1 on fork failure (a suitable error
 * message has been logged on failure).
 *
 * All uses of this routine will dispatch to SubPostmasterMain in the
 * child process.
 */
pid_t
postmaster_forkexec(int argc, char *argv[])
{
    Port        port;

    /* This entry point passes dummy values for the Port variables */
    memset(&port, 0, sizeof(port));
    return internal_forkexec(argc, argv, &port);
}

/*
 * backend_forkexec -- fork/exec off a backend process
 *
 * Some operating systems (WIN32) don't have fork() so we have to simulate
 * it by storing parameters that need to be passed to the child and
 * then create a new child process.
 *
 * returns the pid of the fork/exec'd process, or -1 on failure
 */
static pid_t
backend_forkexec(Port *port)
{
    char       *av[4];
    int         ac = 0;

    av[ac++] = "postgres";
    av[ac++] = "--forkbackend";
    av[ac++] = NULL;            /* filled in by internal_forkexec */

    av[ac] = NULL;
    Assert(ac < lengthof(av));

    return internal_forkexec(ac, av, port);
}

#ifndef WIN32

/*
 * internal_forkexec non-win32 implementation
 *
 * - writes out backend variables to the parameter file
 * - fork():s, and then exec():s the child process
 */
static pid_t
internal_forkexec(int argc, char *argv[], Port *port)
{
    static unsigned long tmpBackendFileNum = 0;
    pid_t       pid;
    char        tmpfilename[MAXPGPATH];
    BackendParameters param;
    FILE       *fp;

    if (!save_backend_variables(&param, port))
        return -1;              /* log made by save_backend_variables */

    /* Calculate name for temp file */
    snprintf(tmpfilename, MAXPGPATH, "%s/%s.backend_var.%d.%lu",
             PG_TEMP_FILES_DIR, PG_TEMP_FILE_PREFIX,
             MyProcPid, ++tmpBackendFileNum);

    /* Open file */
    fp = AllocateFile(tmpfilename, PG_BINARY_W);
    if (!fp)
    {
        /*
         * As in OpenTemporaryFileInTablespace, try to make the temp-file
         * directory, ignoring errors.
         */
        (void) MakePGDirectory(PG_TEMP_FILES_DIR);

        fp = AllocateFile(tmpfilename, PG_BINARY_W);
        if (!fp)
        {
            ereport(LOG,
                    (errcode_for_file_access(),
                     errmsg("could not create file \"%s\": %m",
                            tmpfilename)));
            return -1;
        }
    }

    if (fwrite(&param, sizeof(param), 1, fp) != 1)
    {
        ereport(LOG,
                (errcode_for_file_access(),
                 errmsg("could not write to file \"%s\": %m", tmpfilename)));
        FreeFile(fp);
        return -1;
    }

    /* Release file */
    if (FreeFile(fp))
    {
        ereport(LOG,
                (errcode_for_file_access(),
                 errmsg("could not write to file \"%s\": %m", tmpfilename)));
        return -1;
    }

    /* Make sure caller set up argv properly */
    Assert(argc >= 3);
    Assert(argv[argc] == NULL);
    Assert(strncmp(argv[1], "--fork", 6) == 0);
    Assert(argv[2] == NULL);

    /* Insert temp file name after --fork argument */
    argv[2] = tmpfilename;

    /* Fire off execv in child */
    if ((pid = fork_process()) == 0)
    {
        if (execv(postgres_exec_path, argv) < 0)
        {
            ereport(LOG,
                    (errmsg("could not execute server process \"%s\": %m",
                            postgres_exec_path)));
            /* We're already in the child process here, can't return */
            exit(1);
        }
    }

    return pid;                 /* Parent returns pid, or -1 on fork failure */
}
#else                           /* WIN32 */

/*
 * internal_forkexec win32 implementation
 *
 * - starts backend using CreateProcess(), in suspended state
 * - writes out backend variables to the parameter file
 *  - during this, duplicates handles and sockets required for
 *    inheritance into the new process
 * - resumes execution of the new process once the backend parameter
 *   file is complete.
 */
static pid_t
internal_forkexec(int argc, char *argv[], Port *port)
{
    int         retry_count = 0;
    STARTUPINFO si;
    PROCESS_INFORMATION pi;
    int         i;
    int         j;
    char        cmdLine[MAXPGPATH * 2];
    HANDLE      paramHandle;
    BackendParameters *param;
    SECURITY_ATTRIBUTES sa;
    char        paramHandleStr[32];
    win32_deadchild_waitinfo *childinfo;

    /* Make sure caller set up argv properly */
    Assert(argc >= 3);
    Assert(argv[argc] == NULL);
    Assert(strncmp(argv[1], "--fork", 6) == 0);
    Assert(argv[2] == NULL);

    /* Resume here if we need to retry */
retry:

    /* Set up shared memory for parameter passing */
    ZeroMemory(&sa, sizeof(sa));
    sa.nLength = sizeof(sa);
    sa.bInheritHandle = TRUE;
    paramHandle = CreateFileMapping(INVALID_HANDLE_VALUE,
                                    &sa,
                                    PAGE_READWRITE,
                                    0,
                                    sizeof(BackendParameters),
                                    NULL);
    if (paramHandle == INVALID_HANDLE_VALUE)
    {
        elog(LOG, "could not create backend parameter file mapping: error code %lu",
             GetLastError());
        return -1;
    }

    param = MapViewOfFile(paramHandle, FILE_MAP_WRITE, 0, 0, sizeof(BackendParameters));
    if (!param)
    {
        elog(LOG, "could not map backend parameter memory: error code %lu",
             GetLastError());
        CloseHandle(paramHandle);
        return -1;
    }

    /* Insert temp file name after --fork argument */
#ifdef _WIN64
    sprintf(paramHandleStr, "%llu", (LONG_PTR) paramHandle);
#else
    sprintf(paramHandleStr, "%lu", (DWORD) paramHandle);
#endif
    argv[2] = paramHandleStr;

    /* Format the cmd line */
    cmdLine[sizeof(cmdLine) - 1] = '\0';
    cmdLine[sizeof(cmdLine) - 2] = '\0';
    snprintf(cmdLine, sizeof(cmdLine) - 1, "\"%s\"", postgres_exec_path);
    i = 0;
    while (argv[++i] != NULL)
    {
        j = strlen(cmdLine);
        snprintf(cmdLine + j, sizeof(cmdLine) - 1 - j, " \"%s\"", argv[i]);
    }
    if (cmdLine[sizeof(cmdLine) - 2] != '\0')
    {
        elog(LOG, "subprocess command line too long");
        UnmapViewOfFile(param);
        CloseHandle(paramHandle);
        return -1;
    }

    memset(&pi, 0, sizeof(pi));
    memset(&si, 0, sizeof(si));
    si.cb = sizeof(si);

    /*
     * Create the subprocess in a suspended state. This will be resumed later,
     * once we have written out the parameter file.
     */
    if (!CreateProcess(NULL, cmdLine, NULL, NULL, TRUE, CREATE_SUSPENDED,
                       NULL, NULL, &si, &pi))
    {
        elog(LOG, "CreateProcess call failed: %m (error code %lu)",
             GetLastError());
        UnmapViewOfFile(param);
        CloseHandle(paramHandle);
        return -1;
    }

    if (!save_backend_variables(param, port, pi.hProcess, pi.dwProcessId))
    {
        /*
         * log made by save_backend_variables, but we have to clean up the
         * mess with the half-started process
         */
        if (!TerminateProcess(pi.hProcess, 255))
            ereport(LOG,
                    (errmsg_internal("could not terminate unstarted process: error code %lu",
                                     GetLastError())));
        CloseHandle(pi.hProcess);
        CloseHandle(pi.hThread);
        UnmapViewOfFile(param);
        CloseHandle(paramHandle);
        return -1;              /* log made by save_backend_variables */
    }

    /* Drop the parameter shared memory that is now inherited to the backend */
    if (!UnmapViewOfFile(param))
        elog(LOG, "could not unmap view of backend parameter file: error code %lu",
             GetLastError());
    if (!CloseHandle(paramHandle))
        elog(LOG, "could not close handle to backend parameter file: error code %lu",
             GetLastError());

    /*
     * Reserve the memory region used by our main shared memory segment before
     * we resume the child process.  Normally this should succeed, but if ASLR
     * is active then it might sometimes fail due to the stack or heap having
     * gotten mapped into that range.  In that case, just terminate the
     * process and retry.
     */
    if (!pgwin32_ReserveSharedMemoryRegion(pi.hProcess))
    {
        /* pgwin32_ReserveSharedMemoryRegion already made a log entry */
        if (!TerminateProcess(pi.hProcess, 255))
            ereport(LOG,
                    (errmsg_internal("could not terminate process that failed to reserve memory: error code %lu",
                                     GetLastError())));
        CloseHandle(pi.hProcess);
        CloseHandle(pi.hThread);
        if (++retry_count < 100)
            goto retry;
        ereport(LOG,
                (errmsg("giving up after too many tries to reserve shared memory"),
                 errhint("This might be caused by ASLR or antivirus software.")));
        return -1;
    }

    /*
     * Now that the backend variables are written out, we start the child
     * thread so it can start initializing while we set up the rest of the
     * parent state.
     */
    if (ResumeThread(pi.hThread) == -1)
    {
        if (!TerminateProcess(pi.hProcess, 255))
        {
            ereport(LOG,
                    (errmsg_internal("could not terminate unstartable process: error code %lu",
                                     GetLastError())));
            CloseHandle(pi.hProcess);
            CloseHandle(pi.hThread);
            return -1;
        }
        CloseHandle(pi.hProcess);
        CloseHandle(pi.hThread);
        ereport(LOG,
                (errmsg_internal("could not resume thread of unstarted process: error code %lu",
                                 GetLastError())));
        return -1;
    }

    /*
     * Queue a waiter to signal when this child dies. The wait will be handled
     * automatically by an operating system thread pool.
     *
     * Note: use malloc instead of palloc, since it needs to be thread-safe.
     * Struct will be free():d from the callback function that runs on a
     * different thread.
     */
    childinfo = malloc(sizeof(win32_deadchild_waitinfo));
    if (!childinfo)
        ereport(FATAL,
                (errcode(ERRCODE_OUT_OF_MEMORY),
                 errmsg("out of memory")));

    childinfo->procHandle = pi.hProcess;
    childinfo->procId = pi.dwProcessId;

    if (!RegisterWaitForSingleObject(&childinfo->waitHandle,
                                     pi.hProcess,
                                     pgwin32_deadchild_callback,
                                     childinfo,
                                     INFINITE,
                                     WT_EXECUTEONLYONCE | WT_EXECUTEINWAITTHREAD))
        ereport(FATAL,
                (errmsg_internal("could not register process for wait: error code %lu",
                                 GetLastError())));

    /* Don't close pi.hProcess here - the wait thread needs access to it */

    CloseHandle(pi.hThread);

    return pi.dwProcessId;
}
#endif                          /* WIN32 */


/*
 * SubPostmasterMain -- Get the fork/exec'd process into a state equivalent
 *          to what it would be if we'd simply forked on Unix, and then
 *          dispatch to the appropriate place.
 *
 * The first two command line arguments are expected to be "--forkFOO"
 * (where FOO indicates which postmaster child we are to become), and
 * the name of a variables file that we can read to load data that would
 * have been inherited by fork() on Unix.  Remaining arguments go to the
 * subprocess FooMain() routine.
 */
void
SubPostmasterMain(int argc, char *argv[])
{
    Port        port;

    /* In EXEC_BACKEND case we will not have inherited these settings */
    IsPostmasterEnvironment = true;
    whereToSendOutput = DestNone;

    /* Setup essential subsystems (to ensure elog() behaves sanely) */
    InitializeGUCOptions();

    /* Check we got appropriate args */
    if (argc < 3)
        elog(FATAL, "invalid subpostmaster invocation");

    /* Read in the variables file */
    memset(&port, 0, sizeof(Port));
    read_backend_variables(argv[2], &port);

    /* Close the postmaster's sockets (as soon as we know them) */
    ClosePostmasterPorts(strcmp(argv[1], "--forklog") == 0);

    /*
     * Start our win32 signal implementation. This has to be done after we
     * read the backend variables, because we need to pick up the signal pipe
     * from the parent process.
     */
#ifdef WIN32
    pgwin32_signal_initialize();
#endif

    /* Setup as postmaster child */
    InitPostmasterChild();

    /*
     * Set up memory area for GSS information. Mirrors the code in ConnCreate
     * for the non-exec case.
     */
#if defined(ENABLE_GSS) || defined(ENABLE_SSPI)
    port.gss = (pg_gssinfo *) calloc(1, sizeof(pg_gssinfo));
    if (!port.gss)
        ereport(FATAL,
                (errcode(ERRCODE_OUT_OF_MEMORY),
                 errmsg("out of memory")));
#endif

    /*
     * If appropriate, physically re-attach to shared memory segment. We want
     * to do this before going any further to ensure that we can attach at the
     * same address the postmaster used.  On the other hand, if we choose not
     * to re-attach, we may have other cleanup to do.
     *
     * If testing EXEC_BACKEND on Linux, you should run this as root before
     * starting the postmaster:
     *
     * echo 0 >/proc/sys/kernel/randomize_va_space
     *
     * This prevents using randomized stack and code addresses that cause the
     * child process's memory map to be different from the parent's, making it
     * sometimes impossible to attach to shared memory at the desired address.
     * Return the setting to its old value (usually '1' or '2') when finished.
     */
    if (strcmp(argv[1], "--forkbackend") == 0 ||
        strcmp(argv[1], "--forkavlauncher") == 0 ||
        strcmp(argv[1], "--forkavworker") == 0 ||
        strcmp(argv[1], "--forkboot") == 0 ||
        strncmp(argv[1], "--forkbgworker=", 15) == 0)
        PGSharedMemoryReAttach();
    else
        PGSharedMemoryNoReAttach();

    /* autovacuum needs this set before calling InitProcess */
    if (strcmp(argv[1], "--forkavlauncher") == 0)
        AutovacuumLauncherIAm();
    if (strcmp(argv[1], "--forkavworker") == 0)
        AutovacuumWorkerIAm();

    /* Read in remaining GUC variables */
    read_nondefault_variables();

    /*
     * Check that the data directory looks valid, which will also check the
     * privileges on the data directory and update our umask and file/group
     * variables for creating files later.  Note: this should really be done
     * before we create any files or directories.
     */
    checkDataDir();

    /*
     * (re-)read control file, as it contains config. The postmaster will
     * already have read this, but this process doesn't know about that.
     */
    LocalProcessControlFile(false);

    /*
     * Reload any libraries that were preloaded by the postmaster.  Since we
     * exec'd this process, those libraries didn't come along with us; but we
     * should load them into all child processes to be consistent with the
     * non-EXEC_BACKEND behavior.
     */
    process_shared_preload_libraries();

    /* Run backend or appropriate child */
    if (strcmp(argv[1], "--forkbackend") == 0)
    {
        Assert(argc == 3);      /* shouldn't be any more args */

        /*
         * Need to reinitialize the SSL library in the backend, since the
         * context structures contain function pointers and cannot be passed
         * through the parameter file.
         *
         * If for some reason reload fails (maybe the user installed broken
         * key files), soldier on without SSL; that's better than all
         * connections becoming impossible.
         *
         * XXX should we do this in all child processes?  For the moment it's
         * enough to do it in backend children.
         */
#ifdef USE_SSL
        if (EnableSSL)
        {
            if (secure_initialize(false) == 0)
                LoadedSSL = true;
            else
                ereport(LOG,
                        (errmsg("SSL configuration could not be loaded in child process")));
        }
#endif

        /*
         * Perform additional initialization and collect startup packet.
         *
         * We want to do this before InitProcess() for a couple of reasons: 1.
         * so that we aren't eating up a PGPROC slot while waiting on the
         * client. 2. so that if InitProcess() fails due to being out of
         * PGPROC slots, we have already initialized libpq and are able to
         * report the error to the client.
         */
        BackendInitialize(&port);

        /* Restore basic shared memory pointers */
        InitShmemAccess(UsedShmemSegAddr);

        /* Need a PGPROC to run CreateSharedMemoryAndSemaphores */
        InitProcess();

        /* Attach process to shared data structures */
        CreateSharedMemoryAndSemaphores();

        /* And run the backend */
        BackendRun(&port);      /* does not return */
    }
    if (strcmp(argv[1], "--forkboot") == 0)
    {
        /* Restore basic shared memory pointers */
        InitShmemAccess(UsedShmemSegAddr);

        /* Need a PGPROC to run CreateSharedMemoryAndSemaphores */
        InitAuxiliaryProcess();

        /* Attach process to shared data structures */
        CreateSharedMemoryAndSemaphores();

        AuxiliaryProcessMain(argc - 2, argv + 2);   /* does not return */
    }
    if (strcmp(argv[1], "--forkavlauncher") == 0)
    {
        /* Restore basic shared memory pointers */
        InitShmemAccess(UsedShmemSegAddr);

        /* Need a PGPROC to run CreateSharedMemoryAndSemaphores */
        InitProcess();

        /* Attach process to shared data structures */
        CreateSharedMemoryAndSemaphores();

        AutoVacLauncherMain(argc - 2, argv + 2);    /* does not return */
    }
    if (strcmp(argv[1], "--forkavworker") == 0)
    {
        /* Restore basic shared memory pointers */
        InitShmemAccess(UsedShmemSegAddr);

        /* Need a PGPROC to run CreateSharedMemoryAndSemaphores */
        InitProcess();

        /* Attach process to shared data structures */
        CreateSharedMemoryAndSemaphores();

        AutoVacWorkerMain(argc - 2, argv + 2);  /* does not return */
    }
    if (strncmp(argv[1], "--forkbgworker=", 15) == 0)
    {
        int         shmem_slot;

        /* do this as early as possible; in particular, before InitProcess() */
        IsBackgroundWorker = true;

        /* Restore basic shared memory pointers */
        InitShmemAccess(UsedShmemSegAddr);

        /* Need a PGPROC to run CreateSharedMemoryAndSemaphores */
        InitProcess();

        /* Attach process to shared data structures */
        CreateSharedMemoryAndSemaphores();

        /* Fetch MyBgworkerEntry from shared memory */
        shmem_slot = atoi(argv[1] + 15);
        MyBgworkerEntry = BackgroundWorkerEntry(shmem_slot);

        StartBackgroundWorker();
    }
    if (strcmp(argv[1], "--forkarch") == 0)
    {
        /* Do not want to attach to shared memory */

        PgArchiverMain(argc, argv); /* does not return */
    }
    if (strcmp(argv[1], "--forkcol") == 0)
    {
        /* Do not want to attach to shared memory */

        PgstatCollectorMain(argc, argv);    /* does not return */
    }
    if (strcmp(argv[1], "--forklog") == 0)
    {
        /* Do not want to attach to shared memory */

        SysLoggerMain(argc, argv);  /* does not return */
    }

    abort();                    /* shouldn't get here */
}
#endif                          /* EXEC_BACKEND */


/*
 * ExitPostmaster -- cleanup
 *
 * Do NOT call exit() directly --- always go through here!
 */
static void
ExitPostmaster(int status)
{
#ifdef HAVE_PTHREAD_IS_THREADED_NP

    /*
     * There is no known cause for a postmaster to become multithreaded after
     * startup.  Recheck to account for the possibility of unknown causes.
     * This message uses LOG level, because an unclean shutdown at this point
     * would usually not look much different from a clean shutdown.
     */
    if (pthread_is_threaded_np() != 0)
        ereport(LOG,
                (errcode(ERRCODE_INTERNAL_ERROR),
                 errmsg_internal("postmaster became multithreaded"),
                 errdetail("Please report this to <%s>.", PACKAGE_BUGREPORT)));
#endif

    /* should cleanup shared memory and kill all backends */

    /*
     * Not sure of the semantics here.  When the Postmaster dies, should the
     * backends all be killed? probably not.
     *
     * MUST     -- vadim 05-10-1999
     */

    proc_exit(status);
}

/*
 * sigusr1_handler - handle signal conditions from child processes
 */
static void
sigusr1_handler(SIGNAL_ARGS)
{
    int         save_errno = errno;

    /*
     * We rely on the signal mechanism to have blocked all signals ... except
     * on Windows, which lacks sigaction(), so we have to do it manually.
     */
#ifdef WIN32
    PG_SETMASK(&BlockSig);
#endif

    /* Process background worker state change. */
    if (CheckPostmasterSignal(PMSIGNAL_BACKGROUND_WORKER_CHANGE))
    {
        BackgroundWorkerStateChange();
        StartWorkerNeeded = true;
    }

    /*
     * RECOVERY_STARTED and BEGIN_HOT_STANDBY signals are ignored in
     * unexpected states. If the startup process quickly starts up, completes
     * recovery, exits, we might process the death of the startup process
     * first. We don't want to go back to recovery in that case.
     */
    if (CheckPostmasterSignal(PMSIGNAL_RECOVERY_STARTED) &&
        pmState == PM_STARTUP && Shutdown == NoShutdown)
    {
        /* WAL redo has started. We're out of reinitialization. */
        FatalError = false;
        AbortStartTime = 0;

        /*
         * Crank up the background tasks.  It doesn't matter if this fails,
         * we'll just try again later.
         */
        Assert(CheckpointerPID == 0);
        CheckpointerPID = StartCheckpointer();
        Assert(BgWriterPID == 0);
        BgWriterPID = StartBackgroundWriter();

        /*
         * Start the archiver if we're responsible for (re-)archiving received
         * files.
         */
        Assert(PgArchPID == 0);
        if (XLogArchivingAlways())
            PgArchPID = pgarch_start();

        /*
         * If we aren't planning to enter hot standby mode later, treat
         * RECOVERY_STARTED as meaning we're out of startup, and report status
         * accordingly.
         */
        if (!EnableHotStandby)
        {
            AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_STANDBY);
#ifdef USE_SYSTEMD
            sd_notify(0, "READY=1");
#endif
        }

        pmState = PM_RECOVERY;
    }
    if (CheckPostmasterSignal(PMSIGNAL_BEGIN_HOT_STANDBY) &&
        pmState == PM_RECOVERY && Shutdown == NoShutdown)
    {
        /*
         * Likewise, start other special children as needed.
         */
        Assert(PgStatPID == 0);
        PgStatPID = pgstat_start();

        ereport(LOG,
                (errmsg("database system is ready to accept read only connections")));

        /* Report status */
        AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_READY);
#ifdef USE_SYSTEMD
        sd_notify(0, "READY=1");
#endif

        pmState = PM_HOT_STANDBY;
        connsAllowed = ALLOW_ALL_CONNS;

        /* Some workers may be scheduled to start now */
        StartWorkerNeeded = true;
    }

    if (StartWorkerNeeded || HaveCrashedWorker)
        maybe_start_bgworkers();

    if (CheckPostmasterSignal(PMSIGNAL_WAKEN_ARCHIVER) &&
        PgArchPID != 0)
    {
        /*
         * Send SIGUSR1 to archiver process, to wake it up and begin archiving
         * next WAL file.
         */
        signal_child(PgArchPID, SIGUSR1);
    }

    /* Tell syslogger to rotate logfile if requested */
    if (SysLoggerPID != 0)
    {
        if (CheckLogrotateSignal())
        {
            signal_child(SysLoggerPID, SIGUSR1);
            RemoveLogrotateSignalFiles();
        }
        else if (CheckPostmasterSignal(PMSIGNAL_ROTATE_LOGFILE))
        {
            signal_child(SysLoggerPID, SIGUSR1);
        }
    }

    if (CheckPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER) &&
        Shutdown <= SmartShutdown && pmState < PM_STOP_BACKENDS)
    {
        /*
         * Start one iteration of the autovacuum daemon, even if autovacuuming
         * is nominally not enabled.  This is so we can have an active defense
         * against transaction ID wraparound.  We set a flag for the main loop
         * to do it rather than trying to do it here --- this is because the
         * autovac process itself may send the signal, and we want to handle
         * that by launching another iteration as soon as the current one
         * completes.
         */
        start_autovac_launcher = true;
    }

    if (CheckPostmasterSignal(PMSIGNAL_START_AUTOVAC_WORKER) &&
        Shutdown <= SmartShutdown && pmState < PM_STOP_BACKENDS)
    {
        /* The autovacuum launcher wants us to start a worker process. */
        StartAutovacuumWorker();
    }

    if (CheckPostmasterSignal(PMSIGNAL_START_WALRECEIVER))
    {
        /* Startup Process wants us to start the walreceiver process. */
        /* Start immediately if possible, else remember request for later. */
        WalReceiverRequested = true;
        MaybeStartWalReceiver();
    }

    /*
     * Try to advance postmaster's state machine, if a child requests it.
     *
     * Be careful about the order of this action relative to sigusr1_handler's
     * other actions.  Generally, this should be after other actions, in case
     * they have effects PostmasterStateMachine would need to know about.
     * However, we should do it before the CheckPromoteSignal step, which
     * cannot have any (immediate) effect on the state machine, but does
     * depend on what state we're in now.
     */
    if (CheckPostmasterSignal(PMSIGNAL_ADVANCE_STATE_MACHINE))
    {
        PostmasterStateMachine();
    }

    if (StartupPID != 0 &&
        (pmState == PM_STARTUP || pmState == PM_RECOVERY ||
         pmState == PM_HOT_STANDBY) &&
        CheckPromoteSignal())
    {
        /*
         * Tell startup process to finish recovery.
         *
         * Leave the promote signal file in place and let the Startup process
         * do the unlink.
         */
        signal_child(StartupPID, SIGUSR2);
    }

#ifdef WIN32
    PG_SETMASK(&UnBlockSig);
#endif

    errno = save_errno;
}

/*
 * SIGTERM while processing startup packet.
 *
 * Running proc_exit() from a signal handler would be quite unsafe.
 * However, since we have not yet touched shared memory, we can just
 * pull the plug and exit without running any atexit handlers.
 *
 * One might be tempted to try to send a message, or log one, indicating
 * why we are disconnecting.  However, that would be quite unsafe in itself.
 * Also, it seems undesirable to provide clues about the database's state
 * to a client that has not yet completed authentication, or even sent us
 * a startup packet.
 */
static void
process_startup_packet_die(SIGNAL_ARGS)
{
    _exit(1);
}

/*
 * Dummy signal handler
 *
 * We use this for signals that we don't actually use in the postmaster,
 * but we do use in backends.  If we were to SIG_IGN such signals in the
 * postmaster, then a newly started backend might drop a signal that arrives
 * before it's able to reconfigure its signal processing.  (See notes in
 * tcop/postgres.c.)
 */
static void
dummy_handler(SIGNAL_ARGS)
{
}

/*
 * Timeout while processing startup packet.
 * As for process_startup_packet_die(), we exit via _exit(1).
 */
static void
StartupPacketTimeoutHandler(void)
{
    _exit(1);
}


/*
 * Generate a random cancel key.
 */
static bool
RandomCancelKey(int32 *cancel_key)
{
    return pg_strong_random(cancel_key, sizeof(int32));
}

/*
 * Count up number of child processes of specified types (dead_end children
 * are always excluded).
 */
static int
CountChildren(int target)
{
    dlist_iter  iter;
    int         cnt = 0;

    dlist_foreach(iter, &BackendList)
    {
        Backend    *bp = dlist_container(Backend, elem, iter.cur);

        if (bp->dead_end)
            continue;

        /*
         * Since target == BACKEND_TYPE_ALL is the most common case, we test
         * it first and avoid touching shared memory for every child.
         */
        if (target != BACKEND_TYPE_ALL)
        {
            /*
             * Assign bkend_type for any recently announced WAL Sender
             * processes.
             */
            if (bp->bkend_type == BACKEND_TYPE_NORMAL &&
                IsPostmasterChildWalSender(bp->child_slot))
                bp->bkend_type = BACKEND_TYPE_WALSND;

            if (!(target & bp->bkend_type))
                continue;
        }

        cnt++;
    }
    return cnt;
}


/*
 * StartChildProcess -- start an auxiliary process for the postmaster
 *
 * "type" determines what kind of child will be started.  All child types
 * initially go to AuxiliaryProcessMain, which will handle common setup.
 *
 * Return value of StartChildProcess is subprocess' PID, or 0 if failed
 * to start subprocess.
 */
static pid_t
StartChildProcess(AuxProcType type)
{
    pid_t       pid;
    char       *av[10];
    int         ac = 0;
    char        typebuf[32];

    /*
     * Set up command-line arguments for subprocess
     */
    av[ac++] = "postgres";

#ifdef EXEC_BACKEND
    av[ac++] = "--forkboot";
    av[ac++] = NULL;            /* filled in by postmaster_forkexec */
#endif

    snprintf(typebuf, sizeof(typebuf), "-x%d", type);
    av[ac++] = typebuf;

    av[ac] = NULL;
    Assert(ac < lengthof(av));

#ifdef EXEC_BACKEND
    pid = postmaster_forkexec(ac, av);
#else                           /* !EXEC_BACKEND */
    pid = fork_process();

    if (pid == 0)               /* child */
    {
        InitPostmasterChild();

        /* Close the postmaster's sockets */
        ClosePostmasterPorts(false);

        /* Release postmaster's working memory context */
        MemoryContextSwitchTo(TopMemoryContext);
        MemoryContextDelete(PostmasterContext);
        PostmasterContext = NULL;

        AuxiliaryProcessMain(ac, av);
        ExitPostmaster(0);
    }
#endif                          /* EXEC_BACKEND */

    if (pid < 0)
    {
        /* in parent, fork failed */
        int         save_errno = errno;

        errno = save_errno;
        switch (type)
        {
            case StartupProcess:
                ereport(LOG,
                        (errmsg("could not fork startup process: %m")));
                break;
            case BgWriterProcess:
                ereport(LOG,
                        (errmsg("could not fork background writer process: %m")));
                break;
            case CheckpointerProcess:
                ereport(LOG,
                        (errmsg("could not fork checkpointer process: %m")));
                break;
            case WalWriterProcess:
                ereport(LOG,
                        (errmsg("could not fork WAL writer process: %m")));
                break;
            case WalReceiverProcess:
                ereport(LOG,
                        (errmsg("could not fork WAL receiver process: %m")));
                break;
            default:
                ereport(LOG,
                        (errmsg("could not fork process: %m")));
                break;
        }

        /*
         * fork failure is fatal during startup, but there's no need to choke
         * immediately if starting other child types fails.
         */
        if (type == StartupProcess)
            ExitPostmaster(1);
        return 0;
    }

    /*
     * in parent, successful fork
     */
    return pid;
}

/*
 * StartAutovacuumWorker
 *      Start an autovac worker process.
 *
 * This function is here because it enters the resulting PID into the
 * postmaster's private backends list.
 *
 * NB -- this code very roughly matches BackendStartup.
 */
static void
StartAutovacuumWorker(void)
{
    Backend    *bn;

    /*
     * If not in condition to run a process, don't try, but handle it like a
     * fork failure.  This does not normally happen, since the signal is only
     * supposed to be sent by autovacuum launcher when it's OK to do it, but
     * we have to check to avoid race-condition problems during DB state
     * changes.
     */
    if (canAcceptConnections(BACKEND_TYPE_AUTOVAC) == CAC_OK)
    {
        /*
         * Compute the cancel key that will be assigned to this session. We
         * probably don't need cancel keys for autovac workers, but we'd
         * better have something random in the field to prevent unfriendly
         * people from sending cancels to them.
         */
        if (!RandomCancelKey(&MyCancelKey))
        {
            ereport(LOG,
                    (errcode(ERRCODE_INTERNAL_ERROR),
                     errmsg("could not generate random cancel key")));
            return;
        }

        bn = (Backend *) malloc(sizeof(Backend));
        if (bn)
        {
            bn->cancel_key = MyCancelKey;

            /* Autovac workers are not dead_end and need a child slot */
            bn->dead_end = false;
            bn->child_slot = MyPMChildSlot = AssignPostmasterChildSlot();
            bn->bgworker_notify = false;

            bn->pid = StartAutoVacWorker();
            if (bn->pid > 0)
            {
                bn->bkend_type = BACKEND_TYPE_AUTOVAC;
                dlist_push_head(&BackendList, &bn->elem);
#ifdef EXEC_BACKEND
                ShmemBackendArrayAdd(bn);
#endif
                /* all OK */
                return;
            }

            /*
             * fork failed, fall through to report -- actual error message was
             * logged by StartAutoVacWorker
             */
            (void) ReleasePostmasterChildSlot(bn->child_slot);
            free(bn);
        }
        else
            ereport(LOG,
                    (errcode(ERRCODE_OUT_OF_MEMORY),
                     errmsg("out of memory")));
    }

    /*
     * Report the failure to the launcher, if it's running.  (If it's not, we
     * might not even be connected to shared memory, so don't try to call
     * AutoVacWorkerFailed.)  Note that we also need to signal it so that it
     * responds to the condition, but we don't do that here, instead waiting
     * for ServerLoop to do it.  This way we avoid a ping-pong signaling in
     * quick succession between the autovac launcher and postmaster in case
     * things get ugly.
     */
    if (AutoVacPID != 0)
    {
        AutoVacWorkerFailed();
        avlauncher_needs_signal = true;
    }
}

/*
 * MaybeStartWalReceiver
 *      Start the WAL receiver process, if not running and our state allows.
 *
 * Note: if WalReceiverPID is already nonzero, it might seem that we should
 * clear WalReceiverRequested.  However, there's a race condition if the
 * walreceiver terminates and the startup process immediately requests a new
 * one: it's quite possible to get the signal for the request before reaping
 * the dead walreceiver process.  Better to risk launching an extra
 * walreceiver than to miss launching one we need.  (The walreceiver code
 * has logic to recognize that it should go away if not needed.)
 */
static void
MaybeStartWalReceiver(void)
{
    if (WalReceiverPID == 0 &&
        (pmState == PM_STARTUP || pmState == PM_RECOVERY ||
         pmState == PM_HOT_STANDBY) &&
        Shutdown <= SmartShutdown)
    {
        WalReceiverPID = StartWalReceiver();
        if (WalReceiverPID != 0)
            WalReceiverRequested = false;
        /* else leave the flag set, so we'll try again later */
    }
}


/*
 * Create the opts file
 */
static bool
CreateOptsFile(int argc, char *argv[], char *fullprogname)
{
    FILE       *fp;
    int         i;

#define OPTS_FILE   "postmaster.opts"

    if ((fp = fopen(OPTS_FILE, "w")) == NULL)
    {
        elog(LOG, "could not create file \"%s\": %m", OPTS_FILE);
        return false;
    }

    fprintf(fp, "%s", fullprogname);
    for (i = 1; i < argc; i++)
        fprintf(fp, " \"%s\"", argv[i]);
    fputs("\n", fp);

    if (fclose(fp))
    {
        elog(LOG, "could not write file \"%s\": %m", OPTS_FILE);
        return false;
    }

    return true;
}


/*
 * MaxLivePostmasterChildren
 *
 * This reports the number of entries needed in per-child-process arrays
 * (the PMChildFlags array, and if EXEC_BACKEND the ShmemBackendArray).
 * These arrays include regular backends, autovac workers, walsenders
 * and background workers, but not special children nor dead_end children.
 * This allows the arrays to have a fixed maximum size, to wit the same
 * too-many-children limit enforced by canAcceptConnections().  The exact value
 * isn't too critical as long as it's more than MaxBackends.
 */
int
MaxLivePostmasterChildren(void)
{
    return 2 * (MaxConnections + autovacuum_max_workers + 1 +
                max_wal_senders + max_worker_processes);
}

/*
 * Connect background worker to a database.
 */
void
BackgroundWorkerInitializeConnection(const char *dbname, const char *username, uint32 flags)
{
    BackgroundWorker *worker = MyBgworkerEntry;

    /* XXX is this the right errcode? */
    if (!(worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION))
        ereport(FATAL,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("database connection requirement not indicated during registration")));

    InitPostgres(dbname, InvalidOid, username, InvalidOid, NULL, (flags & BGWORKER_BYPASS_ALLOWCONN) != 0);

    /* it had better not gotten out of "init" mode yet */
    if (!IsInitProcessingMode())
        ereport(ERROR,
                (errmsg("invalid processing mode in background worker")));
    SetProcessingMode(NormalProcessing);
}

/*
 * Connect background worker to a database using OIDs.
 */
void
BackgroundWorkerInitializeConnectionByOid(Oid dboid, Oid useroid, uint32 flags)
{
    BackgroundWorker *worker = MyBgworkerEntry;

    /* XXX is this the right errcode? */
    if (!(worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION))
        ereport(FATAL,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("database connection requirement not indicated during registration")));

    InitPostgres(NULL, dboid, NULL, useroid, NULL, (flags & BGWORKER_BYPASS_ALLOWCONN) != 0);

    /* it had better not gotten out of "init" mode yet */
    if (!IsInitProcessingMode())
        ereport(ERROR,
                (errmsg("invalid processing mode in background worker")));
    SetProcessingMode(NormalProcessing);
}

/*
 * Block/unblock signals in a background worker
 */
void
BackgroundWorkerBlockSignals(void)
{
    PG_SETMASK(&BlockSig);
}

void
BackgroundWorkerUnblockSignals(void)
{
    PG_SETMASK(&UnBlockSig);
}

#ifdef EXEC_BACKEND
static pid_t
bgworker_forkexec(int shmem_slot)
{
    char       *av[10];
    int         ac = 0;
    char        forkav[MAXPGPATH];

    snprintf(forkav, MAXPGPATH, "--forkbgworker=%d", shmem_slot);

    av[ac++] = "postgres";
    av[ac++] = forkav;
    av[ac++] = NULL;            /* filled in by postmaster_forkexec */
    av[ac] = NULL;

    Assert(ac < lengthof(av));

    return postmaster_forkexec(ac, av);
}
#endif

/*
 * Start a new bgworker.
 * Starting time conditions must have been checked already.
 *
 * Returns true on success, false on failure.
 * In either case, update the RegisteredBgWorker's state appropriately.
 *
 * This code is heavily based on autovacuum.c, q.v.
 */
static bool
do_start_bgworker(RegisteredBgWorker *rw)
{
    pid_t       worker_pid;

    Assert(rw->rw_pid == 0);

    /*
     * Allocate and assign the Backend element.  Note we must do this before
     * forking, so that we can handle failures (out of memory or child-process
     * slots) cleanly.
     *
     * Treat failure as though the worker had crashed.  That way, the
     * postmaster will wait a bit before attempting to start it again; if we
     * tried again right away, most likely we'd find ourselves hitting the
     * same resource-exhaustion condition.
     */
    if (!assign_backendlist_entry(rw))
    {
        rw->rw_crashed_at = GetCurrentTimestamp();
        return false;
    }

    ereport(DEBUG1,
            (errmsg("starting background worker process \"%s\"",
                    rw->rw_worker.bgw_name)));

#ifdef EXEC_BACKEND
    switch ((worker_pid = bgworker_forkexec(rw->rw_shmem_slot)))
#else
    switch ((worker_pid = fork_process()))
#endif
    {
        case -1:
            /* in postmaster, fork failed ... */
            ereport(LOG,
                    (errmsg("could not fork worker process: %m")));
            /* undo what assign_backendlist_entry did */
            ReleasePostmasterChildSlot(rw->rw_child_slot);
            rw->rw_child_slot = 0;
            free(rw->rw_backend);
            rw->rw_backend = NULL;
            /* mark entry as crashed, so we'll try again later */