parallel.c

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/*
 *  parallel.c
 *
 *  multi-process support
 *
 *  Copyright (c) 2010-2025, PostgreSQL Global Development Group
 *  src/bin/pg_upgrade/parallel.c
 */
 
#include "postgres_fe.h"
 
#include <sys/wait.h>
#ifdef WIN32
#include <io.h>
#endif
 
#include "pg_upgrade.h"
 
static int  parallel_jobs;
 
#ifdef WIN32
/*
 *  Array holding all active threads.  There can't be any gaps/zeros so
 *  it can be passed to WaitForMultipleObjects().  We use two arrays
 *  so the thread_handles array can be passed to WaitForMultipleObjects().
 */
static HANDLE *thread_handles;
 
typedef struct
{
    char       *log_file;
    char       *opt_log_file;
    char       *cmd;
} exec_thread_arg;
 
typedef struct
{
    DbInfoArr  *old_db_arr;
    DbInfoArr  *new_db_arr;
    char       *old_pgdata;
    char       *new_pgdata;
    char       *old_tablespace;
} transfer_thread_arg;
 
static exec_thread_arg **exec_thread_args;
static transfer_thread_arg **transfer_thread_args;
 
/* track current thread_args struct so reap_child() can be used for all cases */
static void **cur_thread_args;
 
DWORD       win32_exec_prog(exec_thread_arg *args);
DWORD       win32_transfer_all_new_dbs(transfer_thread_arg *args);
#endif
 
/*
 *  parallel_exec_prog
 *
 *  This has the same API as exec_prog, except it does parallel execution,
 *  and therefore must throw errors and doesn't return an error status.
 */
void
parallel_exec_prog(const char *log_file, const char *opt_log_file,
                   const char *fmt,...)
{
    va_list     args;
    char        cmd[MAX_STRING];
 
#ifndef WIN32
    pid_t       child;
#else
    HANDLE      child;
    exec_thread_arg *new_arg;
#endif
 
    va_start(args, fmt);
    vsnprintf(cmd, sizeof(cmd), fmt, args);
    va_end(args);
 
    if (user_opts.jobs <= 1)
        /* exit_on_error must be true to allow jobs */
        exec_prog(log_file, opt_log_file, true, true, "%s", cmd);
    else
    {
        /* parallel */
#ifdef WIN32
        if (thread_handles == NULL)
            thread_handles = pg_malloc(user_opts.jobs * sizeof(HANDLE));
 
        if (exec_thread_args == NULL)
        {
            int         i;
 
            exec_thread_args = pg_malloc(user_opts.jobs * sizeof(exec_thread_arg *));
 
            /*
             * For safety and performance, we keep the args allocated during
             * the entire life of the process, and we don't free the args in a
             * thread different from the one that allocated it.
             */
            for (i = 0; i < user_opts.jobs; i++)
                exec_thread_args[i] = pg_malloc0(sizeof(exec_thread_arg));
        }
 
        cur_thread_args = (void **) exec_thread_args;
#endif
        /* harvest any dead children */
        while (reap_child(false) == true)
            ;
 
        /* must we wait for a dead child? */
        if (parallel_jobs >= user_opts.jobs)
            reap_child(true);
 
        /* set this before we start the job */
        parallel_jobs++;
 
        /* Ensure stdio state is quiesced before forking */
        fflush(NULL);
 
#ifndef WIN32
        child = fork();
        if (child == 0)
            /* use _exit to skip atexit() functions */
            _exit(!exec_prog(log_file, opt_log_file, true, true, "%s", cmd));
        else if (child < 0)
            /* fork failed */
            pg_fatal("could not create worker process: %m");
#else
        /* empty array element are always at the end */
        new_arg = exec_thread_args[parallel_jobs - 1];
 
        /* Can only pass one pointer into the function, so use a struct */
        pg_free(new_arg->log_file);
        new_arg->log_file = pg_strdup(log_file);
        pg_free(new_arg->opt_log_file);
        new_arg->opt_log_file = opt_log_file ? pg_strdup(opt_log_file) : NULL;
        pg_free(new_arg->cmd);
        new_arg->cmd = pg_strdup(cmd);
 
        child = (HANDLE) _beginthreadex(NULL, 0, (void *) win32_exec_prog,
                                        new_arg, 0, NULL);
        if (child == 0)
            pg_fatal("could not create worker thread: %m");
 
        thread_handles[parallel_jobs - 1] = child;
#endif
    }
}
 
 
#ifdef WIN32
DWORD
win32_exec_prog(exec_thread_arg *args)
{
    int         ret;
 
    ret = !exec_prog(args->log_file, args->opt_log_file, true, true, "%s", args->cmd);
 
    /* terminates thread */
    return ret;
}
#endif
 
 
/*
 *  parallel_transfer_all_new_dbs
 *
 *  This has the same API as transfer_all_new_dbs, except it does parallel execution
 *  by transferring multiple tablespaces in parallel
 */
void
parallel_transfer_all_new_dbs(DbInfoArr *old_db_arr, DbInfoArr *new_db_arr,
                              char *old_pgdata, char *new_pgdata,
                              char *old_tablespace)
{
#ifndef WIN32
    pid_t       child;
#else
    HANDLE      child;
    transfer_thread_arg *new_arg;
#endif
 
    if (user_opts.jobs <= 1)
        transfer_all_new_dbs(old_db_arr, new_db_arr, old_pgdata, new_pgdata, NULL);
    else
    {
        /* parallel */
#ifdef WIN32
        if (thread_handles == NULL)
            thread_handles = pg_malloc(user_opts.jobs * sizeof(HANDLE));
 
        if (transfer_thread_args == NULL)
        {
            int         i;
 
            transfer_thread_args = pg_malloc(user_opts.jobs * sizeof(transfer_thread_arg *));
 
            /*
             * For safety and performance, we keep the args allocated during
             * the entire life of the process, and we don't free the args in a
             * thread different from the one that allocated it.
             */
            for (i = 0; i < user_opts.jobs; i++)
                transfer_thread_args[i] = pg_malloc0(sizeof(transfer_thread_arg));
        }
 
        cur_thread_args = (void **) transfer_thread_args;
#endif
        /* harvest any dead children */
        while (reap_child(false) == true)
            ;
 
        /* must we wait for a dead child? */
        if (parallel_jobs >= user_opts.jobs)
            reap_child(true);
 
        /* set this before we start the job */
        parallel_jobs++;
 
        /* Ensure stdio state is quiesced before forking */
        fflush(NULL);
 
#ifndef WIN32
        child = fork();
        if (child == 0)
        {
            transfer_all_new_dbs(old_db_arr, new_db_arr, old_pgdata, new_pgdata,
                                 old_tablespace);
            /* if we take another exit path, it will be non-zero */
            /* use _exit to skip atexit() functions */
            _exit(0);
        }
        else if (child < 0)
            /* fork failed */
            pg_fatal("could not create worker process: %m");
#else
        /* empty array element are always at the end */
        new_arg = transfer_thread_args[parallel_jobs - 1];
 
        /* Can only pass one pointer into the function, so use a struct */
        new_arg->old_db_arr = old_db_arr;
        new_arg->new_db_arr = new_db_arr;
        pg_free(new_arg->old_pgdata);
        new_arg->old_pgdata = pg_strdup(old_pgdata);
        pg_free(new_arg->new_pgdata);
        new_arg->new_pgdata = pg_strdup(new_pgdata);
        pg_free(new_arg->old_tablespace);
        new_arg->old_tablespace = old_tablespace ? pg_strdup(old_tablespace) : NULL;
 
        child = (HANDLE) _beginthreadex(NULL, 0, (void *) win32_transfer_all_new_dbs,
                                        new_arg, 0, NULL);
        if (child == 0)
            pg_fatal("could not create worker thread: %m");
 
        thread_handles[parallel_jobs - 1] = child;
#endif
    }
}
 
 
#ifdef WIN32
DWORD
win32_transfer_all_new_dbs(transfer_thread_arg *args)
{
    transfer_all_new_dbs(args->old_db_arr, args->new_db_arr, args->old_pgdata,
                         args->new_pgdata, args->old_tablespace);
 
    /* terminates thread */
    return 0;
}
#endif
 
 
/*
 *  collect status from a completed worker child
 */
bool
reap_child(bool wait_for_child)
{
#ifndef WIN32
    int         work_status;
    pid_t       child;
#else
    int         thread_num;
    DWORD       res;
#endif
 
    if (user_opts.jobs <= 1 || parallel_jobs == 0)
        return false;
 
#ifndef WIN32
    child = waitpid(-1, &work_status, wait_for_child ? 0 : WNOHANG);
    if (child == (pid_t) -1)
        pg_fatal("%s() failed: %m", "waitpid");
    if (child == 0)
        return false;           /* no children, or no dead children */
    if (work_status != 0)
        pg_fatal("child process exited abnormally: status %d", work_status);
#else
    /* wait for one to finish */
    thread_num = WaitForMultipleObjects(parallel_jobs, thread_handles,
                                        false, wait_for_child ? INFINITE : 0);
 
    if (thread_num == WAIT_TIMEOUT || thread_num == WAIT_FAILED)
        return false;
 
    /* compute thread index in active_threads */
    thread_num -= WAIT_OBJECT_0;
 
    /* get the result */
    GetExitCodeThread(thread_handles[thread_num], &res);
    if (res != 0)
        pg_fatal("child worker exited abnormally: %m");
 
    /* dispose of handle to stop leaks */
    CloseHandle(thread_handles[thread_num]);
 
    /* Move last slot into dead child's position */
    if (thread_num != parallel_jobs - 1)
    {
        void       *tmp_args;
 
        thread_handles[thread_num] = thread_handles[parallel_jobs - 1];
 
        /*
         * Move last active thread arg struct into the now-dead slot, and the
         * now-dead slot to the end for reuse by the next thread. Though the
         * thread struct is in use by another thread, we can safely swap the
         * struct pointers within the array.
         */
        tmp_args = cur_thread_args[thread_num];
        cur_thread_args[thread_num] = cur_thread_args[parallel_jobs - 1];
        cur_thread_args[parallel_jobs - 1] = tmp_args;
    }
#endif
 
    /* do this after job has been removed */
    parallel_jobs--;
 
    return true;
}