interrupt.c

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/*-------------------------------------------------------------------------
 *
 * interrupt.c
 *    Interrupt handling routines.
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/postmaster/interrupt.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <unistd.h>

#include "miscadmin.h"
#include "postmaster/interrupt.h"
#include "storage/ipc.h"
#include "storage/latch.h"
#include "storage/procsignal.h"
#include "utils/guc.h"

volatile sig_atomic_t ConfigReloadPending = false;
volatile sig_atomic_t ShutdownRequestPending = false;

/*
 * Simple interrupt handler for main loops of background processes.
 */
void
HandleMainLoopInterrupts(void)
{
    if (ProcSignalBarrierPending)
        ProcessProcSignalBarrier();

    if (ConfigReloadPending)
    {
        ConfigReloadPending = false;
        ProcessConfigFile(PGC_SIGHUP);
    }

    if (ShutdownRequestPending)
        proc_exit(0);
}

/*
 * Simple signal handler for triggering a configuration reload.
 *
 * Normally, this handler would be used for SIGHUP. The idea is that code
 * which uses it would arrange to check the ConfigReloadPending flag at
 * convenient places inside main loops, or else call HandleMainLoopInterrupts.
 */
void
SignalHandlerForConfigReload(SIGNAL_ARGS)
{
    int         save_errno = errno;

    ConfigReloadPending = true;
    SetLatch(MyLatch);

    errno = save_errno;
}

/*
 * Simple signal handler for exiting quickly as if due to a crash.
 *
 * Normally, this would be used for handling SIGQUIT.
 */
void
SignalHandlerForCrashExit(SIGNAL_ARGS)
{
    /*
     * We DO NOT want to run proc_exit() or atexit() callbacks -- we're here
     * because shared memory may be corrupted, so we don't want to try to
     * clean up our transaction.  Just nail the windows shut and get out of
     * town.  The callbacks wouldn't be safe to run from a signal handler,
     * anyway.
     *
     * Note we do _exit(2) not _exit(0).  This is to force the postmaster into
     * a system reset cycle if someone sends a manual SIGQUIT to a random
     * backend.  This is necessary precisely because we don't clean up our
     * shared memory state.  (The "dead man switch" mechanism in pmsignal.c
     * should ensure the postmaster sees this as a crash, too, but no harm in
     * being doubly sure.)
     */
    _exit(2);
}

/*
 * Simple signal handler for triggering a long-running background process to
 * shut down and exit.
 *
 * Typically, this handler would be used for SIGTERM, but some processes use
 * other signals. In particular, the checkpointer exits on SIGUSR2, the
 * stats collector on SIGQUIT, and the WAL writer exits on either SIGINT
 * or SIGTERM.
 *
 * ShutdownRequestPending should be checked at a convenient place within the
 * main loop, or else the main loop should call HandleMainLoopInterrupts.
 */
void
SignalHandlerForShutdownRequest(SIGNAL_ARGS)
{
    int         save_errno = errno;

    ShutdownRequestPending = true;
    SetLatch(MyLatch);

    errno = save_errno;
}