pmsignal.c

PostgreSQL7.4.6 for Linux

/*-------------------------------------------------------------------------
 *
 * pmsignal.c
 *	  routines for signaling the postmaster from its child processes
 *
 *
 * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/storage/ipc/pmsignal.c,v 1.5 2003/08/04 02:40:03 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <signal.h>
#include <unistd.h>

#include "miscadmin.h"
#include "storage/pmsignal.h"
#include "storage/shmem.h"


/*
 * The postmaster is signaled by its children by sending SIGUSR1.  The
 * specific reason is communicated via flags in shared memory.	We keep
 * a boolean flag for each possible "reason", so that different reasons
 * can be signaled by different backends at the same time.	(However,
 * if the same reason is signaled more than once simultaneously, the
 * postmaster will observe it only once.)
 *
 * The flags are actually declared as "volatile sig_atomic_t" for maximum
 * portability.  This should ensure that loads and stores of the flag
 * values are atomic, allowing us to dispense with any explicit locking.
 */

static volatile sig_atomic_t *PMSignalFlags;


/*
 * PMSignalInit - initialize during shared-memory creation
 */
void
PMSignalInit(void)
{
	PMSignalFlags = (sig_atomic_t *)
		ShmemAlloc(NUM_PMSIGNALS * sizeof(sig_atomic_t));

	MemSet(PMSignalFlags, 0, NUM_PMSIGNALS * sizeof(sig_atomic_t));
}

/*
 * SendPostmasterSignal - signal the postmaster from a child process
 */
void
SendPostmasterSignal(PMSignalReason reason)
{
	/* If called in a standalone backend, do nothing */
	if (!IsUnderPostmaster)
		return;
	/* Atomically set the proper flag */
	PMSignalFlags[reason] = true;
	/* Send signal to postmaster (assume it is our direct parent) */
	kill(getppid(), SIGUSR1);
}

/*
 * CheckPostmasterSignal - check to see if a particular reason has been
 * signaled, and clear the signal flag.  Should be called by postmaster
 * after receiving SIGUSR1.
 */
bool
CheckPostmasterSignal(PMSignalReason reason)
{
	/* Careful here --- don't clear flag if we haven't seen it set */
	if (PMSignalFlags[reason])
	{
		PMSignalFlags[reason] = false;
		return true;
	}
	return false;
}