pqsignal.c

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/*-------------------------------------------------------------------------
 *
 * pqsignal.c
 *    reliable BSD-style signal(2) routine stolen from RWW who stole it
 *    from Stevens...
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/port/pqsignal.c
 *
 *  A NOTE ABOUT SIGNAL HANDLING ACROSS THE VARIOUS PLATFORMS.
 *
 *  pg_config.h defines the macro HAVE_POSIX_SIGNALS for some platforms and
 *  not for others.  We use that here to decide how to handle signalling.
 *
 *  Ultrix and SunOS provide BSD signal(2) semantics by default.
 *
 *  SVID2 and POSIX signal(2) semantics differ from BSD signal(2)
 *  semantics.  We can use the POSIX sigaction(2) on systems that
 *  allow us to request restartable signals (SA_RESTART).
 *
 *  Some systems don't allow restartable signals at all unless we
 *  link to a special BSD library.
 *
 *  We devoutly hope that there aren't any Unix-oid systems that provide
 *  neither POSIX signals nor BSD signals.  The alternative is to do
 *  signal-handler reinstallation, which doesn't work well at all.
 *
 *  Windows, of course, is resolutely in a class by itself.  In the backend,
 *  we don't use this file at all; src/backend/port/win32/signal.c provides
 *  pqsignal() for the backend environment.  Frontend programs can use
 *  this version of pqsignal() if they wish, but beware that Windows
 *  requires signal-handler reinstallation, because indeed it provides
 *  neither POSIX signals nor BSD signals :-(
 * ------------------------------------------------------------------------
 */

#include "c.h"

#include <signal.h>

#if !defined(WIN32) || defined(FRONTEND)

/*
 * Set up a signal handler for signal "signo"
 *
 * Returns the previous handler.
 */
pqsigfunc
pqsignal(int signo, pqsigfunc func)
{
#if !defined(HAVE_POSIX_SIGNALS)
    return signal(signo, func);
#else
    struct sigaction act,
                oact;

    act.sa_handler = func;
    sigemptyset(&act.sa_mask);
    act.sa_flags = 0;
    if (signo != SIGALRM)
        act.sa_flags |= SA_RESTART;
#ifdef SA_NOCLDSTOP
    if (signo == SIGCHLD)
        act.sa_flags |= SA_NOCLDSTOP;
#endif
    if (sigaction(signo, &act, &oact) < 0)
        return SIG_ERR;
    return oact.sa_handler;
#endif   /* !HAVE_POSIX_SIGNALS */
}

#endif /* !defined(WIN32) || defined(FRONTEND) */