source: vendor/current/lib/util/signal.c

/* 
   Unix SMB/CIFS implementation.
   signal handling functions

   Copyright (C) Andrew Tridgell 1998
   
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "replace.h"
#include "system/wait.h"
#include "debug.h"
#include "lib/util/signal.h" /* Avoid /usr/include/signal.h */

/**
 * @file
 * @brief Signal handling
 */

/****************************************************************************
 Catch child exits and reap the child zombie status.
****************************************************************************/

static void sig_cld(int signum)
{
        while (waitpid((pid_t)-1,(int *)NULL, WNOHANG) > 0)
                ;

        /*
         * Turns out it's *really* important not to
         * restore the signal handler here if we have real POSIX
         * signal handling. If we do, then we get the signal re-delivered
         * immediately - hey presto - instant loop ! JRA.
         */

#if !defined(HAVE_SIGACTION)
        CatchSignal(SIGCLD, sig_cld);
#endif
}

/****************************************************************************
catch child exits - leave status;
****************************************************************************/

static void sig_cld_leave_status(int signum)
{
        /*
         * Turns out it's *really* important not to
         * restore the signal handler here if we have real POSIX
         * signal handling. If we do, then we get the signal re-delivered
         * immediately - hey presto - instant loop ! JRA.
         */

#if !defined(HAVE_SIGACTION)
        CatchSignal(SIGCLD, sig_cld_leave_status);
#endif
}

/**
 Block sigs.
**/

void BlockSignals(bool block, int signum)
{
#ifdef HAVE_SIGPROCMASK
        sigset_t set;
        sigemptyset(&set);
        sigaddset(&set,signum);
        sigprocmask(block?SIG_BLOCK:SIG_UNBLOCK,&set,NULL);
#elif defined(HAVE_SIGBLOCK)
        if (block) {
                sigblock(sigmask(signum));
        } else {
                sigsetmask(siggetmask() & ~sigmask(signum));
        }
#else
        /* yikes! This platform can't block signals? */
        static int done;
        if (!done) {
                DEBUG(0,("WARNING: No signal blocking available\n"));
                done=1;
        }
#endif
}

/**
 Catch a signal. This should implement the following semantics:

 1) The handler remains installed after being called.
 2) The signal should be blocked during handler execution.
**/

void (*CatchSignal(int signum,void (*handler)(int )))(int)
{
#ifdef HAVE_SIGACTION
        struct sigaction act;
        struct sigaction oldact;

        ZERO_STRUCT(act);

        act.sa_handler = handler;
#ifdef SA_RESTART
        /*
         * We *want* SIGALRM to interrupt a system call.
         */
        if(signum != SIGALRM)
                act.sa_flags = SA_RESTART;
#endif
        sigemptyset(&act.sa_mask);
        sigaddset(&act.sa_mask,signum);
        sigaction(signum,&act,&oldact);
        return oldact.sa_handler;
#else /* !HAVE_SIGACTION */
        /* FIXME: need to handle sigvec and systems with broken signal() */
        return signal(signum, handler);
#endif
}

/**
 Ignore SIGCLD via whatever means is necessary for this OS.
**/

void (*CatchChild(void))(int)
{
        return CatchSignal(SIGCLD, sig_cld);
}

/**
 Catch SIGCLD but leave the child around so it's status can be reaped.
**/

void (*CatchChildLeaveStatus(void))(int)
{
        return CatchSignal(SIGCLD, sig_cld_leave_status);
}