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/*-------------------------------------------------------------------------
*
* pqsignal.c
* reliable BSD-style signal(2) routine stolen from RWW who stole it
* from Stevens...
*
* Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/port/pqsignal.c
*
* This is the signal() implementation from "Advanced Programming in the UNIX
* Environment", with minor changes. It was originally a replacement needed
* for old SVR4 systems whose signal() behaved as if sa_flags = SA_RESETHAND |
* SA_NODEFER, also known as "unreliable" signals due to races when the
* handler was reset.
*
* By now, all known modern Unix systems have a "reliable" signal() call.
* We still don't want to use it though, because it remains
* implementation-defined by both C99 and POSIX whether the handler is reset
* or signals are blocked when the handler runs, and default restart behavior
* is also unspecified. Therefore we take POSIX's advice and call sigaction()
* so we can provide explicit sa_flags, but wrap it in this more convenient
* traditional interface style. It also provides a place to set any extra
* flags we want everywhere, such as SA_NOCLDSTOP.
*
* Windows, of course, is resolutely in a class by itself. In the backend,
* this relies on pqsigaction() in src/backend/port/win32/signal.c, which
* provides limited emulation of reliable signals.
*
* Frontend programs can use this version of pqsignal() to forward to the
* native Windows signal() call if they wish, but beware that Windows signals
* behave quite differently. Only the 6 signals required by C are supported.
* SIGINT handlers run in another thread instead of interrupting an existing
* thread, and the others don't interrupt system calls either, so SA_RESTART
* is moot. All except SIGFPE have SA_RESETHAND semantics, meaning the
* handler is reset to SIG_DFL each time it runs. The set of things you are
* allowed to do in a handler is also much more restricted than on Unix,
* according to the documentation.
*
* ------------------------------------------------------------------------
*/
#include "c.h"
#include <signal.h>
#ifndef FRONTEND
#include "libpq/pqsignal.h"
#endif
/*
* Set up a signal handler, with SA_RESTART, for signal "signo"
*
* Returns the previous handler.
*/
pqsigfunc
pqsignal(int signo, pqsigfunc func)
{
#if !(defined(WIN32) && defined(FRONTEND))
struct sigaction act,
oact;
act.sa_handler = func;
sigemptyset(&act.sa_mask);
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;
#else
/* Forward to Windows native signal system. */
return signal(signo, func);
#endif
}
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