SIGSUSPEND(3P)

PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME
sigsuspend — wait for a signal

SYNOPSIS

#include <signal.h>

int sigsuspend(const sigset_t *sigmask);

DESCRIPTION
The sigsuspend() function shall replace the current signal mask of the calling thread with the set of signals pointed to by sigmask and then suspend the thread until delivery of a signal whose action is either to execute a signal-catching function or to terminate the process. This shall not cause any other signals that may have been pending on the process to become pending on the thread.

If the action is to terminate the process then sigsuspend() shall never return. If the action is to execute a signal-catching function, then sigsuspend() shall return after the signal-catching function returns, with the signal mask restored to the set that existed prior to the sigsuspend() call.

It is not possible to block signals that cannot be ignored. This is enforced by the system without causing an error to be indicated.

RETURN VALUE
Since sigsuspend() suspends thread execution indefinitely, there is no successful completion return value. If a return occurs, -1 shall be returned and errno set to indicate the error.

ERRORS
The sigsuspend() function shall fail if:

EINTR
    A signal is caught by the calling process and control is returned from the signal-catching function.

The following sections are informative.

EXAMPLES
None.

APPLICATION USAGE
Normally, at the beginning of a critical code section, a specified set of signals is blocked using the sigprocmask() function. When the thread has completed the critical section and needs to wait for the previously blocked signal(s), it pauses by calling sigsuspend() with the mask that was returned by the sigprocmask() call.

RATIONALE
Code which wants to avoid the ambiguity of the signal mask for thread cancellation handlers can install an additional cancellation handler which resets the signal mask to the expected value.

    void cleanup(void *arg)
    {
        sigset_t *ss = (sigset_t *) arg;
        pthread_sigmask(SIG_SETMASK, ss, NULL);
    }

    int call_sigsuspend(const sigset_t *mask)
    {
        sigset_t oldmask;
        int result;
        pthread_sigmask(SIG_SETMASK, NULL, &oldmask);
        pthread_cleanup_push(cleanup, &oldmask);
        result = sigsuspend(sigmask);
        pthread_cleanup_pop(0);
        return result;
    }

FUTURE DIRECTIONS
None.

SEE ALSO
Section 2.4, Signal Concepts, pause(), sigaction(), sigaddset(), sigdelset(), sigemptyset(), sigfillset()

The Base Definitions volume of POSIX.1-2017, <signal.h>

COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

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