The Open Group Base Specifications Issue 7
IEEE Std 1003.1, 2013 Edition
Copyright © 2001-2013 The IEEE and The Open Group

#### NAME

> sigsuspend - wait for a signal

#### SYNOPSIS

> ``[CX] #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

> Signal Concepts, pause , sigaction, sigaddset, sigdelset, sigemptyset, sigfillset

> XBD <signal.h>

#### CHANGE HISTORY

> First released in Issue 3. Included for alignment with the POSIX.1-1988 standard.

#### Issue 5

> The DESCRIPTION is updated for alignment with the POSIX Threads Extension.

#### Issue 6

> The text in the RETURN VALUE section has been changed from "suspends process execution" to "suspends thread execution". This reflects IEEE PASC Interpretation 1003.1c #40.

> Text in the APPLICATION USAGE section has been replaced.

> The SYNOPSIS is marked CX since the presence of this function in the <signal.h> header is an extension over the ISO C standard.

#### Issue 7

> SD5-XSH-ERN-122 is applied, adding the example code in the RATIONALE.

End of informative text.

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