SIGSUSPEND(3P)

💤 SIGSUSPEND(3P) — the POSIX Programmer's Manual, bestie edition 💤

okay so real talk first 🫶 this one is a POSIX Programmer's Manual page, and the Linux version of this interface may lowkey differ (so go check the matching Linux manual page for the Linux tea), or honestly it might not even be implemented on Linux at all. not me warning you before we even start 💀

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✨ 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.

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🎀 NAME 🎀

sigsuspend — wait for a signal 💅

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🌸 SYNOPSIS 🌸

#include <signal.h>

int sigsuspend(const sigset_t *sigmask);

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💖 DESCRIPTION 💖

okay so here's the vibe: sigsuspend() shall replace the current signal mask of the calling thread with the set of signals pointed to by sigmask, and then it shall suspend the thread until delivery of a signal whose action is either to execute a signal-catching function or to terminate the process. that's the whole job, she's a one-trick icon 👑

and important: this shall not cause any other signals that may have been pending on the process to become pending on the thread. no sneaky cross-contamination, periodt.

now, two outcomes, bestie:

• If the action is to terminate the process, then sigsuspend() shall never return. like, never ever. goodbye forever 😭
• 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. so she cleans up after herself, we love a queen who restores state 🫶

one more thing: it is not possible to block signals that cannot be ignored. this is enforced by the system without causing an error to be indicated. so no error, no drama, it just... is what it is 🧚

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⭐ RETURN VALUE ⭐

so because sigsuspend() suspends thread execution indefinitely, there is literally no successful completion return value. none. zero. she doesn't do happy endings.

if a return does occur, -1 shall be returned and errno set to indicate the error.

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💀 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.

also note: the following sections are informative. so like, the required reading is over, everything from here is bonus content bestie 📚

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🌈 EXAMPLES 🌈

None.

(yeah that's it. the example section said "None." and I'm not about to invent one, no cap 🙈)

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🍓 APPLICATION USAGE 🍓

normally, at the beginning of a critical code section, a specified set of signals is blocked using the sigprocmask() function. then 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. it's giving "lock the door, do the thing, then wait by the door for whoever was trying to get in" 🚪✨

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🧠 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. here's the iconic little snippet, verbatim:

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(mask);
    pthread_cleanup_pop(0);
    return result;
}

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🔮 FUTURE DIRECTIONS 🔮

None.

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👑 SEE ALSO 👑

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

also from The Base Definitions volume of POSIX.1‐2017: <signal.h>

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📜 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 .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the whole page, bestie!! 💖 big slay energy from IEEE/The Open Group, 2017 — they ate and left absolutely no crumbs, and this page is officially closed out. go forth and wait for signals responsibly 🦋✨