SIGHOLD(3P)

🎀 PROLOG 🎀

ok bestie so real quick before we get into it — this page is part of the POSIX Programmer's Manual. the Linux implementation of this interface might be different (so like, go check the corresponding Linux manual page for the tea on Linux behavior), or honestly the interface might not even be implemented on Linux at all. 🙈

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✨ NAME ✨

sighold, sigignore, sigpause, sigrelse, sigset — signal management, the whole squad 💅

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🌸 SYNOPSIS 🌸

#include <signal.h>

int sighold(int sig);
int sigignore(int sig);
int sigpause(int sig);
int sigrelse(int sig);
void (*sigset(int sig, void (*disp)(int)))(int);

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💖 DESCRIPTION 💖

okay first things first, no cap: using any of these functions is unspecified in a multi-threaded process. like, unspecified unspecified. don't do it. 😭

The sighold(), sigignore(), sigpause(), sigrelse(), and sigset() functions are giving simplified signal management. it's the low-effort version, iykyk.

The sigset() function shall modify signal dispositions. The sig argument specifies the signal, which may be any signal except SIGKILL and SIGSTOP (those two are untouchable icons, they don't take requests 👑). The disp argument specifies the signal's disposition, which may be SIG_DFL, SIG_IGN, or the address of a signal handler. So here's the deal:

• if sigset() is used and disp is the address of a signal handler, the system shall add sig to the signal mask of the calling process before executing the signal handler. when the signal handler returns, the system shall restore the signal mask of the calling process to its state prior to the delivery of the signal. cute, right? 🦋
• if sigset() is used and disp is equal to SIG_HOLD, sig shall be added to the signal mask of the calling process and sig's disposition shall remain unchanged. it's giving "hold that thought". ✋
• if sigset() is used and disp is not equal to SIG_HOLD, sig shall be removed from the signal mask of the calling process.

The sighold() function shall add sig to the signal mask of the calling process. (blocking era 💅)

The sigrelse() function shall remove sig from the signal mask of the calling process. (unblocking era 💅)

The sigignore() function shall set the disposition of sig to SIG_IGN.

The sigpause() function shall remove sig from the signal mask of the calling process and suspend the calling process until a signal is received. The sigpause() function shall restore the signal mask of the process to its original state before returning. so it just kinda... waits. main character energy honestly.

big one, pay attention bestie: if the action for the SIGCHLD signal is set to SIG_IGN, child processes of the calling processes shall not be transformed into zombie processes when they terminate. 🧟 if the calling process subsequently waits for its children, and the process has no unwaited-for children that were transformed into zombie processes, it shall block until all of its children terminate, and wait(), waitid(), and waitpid() shall fail and set errno to [ECHILD].

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⭐ RETURN VALUE ⭐

Upon successful completion, sigset() shall return SIG_HOLD if the signal had been blocked, and the signal's previous disposition if it had not been blocked. Otherwise, SIG_ERR shall be returned and errno set to indicate the error. so you literally get different flavors of return value depending on the block status, obsessed.

The sigpause() function shall suspend execution of the thread until a signal is received, whereupon it shall return -1 and set errno to [EINTR].

For all other functions, upon successful completion, 0 shall be returned. Otherwise, -1 shall be returned and errno set to indicate the error.

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🌈 ERRORS 🌈

These functions shall fail if:

• EINVAL — The sig argument is an illegal signal number. 🚫

The sigset() and sigignore() functions shall fail if:

• EINVAL — An attempt is made to catch a signal that cannot be caught, or to ignore a signal that cannot be ignored.

The following sections are informative.

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🍓 EXAMPLES 🍓

None. literally none. nothing to see here bestie, moving on. 🙈

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💜 APPLICATION USAGE 💜

The sigaction() function provides a more comprehensive and reliable mechanism for controlling signals; new applications should use the sigaction() function instead of the obsolescent sigset() function. yes that's a gentle way of saying sigset() is old news. 😭

The sighold() function, in conjunction with sigrelse() or sigpause(), may be used to establish critical regions of code that require the delivery of a signal to be temporarily deferred. for broader portability, the pthread_sigmask() or sigprocmask() functions should be used instead of the obsolescent sighold() and sigrelse() functions.

For broader portability, the sigsuspend() function should be used instead of the obsolescent sigpause() function.

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🧚 RATIONALE 🧚

Each of these historic functions has a direct analog in the other functions which are required to be per-thread and thread-safe (aside from sigprocmask(), which is replaced by pthread_sigmask()). it's giving "everything old is new again". ✨

• The sigset() function can be implemented as a simple wrapper for sigaction().
• The sighold() function is equivalent to sigprocmask() or pthread_sigmask() with SIG_BLOCK set.
• The sigignore() function is equivalent to sigaction() with SIG_IGN set.
• The sigpause() function is equivalent to sigsuspend().
• The sigrelse() function is equivalent to sigprocmask() or pthread_sigmask() with SIG_UNBLOCK set.

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🦋 FUTURE DIRECTIONS 🦋

These functions may be removed in a future version. so like... enjoy them while they last? 💀

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👑 SEE ALSO 👑

• Section 2.4, Signal Concepts
• exec
• pause()
• pthread_sigmask()
• sigaction()
• signal()
• sigsuspend()
• wait()
• waitid()

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 🫶 this lil rewrite came to you from IEEE/The Open Group, dated 2017, page SIGHOLD(3P) — slay, stay safe, and please use sigaction() ok bye 💖✨