SIGSETJMP(3P)

✨ hey bestie, it's SIGSETJMP(3P) ✨

Okay so this little page lives inside the POSIX Programmer's Manual, and it's the ✨iconic✨ SIGSETJMP(3P) entry, no cap. Quick heads-up before we dive in, and I'm gonna say it with my whole chest:

PROLOG — This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so go check the corresponding Linux manual page for the deets on Linux behavior), or the interface might not even be implemented on Linux at all. 💀

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🌸 NAME 🌸

sigsetjmp — set jump point for a non-local goto. it's giving "I'm gonna come back here later, don't worry about it." 🦋

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💅 SYNOPSIS 💅

#include <setjmp.h>

int sigsetjmp(sigjmp_buf env, int savemask);

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👑 DESCRIPTION 👑

So sigsetjmp() shall be equivalent to the setjmp() function, bestie — except for these little plot twists:

• References to setjmp() are equivalent to sigsetjmp().
• References to longjmp() are equivalent to siglongjmp().
• If the value of the savemask argument is not 0, sigsetjmp() shall also save the current signal mask of the calling thread as part of the calling environment. that's the whole point tbh, main character behavior. 💖

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🌈 RETURN VALUE 🌈

Two moods, bestie:

• If the return is from a successful direct invocation, sigsetjmp() shall return 0.
• If the return is from a call to siglongjmp(), sigsetjmp() shall return a non-zero value.

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🙈 ERRORS 🙈

No errors are defined. literally none. not a single one. slay.

The following sections are informative. (iykyk — they're the vibe, not the law. 📜)

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🍓 EXAMPLES 🍓

None. 😭 (yes, really. nothing here. we move.)

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🧚 APPLICATION USAGE 🧚

The distinction between setjmp()/longjmp() and sigsetjmp()/siglongjmp() is only significant for programs which use sigaction(), sigprocmask(), or sigsuspend(). so if you're not touching those, this whole thing is lowkey not your problem.

Also important: note that since this function is defined in terms of setjmp(), if savemask is zero, it is unspecified whether the signal mask is saved. unspecified means nobody's promising you anything, so don't build your whole personality on it. 🫶

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💜 RATIONALE 💜

The ISO C standard specifies various restrictions on the usage of the setjmp() macro in order to permit implementors to recognize the name in the compiler and not implement an actual function. These same restrictions apply to the sigsetjmp() macro. (yes bestie, it's a macro situation. iconic.)

There are processors that cannot easily support these calls, but this was not considered a sufficient reason to exclude them. 💅

4.2 BSD, 4.3 BSD, and XSI-conformant systems provide functions named _setjmp() and _longjmp() that, together with setjmp() and longjmp(), provide the same functionality as sigsetjmp() and siglongjmp(). On those systems, setjmp() and longjmp() save and restore signal masks, while _setjmp() and _longjmp() do not. On System V Release 3 and in corresponding issues of the SVID, setjmp() and longjmp() are explicitly defined not to save and restore signal masks. In order to permit existing practice in both cases, the relation of setjmp() and longjmp() to signal masks is not specified, and a new set of functions is defined instead. 🌀

The longjmp() and siglongjmp() functions operate as in the previous issue provided the matching setjmp() or sigsetjmp() has been performed in the same thread. Non-local jumps into contexts saved by other threads would be at best a questionable practice and were not considered worthy of standardization. 🚩 so like… don't do that. it's not a vibe.

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⭐ FUTURE DIRECTIONS ⭐

None. (the future is, in fact, not giving anything here.) 💀

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🌸 SEE ALSO 🌸

• pthread_sigmask()
• siglongjmp()
• signal()
• sigsuspend()

The Base Definitions volume of POSIX.1‐2017, <setjmp.h> — go read it, bestie, it's the source material. 📚

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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!! brought to you by IEEE/The Open Group, 2017 — SIGSETJMP(3P), the original girlies of the POSIX Programmer's Manual. 💖✨🎀 go forth and non-locally goto, but like, responsibly. 👑