NANOSLEEP(3P)

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

okay so first things first, the manual name is NANOSLEEP(3P) and this whole page lives inside the POSIX Programmer's Manual. cute. iconic. let's go.

🫶 PROLOG 🫶

okay real talk before we start: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ — so if you're on Linux, go consult the corresponding Linux manual page for the deets on Linux behavior. Or, plot twist, the interface might not even be implemented on Linux at all. 🙈 so like, check first, bestie.

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✨ NAME ✨

nanosleep — high resolution sleep 🌙

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🌸 SYNOPSIS 🌸

#include <time.h>

int nanosleep(const struct timespec *rqtp, struct timespec *rmtp);

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💖 DESCRIPTION 💖

so the way nanosleep() works is: it shall cause the current thread to be suspended from execution until either:

• the time interval specified by the rqtp argument has elapsed, or
• a signal is delivered to the calling thread, and its action is to invoke a signal-catching function or to terminate the process.

and here's the tea on timing, no cap: the suspension time may be longer than what you requested, because the argument value is rounded up to an integer multiple of the sleep resolution, or because of the scheduling of other activity by the system. but — and this is the important part — except for the case of being interrupted by a signal, the suspension time shall not be less than the time specified by rqtp, as measured by the system clock CLOCK_REALTIME. ⏰

also super important: the use of the nanosleep() function has no effect on the action or blockage of any signal. it's giving "unbothered, moisturized, in its own lane." 💅

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🔥 RETURN VALUE 🔥

• if the nanosleep() function returns because the requested time has elapsed, its return value shall be zero. slay. ✨
• if the nanosleep() function returns because it has been interrupted by a signal, it shall return a value of -1 and set errno to indicate the interruption. if the rmtp argument is non-NULL, the timespec structure referenced by it is updated to contain the amount of time remaining in the interval (the requested time minus the time actually slept). and get this — the rqtp and rmtp arguments can point to the same object. if the rmtp argument is NULL, the remaining time is not returned. 😭
• if nanosleep() fails, it shall return a value of -1 and set errno to indicate the error.

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💀 ERRORS 💀

the nanosleep() function shall fail if:

• EINTR — the nanosleep() function was interrupted by a signal. (the classic "not me getting woken up mid-nap" moment 🙈)
• EINVAL — the rqtp argument specified a nanosecond value less than zero or greater than or equal to 1000 million. 🚫

also, just so you know: the following sections are informative. they're the vibes, not the rules.

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🎀 EXAMPLES 🎀

None. (yeah, literally nothing. we move. 💀)

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🧚 APPLICATION USAGE 🧚

None. (again! nothing! it's giving minimalist. 👑)

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🌈 RATIONALE 🌈

okay so, context: it's common to suspend execution of a thread for an interval in order to poll the status of a non-interrupting function. and honestly, a large number of actual needs can be met with a simple extension to sleep() that provides finer resolution. periodt.

in the POSIX.1‐1990 standard and SVR4, it is possible to implement such a routine, but the frequency of wakeup is limited by the resolution of the alarm() and sleep() functions. in 4.3 BSD, it is possible to write such a routine using no static storage and reserving no system facilities. and like, although it is possible to write a function with similar functionality to sleep() using the remainder of the timer_*() functions, such a function requires the use of signals and the reservation of some signal number. this volume of POSIX.1‐2017 requires that nanosleep() be non-intrusive of the signals function. 🫶

also the nanosleep() function shall return a value of 0 on success and -1 on failure or if interrupted. this latter case is different from sleep(). why though? because the remaining time is returned via an argument structure pointer, rmtp, instead of as the return value. iykyk. 💅

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🦋 FUTURE DIRECTIONS 🦋

None. (the future is... empty. very demure, very mindful. ✨)

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💜 SEE ALSO 💜

• clock_nanosleep(), sleep()
• The Base Definitions volume of POSIX.1‐2017, <time.h>

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👑 COPYRIGHT 👑

okay legal moment, stay with me bestie:

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, and the manual itself is NANOSLEEP(3P). go take a nap — high resolution ones only. 💤💖✨