PTHREAD...HEDPRIO(3POSIX)

🦋 PTHREAD_SETSCHEDPRIO — POSIX Programmer's Manual (3POSIX) 💅

okay bestie, we're in the POSIX Programmer's Manual today, and this one is all about the REALTIME THREADS girlies. buckle up 🎀

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🌸 PROLOG

so like, this manual page is part of the POSIX Programmer's Manual, periodt.

heads up though: the Linux implementation of this interface may differ — so go check the corresponding Linux manual page for the actual Linux behavior. or, plot twist, the interface might not even be implemented on Linux at all. 😭

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✨ NAME

pthread_setschedprio — dynamic thread scheduling parameters access (REALTIME THREADS)

no cap, that's the whole vibe. it's giving "let me change this thread's priority right now" energy. 👑

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🫶 SYNOPSIS

#include <pthread.h>

int pthread_setschedprio(pthread_t thread, int prio);

literally just two arguments bestie, we love a low-effort icon. 💖

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🌈 DESCRIPTION

so the pthread_setschedprio() function shall set the scheduling priority for the thread whose thread ID is given by thread to the value given by prio. that's it. that's the function. 💅

and if you wanna know how this function call affects the ordering of the thread in the thread list for its new priority? go read Scheduling Policies, it's all spelled out there. 📚

important little detail: if the pthread_setschedprio() function fails, the scheduling priority of the target thread shall not be changed. so like, no half-done glow-ups. either she slays or she stays exactly where she was. 🧚

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⭐ RETURN VALUE

• if it worked? returns zero. ate. ✨
• if it didn't? it returns an error number to indicate the error. not a vibe, but at least she tells you. 😌

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💀 ERRORS

the pthread_setschedprio() function may fail if:

• EINVAL — the value of prio is invalid for the scheduling policy of the specified thread. (you picked a priority that just doesn't exist for that policy, bestie, embarrassing 🙈)
• EPERM — the caller does not have appropriate privileges to set the scheduling priority of the specified thread. (you don't have the clearance, girl, this is not your thread to touch 🔥)

and one more thing, super important:

the pthread_setschedprio() function shall not return an error code of [EINTR]. so don't go looking for it. it's not there. 💀

the following sections are informative, btw. (iykyk)

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🎀 EXAMPLES

None.

like, literally none. the standard said "figure it out yourself, gorgeous." 😭

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🦋 APPLICATION USAGE

None.

again. nothing. we're on our own here. 🫶

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💜 RATIONALE

okay this is the part where the standard developers explain themselves, and honestly? they snapped. here's the tea:

the pthread_setschedprio() function gives an application a way to temporarily raise its priority and then lower it again, without having the undesired side-effect of yielding to other threads of the same priority. that side-effect? so annoying. we're avoiding it. 💅

why does that matter? because it's necessary if the application is going to implement its own strategies for bounding priority inversion — think priority inheritance or priority ceilings. 👑

and this capability is especially important if the implementation doesn't support the Thread Priority Protection or Thread Priority Inheritance options. but even if those options are supported, you still need this — if the application is gonna bound priority inheritance for other resources, like semaphores. 🤝

now, the standard developers did consider that conceptually it might be preferable to solve this by modifying the spec of pthread_setschedparam(). but plot twist: it was too late to make that change, because there may be implementations that would need to be changed. so instead? they introduced this whole new function. main character entrance, honestly. ✨

one last thing, and this one's a recommendation, not a rule:

if an implementation detects use of a thread ID after the end of its lifetime, it is recommended that the function should fail and report an [ESRCH] error. so like, if you're texting a dead thread? ghosted. 👻

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🌸 FUTURE DIRECTIONS

None.

the future is empty. the future is now. 😌

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🔥 SEE ALSO

• Scheduling Policies
• pthread_getschedparam()
• The Base Definitions volume of POSIX.1‐2017, <pthread.h>

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👑 COPYRIGHT

okay legal bestie moment, let's be respectful:

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. (she's the final boss, fr fr) 💅

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 absolute banger of a manpage was brought to you by IEEE/The Open Group, 2017, and the manual name is PTHREAD...HEDPRIO(3POSIX) in case you forgot where you were. now go set some priorities and slay. 🎀✨