PTHREAD_RWLOCK_UNLOCK(3P)

💅 PROLOG 💅

okay bestie, real talk before we even start: this manual page is part of the POSIX Programmer's Manual. the Linux implementation of this interface may differ — so like, consult the corresponding Linux manual page for the deets on Linux behavior — or honestly the interface might not even be implemented on Linux at all. 🙈 so keep that in mind, okay?

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✨ NAME ✨

pthread_rwlock_unlock — unlock a read-write lock object 🔓

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🎀 SYNOPSIS 🎀

#include <pthread.h>

int pthread_rwlock_unlock(pthread_rwlock_t *rwlock);

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💖 DESCRIPTION 💖

so pthread_rwlock_unlock() shall release a lock held on the read-write lock object referenced by rwlock. that's the whole job. the way that it's giving "let go of the thing" energy.

⚠️ but listen — results are undefined if the read-write lock rwlock is not held by the calling thread. like, don't try to unlock a lock you don't own. that's not your lock, that's not your business. 💀

here's the tea on what actually happens:

• if this function is called to release a read lock from the read-write lock object, and there are other read locks currently held on this read-write lock object, the read-write lock object remains in the read locked state. it's still locked, just one fewer reader.
• if this function releases the last read lock for this read-write lock object, the read-write lock object shall be put in the unlocked state with no owners. bye bye lock 👋
• if this function is called to release a write lock for this read-write lock object, the read-write lock object shall be put in the unlocked state. periodt.

now, if there are threads blocked on the lock when it becomes available, the scheduling policy shall determine which thread(s) shall acquire the lock. okay so if the Thread Execution Scheduling option is supported, when threads executing with the scheduling policies SCHED_FIFO, SCHED_RR, or SCHED_SPORADIC are waiting on the lock, they shall acquire the lock in priority order when the lock becomes available. 🏆 and for equal priority threads, write locks shall take precedence over read locks.

if the Thread Execution Scheduling option is not supported? it is implementation-defined whether write locks take precedence over read locks. so like, mystery behavior, iykyk. 🤷♀️

💀 also results are undefined if this function is called with an uninitialized read-write lock. do not do that. not the vibe.

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🔥 RETURN VALUE 🔥

if it ate? it returns zero 💖 otherwise, an error number shall be returned to indicate the error.

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😭 ERRORS 😭

the pthread_rwlock_unlock() function shall not return an error code of [EINTR]. nope, not a thing, don't ask.

the following sections are informative. 📝

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🌸 EXAMPLES 🌸

None. (nothing to show, bestie, it's just that iconic on its own ✨)

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🦋 APPLICATION USAGE 🦋

None. 💜

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🧚 RATIONALE 🧚

okay so the reasoning behind it all:

• if an implementation detects that the value specified by the rwlock argument to pthread_rwlock_unlock() does not refer to an initialized read-write lock object, it is recommended that the function should fail and report an [EINVAL] error.
• if an implementation detects that the value specified by the rwlock argument to pthread_rwlock_unlock() refers to a read-write lock object for which the current thread does not hold a lock, it is recommended that the function should fail and report an [EPERM] error.

so like, the implementation could be nice and tell you what went wrong. key word: recommended. 🙈

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🌈 FUTURE DIRECTIONS 🌈

None. we're staying exactly as we are. 💅

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👑 SEE ALSO 👑

• pthread_rwlock_destroy()
• pthread_rwlock_rdlock()
• pthread_rwlock_timedrdlock()
• pthread_rwlock_timedwrlock()
• pthread_rwlock_trywrlock()

and also the Base Definitions volume of POSIX.1‐2017, Section 4.12, Memory Synchronization, plus <pthread.h>. go read those, bestie, they're the moment. ⭐

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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 thing, bestie 🫶 this was IEEE/The Open Group, 2017, serving PTHREAD_RWLOCK_UNLOCK(3P) realness. unlock responsibly, own your locks, and never unlock what isn't yours. mwah 💋