PTHREAD_R...MEDRDLOCK(3P)

💖 PTHREAD_RWLOCK_TIMEDRDLOCK — bestie, it's from the POSIX Programmer's Manual (3P) 🎀

okay so before we even get into it, quick vibe check on the whole PROLOG situation:

• This manual page is part of the POSIX Programmer's Manual ✨
• Heads up though: the Linux implementation of this interface may differ (so like, consult the corresponding Linux manual page for the actual Linux behavior, bestie), or the interface may literally not be implemented on Linux at all 💀
• Also the following sections are informative — noted, no cap.

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🌸 NAME 🌸

pthread_rwlock_timedrdlock — lock a read-write lock for reading 🦋

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✨ SYNOPSIS ✨

#include <pthread.h>
#include <time.h>

int pthread_rwlock_timedrdlock(pthread_rwlock_t *restrict rwlock,
    const struct timespec *restrict abstime);

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💅 DESCRIPTION 💅

So pthread_rwlock_timedrdlock() shall apply a read lock to the read-write lock referenced by rwlock, exactly like the pthread_rwlock_rdlock() function does. Iconic, right? But here's the plot twist: if the lock cannot be acquired without waiting for other threads to unlock the lock, this wait shall be terminated when the specified timeout expires ⏰

The timeout shall expire when the absolute time specified by abstime passes — measured by the clock on which timeouts are based (that is, when the value of that clock equals or exceeds abstime) — or if the absolute time specified by abstime has already been passed at the time of the call. Not me showing up late to my own lock 💀

The timeout shall be based on the CLOCK_REALTIME clock. The resolution of the timeout shall be the resolution of the CLOCK_REALTIME clock. The timespec data type is defined in the <time.h> header, obviously.

Under no circumstances shall the function fail with a timeout if the lock can be acquired immediately. Periodt. And the validity of the abstime parameter need not be checked if the lock can be immediately acquired — like, if you can just walk in, nobody's checking your ID 🫶

If a signal that causes a signal handler to be executed is delivered to a thread blocked on a read-write lock via a call to pthread_rwlock_timedrdlock(), upon return from the signal handler the thread shall resume waiting for the lock as if it was not interrupted. So rude to interrupt, and yet — we carry on 🧚

⚠️ The calling thread may deadlock if at the time the call is made it holds a write lock on rwlock. And the results are undefined if this function is called with an uninitialized read-write lock. Like, undefined. We do not do that. 🙈

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🌈 RETURN VALUE 🌈

• If the lock for reading on the read-write lock object referenced by rwlock is acquired — the pthread_rwlock_timedrdlock() function shall return zero 💖
• Otherwise, an error number shall be returned to indicate the error. That's it, that's the deal ✨

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🔥 ERRORS 🔥

The pthread_rwlock_timedrdlock() function shall fail if:

• ETIMEDOUT — the lock could not be acquired before the specified timeout expired. bestie the clock said no 😭

The pthread_rwlock_timedrdlock() function may fail if:

• EAGAIN — the read lock could not be acquired because the maximum number of read locks for lock would be exceeded. too many besties, not enough lock 👑
• EDEADLK — a deadlock condition was detected, or the calling thread already holds a write lock on rwlock. caught in 4k 🚨
• EINVAL — the abstime nanosecond value is less than zero or greater than or equal to 1000 million. that number is not numbering 💀

🚫 This function shall not return an error code of [EINTR]. Don't even ask.

The following sections are informative.

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🎀 EXAMPLES 🎀

None.

(yeah. literally none. the void. the silence. it's giving minimalism 💅)

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🦋 APPLICATION USAGE 🦋

Applications using this function may be subject to priority inversion, as discussed in the Base Definitions volume of POSIX.1‐2017, Section 3.291, Priority Inversion. iykyk 🌸

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⭐ RATIONALE ⭐

If an implementation detects that the value specified by the rwlock argument to pthread_rwlock_timedrdlock() does not refer to an initialized read-write lock object, it is recommended that the function should fail and report an [EINVAL] error. just a suggestion, but like, a strong one 🙏

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💜 FUTURE DIRECTIONS 💜

None.

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👑 SEE ALSO 👑

• pthread_rwlock_destroy()
• pthread_rwlock_rdlock()
• pthread_rwlock_timedwrlock()
• pthread_rwlock_trywrlock()
• pthread_rwlock_unlock()

Also, the Base Definitions volume of POSIX.1‐2017, Section 3.291, Priority Inversion, Section 4.12, Memory Synchronization, <pthread.h>, <time.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 🫶 brought to you by IEEE/The Open Group, 2017 — PTHREAD_R...MEDRDLOCK(3P), slay, go forth and lock responsibly 💅✨🍓