PTHREAD...DRDLOCK(3POSIX)

💖 PTHREAD_RWLOCK_TIMEDRDLOCK 💖

okay bestie, buckle UP — this one is from the POSIX Programmer's Manual (yes, the 3POSIX girlies, not the Linux man pages). And real talk, we need to have a lil chat first 👇

🚨 PROLOG 🚨

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so pls consult the corresponding Linux manual page for the deets on Linux behavior), or — and I cannot stress this enough — the interface may not be implemented on Linux at all. 💀

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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 the way that pthread_rwlock_timedrdlock() works is it shall apply a read lock to the read-write lock referenced by rwlock, exactly like pthread_rwlock_rdlock() does. iconic behavior honestly

BUT. 💅 And this is the whole point of her existence: if the lock cannot be acquired without waiting for other threads to unlock it, that wait shall be terminated when the specified timeout expires. The timeout expires when the absolute time specified by abstime passes — measured by the clock on which timeouts are based (like, 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. Late queen stays late 🕐

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. 📅

Under no circumstances shall the function fail with a timeout if the lock can be acquired immediately. And the validity of the abstime parameter need not be checked if the lock can be immediately acquired. (She's efficient like that. If she can grab it instantly, she's not reading the fine print. 🫶)

Now — if a signal that causes a signal handler to be executed gets delivered to a thread that's blocked on a read-write lock via a call to pthread_rwlock_timedrdlock(), then upon return from the signal handler the thread shall resume waiting for the lock as if it was not interrupted. Interruption? Not today. ✋

⚠️ DANGER ZONE, bestie: 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. Undefined behavior is not a vibe, it's a jumpscare. 😭

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💜 RETURN VALUE 💜

pthread_rwlock_timedrdlock() shall return zero if the lock for reading on the read-write lock object referenced by rwlock is acquired. Otherwise, an error number shall be returned to indicate the error. No errno games, she just tells you to your face. 💅

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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. ⏰ (she waited, she got ghosted, she's out)

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. 😵‍💫
• EDEADLK — A deadlock condition was detected, or the calling thread already holds a write lock on rwlock. 🚩
• EINVAL — The abstime nanosecond value is less than zero or greater than or equal to 1000 million. 📉

And also, for the record: this function shall not return an error code of [EINTR]. Not her, not ever. 🙅‍♀️

The following sections are informative. — aka, the lore, not the law 👑

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🌈 EXAMPLES 🌈

None. That's it. That's the section. 💀

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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. Priority inversion is giving "the intern is holding the door for the CEO and the CEO is stuck behind the intern" energy. 🙈

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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. Bestie said please check your inputs, she's begging. 🥺

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⭐ FUTURE DIRECTIONS ⭐

None. No notes. She's done evolving. 👑

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💫 SEE ALSO 💫

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

The Base Definitions volume of POSIX.1‐2017, Section 3.291, Priority Inversion, Section 4.12, Memory Synchronization, <pthread.h>, <time.h>

iykyk 🫶

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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. (She's the source of truth, no cap.) 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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okay that's the whole page bestie, you ate that 🍓✨ — brought to you by IEEE/The Open Group, 2017, from the POSIX Programmer's Manual. mwah, go forth and lock responsibly 💖👑