SEM_TRYWAIT(3P)

💖 SEM_TRYWAIT(3P) 💖

okay bestie, welcome to the POSIX Programmer's Manual ✨ this little page is sem_trywait and its ride-or-die sem_wait, and we're gonna lock semaphores together like the icons we are 💅

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🚨 PROLOG 🚨

So real talk first: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (bestie, go consult the corresponding Linux manual page for the deets on Linux behavior), or the interface may literally not be implemented on Linux at all. 🙈 no cap.

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✨ NAME ✨

sem_trywait, sem_wait — lock a semaphore 🔒

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🎀 SYNOPSIS 🎀

#include <semaphore.h>

int sem_trywait(sem_t *sem);
int sem_wait(sem_t *sem);

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🌸 DESCRIPTION 🌸

okay so. The sem_trywait() function shall lock the semaphore referenced by sem only if the semaphore is currently not locked — like, only if the semaphore value is currently positive. Otherwise? It shall not lock the semaphore. No waiting around, no drama. 💅

The sem_wait() function shall lock the semaphore referenced by sem by performing a semaphore lock operation on that semaphore. If the semaphore value is currently zero, then the calling thread shall not return from the call to sem_wait() until it either locks the semaphore or the call is interrupted by a signal. it's giving "patient queen waits her turn" 👑

Upon successful return, the state of the semaphore shall be locked and shall remain locked until the sem_post() function is executed and returns successfully. periodt.

The sem_wait() function is interruptible by the delivery of a signal. ⚡

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🫶 RETURN VALUE 🫶

The sem_trywait() and sem_wait() functions shall return zero if the calling process successfully performed the semaphore lock operation on the semaphore designated by sem. 💖

If the call was unsuccessful, the state of the semaphore shall be unchanged (no sneaky half-locks, we don't do that here), and the function shall return a value of -1 and set errno to indicate the error. 😭

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💀 ERRORS 💀

The sem_trywait() function shall fail if:

• EAGAIN — The semaphore was already locked, so it cannot be immediately locked by the sem_trywait() operation. sorry bestie, it's taken 🚫

The sem_trywait() and sem_wait() functions may fail if:

• EDEADLK — A deadlock condition was detected. 💀 the vibes are rancid
• EINTR — A signal interrupted this function. 😤 so rude of it
• EINVAL — The sem argument does not refer to a valid semaphore. 🚩 not a real one, girl

The following sections are informative.

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🌈 EXAMPLES 🌈

None. (yes, literally none, we're keeping it a mystery 🧚)

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💜 APPLICATION USAGE 💜

Applications using these functions may be subject to priority inversion, as discussed in the Base Definitions volume of POSIX.1‐2017, Section 3.291, Priority Inversion. lowkey a whole situation, highkey worth reading. 📖

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👑 RATIONALE 👑

None.

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🔥 FUTURE DIRECTIONS 🔥

None.

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🦋 SEE ALSO 🦋

• semctl()
• semget()
• semop()
• sem_post()
• sem_timedwait()

The Base Definitions volume of POSIX.1‐2017, Section 3.291, Priority Inversion, Section 4.12, Memory Synchronization, <semaphore.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 thing bestie!! 🎀 this came to you courtesy of IEEE/The Open Group, dated 2017, filed under SEM_TRYWAIT(3P) — mwah, go lock a semaphore responsibly, ily 💖✨🦋