SEM_TRYWAIT(3POSIX)

💖 SEM_TRYWAIT(3POSIX) 💖

okay bestie, so this is a page from the POSIX Programmer's Manual, and we're talking about the sem_trywait and sem_wait girlies. 🎀

🚨 PROLOG (read this first, fr fr)

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

not me warning you up front 💀 always check your own platform's manpage before you come for me

---

✨ NAME ✨

sem_trywait, sem_wait — lock a semaphore

---

🦋 SYNOPSIS 🦋

#include <semaphore.h>

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

---

🌸 DESCRIPTION 🌸

okay so here's the tea. sem_trywait() shall lock the semaphore referenced by sem only if the semaphore is currently not locked — like, if the semaphore value is currently positive. Otherwise, it shall not lock the semaphore. it's giving "no thanks, maybe later" 💅

sem_wait(), on the other hand, 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. she's patient. she waits. main character energy, honestly. 👑

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. like a locked door until someone hands over the key 🔐

The sem_wait() function is interruptible by the delivery of a signal. so if a signal shows up, bestie is out 🏃♀️

---

⭐ 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. zero = slay, we got it. ✨

If the call was unsuccessful, the state of the semaphore shall be unchanged, and the function shall return a value of -1 and set errno to indicate the error. no partial vibes, no half-locked nonsense — unchanged, periodt.

---

💀 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. she said try, and she tried, and it was a no 😭

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

• EDEADLK — A deadlock condition was detected. everyone stuck staring at each other. iconic but bad. 🫠
• EINTR — A signal interrupted this function.
• EINVAL — The sem argument does not refer to a valid semaphore.

The following sections are informative. (translation: the required reading is done, this next bit is bonus content 🍓)

---

🌈 EXAMPLES 🌈

None.

not a single example. we are unbothered. we move on. 🙈

---

🧚 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.

priority inversion is lowkey the drama of scheduling. go read 3.291 if you wanna know more, i'm not making stuff up here 💜

---

🎀 RATIONALE 🎀

None.

---

💜 FUTURE DIRECTIONS 💜

None.

---

🔥 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>

---

👑 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 .

---

and that's the whole page, bestie 💖 this one came to you from IEEE/The Open Group, dated 2017, under the manual name SEM_TRYWAIT(3POSIX) — stay locked, stay hydrated, and don't forget to sem_post() when you're done 🫶✨