SDL_SemTryWait(3)

💖 SDL_SemTryWait(3) — the SDL API Reference, but make it make sense

okay bestie, so this is a page from the SDL API Reference, and today's main character is SDL_SemTryWait. it's giving "I want the semaphore but I refuse to wait in line" energy. let's get into it 🦋

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✨ NAME ✨

SDL_SemTryWait — Attempt to lock a semaphore but don't suspend the thread.

like. it tries. if it can't, it does NOT stand there dramatically waiting. it just leaves. icon behaviour, honestly 💅

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🌸 SYNOPSIS 🌸

#include "SDL.h" #include "SDL_thread.h"

int SDL_SemTryWait(SDL_sem *sem);

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👑 DESCRIPTION 👑

so SDL_SemTryWait is the non-blocking varient of SDL_SemWait. yes bestie, varient — that's the spelling in the original, we don't touch it, we respect it 🙈

here's the vibe: if the value of the semaphore pointed to by sem is positive, it will atomically decrement the semaphore value and return 0. cute. clean. done.

otherwise? it returns SDL_MUTEX_TIMEOUT instead of suspending the thread. it simply does not wait. it has places to be. no cap 🎀

and after SDL_SemTryWait is successful, the semaphore can be released and its count atomically incremented by a successful call to SDL_SemPost. the circle of life, semaphore edition 🌈

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⭐ RETURN VALUE ⭐

• Returns 0 if the semaphore was successfully locked
• or either SDL_MUTEX_TIMEOUT or -1 if the thread would have suspended or there was an error, respectivly. (again — respectivly, that's the original spelling, leave it alone 😭)

💀 if the semaphore was not successfully locked, the semaphore will be unchanged. nothing happened. no side effects. it's giving "I was never here."

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🧚 EXAMPLES 🧚

okay this is the part where it all clicks, watch:

res = SDL_SemTryWait(my_sem);

if (res == SDL_MUTEX_TIMEOUT) {
    return TRY_AGAIN;
}
if (res == -1) {
    return WAIT_ERROR;
}

...

SDL_SemPost(my_sem);

see how it checks SDL_MUTEX_TIMEOUT and goes TRY_AGAIN? that's the "couldn't get it, gonna circle back later" move. and -1 means actual error so it's WAIT_ERROR. then later, when you're done, SDL_SemPost(my_sem). slay 🔥

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🫶 SEE ALSO 🫶

the whole semaphore friend group, go say hi:

• SDL_CreateSemaphore
• SDL_DestroySemaphore
• SDL_SemWait
• SDL_SemWaitTimeout
• SDL_SemPost
• SDL_SemValue

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and that's the page, bestie 💜 this one came straight out of the SDL source, dated Tue 11 Sep 2001, 23:00 — yes, 2001, ancient lore, and it still ate. go lock your semaphores, but like… don't wait around for them. periodt. 💅✨