#pragma section-numbers off
#pragma camelcase off

= SDL_SemTryWait =
Use this function to see if a semaphore has a positive value and decrement it if it does.

<<TableOfContents()>>

== Syntax ==
{{{#!highlight cpp
int SDL_SemTryWait(SDL_sem* sem)
}}}

== Function Parameters ==
||'''sem'''||the semaphore to wait on||

== Return Value ==
Returns 0 if the wait succeeds, SDL_MUTEX_TIMEDOUT if the wait would block, or a negative error code on failure; call [[SDL_GetError]]() for more information.

== Code Examples ==
{{{#!highlight cpp
SDL_atomic_t done;
SDL_sem *sem;

SDL_AtomicSet(&done, 0);
sem = SDL_CreateSemaphore(0);
.
.
Thread A:
    while (!SDL_AtomicGet(&done)) {
        add_data_to_queue();
        SDL_SemPost(sem);
    }

Thread B:
    while (!SDL_AtomicGet(&done)) {
        if (SDL_SemTryWait(sem) == 0 && data_available()) {
            get_data_from_queue();
        }
        ... do other processing
    }
.
.
SDL_AtomicSet(&done, 1);
SDL_SemPost(sem);
wait_for_threads();
SDL_DestroySemaphore(sem);
}}}

== Remarks ==
This function checks to see if the semaphore pointed to by '''sem''' has a positive value and atomically decrements the semaphore value if it does.  If the semaphore doesn't have a positive value, the function immediately returns SDL_MUTEX_TIMEDOUT.

== Related Functions ==
 .[[SDL_CreateSemaphore]]
 .[[SDL_DestroySemaphore]]
 .[[SDL_SemPost]]
 .[[SDL_SemValue]]
 .[[SDL_SemWait]]
 .[[SDL_SemWaitTimeout]]

----
[[CategoryAPI]], [[CategoryMutex]]