#pragma section-numbers off
#pragma camelcase off

= SDL_SemWaitTimeout =
Use this function to wait until a semaphore has a positive value and then decrements it.

<<TableOfContents()>>

== Syntax ==
{{{#!highlight cpp
int SDL_SemWaitTimeout(SDL_sem* sem,
                       Uint32   ms)
}}}

== Function Parameters ==
||'''sem'''||the semaphore to wait on||
||'''ms'''||the length of the timeout in milliseconds||

== Return Value ==
Returns 0 if the wait succeeds, SDL_MUTEX_TIMEDOUT if the wait does not succeed in the allotted time, 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:
    const Uint32 timeout = 1000; /* wake up every second */

    while (!SDL_AtomicGet(&done)) {
        if (SDL_SemWaitTimeout(sem, timeout) == 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 suspends the calling thread until either the semaphore pointed to by '''sem''' has a positive value, the call is interrupted by a signal or error, or the specified time has elapsed. If the call is successful it will atomically decrement the semaphore value.

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

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