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SDL Wiki

SDL_SemTryWait

See if a semaphore has a positive value and decrement it if it does.

Syntax

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.

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.

Code Examples

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);
SDL_CreateSemaphore
SDL_DestroySemaphore
SDL_SemPost
SDL_SemValue
SDL_SemWait
SDL_SemWaitTimeout

CategoryAPI, CategoryMutex


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