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SDL_CreateSemaphore

Create a semaphore.

Syntax

SDL_sem* SDL_CreateSemaphore(Uint32 initial_value);

Function Parameters

initial_value

the starting value of the semaphore

Return Value

Returns a new semaphore or NULL on failure; call SDL_GetError() for more information.

Remarks

This function creates a new semaphore and initializes it with the value initial_value. Each wait operation on the semaphore will atomically decrement the semaphore value and potentially block if the semaphore value is 0. Each post operation will atomically increment the semaphore value and wake waiting threads and allow them to retry the wait operation.

Code Examples

Typical use of semaphores:

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)) {
        SDL_SemWait(sem);
        if (data_available()) {
            get_data_from_queue();
        }
    }
.
.
SDL_AtomicSet(&done, 1);
SDL_SemPost(sem);
wait_for_threads();
SDL_DestroySemaphore(sem);
SDL_DestroySemaphore
SDL_SemPost
SDL_SemTryWait
SDL_SemValue
SDL_SemWait
SDL_SemWaitTimeout

CategoryAPI, CategoryMutex


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