Avoid multiple Executions of a method at any given time

ExecuteOnceAtATime.m

dispatch_semaphore_t semaphore = dispatch_semaphore_create(1);
dispatch_queue_t renderQueue = dispatch_queue_create("com.throttling.queue", NULL);

- (void) onlyExecuteOnceAtATime {
    if (dispatch_semaphore_wait(semaphore, DISPATCH_TIME_NOW) == 0) {
        dispatch_async(renderQueue, ^{
            // execution code goes here
            dispatch_semaphore_signal(semaphore);
        });
    }
}