GCD可以设置线程最大并发量

-(void)dispatchSignal{

    //crate的value表示，最多几个资源可访问
    dispatch_semaphore_t semaphore = dispatch_semaphore_create(2);
    dispatch_queue_t quene = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

    //任务1
    dispatch_async(quene, ^{
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        NSLog (@ "run task 1" );
        sleep(1);
        NSLog (@ "complete task 1" );
        dispatch_semaphore_signal(semaphore);
    });
    //任务2
    dispatch_async(quene, ^{
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        NSLog (@ "run task 2" );
        sleep(1);
        NSLog (@ "complete task 2" );
        dispatch_semaphore_signal(semaphore);
    });
    //任务3
    dispatch_async(quene, ^{
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        NSLog (@ "run task 3" );
        sleep(1);
        NSLog (@ "complete task 3" );
        dispatch_semaphore_signal(semaphore);
    });
}

转载于:https://www.cnblogs.com/dashengios/p/10694945.html