dispatch_set_target_queue测试-优快云博客

本文介绍了dispatch_set_target_queue函数的使用方法，并通过一个具体的示例展示了如何将多个并发队列的任务转换为串行执行。当我们将不同队列的目标队列设置为同一个串行队列时，即使原始队列为并发队列，所有任务也会按顺序执行。

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dispatch_set_target_queue会将其他queue转为和targetqueue一样的优先级和执行时序，看下面的例子

即使queue1，queue2，queue3，都是并行的queue，但是输出结果仍然是串行的结果；

- (void)testTargetQueue
{
    dispatch_queue_t targetQueue = dispatch_queue_create("test.target.queue", DISPATCH_QUEUE_SERIAL);
    dispatch_queue_t queue1 = dispatch_queue_create("test.1", DISPATCH_QUEUE_CONCURRENT);
    dispatch_queue_t queue2 = dispatch_queue_create("test.2", DISPATCH_QUEUE_CONCURRENT);
    dispatch_queue_t queue3 = dispatch_queue_create("test.3", DISPATCH_QUEUE_CONCURRENT);
    dispatch_set_target_queue(queue1, targetQueue);
    dispatch_set_target_queue(queue2, targetQueue);
    dispatch_set_target_queue(queue3, targetQueue);
    
    dispatch_async(queue1, ^{
        NSLog(@"1 in");
        [NSThread sleepForTimeInterval:3.f];
        NSLog(@"1 out");
    });
    
    dispatch_async(queue2, ^{
        NSLog(@"2 in");
        [NSThread sleepForTimeInterval:2.f];
        NSLog(@"2 out");
    });
    dispatch_async(queue3, ^{
        NSLog(@"3 in");
        [NSThread sleepForTimeInterval:1.f];
        NSLog(@"3 out");
    });
}

2017-03-07 20:31:11.636 DispatchTargetQueueTest[42985:377250] 1 in

2017-03-07 20:31:14.711 DispatchTargetQueueTest[42985:377250] 1 out

2017-03-07 20:31:14.711 DispatchTargetQueueTest[42985:377250] 2 in

2017-03-07 20:31:16.784 DispatchTargetQueueTest[42985:377250] 2 out

2017-03-07 20:31:16.784 DispatchTargetQueueTest[42985:377250] 3 in

2017-03-07 20:31:17.859 DispatchTargetQueueTest[42985:377250] 3 out

转载于:https://www.cnblogs.com/wxm5558/p/6516675.html