dispatch_barrier_async
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代码：
dispatch_queue_t queue = dispatch_queue_create("queue", DISPATCH_QUEUE_CONCURRENT); dispatch_async(queue, ^{ NSLog(@"Before Barrier Block - 1"); }); dispatch_async(queue, ^{ NSLog(@"Before Barrier Block - 2"); }); dispatch_async(queue, ^{ NSLog(@"Before Barrier Block - 3"); }); dispatch_async(queue, ^{ NSLog(@"Before Barrier Block - 4"); }); dispatch_async(queue, ^{ NSLog(@"Before Barrier Block - 5"); }); dispatch_barrier_async(queue, ^{ NSLog(@"Barrier Block"); }); dispatch_async(queue, ^{ NSLog(@"After Barrier Block - 1"); }); dispatch_async(queue, ^{ NSLog(@"After Barrier Block - 2"); }); dispatch_async(queue, ^{ NSLog(@"After Barrier Block - 3"); }); dispatch_async(queue, ^{ NSLog(@"After Barrier Block - 4"); }); dispatch_async(queue, ^{ NSLog(@"After Barrier Block - 5"); });
可能的输出：
Before Barrier Block - 1 Before Barrier Block - 2 Before Barrier Block - 3 Before Barrier Block - 5 Before Barrier Block - 4 Barrier Block After Barrier Block - 1 After Barrier Block - 3 After Barrier Block - 2 After Barrier Block - 5 After Barrier Block - 4
备注：
dispatch_barrier_async用于在同一个并发队列中，同步多个并发操作
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