dispatch_queue_t初学

柔光的暖阳◎ 2022-04-08 14:43 167阅读 0赞

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 1. GCD 使用后不用程序去管理线程的开闭，GCD会在系统层面上去动态检测系统状态，开闭线程 
 2. Dispatch Queues &nbsp; 串行 并行 2种&nbsp; FIFO&nbsp; 把task依次放入串行queue可以实现顺序执行 
 3. Operation Queues 可以指定任务之间的优先级&nbsp; task之间的先后依赖关系 4. __block变量是可以改变的　共享的，保持一致的 &nbsp;&nbsp;&nbsp; dispatch_queue_t aQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0); // 并行queue &nbsp;&nbsp;&nbsp; for (__block int i = 0; i&lt;10000; i++) { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; dispatch_async(aQueue, ^{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; NSLog(@"%d",i); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }); &nbsp;&nbsp;&nbsp; } 2011-07-05 17:11:38.346 ttt[41418:1803] 61 2011-07-05 17:11:38.346 ttt[41418:5f03] 1292 2011-07-05 17:11:38.348 ttt[41418:1803] 4096 2011-07-05 17:11:38.348 ttt[41418:5f03] 4954 2011-07-05 17:11:38.349 ttt[41418:1803] 5823 2011-07-05 17:11:38.349 ttt[41418:5f03] 6159 2011-07-05 17:11:38.349 ttt[41418:1803] 6575 2011-07-05 17:11:38.349 ttt[41418:5f03] 6634 2011-07-05 17:11:38.350 ttt[41418:1803] 7936 2011-07-05 17:11:38.350 ttt[41418:5f03] 8428 2011-07-05 17:11:38.351 ttt[41418:1803] 8895 2011-07-05 17:11:38.351 ttt[41418:5f03] 9364 2011-07-05 17:11:38.351 ttt[41418:1803] 9836 2011-07-05 17:11:38.351 ttt[41418:5f03] 10000 2011-07-05 17:11:38.354 ttt[41418:1803] 10000 5. 一般外部变量是copy正在运行时的外部状态 &nbsp;&nbsp;&nbsp; dispatch_queue_t aQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0); &nbsp;&nbsp;&nbsp; for (int i = 0; i&lt;1000; i++) { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; dispatch_async(aQueue, ^{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; NSLog(@"%d",i); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }); &nbsp;&nbsp;&nbsp; } 2011-07-05 17:15:37.525 ttt[41697:1803] 0 2011-07-05 17:15:37.526 ttt[41697:1803] 2 2011-07-05 17:15:37.527 ttt[41697:1803] 3 2011-07-05 17:15:37.527 ttt[41697:1803] 4 2011-07-05 17:15:37.527 ttt[41697:1803] 5 2011-07-05 17:15:37.527 ttt[41697:1803] 6 2011-07-05 17:15:37.526 ttt[41697:5f03] 1 2011-07-05 17:15:37.530 ttt[41697:5f03] 8 2011-07-05 17:15:37.530 ttt[41697:5f03] 9 2011-07-05 17:15:37.530 ttt[41697:5f03] 10 2011-07-05 17:15:37.530 ttt[41697:5f03] 11 2011-07-05 17:15:37.532 ttt[41697:6203] 13 6. queue可以有结束时执行的方法 void myFinalizerFunction(){ &nbsp;&nbsp;&nbsp; NSLog(@"xxx"); } - (void)viewDidLoad { &nbsp;&nbsp;&nbsp; [superviewDidLoad]; &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; dispatch_queue_t queue = dispatch_queue_create("com.example.MyQueue", NULL); // 串行queue &nbsp;&nbsp;&nbsp; dispatch_set_context(queue, @"xxx"); &nbsp;&nbsp;&nbsp; dispatch_set_finalizer_f(queue, &amp;myFinalizerFunction); &nbsp;&nbsp;&nbsp; for (int i = 0; i&lt;1000; i++) { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; dispatch_async(queue, ^{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; NSLog(@"%d",i); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }); &nbsp;&nbsp;&nbsp; } &nbsp;&nbsp;&nbsp; dispatch_release(queue); 7. dispatch_sync(queue,task)&nbsp;&nbsp;会阻塞当前线程, 直到queue完成了你给的task，但queue要完成你给的task，因为queue是FIFO的，意味着要完成之前的任务，才有机会执行你刚才给的task, 相当于当前线程等待queue里面所有任务执行完毕，所以这句话不能在当前queue的任务代码里面调用，会造成阻塞 &nbsp;&nbsp;&nbsp; dispatch_queue_t queue = dispatch_queue_create("com.example.MyQueue", NULL); // 串行queue &nbsp;&nbsp;&nbsp; dispatch_set_context(queue, @"xxx"); &nbsp;&nbsp;&nbsp; dispatch_set_finalizer_f(queue, &amp;myFinalizerFunction); &nbsp;&nbsp;&nbsp; for (int i = 0; i&lt;10; i++) { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; dispatch_async(queue, ^{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; NSLog(@"%d",i); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }); &nbsp;&nbsp;&nbsp; } &nbsp;&nbsp;&nbsp; NSLog(@"waiting"); &nbsp;&nbsp;&nbsp; dispatch_sync(queue, ^{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; NSLog(@"wait done"); &nbsp;&nbsp;&nbsp; }); &nbsp;&nbsp;&nbsp; dispatch_release(queue); 2011-07-05 17:54:35.479 ttt[44203:207] waiting 2011-07-05 17:54:35.479 ttt[44203:1803] 0 2011-07-05 17:54:35.481 ttt[44203:1803] 1 2011-07-05 17:54:35.482 ttt[44203:1803] 2 2011-07-05 17:54:35.482 ttt[44203:1803] 3 2011-07-05 17:54:35.483 ttt[44203:1803] 4 2011-07-05 17:54:35.483 ttt[44203:1803] 5 2011-07-05 17:54:35.484 ttt[44203:1803] 6 2011-07-05 17:54:35.484 ttt[44203:1803] 7 2011-07-05 17:54:35.485 ttt[44203:1803] 8 2011-07-05 17:54:35.485 ttt[44203:1803] 9 2011-07-05 17:54:35.486 ttt[44203:207] wait done 2011-07-05 17:54:35.487 ttt[44203:1803] xxx 8. Waiting on Groups of Queued Tasks　　　　// dispatch_sync只能对一个queue等待 &nbsp;&nbsp;&nbsp; dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); &nbsp;&nbsp;&nbsp; dispatch_group_t group = dispatch_group_create(); &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; // Add a task to the group &nbsp;&nbsp;&nbsp; dispatch_group_async(group, queue, ^{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; NSLog(@"first task"); &nbsp;&nbsp;&nbsp; }); &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; dispatch_queue_t otherqueue = dispatch_queue_create("com.example.MyQueue", NULL); &nbsp;&nbsp;&nbsp; for (int i = 0; i&lt;100; i++) { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; dispatch_group_async(group, otherqueue, ^{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; NSLog(@"otherqueue task"); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }); &nbsp;&nbsp;&nbsp; } &nbsp;&nbsp;&nbsp; dispatch_group_wait(group, DISPATCH_TIME_FOREVER); &nbsp;&nbsp;&nbsp; NSLog(@"end waiting"); &nbsp;&nbsp;&nbsp; dispatch_release(group); 2011-07-05 19:32:31.919 ttt[50138:5f03] otherqueue task 2011-07-05 19:32:31.919 ttt[50138:1803] first task 2011-07-05 19:32:31.922 ttt[50138:5f03] otherqueue task 2011-07-05 19:32:31.923 ttt[50138:5f03] otherqueue task ... 2011-07-05 19:32:32.078 ttt[50138:5f03] otherqueue task 2011-07-05 19:32:32.079 ttt[50138:5f03] otherqueue task 2011-07-05 19:32:32.080 ttt[50138:207] end waiting 9. Although you can obtain information about the underlying thread running a task, it is better to avoid doing so 
 
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