詳解IOS串行隊列與并行隊列進行同步或者異步的實例
IOS中GCD的隊列分為串行隊列和并行隊列，任務分為同步任務和異步任務，他們的排列組合有四種情況，下面分析這四種情況的工作方式。
同步任務，使用GCD dispatch_sync 進行派發(fā)任務
- (void)testSync { dispatch_queue_t serialQueue = dispatch_queue_create("com.zyt.queue", DISPATCH_QUEUE_SERIAL); dispatch_queue_t concurrentQueue = dispatch_queue_create("com.zyt.queue", DISPATCH_QUEUE_CONCURRENT); NSLog(@"====serialQueue===="); for (int i = 0; i<10; i++) { dispatch_sync(serialQueue, ^{ [NSThread sleepForTimeInterval:0.3]; NSLog(@"==>%@ sync serial XXX>%d", [NSThread currentThread], i); }); } NSLog(@"====concurrentQueue===="); for (int i = 0; i<10; i++) { dispatch_sync(concurrentQueue, ^{ [NSThread sleepForTimeInterval:0.3]; NSLog(@"==>%@ sync concurrent ====>%d", [NSThread currentThread], i*i); }); }}結(jié)果如下：
2017-03-01 01:36:22.835 Demo ====serialQueue====2017-03-01 01:36:23.207 {number = 1, name = main} sync serial XXX>02017-03-01 01:36:23.578 {number = 1, name = main} sync serial XXX>12017-03-01 01:36:23.952 {number = 1, name = main} sync serial XXX>22017-03-01 01:36:24.325 {number = 1, name = main} sync serial XXX>32017-03-01 01:36:24.699 {number = 1, name = main} sync serial XXX>42017-03-01 01:36:25.072 {number = 1, name = main} sync serial XXX>52017-03-01 01:36:25.446 {number = 1, name = main} sync serial XXX>62017-03-01 01:36:25.746 {number = 1, name = main} sync serial XXX>72017-03-01 01:36:26.122 {number = 1, name = main} sync serial XXX>82017-03-01 01:36:26.489 {number = 1, name = main} sync serial XXX>92017-03-01 01:36:26.489 Demo ====concurrentQueue====2017-03-01 01:36:26.864 {number = 1, name = main} sync concurrent ====>02017-03-01 01:36:27.236 {number = 1, name = main} sync concurrent ====>12017-03-01 01:36:27.611 {number = 1, name = main} sync concurrent ====>42017-03-01 01:36:27.985 {number = 1, name = main} sync concurrent ====>92017-03-01 01:36:28.354 {number = 1, name = main} sync concurrent ====>162017-03-01 01:36:28.726 {number = 1, name = main} sync concurrent ====>252017-03-01 01:36:29.100 {number = 1, name = main} sync concurrent ====>362017-03-01 01:36:29.474 {number = 1, name = main} sync concurrent ====>492017-03-01 01:36:29.849 {number = 1, name = main} sync concurrent ====>642017-03-01 01:36:30.223 {number = 1, name = main} sync concurrent ====>81testSync方法是在主線程中調(diào)用的，結(jié)果看到使用的串行隊列和使用并行隊列看到的結(jié)果都是發(fā)生在當前線程：主線程中，沒有開啟新的線程處理任務，任務的調(diào)度也是串行調(diào)度的。
異步任務，使用GCD dispatch_async 進行派發(fā)任務
- (void)testAsync { dispatch_queue_t serialQueue = dispatch_queue_create("com.zyt.queue", DISPATCH_QUEUE_SERIAL); dispatch_queue_t concurrentQueue = dispatch_queue_create("com.zyt.queue", DISPATCH_QUEUE_CONCURRENT); NSLog(@"====serialQueue===="); for (int i = 0; i<10; i++) { dispatch_async(serialQueue, ^{ [NSThread sleepForTimeInterval:0.3]; NSLog(@"==>%@ async serial XXX>%d", [NSThread currentThread], i); }); } NSLog(@"====concurrentQueue===="); for (int i = 0; i<10; i++) { dispatch_async(concurrentQueue, ^{ [NSThread sleepForTimeInterval:0.3]; NSLog(@"==>%@ async concurrent ====>%d", [NSThread currentThread], i*i); }); }}`結(jié)果如下：
2017-03-01 01:45:36.125 Demo ====serialQueue====2017-03-01 01:45:36.125 Demo ====concurrentQueue====2017-03-01 01:45:36.494 {number = 3, name = (null)} async concurrent ====>02017-03-01 01:45:36.494 {number = 5, name = (null)} async concurrent ====>42017-03-01 01:45:36.494 {number = 4, name = (null)} async concurrent ====>12017-03-01 01:45:36.494 {number = 6, name = (null)} async concurrent ====>162017-03-01 01:45:36.494 {number = 8, name = (null)} async serial XXX>02017-03-01 01:45:36.494 {number = 7, name = (null)} async concurrent ====>92017-03-01 01:45:36.494 {number = 9, name = (null)} async concurrent ====>252017-03-01 01:45:36.494 {number = 11, name = (null)} async concurrent ====>492017-03-01 01:45:36.494 {number = 10, name = (null)} async concurrent ====>362017-03-01 01:45:36.501 {number = 13, name = (null)} async concurrent ====>812017-03-01 01:45:36.501 {number = 12, name = (null)} async concurrent ====>642017-03-01 01:45:36.869 {number = 8, name = (null)} async serial XXX>12017-03-01 01:45:37.244 {number = 8, name = (null)} async serial XXX>22017-03-01 01:45:37.615 {number = 8, name = (null)} async serial XXX>32017-03-01 01:45:37.986 {number = 8, name = (null)} async serial XXX>42017-03-01 01:45:38.358 {number = 8, name = (null)} async serial XXX>52017-03-01 01:45:38.730 {number = 8, name = (null)} async serial XXX>62017-03-01 01:45:39.103 {number = 8, name = (null)} async serial XXX>72017-03-01 01:45:39.472 {number = 8, name = (null)} async serial XXX>82017-03-01 01:45:39.842 {number = 8, name = (null)} async serial XXX>9 testSync方法是在主線程中調(diào)用的，結(jié)果看到使用的串行隊列的異步任務會開啟一個子線程執(zhí)行任務，任務的調(diào)度是串行的
使用并行隊列的異步任務會開啟多個子線程并行的處理任務，任務的先后順序是不固定的，任務的調(diào)度方式是并行的
總結(jié)
同步任務：和使用的隊列無關(guān)，不會開啟子線程處理任務，會在當前的線程中串行的調(diào)度任務，即一個任務完成之后繼續(xù)下一個任務，如果同步任務在主線程中調(diào)用，會阻塞主線程
異步任務：a. 使用串行隊列，會開啟一個子線程串行的調(diào)度任務 b. 使用并行隊列，會開啟多個子線程并行的調(diào)度任務，這種情況用的是最多的。
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