GCD小总结 GCD小总结

单例模式

- (void)once{ static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ //这里的内容程序开始到结束只执行一次 }); }

串行队列同步／异步执行任务

- (void)serial{ //创建串行队列 dispatch_queue_t serialQueue = dispatch_queue_create("串行队列", DISPATCH_QUEUE_SERIAL); //获取主队列 -- 系统创建的串行队列 //dispatch_queue_t serialQueue = dispatch_get_main_queue(); dispatch_sync(serialQueue, ^{ //以同步方式在串行队列中添加任务并执行 }); dispatch_async(serialQueue, ^{ //以异步方式在串行队列中添加任务并执行 }); }

并发队列同步／异步执行任务

- (void)concurrent{ //创建并发队列 dispatch_queue_t concurrent = dispatch_queue_create("并发队列 ", DISPATCH_QUEUE_CONCURRENT); //获取全局队列 -- 系统创建的并发队列 //dispatch_queue_t concurrent = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); dispatch_sync(concurrent, ^{ //以同步的方式在并发队列中添加任务并执行 }); dispatch_async(concurrent, ^{ //以异步的方式在并发队列中添加任务并执行 }); }

队列组

- (void)group{ //创建队列组 dispatch_group_t group = dispatch_group_create(); //获取全局队列（优先级，0） dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); dispatch_group_async(group, queue, ^{ //异步操作1 }); dispatch_group_async(group, queue, ^{ //异步操作2 }); dispatch_group_notify(group, queue, ^{ //在上述异步操作结束后的操作 dispatch_async(dispatch_get_main_queue(), ^{ //回到主线程执行 }); }); }

延时执行

- (void)delay{ //发送消息实现 //[self performSelector:@selector(test) withObject:nil afterDelay:4.0]; //NSTimer实现 //[NSTimer scheduledTimerWithTimeInterval:4.0 target:self selector:@selector(test) userInfo:nil repeats:NO]; //GCD实现 dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(4 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{ NSLog(@"延时执行 -- test"); }); } - (void)test{ NSLog(@"延时执行 -- test"); }

barrier

- (void)barrier{ dispatch_queue_t barrierQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); dispatch_async(barrierQueue, ^{ NSLog(@"异步操作1"); }); dispatch_async(barrierQueue, ^{ NSLog(@"异步操作2"); }); dispatch_barrier_async(barrierQueue, ^{ //barrier之前的操作（异步操作1，2）执行完才会执行后面的操作（异步操作3，4） NSLog(@"barrier"); }); dispatch_async(barrierQueue, ^{ NSLog(@"异步操作3"); }); dispatch_async(barrierQueue, ^{ NSLog(@"异步操作4"); }); }