线程添加依赖的两种方法

一、GCD

dispatch_semaphore_t sephore = dispatch_semaphore_create(0);

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ NSLog(@"222"); dispatch_semaphore_wait(sephore, DISPATCH_TIME_FOREVER); });

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ NSLog(@"123"); dispatch_semaphore_signal(sephore); });

注意：dispatch_semaphore_wait(sephore, DISPATCH_TIME_FOREVER);不能写在主线程中，会卡死的，一直等待。

输出结果： 123

                   222

一、NSOperation

NSOperationQueue * queue = [[NSOperationQueue alloc] init]; NSBlockOperation * o1 = [NSBlockOperation blockOperationWithBlock:^{ NSLog(@"o1 finish"); }]; NSBlockOperation * o2 = [NSBlockOperation blockOperationWithBlock:^{ NSLog(@"o2 finish"); }]; [op1 addDependency:op2]; [queue addOperation:op1]; [queue addOperation:op2];

输出结果： o2 finish

                   o1 finish