1、dispatch_group

dispatch_group_t group =  dispatch_group_create();dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0), ^{    // 执行1个耗时的异步操作});dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0), ^{    // 执行1个耗时的异步操作});dispatch_group_notify(group, dispatch_get_main_queue(), ^{    // 等前面的异步操作都执行完毕后，回到主线程...});

2、dispatch_barrier_async

dispatch_queue_tqueue =dispatch_queue_create("12312312",DISPATCH_QUEUE_CONCURRENT);dispatch_async(queue,^{        NSLog(@"----1-----%@", [NSThread currentThread]);});dispatch_async(queue,^{        NSLog(@"----2-----%@", [NSThread currentThread]);});dispatch_barrier_async(queue,^{        NSLog(@"----barrier-----%@", [NSThread currentThread]);});dispatch_async(queue,^{        NSLog(@"----3-----%@", [NSThread currentThread]);});dispatch_async(queue,^{        NSLog(@"----4-----%@", [NSThread currentThread]);});