iOS 控制异步回调

dispatch_group_t group = dispatch_group_create();

dispatch_group_enter(group);
AFHTTPRequestOperation *operation1 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
 [operation1 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
dispatch_group_leave(group);
}];
[operation1 start];

dispatch_group_enter(group);
AFHTTPRequestOperation *operation2 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation2 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
dispatch_group_leave(group);
}];
[operation2 start];

dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
dispatch_release(group);