Objectivec 等到多个网络请求都执行完毕 包括它们的完成块

我有多个操作(它们是AFNetworking请求)，带有需要一些时间才能执行的完成块，以及一个需要在所有请求结束时保存的核心数据对象.

MyCoreDataObject *coreDataObject;

AFHTTPRequestOperation *operation1 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation1 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
    coreDataObject.attribute1 = responseObject;
    sleep(5);
}];
[operation1 start];

AFHTTPRequestOperation *operation2 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation2 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
    coreDataObject.attribute2 = responseObject;
    sleep(10);
}];
[operation1 operation2];

[context save:nil];

当然，这并不是我想要的那样，因为请求是异步的.我try 添加一个NSOperationQueue，如下所示:

NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
[operationQueue setMaxConcurrentOperationCount:2];

AFHTTPRequestOperation *operation1 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation1 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
    coreDataObject.attribute1 = responseObject;
    sleep(5);
}];
[operationQueue addOperation:operation1];

AFHTTPRequestOperation *operation2 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation2 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
    coreDataObject.attribute2 = responseObject;
    sleep(10);
}];
[operationQueue addOperation:operation2];

[imageQueue waitUntilAllOperationsAreFinished];
[context save:nil];

看起来好多了.使用waitUntilAllOperationsAreFinished，我的队列将阻塞当前线程，直到我的请求完成，但直到我的成功块完成，这才是我真正需要的.

关于如何以一种好的方式实现这一点，有什么 idea 吗？