How to know all concurrent NSOperations are completed - ios

Question

My situation is:
I have users
Each user has some history data that can be fetched via user objects
What I want to do is:
Max 2 users must be fetching their history data at the same time (this is the reason that I want to use NSOperationQueue)
I need to get notified when any user finished fetching its history data
I need to get notified when every user finished fetching their history data
What I ask is:
How can I achieve what I want to do since I can't make it thru with the code below?
Any help is appreciated.
NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
[operationQueue setMaxConcurrentOperationCount:2];
for (User *user in users) {
NSBlockOperation *operationObject = [NSBlockOperation blockOperationWithBlock:^{
[user loadHistoryData:^{
[NSNotificationCenter postNotificationToMainThread:#"oneUserFetchedHistory"];
}];
}];
[operationQueue addOperation:operationObject];
}
This question differs from this question because I don't want to chain any requests. I just want to know when they are all finished executing.
This answer has a completion block for only one operation queue.
This answer offers a way to make operation block to wait until async call to loadHistoryData is completed. As writing setSuspended
I could not find an answer for my need. Is there any?

Answer 1

I've used AsyncBlockOperation and NSOperationQueue+CompletionBlock
Combining them is working for me like this:
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[queue setMaxConcurrentOperationCount:1];
// 1 is serial, more is concurrent
queue.completionBlock = ^{
[NSNotificationCenter postNotificationToMainThread:#"allUsersFetchedHistory"];
};
for (User *user in users){
[queue addOperationWithAsyncBlock:^(AsyncBlockOperation *op) {
[user loadHistoryData:^{
[op complete];
[NSNotificationCenter postNotificationToMainThread:#"oneUserFetchedHistory"];
}];
}];
}