NSOperationQueue Usage

gistfile1.m

// to initialize the nsoperationqueue
NSOperationQueue * queue = [[NSOperationQueue alloc] init];
[queue setMaxConcurrentOperationCount:4];

// to add an operation to the context
NSOperation * op = [NSBlockOperation blockOperationWithBlock:^{
  int i = 0;
  dispatch_async(dispatch_get_main_queue(), ^{
    // update ui
  });
}];
[queue addOperation:op];
    

// if you ever want to cancel the operation
[op cancel];