NSBlockOperation retain cycle

Question

I have to used NSOperations to download images (and save to disk), but memory didn't released! After some googling i found hook, that my operations in the retention cycle. I tried to fix my code, but problem is still here.

Can anyone find the error in my code?

There is my code:

NSOperationQueue *queue = [[NSOperationQueue alloc] init];
queue.maxConcurrentOperationCount = 10;

__block NSBlockOperation *completionOperation = [NSBlockOperation blockOperationWithBlock:^{
    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
        complection(YES); // this is a method's callback actually
    }];
}];

for (NSURL* url in imagesURLs) {
    __weak NSBlockOperation *downdloadOperation = [NSBlockOperation blockOperationWithBlock:^{
        NSData *imageData = [NSData dataWithContentsOfURL:url];
        if (imageData) {
            [[RuzaImageDiskHandler instance] saveImage:imageData forUrlKey:url];
        }
    }];

    [completionOperation addDependency:downdloadOperation];
}

[queue addOperations:completionOperation.dependencies waitUntilFinished:NO];
[queue addOperation:completionOperation];