NSOperationQueue has waitUntilAllOperationsAreFinished, but I don't want to wait synchronously for it. I just want to hide progress indicator in UI when queue finishes. What's the best way to accomplish this? I can't send notifications from my NSOperations, because I don't know which one is going to be last, and [queue operations] might not be empty yet (or worse - repopulated) when notification i
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