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POSlow deletes and saves in nested NSManagedObjectContext
 

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    <p>In my app I have a "master" <code>NSPrivateQueueConcurrencyType</code> context which serves as a parent to a <code>NSMainQueueConcurrencyType</code> context that the view controller's rely on and pass around. I wanted to do this to take advantage of async saves (this app uses iCloud with Core Data and saves do a lot of work exporting ubiquity logs). The setup is similar to the Zarra approach mentioned at the bottom of <a href="http://www.cocoanetics.com/2012/07/multi-context-coredata/" rel="noreferrer">this article</a></p> <p>Saves within the app typically look like:</p> <pre><code>[context save:nil]; [context.parentContext performBlock:^{ [context.parentContext save:nil]; }]; </code></pre> <p>This seems to work well for small edits/updates, but I'm confused about what I see when I delete many objects (eg, delete a project that has hundreds of task objects related to it).</p> <p>In that situation the save is async but it looks like the main thread gets into a semaphore wait situation (as seen when I pause the debugger) and is effectively blocked (I can't scroll in the UI) until the background private context finishes the save.</p> <p>Actually, I just noticed that swipe-to-delete deletions of a single object incur a noticeable delay, despite this async save pattern, so it seems all deletions in the app are slow.</p> <p>If, alternatively, I alloc a new <code>NSPrivateQueueConcurrencyType</code> context, set its persistent store coordinator to the main PSC in the AppDelegate, and perform the delete and save, it still does a lot of work but the UI is never blocked (but then I have to worry about coordinating the contexts, refetching in the main context).</p> <p>Any ideas what I might have done wrong, or have you seen this behavior also?</p>
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