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POBizarre NSSet copying crash
 

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    <p>I have a class that contains an <code>NSSet</code>. That object is called <code>_collectibles</code>, and in a method, I make a copy of that set in order to do some processing, something like:</p> <pre><code>NSSet* collectibleCopy = [_collectibles copy]; </code></pre> <p>In practice, I see this regularly crash with this message:</p> <pre><code>[__NSPlaceholderSet initWithObjects:count:]: attempt to insert nil object from objects </code></pre> <p>I've resolved the issue by changing the above code to:</p> <pre><code>NSMutableSet* collectibleCopy = [[NSMutableSet alloc] initWithCapacity: [_collectibles count]]; for ( id thing in _collectibles ) { [collectibleCopy addObject: thing]; } </code></pre> <p>And now I can no longer reproduce any such crash. I'm betting <code>[copy]</code> is more efficient, and I'd rather use it, but I can't figure out why it's completely wonky!</p> <p>Update: while full context would take a ton of explanation, the keys to me solving this were that, a, the code was invoked this way:</p> <pre><code>NSBlockOperation* operation = [NSBlockOperation blockOperationWithBlock: ^{ [thing doStuff]; }]; [operationQueue addOperation: operation]; </code></pre> <p>And that I was, basically by making a bunch of things slower, catch the app with 2 threads running 2 threads for a queue initialized thusly:</p> <pre><code>operationQueue.maxConcurrentOperationCount = 1; </code></pre> <p>Which I thought impossible. The clue was that the second thread was in [NSAutoreleasePool drain], which led me to learn that NSOperationQueue can do autorelease stuff whenever/however it wants.</p>
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    1. USGoldenBoy
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    1. COI wasn't able to reproduce your bug. Could you post a bit more code for context?
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      1. USaLevelOfIndirection
    2. COis the set that you are copying a core data relationship?
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      1. USGrady Player
    3. COThe entire context would require a huge pile of code. :)
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      1. USGoldenBoy
 

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