Monthly Archives: October 2011

Race Condition when Moving NSDocuments to iCloud

Posted on by optshiftk
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Update: I just re-read a cocoa-dev post from last month in which Kevin Perry from Apple states the following:

I don’t see the nested uses of performSynchronousFileAccessUsingBlock: you mentioned in that code, but that’s not a problem anyway, since file access is recursive, as long as it happens synchronously within the outer-most file access block (a fact that admittedly may not be documented well anywhere).

That would certainly change things. Perhaps the reason that -relinquishPresentedItemToWriter: was deadlocking on me is because it calls -performActivityWithSynchronousWaiting:, not just -performSynchronousFileAccess? I’ll have to experiment.

Now that iCloud is out, I can finally talk about this in a public forum. Unfortunately, the cocoa-dev mailing list is down. But I really need to get this question out there, or at least written down, because it involves one of the most confusing new APIs in Lion: -[NSDocument performSynchronousFileAccess:] (or -performAsynchronousFileAccess: if you really hate your sanity).

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NSWindowController and -[NSWindow isReleasedWhenClosed]

Posted on by optshiftk
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I noticed that the Resource Programming Guide has been updated for ARC, which prompted me to investigate something that has puzzled me for a long time: how does NSWindowController interact with NSWindow’s “convenience” method -isReleasedWhenClosed? It turns out that NSWindowController actually calls -setReleasedWhenClosed:NO on its window as part of -setWindow:. It doesn’t matter if NSWindowController loaded the window from nib, or if it was initialized with -initWithWindow: directly.

This makes memory management of NSWindowController-owned windows saner. And nowadays, with our multi-core multi-GHz machines packed with oodles of RAM, it’s worth spending the extra bytes to create an NSWindowController to manage your windows rather than rely on the arcane -isReleaedWhenClosed method (and its equally-outmoded companion, the “visible at launch” flag in Interface Builder).

I’d really prefer if the Window nib templates assumed File’s Owner was an NSWindowController and unchecked the “Release when closed” checkbox by default. NSWindowController’s cleanup behavior means you can leave the “Release when Closed” checkbox checked but still reopen a closed window, which is misleading and probably the source of my confusion in the first place. I’ve filed this request as rdar://10349276 (also viewable on OpenRadar).