Can you just manually retain it before cleaning, and manually release it afterwards? You can use CFRetain()/CFRelease() for that, or use runtime functions objc_retain() and objc_release(). The latter two is not documented by Apple per sé, but it is documented by LLVM as requirements of ARC.
Sent from my iPhone > On 2013年10月22日, at 3:11, Jens Alfke <[email protected]> wrote: > > I’ve just gotten a nasty bug report involving an iOS app hanging when it goes > into the background. The problem is a deadlock involving NSCache. I can see > what the problem is, but I don’t know what to do about it. > > In a nutshell: An NSCache is evicting objects, and as a result of that its > last reference goes away so the cache gets dealloced. Only the dealloc method > needs the same (non-recursive) lock the eviction call is using, so it > deadlocks. > > Specifically, there is a “database” object that has a strong reference to an > NSCache which maps to various ‘document’ objects (indexed by key.) The > document objects have strong references back to the database. > > In the situation that hangs, there is a database with one document, neither > of which have any external strong references to them. (They probably used to > at one point, but the app stopped using that database.) That’s fine, it’s not > a reference cycle because the NSCache will get cleaned up. Only the cleanup > doesn’t work because: > > 1. OS tells NSCache to flush value objects (`cache_remove_with_block`) > 2. NSCache releases the document, causing it to be dealloced > 3. Document’s dealloc implicitly releases its reference to the database > 4. Database is released and dealloced, implicitly releasing the NSCache > 5. NSCache is dealloced … but the `cache_destroy` call needs the mutex that’s > already being held by `cache_remove_with_block`. > > (You can see the full backtrace in the bug report on github.) > > Has anyone else run into this? Is there a workaround? This has come up once > before for me, and I was able to work around it by making the cache-owner > object call -autorelease instead of -release on the NSCache, to defer the > call to the cache’s dealloc. But I’m now using ARC so that isn’t an option. > > ―Jens > _______________________________________________ > > Cocoa-dev mailing list ([email protected]) > > Please do not post admin requests or moderator comments to the list. > Contact the moderators at cocoa-dev-admins(at)lists.apple.com > > Help/Unsubscribe/Update your Subscription: > https://lists.apple.com/mailman/options/cocoa-dev/xcvista%40me.com > > This email sent to [email protected] _______________________________________________ Cocoa-dev mailing list ([email protected]) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [email protected]
