Don't overload release or retainCount in JSCocoa

Overloading release or retainCount in JSCocoa will crash your app. To handle ObjC objects, JSCocoa boxes them as a Javascript object's private data. When the Javascript object is destroyed (finalized in JavascriptCore parlance) , JSCocoa will destroy its private data, thereby releasing the boxed ObjC object.

Finalization happens during garbage collection and JavascriptCore has an assert in place to prevent object creation during that time. Therefore creating Javascript objects during collection will crash. This could be fixed by delaying the destroying to the next run loop cycle, but for now : just don't do it :)

Now retainCount is not called during release (surely the ObjCRuntime is getting the ivar) so it should be safe to overload. Right ?

Crashing while running in Instruments

I overloaded retainCount in JSCocoa tests. While fixing memory leaks and running in Instruments, I encountered a crash in … retainCount. Turns out Instruments does calls retainCount during alloc and init. BUT it does not crash just yet, I have to repeatedly run the tests. And different runs yield different results :

  • Running from Instruments' Leaks template : retainCount called twice → CRASH
  • Running from Instruments' ObjectAlloc template then adding Leaks : retainCount called once → no crash
More debugging ahead.

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Planet Cocoa

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