How can I debug an EXC_BAD_ACCESS from an invalidated NSTimer

Question

I've got a repeating NSTimer that I invalidate manually some time before I dealloc the object that owns the callback that is invoked by the timer. I verify that when I invalidate the timer, the callback is not being called anymore. When the object deallocs, an instant later I get an EXC_BAD_ACCESS. The crash is correlated with whether I invalidate the timer or not, i.e. if I don't invalidate it, there is no crash.

Does anyone know why this might be happening? I don't see why the timer would try to access the callback for the dealloc'ed object, which is what seems to be happening. I'm at a loss how to debug this further. The callstack just says:

#0  0x02f05c93 in objc_msgSend
#1  0x00000001 in ??
#2  0x02d255fa in CFRunLoopRunSpecific
#3  0x02d248a8 in CFRunLoopRunInMode
#4  0x037de89d in GSEventRunModal
#5  0x037de962 in GSEventRun
#6  0x00863372 in UIApplicationMain
#7  0x00002e40 in main at main.m:13

UPDATE: I have determined it is not the timer but a leak resulting from my parent object calling dealloc (the non-invalidating timer was preventing dealloc from calling). It would still be useful to hear advice on how to debug things when I hit a wall with the callstack, if it is even possible, so I'll leave this question up.

Answer 1

When you invalidate an NSTimer, the receiver sends a release to the target and userInfo parameters of timerWithTimeInterval:target:selector:userInfo:repeats:. Is it possible you are referring to these objects or have some incorrect memory-management with one of these objects?

One way to debug this is to make use of NSZombie.