未分配的KVO发生奇怪的崩溃

Question

This has been dogging me for a while.

I have a NSOperation subclass running in an operation queue. I have had occasional, infrequent (but significant portions of our crashes) instances of crashes on what looks like a key-value observer.

The crash looks like

Crashed: Thread
EXC_BAD_ACCESS KERN_INVALID_ADDRESS 0x300000001099d05d
NSKeyValueDidChangeWithPerThreadPendingNotifications.llvm.93060043671412

[OperationClass markAsFinished]

...Which strongly implies an un-deregistered KVO object. Problem is I can't find any references to KVO being added to this object. I've even gone to the trick of object swizzling to track calls to addObserver:forKeyPath:options:context: and there are no registrations to thse classes.

The only thing I can think of is something is implicitly registering a KVO, outside of the context of my source, but I don't know what would do this.

Does anyone have any ideas?

Answer 1

You haven't provided any code, so I can only talk in generalities, but if you look at the docs for NSOperation and NSOperationQueue , you'll see that they use KVC and KVO for monitoring dependencies, priorities, and execution states. Based on the error statement, I'd say the code trying to send an 'Operation is Finished' notification that's being watched by KVO, and that's where things fall apart. Maybe an operation is pulled off the queue and deallocated before the notification goes through? Maybe a queue is deallocating before one of its operations finishes? Maybe an operation is deallocating before one of its dependencies completes? That's where I'd start looking, at any rate. Maybe put a breakpoint on the 'finished' property of NSOperation, see what comes up...