Core data + NSOperationQueue - multithreading

Question

i have a subclass of NSOperation which have managedObject as one of its property.
I need to add multiple operation to nsoperationqueue & observe their finish.
For each NSOperation instance i created a new managed object as Apple documentation state "Create a separate managed object context for each thread and share a single persistent store coordinator.".
Once the first operation is finished i get following crash log
#0 0x34970c98 in objc_msgSend ()
#1 0x3608704e in -[_PFArray dealloc] ()
#2 0x36084b80 in -[_PFArray release] ()
#3 0x3179b1a0 in CFRelease ()
#4 0x3179deba in _CFAutoreleasePoolPop ()
#5 0x30d7bbb4 in NSPopAutoreleasePool ()
#6 0x30d91e1c in -[__NSOperationInternal start] ()
#7 0x30d91a7e in -[NSOperation start] ()
#8 0x30df7eca in ____startOperations_block_invoke_2 ()
#9 0x33a248e6 in _dispatch_call_block_and_release ()
#10 0x33a1a532 in _dispatch_worker_thread2 ()
#11 0x368bf590 in _pthread_wqthread ()
#12 0x368bfbc4 in start_wqthread ()
From logs it seems some object is getting over-release.How i can get which object is over-release?
App is run with NSZombieEnabled but only above info is received.
do the NsOperation maintain its own autorelease pool?

Answer 1

Here are your clues:
#7 0x30d91a7e in -[NSOperation start] ()
It is something you are releasing in your operation.
#5 0x30d7bbb4 in NSPopAutoreleasePool ()
It is an object that is autoreleased. That does not necessarily mean you have written the autorelease method call. Objects that are created by convenience methods like [NSString stringWithFormat:...] are autoreleased before they are returned. So look for either a place in your operation code where you are calling autorelease or a place where you are creating an object without the alloc-init pattern.
Yes, an NSOperation maintains its own autorelease pool. You shouldn't have to worry about that. If you only release objects when you are done with them, and only autorelease objects when you will be done with them by the end of the method scope (or calling method scope if returning them) you should be fine.
#2 0x36084b80 in -[_PFArray release] ()
It is an object stored in an array (not the array itself) that is being overreleased.
An error of that kind means you are either releasing or autoreleasing an object when you shouldn't, or you are not retaining an object when you should. It could be either an incorrect release or an incorrect autorelease, even though the error occurs with the autorelease pool. The autorelease could be correct and the release could be incorrect. Either way the error will happen when the autorelease pool is drained because that happens later.