IOS4.2 app quits with EXC_BAD_ACCESS

An iPad app that runs fine under IOS3 fails under IOS4.2 It has a class that runs an http session from an operation queue and the failure is linked to this activity. Here is the console output:

Program received signal:  “EXC_BAD_ACCESS”.
[Switching to thread 11523]

Running NSZombies enabled didn't reveal anything so I have been putting NSLog statements in the code and found that the crash occurs when a local variable is changed. Here is the code section:

self.currentOperation = [[[DeduceAccessOperation alloc] init] autorelease];
[self.currentOperation addObserver:self forKeyPath:@"isFinished"
 options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld)
 context:NULL];
NSLog (@"Start observer added");    
[operationQueue addOperation:self.currentOperation];
NSLog (@"Start operation added");
NSLog(@"State is %d", self.status);
self.status = IEnablerServiceUpdating;
NSLog (@"State updated");

And here is the console log output:

2010-12-08 21:26:44.548 UCiEnabler[5180:307] Start observer added
2010-12-08 21:26:44.550 UCiEnabler[5180:307] Start operation added
2010-12-08 21:26:44.552 UCiEnabler[5180:307] State is 1
Program received signal:  “EXC_BAD_ACCESS”.
[Switching to thread 11523]

It is like status has become read-only (It's property is declared as atomic and readwrite).

The other relevant piece of information is that a sub-view has just been changed and it triggers开发者_StackOverflow the call on the above routine. It's code is:

//Start the update      
UCiEnablerAppDelegate *controller = (UCiEnablerAppDelegate *)[[UIApplication sharedApplication] delegate];
[controller deduceIEnablerServiceAccess];
controller.serviceBusy = TRUE; //1.04

Has anyone seen anything like this?

Has anyone ideas where to look next?

Regards Robin

Here's the stack trace:

#0  0x34a80464 in objc_msgSend
#1  0x3119543e in NSKVOPendingNotificationCreate
#2  0x3119535a in NSKeyValuePushPendingNotificationPerThread
#3  0x3117009a in NSKeyValueWillChange
#4  0x311682c6 in -[NSObject(NSKeyValueObserverNotification) willChangeValueForKey:]
#5  0x311cc718 in _NSSetIntValueAndNotify
#6  0x000097ce in -[IEnablerService startDeducingAccessState] at IEnablerService.m:55
#7  0x00002bc0 in -[UCiEnablerAppDelegate deduceIEnablerServiceAccess] at UCiEnablerAppDelegate.m:100
#8  0x0000a33e in -[RootViewControlleriPad animationDidStop:finished:context:] at RootViewController-iPad.m:43
#9  0x341bb336 in -[UIViewAnimationState sendDelegateAnimationDidStop:finished:]

NSOperationQueue in iOS 4.2 now uses GrandCentralDispatch when starting NSOperations. There's a Technical Q&A here

Pretty much the queue now calls the NSOperation subclass's start method in a new thread regardless of the isConcurrent property. In my experience it means that if you are using NSURLConnection inside a start method your code will no longer run because the thread start is running on doesn't have an NSRunLoop.

Apple says that this change doesn't break compatibility because you were supposed to spawn a new thread in the start method anyway.

For backwards compatibility you should change your subclass from using start to using run.