Crashing with ASIHTTPRequest and NSOperationQueue when cancelling operations - iphone

Question

I'm having a really hard time when trying to cancel requests in an NSOperationQueue.
Before deallocating my 'engine' object, I call a cancelOperations method to cancel everything in the queue, so this will include in flight ASIHTTPRequests and queued ones... e.g.
Engine.m
-(void)getContent {
if (![self queue]) {
[self setQueue:[[[NSOperationQueue alloc] init] autorelease]];
}
NSURL *url = [NSURL URLWithString:#"http://allseeing-i.com"];
ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];
[request setDelegate:self];
[request setDidFinishSelector:#selector(requestDone:)];
[[self queue] addOperation:request]; //queue is an NSOperationQueue
}
-(void)requestDone:(ASIHTTPRequest)*request {
// Do something with request
}
-(void)cancelOperations {
[self.queue cancelAllOperations];
[self.queue waitUntilAllOperationsAreFinished];
}
-(void)dealloc {
[super dealloc];
}
Now, In my engine I have a number of getContent type methods, so my queue has different request objects in it. The flow when using an Engine object is:
1) Open View Controller - view did load - alloc and init Engine object
2) // Call various getContent style methods to queue up some operations
3) Upon view exit, call [engine cancelOperations]; in order to (a) Stop any network requests in flight, and to also empty the queue
4) Deallocate the view, and with that the engine: [engine release];
This works fine if all requests have finished in the queue (as it's empty), however if I cancelOperations whilst a request is active, the application crashes with a EXC_BAD_ACCESS error... but AFTER the engine is deallocated successfully...
Any ideas why this would be?
--EDIT--
Adding Backtrace for error:
Exception Type: EXC_BAD_ACCESS (SIGBUS)
Exception Codes: KERN_PROTECTION_FAILURE at 0x00000000b0000000
Crashed Thread: 0 Dispatch queue: com.apple.main-thread
Application Specific Information:
objc_msgSend() selector name: respondsToSelector:
iPhone Simulator 225, iPhone OS 4.1 (iPhone 4/8B117)
Thread 0 Crashed: Dispatch queue: com.apple.main-thread
0 libobjc.A.dylib 0x02cb5907 objc_msgSend + 27
1 CoreFoundation 0x02ac95cd __invoking___ + 29
2 CoreFoundation 0x02ac94a1 -[NSInvocation invoke] + 145
3 Foundation 0x0015a3ca __NSThreadPerformPerform + 251
4 CoreFoundation 0x02b39faf __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15
5 CoreFoundation 0x02a9839b __CFRunLoopDoSources0 + 571
6 CoreFoundation 0x02a97896 __CFRunLoopRun + 470
7 CoreFoundation 0x02a97350 CFRunLoopRunSpecific + 208
8 CoreFoundation 0x02a97271 CFRunLoopRunInMode + 97
9 GraphicsServices 0x0320c00c GSEventRunModal + 217
10 GraphicsServices 0x0320c0d1 GSEventRun + 115
11 UIKit 0x003e9af2 UIApplicationMain + 1160
12 Clicky 0x000027d4 main + 102 (main.m:14)
13 Clicky 0x00002765 start + 53
Thread 1: Dispatch queue: com.apple.libdispatch-manager
0 libSystem.B.dylib 0x97cfe942 kevent + 10
1 libSystem.B.dylib 0x97cff05c _dispatch_mgr_invoke + 215
2 libSystem.B.dylib 0x97cfe519 _dispatch_queue_invoke + 163
3 libSystem.B.dylib 0x97cfe2be _dispatch_worker_thread2 + 240
4 libSystem.B.dylib 0x97cfdd41 _pthread_wqthread + 390
5 libSystem.B.dylib 0x97cfdb86 start_wqthread + 30
Thread 2:
0 libSystem.B.dylib 0x97cfd9d2 __workq_kernreturn + 10
1 libSystem.B.dylib 0x97cfdf68 _pthread_wqthread + 941
2 libSystem.B.dylib 0x97cfdb86 start_wqthread + 30
Thread 3: WebThread
0 libSystem.B.dylib 0x97cd80fa mach_msg_trap + 10
1 libSystem.B.dylib 0x97cd8867 mach_msg + 68
2 CoreFoundation 0x02b3a436 __CFRunLoopServiceMachPort + 150
3 CoreFoundation 0x02a97984 __CFRunLoopRun + 708
4 CoreFoundation 0x02a97350 CFRunLoopRunSpecific + 208
5 CoreFoundation 0x02a97271 CFRunLoopRunInMode + 97
6 WebCore 0x034093a3 RunWebThread(void*) + 483
7 libSystem.B.dylib 0x97d0581d _pthread_start + 345
8 libSystem.B.dylib 0x97d056a2 thread_start + 34
Thread 4:
0 libSystem.B.dylib 0x97cfd9d2 __workq_kernreturn + 10
1 libSystem.B.dylib 0x97cfdf68 _pthread_wqthread + 941
2 libSystem.B.dylib 0x97cfdb86 start_wqthread + 30
Thread 5:
0 libSystem.B.dylib 0x97cd80fa mach_msg_trap + 10
1 libSystem.B.dylib 0x97cd8867 mach_msg + 68
2 CoreFoundation 0x02b3a436 __CFRunLoopServiceMachPort + 150
3 CoreFoundation 0x02a97984 __CFRunLoopRun + 708
4 CoreFoundation 0x02a97350 CFRunLoopRunSpecific + 208
5 CoreFoundation 0x02a9a614 CFRunLoopRun + 84
6 Clicky 0x0001fdb7 +[ASIHTTPRequest runRequests] + 167 (ASIHTTPRequest.m:4093)
7 Foundation 0x0014576c -[NSThread main] + 81
8 Foundation 0x001456f8 __NSThread__main__ + 1387
9 libSystem.B.dylib 0x97d0581d _pthread_start + 345
10 libSystem.B.dylib 0x97d056a2 thread_start + 34
Thread 6:
0 libSystem.B.dylib 0x97cd80fa mach_msg_trap + 10
1 libSystem.B.dylib 0x97cd8867 mach_msg + 68
2 CoreFoundation 0x02b3a436 __CFRunLoopServiceMachPort + 150
3 CoreFoundation 0x02a97984 __CFRunLoopRun + 708
4 CoreFoundation 0x02a97350 CFRunLoopRunSpecific + 208
5 CoreFoundation 0x02a97271 CFRunLoopRunInMode + 97
6 Foundation 0x0017ab86 +[NSURLConnection(NSURLConnectionReallyInternal) _resourceLoadLoop:] + 398
7 Foundation 0x0014576c -[NSThread main] + 81
8 Foundation 0x001456f8 __NSThread__main__ + 1387
9 libSystem.B.dylib 0x97d0581d _pthread_start + 345
10 libSystem.B.dylib 0x97d056a2 thread_start + 34
Thread 7:
0 libSystem.B.dylib 0x97cf7086 select$DARWIN_EXTSN + 10
1 CoreFoundation 0x02acbb5e __CFSocketManager + 798
2 libSystem.B.dylib 0x97d0581d _pthread_start + 345
3 libSystem.B.dylib 0x97d056a2 thread_start + 34
Thread 8:
0 libSystem.B.dylib 0x97cfd9d2 __workq_kernreturn + 10
1 libSystem.B.dylib 0x97cfdf68 _pthread_wqthread + 941
2 libSystem.B.dylib 0x97cfdb86 start_wqthread + 30
Thread 0 crashed with X86 Thread State (32-bit):
eax: 0x06641500 ebx: 0x000143f3 ecx: 0x0008e1c8 edx: 0x06606075
edi: 0xb0000000 esi: 0x066554c4 ebp: 0xbfffdef8 esp: 0xbfffdec4
ss: 0x0000001f efl: 0x00010206 eip: 0x02cb5907 cs: 0x00000017
ds: 0x0000001f es: 0x0000001f fs: 0x00000000 gs: 0x00000037
cr2: 0xb0000000

Answer 1

You do not release your operation queue in dealloc...
One suspect is the delegation pattern:
[request setDelegate:self];
If the self object is destroyed, and the request isn't, when the request 'completes', it will try to notify some garbage in memory, hence crash.
UPDATE: to patch this, add this code before canceling:
for (ASIHTTPRequest *request in queue.operations)
{
[request setDelegate: nil];
[request setDidFinishSelector: nil];
}

Answer 2

I think jv42 is correct about the cause. However, there's a handy helper for cleaning up delegates...
-(void)dealloc {
for (ASIHTTPRequest *request in queue.operations) {
[request clearDelegatesAndCancel];
}
[queue release];
[super dealloc];
}
Has anyone found a quicker method for this... maybe one that doesn't involve looping over the requests?

Answer 3

Make sure you are running a recent git version of ASIHTTPRequest - v1.7 contains a couple of race conditions that will causes crashes when cancelling requests.

Answer 4

I was having the same situation while running a ASINetworkQueue with multiple requests.
I removed the dealloc release for the queue, and the autorelease. I then applied Leah's excellent suggestion to loop through to nil the delegates. Then I put the queue's release in the queueRequestFinished delegate and it resolved my issue!
bulkQueue = [[ASINetworkQueue alloc] init];
[bulkQueue setQueueDidFinishSelector:#selector(queueRequestFinished:)];
-(void)queueRequestFinished:(ASINetworkQueue *)queue
{
for (ASIHTTPRequest *request in queue.operations)
{
[request setDelegate: nil];
[request setDidFinishSelector: nil];
}
}
Hope this helps someone out! :-)