Crash in release, but not debug - macos

Question

I am writing an app that uses Audio Queue Services to play music. When it gets to the end of one song, it should move on to the next. It works fine in the debug scheme, but it crashes in the release scheme
Process: xxx [1136]
Path: /Users/USER/Desktop/btunes.app/Contents/MacOS/xxx
Identifier: xxx
Version: 1.0 (1)
Code Type: X86-64 (Native)
Parent Process: launchd [152]
Responsible: xxx [1136]
User ID: 501
Date/Time: 2014-03-18 09:33:15.557 -0700
OS Version: Mac OS X 10.9.2 (13C64)
Report Version: 11
Anonymous UUID: 57FFD284-4D30-889E-73D0-CE978BAFC774
Crashed Thread: 6 com.apple.coreaudio.AQClient
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x0000000280000018
VM Regions Near 0x280000018:
CG shared images 00000001c7eb2000-00000001c7eba000 [ 32K] r--/r-- SM=SHM
-->
JS JIT generated code 00005b8cc8000000-00005b8cc8001000 [ 4K] ---/rwx SM=NUL
Application Specific Information:
objc_msgSend() selector name: delegate
Thread 6 Crashed:: com.apple.coreaudio.AQClient
0 libobjc.A.dylib 0x00007fff85742097 objc_msgSend + 23
1 com.cluttered.btunes 0x000000010aced249 -[BTSAudioStreamer handleAudioQueueProperty] + 136 (BTSAudioStreamer.m:180)
2 com.apple.audio.toolbox.AudioToolbox 0x00007fff87af6f6d ClientAudioQueue::PropertyChanged(unsigned int) + 415
3 com.apple.audio.toolbox.AudioToolbox 0x00007fff87afc97c AQClientCallbackMessageReader::DispatchCallbacks(void const*, unsigned long) + 440
4 com.apple.audio.toolbox.AudioToolbox 0x00007fff87af742e ClientAudioQueue::FetchAndDeliverPendingCallbacks(unsigned int) + 334
5 com.apple.audio.toolbox.AudioToolbox 0x00007fff87af7554 AQCallbackReceiver_CallbackNotificationsAvailable + 129
6 com.apple.audio.toolbox.AudioToolbox 0x00007fff87b1777c _XCallbackNotificationsAvailable + 48
7 com.apple.audio.toolbox.AudioToolbox 0x00007fff87b111bf mshMIGPerform + 153
8 com.apple.CoreFoundation 0x00007fff81adc9a9 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 41
9 com.apple.CoreFoundation 0x00007fff81adc91e __CFRunLoopDoSource1 + 478
10 com.apple.CoreFoundation 0x00007fff81acda16 __CFRunLoopRun + 1830
11 com.apple.CoreFoundation 0x00007fff81acd0b5 CFRunLoopRunSpecific + 309
12 com.apple.audio.toolbox.AudioToolbox 0x00007fff87afe479 GenericRunLoopThread::Entry(void*) + 187
13 com.apple.audio.toolbox.AudioToolbox 0x00007fff87ab7c0d CAPThread::Entry(CAPThread*) + 109
14 libsystem_pthread.dylib 0x00007fff87db1899 _pthread_body + 138
15 libsystem_pthread.dylib 0x00007fff87db172a _pthread_start + 137
16 libsystem_pthread.dylib 0x00007fff87db5fc9 thread_start + 13
Line 180 is
if (self.delegate) {
The delegate is (weak), and I set self.delegate to nil in dealloc. It looks like the Audio Queue Property Listener keeps running even after I remove it (which I'm also doing in dealloc).
I don't understand why it only happens in Release mode though. For now I'm just archiving the app in Debug but this obviously not ideal. Any ideas?

Answer 1

Paraphrasing/Quoting this post so that the knowledge is retained.
Looks like there is an issue with different optimization levels. Running with optimization at fast causes a crash in some environments.
"One of the differences that jumped out at me was the Optmization Level setting. The Debug version was set to None [-O0], while the Release version was set to Fastest, Smallest [-Os].
I changed the Debug setting to Fastest, Smallest [-Os] and BOOM, it crashed on the iPhone 3G every time I ran it. Switching it back to None [-O0] brought back the correct behavior."
Also see Related SO Question.