For some time, our audio app crashed when an audio device was plugged in (or when Facetime was
connecting). Strangely, this only happened when the app was built on OS X 10.7 or later and run on
10.7 or later. That is, the 10.6 built app (which we distributed) didn't crash on any version of OS
X and the 10.7-up built version didn't crash on 10.6.
The backtrace would typically look like
Thread 7 Crashed:: Dispatch queue: com.apple.audio.CADispatchQueue.SerialQueue
0
1 -- application exception handler here --
2 com.apple.audio.CoreAudio 0x99ddcd42 HALObject::PropertiesChanged(unsigned long,
AudioObjectPropertyAddress const*) + 714
3 com.apple.audio.CoreAudio 0x99de11d8 HALSystem::ObjectsPublishedAndDied(unsigned long,
unsigned long const*, unsigned long, unsigned long const*) + 1242
4 com.apple.audio.CoreAudio 0x99de1553
HALSystem::AudioObjectsPublishedAndDied(AudioHardwarePlugInInterface**, unsigned long, unsigned
long, unsigned long const*, unsigned long, unsigned long const*) + 187
5 com.apple.audio.CoreAudio 0x99dcf101
HALC_ShellPlugIn::ProxyObject_PropertiesChanged(unsigned long, unsigned long,
AudioObjectPropertyAddress const*) + 787
6 com.apple.audio.CoreAudio 0x99dbdc00 HALC_ProxyNotifications::CallListener(unsigned long,
unsigned long, unsigned long, AudioObjectPropertyAddress const*) + 56
7 com.apple.audio.CoreAudio 0x99da97ed
HALC_ProxyNotifications::CallListener_f(void*) + 41
8 libdispatch.dylib 0x93cbe130 _dispatch_client_callout + 50
9 libdispatch.dylib 0x93cc1d05 _dispatch_queue_drain + 1017
10 libdispatch.dylib 0x93cc399d _dispatch_queue_invoke + 186
11 libdispatch.dylib 0x93cc0f89 _dispatch_root_queue_drain +
395
12 libdispatch.dylib 0x93cd063d _dispatch_worker_thread3 + 97
13 libsystem_pthread.dylib 0x914c5653 _pthread_wqthread + 724
14 libsystem_pthread.dylib 0x914c2e0e start_wqthread + 30
Finally, we found out that not calling GetDefaultOutputVolume at application startup, resolved the
issue. No more crashes on plugging in audio devices.
I did some low-level debugging. Even on OS X 10.6 (where it doesn't crash), GetDefaultOutputVolume
calls
AudioObjectAddPropertyListener 3x
AudioObjectRemovePropertyListener 0x
AudioHardwareAddPropertyListener 3x
AudioHardwareRemovePropertyListener 2x
AudioDeviceAddPropertyListener 10x
AudioDeviceRemovePropertyListener 8x
The crash backtrace suggests that an invalid property listener is getting called when the input or
output device list gets changed. And the above list suggests that not all installed property
listeners are being removed by GetDefaultOutputVolume. Unless there is some unknown logic behind
this that I am not aware of. Can you shed some light on this ?
Regards,
Adriaan van Os
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