How to avoid exception EXC_RESOURCE - WAKEUPS? - ios

Question

In my iPad app I often get a crash report with the exception EXC_RESOURCE and the subtype WAKEUPS.
However the strange thing is that the message says (Limit 150/sec) Observed 0/sec over 300 sec
How can it become an exception when it observed 0 wakeups/sec? - and how do I avoid it?
The reason I care is that the generation of the report delays some time critical threads in the app.
Mainly are we recording from the microphone and playing audio at the same time, and while the report is generated, the audio stutters.
The exception is always triggered by one of 3 threads: Main thread, AURemoteIO: IOThread and com.apple.coreaudio.AQClient. See fragments of report below:
Hardware Model: iPad2,5
Code Type: ARM (Native)
Parent Process: debugserver [3109]
Date/Time: 2016-05-18 12:15:59.59 +0200
Launch Time: 2016-05-18 12:11:44.44 +0200
OS Version: iOS 9.1 (13B143)
Report Version: 104
Exception Type: EXC_RESOURCE
Exception Subtype: WAKEUPS
Exception Message: (Limit 150/sec) Observed 0/sec over 300 secs
Exception Note: NON-FATAL CONDITION (this is NOT a crash)
Triggered by Thread: 0
Thread 0 name: Dispatch queue: com.apple.main-thread
Thread 0 Attributed:
0 CoreFoundation 0x25ef8c4e 0x25ef6000 + 11342
1 CoreFoundation 0x25fab760 0x25ef6000 + 743264
...
Thread 10 name: AURemoteIO::IOThread
Thread 10:
0 libsystem_kernel.dylib 0x382acff0 mach_msg_trap + 20
1 libsystem_kernel.dylib 0x382acdf4 mach_msg + 40
2 AudioToolbox 0x2544ec50 AURemoteIO::IOThread::Run() + 104
3 AudioToolbox 0x25452500 AURemoteIO::IOThread::Entry(void*) + 8
4 AudioToolbox 0x25369fee CAPThread::Entry(CAPThread*) + 186
5 libsystem_pthread.dylib 0x3836385a _pthread_body + 138
6 libsystem_pthread.dylib 0x383637ce _pthread_start + 110
7 libsystem_pthread.dylib 0x38361724 thread_start + 8
...
Thread 12 name: com.apple.coreaudio.AQClient
Thread 12:
0 libsystem_kernel.dylib 0x382acff0 mach_msg_trap + 20
1 libsystem_kernel.dylib 0x382acdf4 mach_msg + 40
2 CoreFoundation 0x25fad8c4 __CFRunLoopServiceMachPort + 136
3 CoreFoundation 0x25fabc4c __CFRunLoopRun + 1036
4 CoreFoundation 0x25eff118 CFRunLoopRunSpecific + 520
5 CoreFoundation 0x25efef04 CFRunLoopRunInMode + 108
6 AudioToolbox 0x253810b4 GenericRunLoopThread::Entry(void*) + 132
7 AudioToolbox 0x25369fee CAPThread::Entry(CAPThread*) + 186
8 libsystem_pthread.dylib 0x3836385a _pthread_body + 138
9 libsystem_pthread.dylib 0x383637ce _pthread_start + 110
10 libsystem_pthread.dylib 0x38361724 thread_start + 8

Answer 1

The main confusion was the Observed 0/sec statement, but I found that this number was wrong. When running the same code on a newer and faster iPad it suddenly showed a number here (200-400), so it was simply due to a slow iPad that it could not calculate a number.
Secondly I found that there was indeed a thread that was starting and stopping way too often, but it was not the one that triggered the error, so that made it a lot more difficult to locate.