Swift Crash libobjc.A.dylib objc_msgSend

Question

I use crashlytics to get the crashes of my app that is in the AppStore. Some users are getting a crash that I cannot seem to repro on my machine (neither the few friends that tested my app through TestFlight). This is the logs from Fabric:

Thread : Crashed: com.apple.main-thread
0  libobjc.A.dylib                0x181d09bdc objc_msgSend + 28
1  Foundation                     0x18304be20 __NSThreadPerformPerform + 340
2  CoreFoundation                 0x182640efc __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 24
3  CoreFoundation                 0x182640990 __CFRunLoopDoSources0 + 540
4  CoreFoundation                 0x18263e690 __CFRunLoopRun + 724
5  CoreFoundation                 0x18256d680 CFRunLoopRunSpecific + 384
6  GraphicsServices               0x183a7c088 GSEventRunModal + 180
7  UIKit                          0x1873e4d90 UIApplicationMain + 204
8  <App Name>                     0x1000b2f0c main (AppDelegate.swift:14)
9  libdispatch.dylib              0x18210e8b8 (Missing)

I can't seem to understand what this means and searched other questions for help but can't seem to find an answer. I also quickly contacted the Crashlytics team, and they told me the following:

It sounds like the source of this crash is some sort of out of memory crash. This causing Crashlytics to close before it finishes writing, resulting in this in your crash report.

Any nice ways to debug this in order to pinpoint the source of the crash? Appreciate the help!

EDIT: Added screenshot of Threads in the crash report from crashlytics in case someone wants some info from there:

Thread : com.apple.NSURLConnectionLoader
0  libsystem_kernel.dylib         0x1823354bc mach_msg_trap + 8
1  libsystem_kernel.dylib         0x182335338 mach_msg + 72
2  CoreFoundation                 0x182764ac0 __CFRunLoopServiceMachPort + 196
3  CoreFoundation                 0x1827627c4 __CFRunLoopRun + 1032
4  CoreFoundation                 0x182691680 CFRunLoopRunSpecific + 384
5  CFNetwork                      0x182e01434 +[NSURLConnection(Loader) _resourceLoadLoop:] + 412
6  Foundation                     0x18316fc40 __NSThread__start__ + 1000
7  libsystem_pthread.dylib        0x182417b28 _pthread_body + 156
8  libsystem_pthread.dylib        0x182417a8c _pthread_body + 154
9  libsystem_pthread.dylib        0x182415028 thread_start + 4

Thread : AVAudioSession Notify Thread
0  libsystem_kernel.dylib         0x1823354bc mach_msg_trap + 8
1  libsystem_kernel.dylib         0x182335338 mach_msg + 72
2  CoreFoundation                 0x182764ac0 __CFRunLoopServiceMachPort + 196
3  CoreFoundation                 0x1827627c4 __CFRunLoopRun + 1032
4  CoreFoundation                 0x182691680 CFRunLoopRunSpecific + 384
5  libAVFAudio.dylib              0x188959834 GenericRunLoopThread::Entry(void*) + 164
6  libAVFAudio.dylib              0x18892e3a8 CAPThread::Entry(CAPThread*) + 84
7  libsystem_pthread.dylib        0x182417b28 _pthread_body + 156
8  libsystem_pthread.dylib        0x182417a8c _pthread_body + 154
9  libsystem_pthread.dylib        0x182415028 thread_start + 4

EDIT 2: I am using all Swift code, and the way I am forwarding a messages to Selectors is the following:

NSTimer.scheduledTimerWithTimeInterval(0.02, target: self, selector: Selector("updateProgressCircle"), userInfo: nil, repeats: true)

func updateProgressCircle() {
   // Do something
}

Problem is that I can't repro any crash from this locally. Only users are facing that. I call selectors in a similar fashion.

Answer 1

An objc_msgSend crash happens when you try to forward a message to a selector (using good old Objective-C forward messaging). This can be produced by target-action, notifications, protocol declarations, timers, perform selectors or any other function that involves passing in a function's selector syntax: i.e: "doSomethingWithThis:".

I can see from your crash logs that you have swift components in your app (at least the AppDelegate). Swift components, unlike Obj-C components, aren't compatible with the Obj-C forward messaging system out of the box.

My gut feeling is that you have a swift object in your code that conforms to a protocol, is added as a target/notification observer or is somehow expecting one of its functions to be called by forward messaging. I suggest you go through your classes and see if this is the case. Once you find the culprit you can easily fix this error by appending @objc to the function expecting the message.

i.e: if your function, in a swift class is called (and is, say, registered for a notification):

func yourFunction() {
   //your code
}

call it:

@objc func yourFunction() {
  //your code
}

It's a long shot but I hope this helps!

Answer 2

I believe this may have to do with AVAudioPlayer. In my case I had this same bug and got some hints by noticing 2 of my running threads had AVAudioPlayer-related content.

I had an AVAudioPlayer class variable that I reinitialized without resetting to nil first. I added the code below before my AVAudioPlayer variable initialization and the bug hasn't occurred since.

audioPlay is the variable name.

if audioPlay != nil
{
    //print( "blabla" )
    audioPlay?.stop()
    audioPlay = nil
}