Unable to understand where MyApp is crashing

Question

My App is crashing in some scenarios. Unable to find the reason & place of crash.

Below is crash log (iPad/iOS 8.0.2).

Hardware Model:      iPad2,5
OS Version:          iOS 8.0.2 (12A405)
Report Version:      105

Exception Type:  EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Triggered by Thread:  0
Thread 0 Crashed:
0   libsystem_kernel.dylib          0x306b3dfc __pthread_kill + 8
1   libsystem_pthread.dylib         0x30733d0e pthread_kill + 58
2   libsystem_c.dylib               0x30653934 abort + 72
3   libc++abi.dylib                 0x2f864bb8 abort_message + 84
4   libc++abi.dylib                 0x2f87e66a default_terminate_handler() + 262
5   libobjc.A.dylib                     0x30052f0e _objc_terminate() + 190
6   libc++abi.dylib                 0x2f87bdec std::__terminate(void (*)()) + 76
7   libc++abi.dylib                 0x2f87b5ac __cxa_throw + 108
8   libobjc.A.dylib                     0x30052d46 objc_exception_throw + 246
9   CoreFoundation                  0x225dfe58 +[NSException raise:format:arguments:] + 100
10  Foundation                      0x232af2c4 -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 88
11  BaseBoard                       0x270a08d8 __25-[BSAction sendResponse:]_block_invoke + 140
12  libdispatch.dylib               0x305bc99c _dispatch_barrier_sync_f_invoke + 44
13  BaseBoard                       0x270a0842 -[BSAction sendResponse:] + 98
14  UIKit                               0x25fd54d0 -[UIFetchContentInBackgroundAction sendResponse:] + 212
15  libdispatch.dylib               0x305b3610 _dispatch_call_block_and_release + 8
16  libdispatch.dylib               0x305b35fc _dispatch_client_callout + 20
17  libdispatch.dylib               0x305be2b2 _dispatch_main_queue_callback_4CF$VARIANT$mp + 714
18  CoreFoundation                  0x225a5e5c __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 4
19  CoreFoundation                  0x225a457c __CFRunLoopRun + 1508
20  CoreFoundation                  0x224f1dac CFRunLoopRunSpecific + 472
21  CoreFoundation                  0x224f1bbe CFRunLoopRunInMode + 102
22  GraphicsServices                0x2985404c GSEventRunModal + 132
23  UIKit                               0x25abda2c UIApplicationMain + 1436
24  MyApp                               0x000fb9f2 main (main.m:15)
25  libdyld.dylib                       0x305eeaac start + 0

Thanks in advance..

Answer 1

The exception message that corresponds to the stack trace is:

"this request has been neutered - you can't call -sendResponse: twice nor after encoding it"

While it's not possible to tell for sure from the stack alone, you most likely called the completionHandler passed to your app delegate's -application:performFetchWithCompletionHandler: method twice.

Answer 2

The background fetch is triggered by the OS, based on the value you set in setMinimumBackgroundFetchInterval: method. What you are seeing looks like the what the OS does with your app if the background fetch takes too long.

You are assigned a window of time (30 seconds) to do your work. If you don't finish, the OS kills your app with the above exception. Read more about how to extend the time needed here.

Basically, you need to ask for more time to complete your background work like this:

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    bgTask = [application beginBackgroundTaskWithName:@"MyTask" expirationHandler:^{
        // Clean up any unfinished task business by marking where you
        // stopped or ending the task outright.
        [application endBackgroundTask:bgTask];
        bgTask = UIBackgroundTaskInvalid;
    }];

    // Start the long-running task and return immediately.
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        // Do the work associated with the task, preferably in chunks.

        [application endBackgroundTask:bgTask];
        bgTask = UIBackgroundTaskInvalid;
    });
}