title: iOS: Understanding SIGABRT crash from Crashlytics
body: <p>So I am receiving Crashlytics crash report for my iOS App. For some of the users the app has been crashing giving SIGABRT in the crash log. </p>
  
  <p>I have been trying to find the cause of this error for countless hours but due to rarity of the error (around 1-2% users) I have been unable to reproduce the error and, due to limited amount of information from Crashlytics, I have been unable to find the root cause of this error.</p>
  
  <p>The deployment target is iOS 7 for the app and devices of all sizes with iOS 10+ are experiencing the crash (I am not sure if iOS 9, 8 or 7 are also experiencing the error — Crashlytics is only showing crashes on iOS 10+)</p>
  
  <p>Here is the stack trace:</p>
  
  <pre><code>CRASH_INFO_ENTRY_1
  *** error for object 0x17127f4c0: Invalid pointer dequeued from free list
  CRASH_INFO_ENTRY_0
  abort() called
  
  Crashed: com.apple.main-thread
  SIGABRT ABORT 0x000000018e2ea014
  
  #0. Crashed: com.apple.main-thread
  0  libsystem_kernel.dylib         0x18f6ca014 __pthread_kill + 8
  1  libsystem_pthread.dylib        0x18f791460 pthread_kill + 112
  2  libsystem_c.dylib              0x18f63e3f4 abort + 140
  3  libsystem_malloc.dylib         0x18f70ea38 
  _nano_vet_and_size_of_live + 330
  4  libsystem_malloc.dylib         0x18f710bf0 
  _nano_malloc_check_clear + 392
  5  libsystem_malloc.dylib         0x18f70fbb4 nano_calloc + 80
  6  libsystem_malloc.dylib         0x18f701180 malloc_zone_calloc + 152
  7  libsystem_malloc.dylib         0x18f7010c4 calloc + 40
  8  libobjc.A.dylib                0x18f131cfc cache_t::reallocate(unsigned int, unsigned int) + 52
  9  libobjc.A.dylib                0x18f1321fc cache_fill + 216
  10 libobjc.A.dylib                0x18f13cd00 lookUpImpOrForward + 412
  11 libobjc.A.dylib                0x18f147258 _objc_msgSend_uncached + 56
  12 UIKit                          0x1967274e8 -[UITableView _endCellAnimationsWithContext:] + 13964
  13 Champion                       0x100097bf4 -[MatchdayComposeController controllerDidChangeContent:] (MatchdayComposeController.m:427)
  14 CoreData                       0x192abfe28 __82-[NSFetchedResultsController(PrivateMethods) _core_managedObjectContextDidChange:]_block_invoke + 4760
  15 CoreData                       0x192abeb80 -[NSFetchedResultsController(PrivateMethods) _core_managedObjectContextDidChange:] + 124
  16 CoreFoundation                 0x19069622c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 20
  17 CoreFoundation                 0x190695930 _CFXRegistrationPost + 400
  18 CoreFoundation                 0x1906956ac ___CFXNotificationPost_block_invoke + 60
  19 CoreFoundation                 0x190704b9c -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1504
  20 CoreFoundation                 0x1905d7bf4 _CFXNotificationPost + 376
  21 Foundation                     0x1910de6bc -[NSNotificationCenter postNotificationName:object:userInfo:] + 68
  22 CoreData                       0x1929eed1c -[NSManagedObjectContext(_NSInternalNotificationHandling) _postObjectsDidChangeNotificationWithUserInfo:] + 724
  23 CoreData                       0x192a75170 -[NSManagedObjectContext(_NSInternalChangeProcessing) _createAndPostChangeNotification:deletions:updates:refreshes:deferrals:wasMerge:] + 1336
  24 CoreData                       0x1929ed338 -[NSManagedObjectContext(_NSInternalChangeProcessing) _processRecentChanges:] + 2116
  25 CoreData                       0x1929ebe3c -[NSManagedObjectContext save:] + 416
  26 Champion                       0x10008e2ac -[AppDelegate saveContext] (AppDelegate.m:263)
  27 Champion                       0x10009d1d4 +[Globals saveManagedObjectContext] (Globals.m:157)
  28 Champion                       0x10006ee4c -[EntitySyncClient saveUpdates:] (EntitySyncClient.m:232)
  29 Champion                       0x1000690a0 -[MatchController datepickerDidChangeValue:] (MatchController.m:994)
  30 UIKit                          0x1965799a0 -[UIApplication sendAction:to:from:forEvent:] + 96
  31 UIKit                          0x196579920 -[UIControl sendAction:to:forEvent:] + 80
  32 UIKit                          0x196563dd0 -[UIControl _sendActionsForEvents:withEvent:] + 452
  33 UIKit                          0x196e62c44 -[_UIDatePickerView pickerView:didSelectRow:inComponent:] + 540
  34 UIKit                          0x1967b965c -[UIPickerView _sendSelectionChangedForComponent:notify:] + 116
  35 UIKit                          0x1967b9894 -[UIPickerView _sendSelectionChangedFromTable:notify:] + 344
  36 UIKit                          0x196ce6878 -[UIPickerTableView _scrollingFinished] + 188
  37 UIKit                          0x196ce6a50 -[UIPickerTableView scrollViewDidEndDecelerating:] + 28
  38 UIKit                          0x196857abc -[UIScrollView(UIScrollViewInternal) _scrollViewDidEndDeceleratingForDelegate] + 132
  39 UIKit                          0x1966ed2cc -[UIScrollView(UIScrollViewInternal) _stopScrollDecelerationNotify:] + 332
  40 UIKit                          0x1966ece08 -[UIScrollView _smoothScrollWithUpdateTime:] + 2356
  41 QuartzCore                     0x1938ff640 CA::Display::DisplayLinkItem::dispatch(unsigned long long) + 44
  42 QuartzCore                     0x1938ff4ec CA::Display::DisplayLink::dispatch_items(unsigned long long, unsigned long long, unsigned long long) + 444
  43 IOKit                          0x190968570 IODispatchCalloutFromCFMessage + 372
  44 CoreFoundation                 0x19069256c __CFMachPortPerform + 180
  45 CoreFoundation                 0x1906aa934 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 56
  46 CoreFoundation                 0x1906aa0e8 __CFRunLoopDoSource1 + 436
  47 CoreFoundation                 0x1906a7bcc __CFRunLoopRun + 1840
  48 CoreFoundation                 0x1905d6048 CFRunLoopRunSpecific + 444
  49 GraphicsServices               0x192059198 GSEventRunModal + 180
  50 UIKit                          0x1965af818 -[UIApplication _run] + 684
  51 UIKit                          0x1965aa550 UIApplicationMain + 208
  52 Champion                       0x1000b082c main (main.m:14)
  53 libdispatch.dylib              0x18f5b85b8 (Missing)
  </code></pre>
  
  <p>I would be extremely grateful for any kind of assistance. I would also be grateful if I can get any kind of pointers for reproducing Crashlytics errors.</p>
  
  <p><strong>Updating the Question with Code</strong></p>
  
  <p>In the <code>controllerDidChangeContent:</code> mainly the table view is ending updates.</p>
  
  <pre><code>- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
      [self.tableView endUpdates];
      if(controller.fetchedObjects.count == 0){
        self.showsNoMatchesHint = YES;
      }
      else{
        self.showsNoMatchesHint = NO;
      }
  }
  </code></pre>