title: "NSInternalInconsistencyException: threading violation: expected the main thread" outside of my code
body: <p>My iOS App is crashing with the following error:</p>
  
  <pre><code>*** Assertion failure in -[FBSSerialQueue assertOnQueue], /BuildRoot/Library/Caches/com.apple.xbs/Sources/FrontBoardServices/FrontBoard-626.4.1/FrontBoardServices/FBSSerialQueue.m:98
  *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'threading violation: expected the main thread'
  </code></pre>
  
  <p>And this is the stacktrace:</p>
  
  <pre><code>Exception: NSInternalInconsistencyException
  
  Reason: threading violation: expected the main thread
  
  Stacktrace: (
  0   CoreFoundation                      0x000000018d56c980 DC2C95C6-B954-39E8-86A2-5E0AF8801E87 + 1255808
  1   libobjc.A.dylib                     0x000000018d285028 objc_exception_throw + 60
  2   CoreFoundation                      0x000000018d4694fc DC2C95C6-B954-39E8-86A2-5E0AF8801E87 + 193788
  3   Foundation                          0x000000018d8aa690 7A7A96AF-79E4-3DB1-8904-42E61CAE8999 + 571024
  4   FrontBoardServices                  0x00000001927ae7ec 370F1F18-E8A9-36B5-B0EB-9735A02CE2DE + 366572
  5   FrontBoardServices                  0x0000000192760460 370F1F18-E8A9-36B5-B0EB-9735A02CE2DE + 46176
  6   FrontBoardServices                  0x00000001927606ec 370F1F18-E8A9-36B5-B0EB-9735A02CE2DE + 46828
  7   FrontBoardServices                  0x00000001927605e4 370F1F18-E8A9-36B5-B0EB-9735A02CE2DE + 46564
  8   UIKitCore                           0x00000001911e1c40 AAFEFEBE-C172-3346-8972-810EB8F2F2C6 + 5995584
  9   UIKitCore                           0x00000001912d1870 AAFEFEBE-C172-3346-8972-810EB8F2F2C6 + 6977648
  10  UIKitCore                           0x00000001912d2640 AAFEFEBE-C172-3346-8972-810EB8F2F2C6 + 6981184
  11  CameraUI                            0x00000001afbb8514 289C074B-4FFE-3D83-927A-98B268DD914F + 652564
  12  libobjc.A.dylib                     0x000000018d29f3f8 objc_release + 136
  13  CameraUI                            0x00000001afc5b118 289C074B-4FFE-3D83-927A-98B268DD914F + 1319192
  14  libobjc.A.dylib                     0x000000018d284130 2C18C54E-6C84-310C-851F-F9602890D908 + 20784
  15  libobjc.A.dylib                     0x000000018d296f80 objc_destructInstance + 92
  16  libobjc.A.dylib                     0x000000018d29de44 _objc_rootDealloc + 52
  17  CameraUI                            0x00000001afc502c4 289C074B-4FFE-3D83-927A-98B268DD914F + 1274564
  18  libobjc.A.dylib                     0x000000018d29f3f8 objc_release + 136
  19  CoreFoundation                      0x000000018d4b243c DC2C95C6-B954-39E8-86A2-5E0AF8801E87 + 492604
  20  CoreFoundation                      0x000000018d43cfc0 DC2C95C6-B954-39E8-86A2-5E0AF8801E87 + 12224
  21  libobjc.A.dylib                     0x000000018d29f3f8 objc_release + 136
  22  CameraUI                            0x00000001afcb3704 289C074B-4FFE-3D83-927A-98B268DD914F + 1681156
  23  libobjc.A.dylib                     0x000000018d284130 2C18C54E-6C84-310C-851F-F9602890D908 + 20784
  24  libobjc.A.dylib                     0x000000018d296f80 objc_destructInstance + 92
  25  libobjc.A.dylib                     0x000000018d29de44 _objc_rootDealloc + 52
  26  CameraUI                            0x00000001afca48ac 289C074B-4FFE-3D83-927A-98B268DD914F + 1620140
  27  libobjc.A.dylib                     0x000000018d29f3f8 objc_release + 136
  28  libsystem_blocks.dylib              0x000000018d18fa08 _Block_release + 168
  29  libobjc.A.dylib                     0x000000018d29f3f8 objc_release + 136
  30  libsystem_blocks.dylib              0x000000018d18fa08 _Block_release + 168
  31  libdispatch.dylib                   0x0000000102d3b27c _dispatch_client_callout + 20
  32  libdispatch.dylib                   0x0000000102d4290c _dispatch_lane_serial_drain + 720
  33  libdispatch.dylib                   0x0000000102d434fc _dispatch_lane_invoke + 408
  34  libdispatch.dylib                   0x0000000102d4e4dc _dispatch_workloop_worker_thread + 1344
  35  libsystem_pthread.dylib             0x000000018d2776d0 _pthread_wqthread + 280
  36  libsystem_pthread.dylib             0x000000018d27d9e8 start_wqthread + 8
  )
  </code></pre>
  
  <p>Is seems to be completely outside of my code. Is there any way to debug this? Is it a bug in an iOS component? </p>
  
  <p>The UIImagePickerController seems to be involved. It seems to happen shortly after picking a foto via the camera.</p>
  
  <p><strong>EDIT:</strong> Here is what the debug navigator is showing right after the crash:</p>
  
  <p><a href="https://i.stack.imgur.com/lC52A.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/lC52A.jpg" alt="enter image description here"></a></p>
  
  <p>And one more screenshot:</p>
  
  <p><a href="https://i.stack.imgur.com/ieOSA.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ieOSA.jpg" alt="enter image description here"></a></p>
  
  <p>I cannot identify a single action in the app that reproduces the crash. I need to click around in a component that takes a picture from the camera and saves it into a UICollectionView. Only sometimes and eventually, the crash happens at different points.</p>
  
  <p>I've verified that the code inside <code>imagePickerController:didFinishPickingMediaWithInfo:</code> is running on the main thread.</p>
  
  <p>How can I locate the exact place in my the code where this crash is happening?</p>
  
  <p><strong>EDIT 2</strong>: Update from Apple developer technical support; they believe that it is a bug and they suggest filing a bug report.</p>