I am calling AVSampleBufferDisplayLayer.flush from a background queue but this seems to occasionally crash the app. I am calling it from the same thread I pass to - (void)requestMediaDataWhenReadyOnQueue:(dispatch_queue_t)queue usingBlock:(void (^)(void))block;.
My question is, is this API threadsafe, or do I need to call flush from the main thread? Or is there another issue that I am not considering? It seems strange to me that this API would trigger an autolayout pass.
0 CoreFoundation 0x00000001bb384e38 __exceptionPreprocess + 164
1 libobjc.A.dylib 0x00000001b451b8d8 objc_exception_throw + 59
2 CoreAutoLayout 0x00000001d7e09e84 _AssertAutoLayoutOnAllowedThreadsOnly + 327
3 CoreAutoLayout 0x00000001d7e00e60 -[NSISEngine withBehaviors:performModifications:] + 35
4 UIKitCore 0x00000001be58fd40 -[UIView _postMovedFromSuperview:] + 671
5 UIKitCore 0x00000001bd56dfec -[UIView(Internal) _addSubview:positioned:relativeTo:] + 1903
6 UIKitCore 0x00000001bda57ccc -[_UITextLayoutCanvasView textViewportLayoutController:configureRenderingSurfaceForTextLayoutFragment:] + 455
7 UIFoundation 0x00000001c588bc9c __48-[NSTextViewportLayoutController layoutViewport]_block_invoke_4 + 151
8 UIFoundation 0x00000001c5836b50 __80-[NSTextLayoutManager enumerateViewportElementsFromLocation:options:usingBlock:]_block_invoke + 43
9 UIFoundation 0x00000001c580e158 __83-[NSTextLayoutManager enumerateTextLayoutFragmentsFromLocation:options:usingBlock:]_block_invoke_2 + 535
10 CoreFoundation 0x00000001bb385350 __NSARRAY_IS_CALLING_OUT_TO_A_BLOCK__ + 23
11 CoreFoundation 0x00000001bb3b24dc -[__NSSingleObjectArrayI enumerateObjectsWithOptions:usingBlock:] + 91
12 UIFoundation 0x00000001c580de28 __83-[NSTextLayoutManager enumerateTextLayoutFragmentsFromLocation:options:usingBlock:]_block_invoke + 775
13 UIFoundation 0x00000001c57f7504 -[NSTextLayoutManager enumerateTextLayoutFragmentsFromLocation:options:usingBlock:] + 659
14 UIFoundation 0x00000001c57f7264 -[NSTextLayoutManager enumerateViewportElementsFromLocation:options:usingBlock:] + 99
15 UIFoundation 0x00000001c57f6d7c -[NSTextViewportLayoutController layoutViewport] + 1299
16 UIKitCore 0x00000001bd580a3c +[UIView(Animation) performWithoutAnimation:] + 75
17 UIKitCore 0x00000001bd5582d0 -[_UITextLayoutCanvasView layoutSubviews] + 139
18 UIKitCore 0x00000001bd5544c8 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1979
19 QuartzCore 0x00000001bca277fc CA::Layer::layout_if_needed(CA::Transaction*) + 499
20 QuartzCore 0x00000001bca3aeb0 CA::Layer::layout_and_display_if_needed(CA::Transaction*) + 147
21 QuartzCore 0x00000001bca4c234 CA::Context::commit_transaction(CA::Transaction*, double, double*) + 443
22 QuartzCore 0x00000001bca81630 CA::Transaction::commit() + 651
23 MediaToolbox 0x00000001ca8d0da0 videoQueueRemote_SetProperty + 367
24 AVFCore 0x00000001cad191b4 __63-[AVSampleBufferVideoRenderer _setContentLayerOnFigVideoQueue:]_block_invoke + 179
25 libdispatch.dylib 0x00000001c299cf88 _dispatch_client_callout + 19
26 libdispatch.dylib 0x00000001c29ac574 _dispatch_lane_barrier_sync_invoke_and_complete + 55
27 AVFCore 0x00000001cad190d0 -[AVSampleBufferVideoRenderer _setContentLayerOnFigVideoQueue:] + 167
28 AVFCore 0x00000001cad14674 -[AVSampleBufferVideoRenderer _createVideoQueue:errorStep:] + 195
29 AVFCore 0x00000001cad14ac8 -[AVSampleBufferVideoRenderer createVideoQueue:] + 55
30 AVFCore 0x00000001cad179cc -[AVSampleBufferVideoRenderer flushWithRemovalOfDisplayedImage:completionHandler:] + 439
31 App 0x0000000102370214 -[AVSampleBufferDisplayLayer flush] + 51