Fix possible segfault with Reanimated

[tyronet-sportsbet]

This is my attempt to fix a segfault we were seeing in Detox. For reference, the segfault stack trace looks like this:

Stack trace

The app has crashed, see the details below:

Signal 11 was raised
(
	0   Detox                               0x0000000101a74bb8 +[NSThread(DetoxUtils) dtx_demangledCallStackSymbols] + 36
	1   Detox                               0x0000000101a77758 __DTXHandleCrash + 440
	2   Detox                               0x0000000101a77d88 __DTXHandleSignal + 72
	3   libsystem_platform.dylib            0x00000001cc0a7c80 _sigtramp + 52
	4   DetoxSync                           0x00000001028c7ce0 -[_DTXTimerTrampoline setDisplayLink:] + 96
	5   DetoxSync                           0x00000001028c7ce0 -[_DTXTimerTrampoline setDisplayLink:] + 96
	6   DetoxSync                           0x00000001028c54b8 +[DTXTimerSyncResource _timerProxyWithDisplayLink:] + 92
	7   DetoxSync                           0x00000001028c5568 +[DTXTimerSyncResource existingTimerProxyWithDisplayLink:create:] + 152
	8   DetoxSync                           0x00000001028bb29c +[DTXSyncManager trackDisplayLink:name:] + 84
	9   DetoxSync                           0x00000001028ae850 -[NSObject(REANodesManagerDTXSpy) __detox_sync_startUpdatingOnAnimationFrame] + 104
	10  Sportsbet Beta                      0x0000000100fc5728 RNGHHitSlopInsetRect + 71804
	11  Sportsbet Beta                      0x0000000100fc5698 RNGHHitSlopInsetRect + 71660
	12  Sportsbet Beta                      0x0000000100fc692c RNGHHitSlopInsetRect + 76416
	13  Sportsbet Beta                      0x0000000100fc4fec RNGHHitSlopInsetRect + 69952
	14  Sportsbet Beta                      0x00000001010456ac RCTSurfaceStageIsPreparing + 32436
	15  Sportsbet Beta                      0x000000010104579c RCTSurfaceStageIsPreparing + 32676
	16  DetoxSync                           0x00000001028afc08 ____detox_sync_dispatch_wrapper_block_invoke + 44
	17  libdispatch.dylib                   0x000000018010d244 _dispatch_call_block_and_release + 24
	18  libdispatch.dylib                   0x000000018010ea98 _dispatch_client_callout + 16
	19  libdispatch.dylib                   0x000000018011c41c _dispatch_main_queue_drain + 976
	20  libdispatch.dylib                   0x000000018011c03c _dispatch_main_queue_callback_4CF + 40
	21  CoreFoundation                      0x0000000180361c2c __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 12
	22  CoreFoundation                      0x000000018035c0b0 __CFRunLoopRun + 2432
	23  CoreFoundation                      0x000000018035b218 CFRunLoopRunSpecific + 572
	24  GraphicsServices                    0x000000018c25f60c GSEventRunModal + 160
	25  UIKitCore                           0x0000000184d88a98 -[UIApplication _run] + 992
	26  DetoxSync                           0x00000001028b6084 __detox_sync_UIApplication_run + 376
	27  UIKitCore                           0x0000000184d8d634 UIApplicationMain + 112
	28  Sportsbet Beta                      0x0000000100e6d054 main + 124
	29  dyld                                0x00000001019e1cd8 start_sim + 20
	30  ???                                 0x0000000101c61f28 0x0 + 4324728616
	31  ???                                 0x8e27800000000000 0x0 + -8203447458743713792

This was using Detox 20.17.0, Xcode 14.1, React Native 0.68.1, react-native-reanimated 1.13.4.

Anyway to explain the change, if you look in react-native-reanimated master branch or 1.13.4 in either case this method that DetoxSync is hooking startUpdatingOnAnimationFrame will lazily create a CADisplayLink instance if one does not exist. But in DetoxSync as it stands today, it calls [self valueForKey:@"displayLink"] before it calls the upstream -startUpdatingOnAnimationFrame: from react-native-reanimated. This means it's possible the CADisplayLink instance will not have been created yet, so the value returned is just some dangling pointer!

This tiny PR just changes it so upstream -startUpdatingOnAnimationFrame: from react-native-reanimated is called first, before DetoxSync attempts to call [self valueForKey:@"displayLink"], ensuring that it's always lazily instantiated. I've tested it against our app and it fixes the segfault.

[asafkorem]

Hi @tyronet-sportsbet, I'll review this later today.

[asafkorem]

You're right @tyronet-sportsbet, getDisplayLink indeed generates the CADisplayLink in case it's missing (here)

Thanks for the contribution!

[asafkorem]

@tyronet-sportsbet the fix has released in Detox v20.18.4