Crash when closing game with running request

[ncryptedV1]

Problem description

Especially noticeable in play-in-editor mode, UE crashes when the game/PIE is exited while a VaRest request is still running. The crash occurs in the response processing callback. More precisely here. When entering the if (ContinueAction) block, the pointer value of ContinueAction is copied into K, ContinueAction is set to nullptr and FVaRestLatentAction's Call method is invoked on the copied pointer value in K.

Impact: This shouldn't be too problematic for production releases as a crash during game exit often isn't noticeable. During development, this is productivity-killing.

Error analysis

I guess during game end, the garbage collector marks ContinueActions's underlying FVaRestLatentAction object as "pending delete". When setting ContinueAction to nullptr, the underlying FVaRestLatentAction object is destroyed as K is not a member variable but merely a scoped variable, nor is it a shared pointer. Therefore, K is a dangling pointer when reaching the final Call method call (so far my theory goes).

Solution attempt

I tried replacing the raw C++ pointer to FVaRestLatentAction with TSharedPtr and added a ContinueAction.IsValid() check in the surrounding if-block, but this led to memory allocation exceptions during normal operation. As I'm no UE expert, my knowledge about memory management in UE is limited and I cannot give any comprehensive insights into why.

Final question

Any clue on how to fix this?

Error log:

Fatal error!

Unhandled Exception: EXCEPTION_ACCESS_VIOLATION 0x000005c468229fd0

0x000005c468229fd0 UnknownFunction []
0x00007ffa837b44aa UnrealEditor-VaRest.dll!UVaRestRequestJSON::OnProcessRequestComplete() [<redacted>\build\U5M-Marketplace\Sync\LocalBuilds\PluginTemp\HostProject\Plugins\VaRest\Source\VaRest\Private\VaRestRequestJSON.cpp:581]
0x00007ffa837ae1c6 UnrealEditor-VaRest.dll!TBaseUObjectMethodDelegateInstance<0,UVaRestRequestJSON,void __cdecl(TSharedPtr<IHttpRequest,1>,TSharedPtr<IHttpResponse,1>,bool),FDefaultDelegateUserPolicy>::ExecuteIfSafe() [<redacted>\5.3.0-27405482+++UE5+Release-5.3\Working\Engine\Source\Runtime\Core\Public\Delegates\DelegateInstancesImpl.h:665]
0x00007ffaac0e77cf UnrealEditor-HTTP.dll!UnknownFunction []
0x00007ffaac1026d9 UnrealEditor-HTTP.dll!UnknownFunction []
0x00007ffaac1327ff UnrealEditor-HTTP.dll!UnknownFunction []
0x00007ffab7c95115 UnrealEditor-Core.dll!UnknownFunction []
0x00007ffab7c96870 UnrealEditor-Core.dll!UnknownFunction []
0x00007ffab7cb541b UnrealEditor-Core.dll!UnknownFunction []
0x00007ffab7c81778 UnrealEditor-Core.dll!UnknownFunction []
0x00007ffab7c9508e UnrealEditor-Core.dll!UnknownFunction []
0x00007ffab7c96870 UnrealEditor-Core.dll!UnknownFunction []
0x00007ffab7cb541b UnrealEditor-Core.dll!UnknownFunction []
0x00007ff66497cea9 UnrealEditor.exe!UnknownFunction []
0x00007ff66499d28c UnrealEditor.exe!UnknownFunction []
0x00007ff66499d37a UnrealEditor.exe!UnknownFunction []
0x00007ff6649a0854 UnrealEditor.exe!UnknownFunction []
0x00007ff6649b6984 UnrealEditor.exe!UnknownFunction []
0x00007ff6649b9d7a UnrealEditor.exe!UnknownFunction []
0x00007ffb7935257d KERNEL32.DLL!UnknownFunction []

Crash in runnable thread StallDetectorThread