ServerTravel crashes Play In Editor (packaged build works)

Development Programming & Scripting
1

ServerTravel crashes when called in the Play In Editor mode. However, for a packaged build it seems to work just fine. Since I am absolutely new to Unreal Engine, I might do something completely wrong that just happens to work for packaged builds.

Here’s what I did:

  • Created a new project based on the C++ “ThirdPerson” template

  • I added a second level /Game/ThirdPerson/Maps/SecondMap

  • I added a third level that I configured in the Project Settings to be the Transition Map (not sure if this was required)

  • I exposed ServerTravel by creating a UBlueprintFunctionLibrary for it:

    void UMyBpLibrary::ServerTravel(UObject* WorldContextObject, const FString URL, bool bAbsolute, bool bShouldSkipGameNotify)
    {
    UWorld* World = WorldContextObject->GetWorld();
    AGameMode* mode = World->GetAuthGameMode();
    if (mode != nullptr)
    {
    World->ServerTravel(URL, bAbsolute, bShouldSkipGameNotify);
    }
    }

  • In my AGameMode I set bUseSeamlessTravel = true; in the constructor.

  • In the default level blueprint I made the T key change the level:

37346-blueprint.png
37346-blueprint.png823×437 56.3 KB

  • Finally I made a packaged development build and ran the server and client as:

    MyProject.exe ?listen
    MyProject.exe 127.0.0.1

The packaged development build works fine; both players start in the same level and are transferred to the new map (via the configured transition map). However, if I start to play in editor with 2 players and press T, I get an access violation.

This is the call stack:

UE4Editor-Engine.dll!UActorChannel::CleanUp(const bool bForDestroy) Line 1443 C++

UE4Editor-Engine.dll!UChannel::ReceivedSequencedBunch(FInBunch & Bunch) Line 279

UE4Editor-Engine.dll!UChannel::ReceivedNextBunch(FInBunch & Bunch, bool & bOutSkipAck) Line 588

UE4Editor-Engine.dll!UChannel::ReceivedRawBunch(FInBunch & Bunch, bool & bOutSkipAck) Line 344

UE4Editor-Engine.dll!UNetConnection::ReceivedPacket(FBitReader & Reader) Line 979

UE4Editor-Engine.dll!UNetConnection::ReceivedRawPacket(void * InData, int Count) Line 457

UE4Editor-OnlineSubsystemUtils.dll!UIpNetDriver::TickDispatch(float DeltaTime) Line 174

UE4Editor-Engine.dll!TBaseUObjectMethodDelegateInstance<0,UNetDriver,void __cdecl(float)>::ExecuteIfSafe(float ) Line 772

UE4Editor-Engine.dll!TBaseMulticastDelegate::Broadcast(float ) Line 1030

UE4Editor-Engine.dll!UWorld::Tick(ELevelTick TickType, float DeltaSeconds) Line 1027

UE4Editor-UnrealEd.dll!UEditorEngine::Tick(float DeltaSeconds, bool bIdleMode) Line 1329

UE4Editor-UnrealEd.dll!UUnrealEdEngine::Tick(float DeltaSeconds, bool bIdleMode) Line 347

UE4Editor.exe!FEngineLoop::Tick() Line 2257

UE4Editor.exe!GuardedMain(const wchar_t * CmdLine, HINSTANCE__ * hInInstance, HINSTANCE__ * hPrevInstance, int nCmdShow) Line 142

UE4Editor.exe!WinMain(HINSTANCE__ * hInInstance, HINSTANCE__ * hPrevInstance, char * __formal, int nCmdShow) Line 191

I’m probably reading it wrong, but it looks like the line where it crashes just sets the RF_PendingKill flag that is already set through the call on the line above it (which seems to end up in UActorComponent::DestroyComponent).

Please let me know whether I am using ServerTravel in the wrong context or that this is a valid bug report. I am using version 4.7.4-2497108+++depot+UE4-Releases+4.7 on Windows.

2

I know this bug and asked a question about this here about a month ago.

After two days without answer, I asked on reddit and someone told me that it’s a known bug.

As far as I know you don’t have much choice. You’ll need to rebuild the game every time you want to test it…

This engine is great in many ways, but still I’d really appreciate epic focusing on bugfixing more than on feature development :frowning:

3

Oh, and there’s one other thing:

Sometimes it works when you open the advanced settings (in the menu under the play button) and turn off “use single process” and select “Play as Client”.

No guarantees, but sometimes it works.