GC FSM - Event-driven, hierarchical finite state machines in blueprint

[woodzong]

@eanticev

Hi there, there seems to be a garbage collection bug / issue with how this plugin works with a dedicated server multiplayer (not replication).

Find sample project here: https://1drv.ms/u/s!Asdf-Mafqv3XjypqwvW37ahuXXmW

Steps to reproduce without sample project:

1. Create game mode with a simple PING-PONG state machine that switches from ping to pong (etc) every 1s.
2. Launch FSM in BeginPlay (note that it’s not intended to be a replicating FSM, just a local FSM to the server in the game mode)
3. OnTick log out “FSM is running: {0} in State {1}”
4. Launch dedicated server using a command (with your UE4 path and IP address) such as

"C:\Program Files\Epic Games\UE_4.20\Engine\Binaries\Win64\UE4Editor.exe" "%CD%\..\FSMTest.uproject" ThirdPersonExampleMap?listen -server -log -nosteam -port=1234

5. Launch client to connect to server using a command such as

"C:\Program Files\Epic Games\UE_4.20\Engine\Binaries\Win64\UE4Editor.exe" "%CD%\..\FSMTest.uproject" 192.168.1.157:1234 -game -ResX=1280 -ResY=720 -WinX=0 -WinY=20 -log -nosteam -WINDOWED

After about 20 seconds the FSM context gets garbage collected and you see a transition in the server log that looks like:

[2018.08.11-19.45.33:584][807]LogBlueprintUserMessages: [ThirdPersonGameMode_C_0] FSM is running: 1 in State Ping
[2018.08.11-19.45.34:583][837]LogBlueprintUserMessages: [ThirdPersonGameMode_C_0] FSM is running: 1 in State Pong
[2018.08.11-19.45.34:627][838]LogGCFSM: Error: Object ThirdPersonGameMode_C_0 is not running FSMs
[2018.08.11-19.45.34:698][840]LogBlueprintUserMessages: [ThirdPersonGameMode_C_0] FSM is running: 0 in State

What you see above is that** GetContext() in the FSM is failing because the weak pointer starts pointing to NULL** about 20s after the first client connects.

I got the same error in the similar situation.
In my case, FSM is not running in server.
My FSM is created in one actor’s blue print. and it Launched in the “Event BeginPlay” node. and after running some seconds or minutes; It will log “LogGC FSM: Error: Object xxx is not running FSMs” just like eanticev 's report. The actor is still in the map, and running fine, but the FSM in it seens be destoried. I tried to trace the bug in the source code. It seems there is something wrong with the FSM’s garbage collection.
Waiting for help… I can’t keep going with my work until this bug is fixed. so sad…
https://forums.unrealengine.com/core/image/gif;base64
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