java.util.ConcurrentModificationException: null Server Chunk Cache

[Mikeatron-User]

Specifications

Minecraft Version: 1.20.1 Forge Version: 1.20.1-47.1.0 Mod Version: 1.20.1-0.8.5 Modpack Version: Wrath of the Sculk Horde-1.27

Details

• So by leaving the server on by itself, this causes the server to crash.
• Crash log only mentions serverchunk cache, so its likely my chunk loading system.
• Crash Log: https://gist.github.com/Mikeatron-User/9cf20211a3b18e3a857df82331d820db

[Mikeatron-User]

Its not any of these

[Mikeatron-User]

I disabled Phantoms, node, and ancient node from being able to request chunk loading. It still crashes. I suspect that it maybe has to do with me loading / saving data related to the chunk loading system? Not sure, but its my next lead.

[Mikeatron-User]

Its not the chunkloading system at all, I completly deleted it from the code, and were still getting this error. My next lead is that maybe its argonauts. I know they have a chunk loading system, and its never worked in the game. Going to delete this mod and see what happens. Perhaps I misjudged this when i deleted my mod from the server and it suddenly started working

[Mikeatron-User]

Wasnt that, its probably still my mod. : /

[Mikeatron-User]

Was told it could be because spawning mobs, while a mob is ticking, is an issue. The solution is the following:

level().getServer().tell(new net.minecraft.server.TickTask(level().getServer().getTickCount() + 1, () -> {
  spawnMob();
}));

However, doing this did not fix the crash

[Mikeatron-User]

Disabled reinforcement system, no dice. I disabled some internal ticking systems that run every world tick, bingo. The server stopped crashing. Going to investigate this further.

[Mikeatron-User]

Enabling these two caused the server to crash. Finally

SculkHorde.raidHandler.raidTick(); // Tick the raid handler
SculkHorde.deathAreaInvestigator.tick();

[Mikeatron-User]

Its the death area investigator apparently. Commenting it out causes the game not to crash. I cant imagine what has caused this to happen and why its only happening now.

[Mikeatron-User]

For now, i made the death area investigator avoid ticking if raids are disabled in 1.20.1-0.8.5. The cause of the bug will be fixed soon.

[Mikeatron-User]

It looks like it might be related to apply effects to entities, im going to investigate and see if there is a standard practice for apply effects to entities

[Mikeatron-User]

Removing all code related to apply affects to entities has been removed. This stopped the server from crashing.

[Mikeatron-User]

After some updates to make my code safer, iv made a new branch to do some more testing

[Mikeatron-User]

Summary of Progress so far:

• I made mob spawning safer by only allowing it to occur next tick.
• Effects are only added / removed next tick aswell. This seems to have stopped the game from crashing randomly.
• The game no longer crashes on /forceload remove all
• The game no longer crashes after a minute of loading.
• The game crashes when trying to save.

[Mikeatron-User]

Got more information this time, what on earth is this?

[Mikeatron-User]

Disabling this stopped the crashing on world unload. This might be it

[Mikeatron-User]

Telling the server to do this a tick later solved the problem.