ConcurrentModificationException during chunk feature placement

[15:17:55] [DH-World Gen Thread[0]/WARN]: Unexpected issue when generating features for chunk at pos [C[123,65]], error: [Feature placement].
net.minecraft.class_148: Feature placement
    at net.minecraft.class_2794.method_12102(class_2794.java:377) ~[client-intermediary.jar:?]
    at loaderCommon.fabric.com.seibel.distanthorizons.common.wrappers.worldGeneration.step.StepFeatures.generateGroup(StepFeatures.java:81) ~[DistantHorizons-2.1.2-a-1.20.1-forge-fabric.jar:?]

[15:17:55] [DH-World Gen Thread[0]/WARN]: Unexpected issue when generating features for chunk at pos [C[123,65]], error: [Feature placement].
net.minecraft.class_148: Feature placement
    at net.minecraft.class_2794.method_12102(class_2794.java:377) ~[client-intermediary.jar:?]
    at loaderCommon.fabric.com.seibel.distanthorizons.common.wrappers.worldGeneration.step.StepFeatures.generateGroup(StepFeatures.java:81) ~[DistantHorizons-2.1.2-a-1.20.1-forge-fabric.jar:?]

Further stacktrace in logs shows the ConcurrentModificationException. Log with mod list: https://mclo.gs/vUAb1r2 Error is observed in both single and multiplayer situations. This seems to be impacting LOD generation and causing extra CPU load

mclo.gs

Vanilla Server Log [#ggLmUUH]

22849 lines | 360 errors

mclo.gs

Fabric 1.20.1 Server Log [#vUAb1r2]

664 lines

5 Replies

Miki_P98•6mo ago

I don't think it is fixable

TrynOP•6mo ago

guessing here - is this bc LOD is trying to generate for chunks that are not themselves generated yet? So the overlap of timing causes issues?

Miki_P98•6mo ago

LOD generation is multithreaded, the error happens if a thread generates a structure that has a part on a chunk on a different thread

TrynOP•6mo ago

Cross thread is ok though as long as whatever resource is handled properly? Via lock mechanism or other thread-safe behavior Or would that slow things down too much and this exception is generally non harmful?

Miki_P98•6mo ago

As far as I know it only takes space in logs and that is it

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ConcurrentModificationException during chunk feature placement