ConcurrentModificationException in TileStreamUpdateTracker.syncVisualUpdates (Forestry 2.6.2, MC 1.20.1) #264
Description
Description
Game crashes with a java.util.ConcurrentModificationException during client tick when Forestry’s TileStreamUpdateTracker runs.
Crash seems tied to Forestry tile entities updating visuals (apiaries/machines/etc.) in loaded chunks.
Embeddium marks the instance “tainted” but stacktrace points directly to Forestry’s TileStreamUpdateTracker.
Crash report
Full log
java.util.ConcurrentModificationException: null at java.util.HashMap$HashIterator.nextNode(HashMap.java:1597) ~[?:?] {} at java.util.HashMap$KeyIterator.next(HashMap.java:1620) ~[?:?] {} at forestry.core.blocks.TileStreamUpdateTracker.syncVisualUpdates(TileStreamUpdateTracker.java:38) ~[forestry-1.20.1-2.6.2.jar%23766!/:2.6.2] {re:classloading} at forestry.core.ModuleCore.onLevelTick(ModuleCore.java:151) ~[forestry-1.20.1-2.6.2.jar%23766!/:2.6.2] {re:classloading} at net.minecraftforge.eventbus.EventBus.doCastFilter(EventBus.java:260) ~[eventbus-6.0.5.jar%2387!/:?] {} ...Minecraft: 1.20.1
Forge: 47.4.0
Forestry CE: 2.6.2
Java: 17
Other performance mods present: Embeddium, Oculus, ModernFix, SodiumDynamicLights, Fusion, Supplementaries.
(Crash still points to Forestry core, not renderer.)
Steps to Reproduce
Load a world with Forestry tiles (apiary/machines/farms).
Play for a while → eventually crash occurs.
In my case, near x=69, y=59, z=89 (chunk 4,5).
Crash log shows CME in TileStreamUpdateTracker.syncVisualUpdates.
Additional notes
Looks like a thread-safety / iteration modification issue: HashMap is being mutated while Forestry is iterating during visual update sync.
Disabling ModernFix’s concurrency mixins reduces frequency but doesn’t fix root cause.
Clearing the offending chunk or removing Forestry tiles allows world to load again.
Expected Behavior
Forestry’s visual update tracker should handle updates safely without throwing a CME.
This report was made use GPT ;)
Had this happen multiple times over many sessions, and the reason I tried pulling a fork. Did not have the time to look further hope it helps, if not delete, or remove the post alt right