[ConcurrentModificationException] Concurrently Modified Container StitchedSprite#ALL in modloading-worker thread

[Viola-Siemens]

minecraft-exported-crash-info-2025-08-31T22-09-51.zip

I used this project to find this bug.

You should NOT modify the container in modloading-worker threads. Move it to main thread.

[Viola-Siemens]

iglee42/CreateCasing#149

[talrey]

This is an interesting report. If I understand the crash report correctly, this is happening because other addons are adding their own sprite shifts at similar times?

You're welcome to suggest a fix with a PR (or in a comment, if the implementation of that fix is simple enough). Just telling mod authors to "fix it" is redundant and doesn't move us any closer to resolution.

[Viola-Siemens]

This is an interesting report. If I understand the crash report correctly, this is happening because other addons are adding their own sprite shifts at similar times?

Yes.

You're welcome to suggest a fix with a PR (or in a comment, if the implementation of that fix is simple enough).

Use Event#enqueueWork instead of just modifying the container it in the listener.

[Viola-Siemens]

Here's an example： DivineRPG/DivineRPG#730

[Viola-Siemens]

Just telling mod authors to "fix it" is redundant and doesn't move us any closer to resolution.

@talrey I assumed that you have a good understanding of the basics of Java multithreading, but it seems not. Sorry for that, let me introduce why it is a bug. Here the history of modifications of map StitchedSprite#ALL:

[2025-08-31 22:08:41.105] [modloading-worker-0] [INFO] [2147bf95]: com.hexagram2021.cme_suck_my_duck.utils.SuckTrace: [Modify] computeIfAbsent(Object, Function)
	at TRANSFORMER/cme_suck_my_duck@1.0.8/com.hexagram2021.cme_suck_my_duck.utils.TraceLogger.info(TraceLogger.java:15)
	at TRANSFORMER/cme_suck_my_duck@1.0.8/com.hexagram2021.cme_suck_my_duck.containers.AbstractWrappedContainer.logModify(AbstractWrappedContainer.java:40)
	at TRANSFORMER/cme_suck_my_duck@1.0.8/com.hexagram2021.cme_suck_my_duck.containers.WrappedMap.computeIfAbsent(WrappedMap.java:176)
	at TRANSFORMER/ponder@1.0.80/net.createmod.catnip.render.StitchedSprite.<init>(StitchedSprite.java:23)
	at TRANSFORMER/ponder@1.0.80/net.createmod.catnip.render.StitchedSprite.<init>(StitchedSprite.java:27)
	at TRANSFORMER/ponder@1.0.80/net.createmod.catnip.render.SpriteShiftEntry.set(SpriteShiftEntry.java:15)
	at TRANSFORMER/create@6.0.6/com.simibubi.create.foundation.block.connected.CTSpriteShifter.lambda$getCT$0(CTSpriteShifter.java:19)
	at LAYER PLUGIN/fmlcore@1.20.1-47.4.6/net.minecraftforge.fml.DistExecutor.unsafeRunWhenOn(DistExecutor.java:111)
	at TRANSFORMER/ponder@1.0.80/net.createmod.catnip.platform.ForgePlatformHelper.executeOnClientOnly(ForgePlatformHelper.java:54)
	at TRANSFORMER/create@6.0.6/com.simibubi.create.foundation.block.connected.CTSpriteShifter.getCT(CTSpriteShifter.java:19)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.connected.SpriteShifts.lambda$vault$0(SpriteShifts.java:32)
	at TRANSFORMER/ponder@1.0.80/net.createmod.catnip.data.Couple.createWithContext(Couple.java:36)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.connected.SpriteShifts.vault(SpriteShifts.java:32)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.connected.SpriteShifts.populateMaps(SpriteShifts.java:40)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.connected.SpriteShifts.<clinit>(SpriteShifts.java:26)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.api.Catwalks.build(Catwalks.java:71)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.BlockRegistry.registerCatwalks(BlockRegistry.java:187)
	at java.base/java.util.HashMap.forEach(HashMap.java:1421)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.BlockRegistry.init(BlockRegistry.java:103)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.CreateDecoMod.init(CreateDecoMod.java:17)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.forge.CreateDecoModForge.<init>(CreateDecoModForge.java:17)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:480)
	at LAYER PLUGIN/javafmllanguage@1.20.1-47.4.6/net.minecraftforge.fml.javafmlmod.FMLModContainer.constructMod(FMLModContainer.java:77)
	at LAYER PLUGIN/fmlcore@1.20.1-47.4.6/net.minecraftforge.fml.ModContainer.lambda$buildTransitionHandler$5(ModContainer.java:126)
	at java.base/java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1804)
	at java.base/java.util.concurrent.CompletableFuture$AsyncRun.exec(CompletableFuture.java:1796)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622)
	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165)

...

[2025-08-31 22:08:41.105] [modloading-worker-0] [INFO] [2147bf95]: com.hexagram2021.cme_suck_my_duck.utils.SuckTrace: [Modify] computeIfAbsent(Object, Function)
	at TRANSFORMER/cme_suck_my_duck@1.0.8/com.hexagram2021.cme_suck_my_duck.utils.TraceLogger.info(TraceLogger.java:15)
	at TRANSFORMER/cme_suck_my_duck@1.0.8/com.hexagram2021.cme_suck_my_duck.containers.AbstractWrappedContainer.logModify(AbstractWrappedContainer.java:40)
	at TRANSFORMER/cme_suck_my_duck@1.0.8/com.hexagram2021.cme_suck_my_duck.containers.WrappedMap.computeIfAbsent(WrappedMap.java:176)
	at TRANSFORMER/ponder@1.0.80/net.createmod.catnip.render.StitchedSprite.<init>(StitchedSprite.java:23)
	at TRANSFORMER/ponder@1.0.80/net.createmod.catnip.render.StitchedSprite.<init>(StitchedSprite.java:27)
	at TRANSFORMER/ponder@1.0.80/net.createmod.catnip.render.SpriteShiftEntry.set(SpriteShiftEntry.java:16)
	at TRANSFORMER/create@6.0.6/com.simibubi.create.foundation.block.connected.CTSpriteShifter.lambda$getCT$0(CTSpriteShifter.java:19)
	at LAYER PLUGIN/fmlcore@1.20.1-47.4.6/net.minecraftforge.fml.DistExecutor.unsafeRunWhenOn(DistExecutor.java:111)
	at TRANSFORMER/ponder@1.0.80/net.createmod.catnip.platform.ForgePlatformHelper.executeOnClientOnly(ForgePlatformHelper.java:54)
	at TRANSFORMER/create@6.0.6/com.simibubi.create.foundation.block.connected.CTSpriteShifter.getCT(CTSpriteShifter.java:19)
	at TRANSFORMER/create@6.0.6/com.simibubi.create.AllSpriteShifts.getCT(AllSpriteShifts.java:152)
	at TRANSFORMER/create@6.0.6/com.simibubi.create.AllSpriteShifts.getCT(AllSpriteShifts.java:157)
	at TRANSFORMER/create@6.0.6/com.simibubi.create.AllSpriteShifts.horizontal(AllSpriteShifts.java:138)
	at TRANSFORMER/create@6.0.6/com.simibubi.create.AllSpriteShifts.<clinit>(AllSpriteShifts.java:34)
	at TRANSFORMER/createcasing@1.7.2-fix1/fr.iglee42.createcasing.registries.EncasedBlocks.<clinit>(EncasedBlocks.java:76)
	at TRANSFORMER/createcasing@1.7.2-fix1/fr.iglee42.createcasing.CreateCasing.<init>(CreateCasing.java:62)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:480)
	at LAYER PLUGIN/javafmllanguage@1.20.1-47.4.6/net.minecraftforge.fml.javafmlmod.FMLModContainer.constructMod(FMLModContainer.java:77)
	at LAYER PLUGIN/fmlcore@1.20.1-47.4.6/net.minecraftforge.fml.ModContainer.lambda$buildTransitionHandler$5(ModContainer.java:126)
	at java.base/java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1804)
	at java.base/java.util.concurrent.CompletableFuture$AsyncRun.exec(CompletableFuture.java:1796)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622)
	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165)
[2025-08-31 22:08:41.105] [modloading-worker-0] [ERROR] [SYSTEM]: com.hexagram2021.cme_suck_my_duck.exceptions.TracedException: Check CMESuckMyDuck.log for details. Trace ID: 2147bf95
	at TRANSFORMER/cme_suck_my_duck@1.0.8/com.hexagram2021.cme_suck_my_duck.exceptions.TracedException.create(TracedException.java:14)
	at TRANSFORMER/cme_suck_my_duck@1.0.8/com.hexagram2021.cme_suck_my_duck.containers.WrappedMap.computeIfAbsent(WrappedMap.java:180)
	at TRANSFORMER/ponder@1.0.80/net.createmod.catnip.render.StitchedSprite.<init>(StitchedSprite.java:23)
	at TRANSFORMER/ponder@1.0.80/net.createmod.catnip.render.StitchedSprite.<init>(StitchedSprite.java:27)
	at TRANSFORMER/ponder@1.0.80/net.createmod.catnip.render.SpriteShiftEntry.set(SpriteShiftEntry.java:15)
	at TRANSFORMER/create@6.0.6/com.simibubi.create.foundation.block.connected.CTSpriteShifter.lambda$getCT$0(CTSpriteShifter.java:19)
	at LAYER PLUGIN/fmlcore@1.20.1-47.4.6/net.minecraftforge.fml.DistExecutor.unsafeRunWhenOn(DistExecutor.java:111)
	at TRANSFORMER/ponder@1.0.80/net.createmod.catnip.platform.ForgePlatformHelper.executeOnClientOnly(ForgePlatformHelper.java:54)
	at TRANSFORMER/create@6.0.6/com.simibubi.create.foundation.block.connected.CTSpriteShifter.getCT(CTSpriteShifter.java:19)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.connected.SpriteShifts.lambda$vault$0(SpriteShifts.java:32)
	at TRANSFORMER/ponder@1.0.80/net.createmod.catnip.data.Couple.createWithContext(Couple.java:36)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.connected.SpriteShifts.vault(SpriteShifts.java:32)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.connected.SpriteShifts.populateMaps(SpriteShifts.java:40)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.connected.SpriteShifts.<clinit>(SpriteShifts.java:26)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.api.Catwalks.build(Catwalks.java:71)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.BlockRegistry.registerCatwalks(BlockRegistry.java:187)
	at java.base/java.util.HashMap.forEach(HashMap.java:1421)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.BlockRegistry.init(BlockRegistry.java:103)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.CreateDecoMod.init(CreateDecoMod.java:17)
	at TRANSFORMER/createdeco@2.0.3-1.20.1-forge/com.github.talrey.createdeco.forge.CreateDecoModForge.<init>(CreateDecoModForge.java:17)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:480)
	at LAYER PLUGIN/javafmllanguage@1.20.1-47.4.6/net.minecraftforge.fml.javafmlmod.FMLModContainer.constructMod(FMLModContainer.java:77)
	at LAYER PLUGIN/fmlcore@1.20.1-47.4.6/net.minecraftforge.fml.ModContainer.lambda$buildTransitionHandler$5(ModContainer.java:126)
	at java.base/java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1804)
	at java.base/java.util.concurrent.CompletableFuture$AsyncRun.exec(CompletableFuture.java:1796)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622)
	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165)
Caused by: java.util.ConcurrentModificationException
	at java.base/java.util.HashMap.computeIfAbsent(HashMap.java:1221)
	at TRANSFORMER/cme_suck_my_duck@1.0.8/com.hexagram2021.cme_suck_my_duck.containers.WrappedMap.computeIfAbsent(WrappedMap.java:178)
	... 32 more

Note that the modloading-worker-0 thread where createdeco calls CTSpriteShifter#getCT is NOT the modloading-worker-0 thread where createcasing calls AllSpriteShifts#<clinit> (blame Forge, they just have the same name but are different!), which makes it crashes.

When Forge tries to load both createcasing and createdeco, this container was modified concurrently:

[talrey]

@Viola-Siemens I apologize, it seems we were talking past each other. I understand multithreading and why this is an issue, I was just asking about the best way to solve it here because I don't want to screw up something else by running mod code when or where it shouldn't be.

Looking at the other PRs you've made, it looks like your suggested solution is to just run all client init code as an enqueued task on the main thread? Doesn't that defeat the purpose of initializing mods in threads?

[talrey]

Alright, I've moved the sprite shift registration to FMLClientSetupEvent with an enqueueWork after talking with the Create team. They say it's an issue with Create, but this approach should be safer, correct?

[Viola-Siemens]

Looking at the other PRs you've made, it looks like your suggested solution is to just run all client init code as an enqueued task on the main thread? Doesn't that defeat the purpose of initializing mods in threads?

You can also enqueueWork your task in DeferredWorkQueue. Here's an example: queue#enqueueWork, runLater#accept.

but this approach should be safer, correct?

Yes. Thanks, I appreciate your work.

[talrey]

Thanks for the examples. Unfortunately, it seems that moving to the event.enqueueWork approach has caused the connected textures to not function. I'm not sure exactly why... might have something to do with Create's internals. I'd really like to fix this bug before the 1.21 release, so I'll keep poking at it.

Also, DeferredWorkQueue#lookup doesn't seem to exist in 1.21, or so IntelliJ tells me.

[talrey]

Okay, I found a fix! I didn't have to enqueue anything, I just copied CTSpriteShifter#getCT into my own code and removed the references to the cache, because Jozufozu said

I'm not entirely sure why it needs to have the cache at all, unless there's some cursed runtime dynamic usage hiding somewhere

I'm going to close this issue as fixed for now. When the 1.21 update comes out, feel free to try it and I'll reopen the issue if it persists. Thanks for the insights.

Commit ref just in case: d5028d6