Crash: ConcurrentModificationException on tandem with Catenation

[Krutoy242]

I'm changing string list inside catenation and getting this server crash:

java.util.ConcurrentModificationException
    at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:911)
    at java.util.ArrayList$Itr.next(ArrayList.java:861)
    at commands\Restart_server.clearPending(commands/restart_server.zs:59)
    at commands\Restart_server.cancelVoting(commands/restart_server.zs:66)
    at Crafttweakercommands\Restart_server89.apply(commands/restart_server.zs:91)
    at youyihj.zenutils.impl.util.catenation.InstantTask.run(InstantTask.java:20)
    at youyihj.zenutils.api.util.catenation.Catenation.tick(Catenation.java:38)
    at youyihj.zenutils.impl.util.catenation.CatenationManager.lambda$onWorldTick$0(CatenationManager.java:31)
    at java.util.Collection.removeIf(Collection.java:414)
    at youyihj.zenutils.impl.util.catenation.CatenationManager.onWorldTick(CatenationManager.java:31)
    at net.minecraftforge.fml.common.eventhandler.ASMEventHandler_1352_CatenationManager_onWorldTick_WorldTickEvent.invoke(.dynamic)

My code: https://github.com/Krutoy242/Enigmatica2Expert-Extended/blob/7ae848b7b5df53c85416e4c5b8d5cde74da9ba6f/scripts/commands/restart_server.zs#L59
Full crash log:
crash-2022-08-31_19.20.37-server.txt

[youyihj]

You can not edit the list when you are iterating it. Yea, I forgot to expose clear method. In version 1.11.3, just call this method to fix the issue.

[Krutoy242]

Thank you!

Can you add additional checks so that the game does not crash under these conditions? I like that ZenScript is pretty crash-resistant, and strive that scripts can never crash, only erroring in logs.

Also, I don't know how to program in Java, and I don't know what ConcurrentModificationException is. In JavaScript, I can remove from an array without a problem as long as I iterate it 😁

[youyihj]

I don't know how JS implements it. I just try to explain why the exception exists.
Since all loops can be written by while statement. (for and foreach are more like syntactic sugar) I translate the code to while style.
Pseudocode:

var list = ["a", "b", "c", "d"];
var length = list.length;
var i = 0;
while (i < length) { // for i, element in list
    // removes the element at the given index
    list.remove(i);
    i++;
};

In the first loop, list.remove(0) removes the first element a, now the list is ["b", "c", "d"] Then, in the second loop, list.remove(1) removes the second element of the list. But since the list is ["b", "c", "d"], so the statement removes "c" , rather than "b". This is a unexpected behavior. So Java uses fast fail mode, throws an exception to avoid this operation.

[Krutoy242]

Ok, thank you.
So, i guess each other ZenUtils user would encounter this issue if they dont know how java work...

If there any other places where ZenUtils could crash my game, i want to know. Can you add Wiki note for this? Maybe, under function description.