I have the following code (Note it is being run in a separate thread, and the entire thread needs to pause until its done):

public void BreakBlock(boolean enforceRotation){
        Minecraft mc = Minecraft.getMinecraft();
        RayTraceResult result = rayTrace(5);
        int rotation = (int)mc.player.rotationYaw;
        int pitch  = (int)mc.player.rotationPitch;
        try {
            int elapsed = 0;
            while (mc.world.getBlockState(result.getBlockPos()).getMaterial() != Material.AIR && elapsed < 15000) {
                if (enforceRotation) HardSetFacing(rotation, pitch);
                if (mc.playerController.onPlayerDamageBlock(result.getBlockPos(), result.sideHit)) mc.player.swingArm(EnumHand.MAIN_HAND);
                Thread.sleep(40);
                elapsed += 40;
            }
        }
        catch (Exception ex)
        {
            Main.logger.error(ex.getMessage());
        }
    }

However, occasionally, this will lead to the following crash (Game fully crashes and returns to launcher):

[21:55:28] [main/FATAL] [net.minecraft.client.Minecraft]: Unreported exception thrown!
java.util.ConcurrentModificationException: null
	at com.google.common.collect.HashBiMap$Itr.hasNext(HashBiMap.java:401) ~[guava-21.0.jar:?]
	at net.minecraft.client.audio.SoundManager.func_148605_d(SoundManager.java:252) ~[chm.class:?]
	at net.minecraft.client.audio.SoundHandler.func_73660_a(SoundHandler.java:293) ~[cho.class:?]
	at net.minecraft.client.Minecraft.func_71407_l(Minecraft.java:1857) ~[bib.class:?]
	at net.minecraft.client.Minecraft.func_71411_J(Minecraft.java:1097) ~[bib.class:?]
	at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:397) [bib.class:?]
	at net.minecraft.client.main.Main.main(SourceFile:123) [Main.class:?]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_51]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_51]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_51]
	at java.lang.reflect.Method.invoke(Method.java:497) ~[?:1.8.0_51]
	at net.minecraft.launchwrapper.Launch.launch(Launch.java:135) [launchwrapper-1.12.jar:?]
	at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.12.jar:?]

Any thoughts on how to solve this?

1 minute ago, diesieben07 said:

Minecraft code must be accessed from the main thread only.

Why do you need a separate thread?

As i need to pause execution of my mod until this is done while not blocking the game, i also need to be able to sleep the thread to ensure timing while not blocking the game

Just now, diesieben07 said:

Do not sleep threads for delays. Count ticks. A tick happens 20 times a second. If you want something to wait for 5 seconds, count to 5x20 = 100.

I'm assuming you mean this in a way similar to the way the java.util timer works. Unfortunately due to the way my codebase is setup, this isnt going to work efficiently. Plus, the while loop in the break block code has a tendency to kill the game if its not threaded.

For the time being i will just write some code for thread cross talk to execute the player controller stuffs on the main thread, seeing as its usually idle at this point, or see if java has an async system similar to .NET

1 minute ago, NateKomodo said:

I'm assuming you mean this in a way similar to the way the java.util timer works.

Nope that is not what he means. He means use a tick event Such as ClientTickEvent to count ticks until a specified amount has passed. Then do what you need to do like tell the player to break a block.

4 minutes ago, Animefan8888 said:

Nope that is not what he means. He means use a tick event Such as ClientTickEvent to count ticks until a specified amount has passed. Then do what you need to do like tell the player to break a block.

Yep, im going to move over to the tick event for breaking block and control that via a boolean, seems to be the easiest and most effective solution for my particular situation.