[1.11] Avoiding a Concurrent Mod. Except.

[Lambda]

Hey there!

 

So I'm creating a network that has 'tethers' that send energy to nearby acceptable tiles (5x5) however, it seems I'm getting a concurrent modification execption, I know where the error is happening, but I do not know how to 'avoid' it.

 

Here is the code:

public class TileEntityNetworkTethers extends TileEntityBase implements ISharingEnergyHandler {

    public CustomEnergyStorage storage = new CustomEnergyStorage(50000, 50, 50);

    public static final int MAX_SEND = 50;

    public boolean removingFromList = false;

    public List<TileEntity> energyUsers = new ArrayList<>();

    public TileEntityNetworkTethers() {
        super("networkTethers");
    }

    @Override
    public void updateEntity() {
        super.updateEntity();

        if(!world.isRemote) {
            storage.receiveEnergyInternal(2, false);
            Iterable<BlockPos> blockPos = BlockPos.getAllInBox(pos.add(-5, -5, -5),
                                                               pos.add(+5, +5, +5));
            if(blockPos != null) {
                for (BlockPos position : blockPos) {
                    TileEntity te = world.getTileEntity(position);
                    if (te != null) {
                        if (!energyUsers.contains(te)) {
                            energyUsers.add(te);
                        }
                    }
                }
            }

            if(energyUsers.size() != 0) {
                for(TileEntity te : energyUsers) {
                    if(te != null) {
                        System.out.println(removingFromList);
                        for(EnumFacing facing : EnumFacing.VALUES) {
                            handleEnergy(te, facing, MAX_SEND);
                        }
                    }
                }
            }

            validateList();

            if(sendUpdateWithInterval()) {

            }
        }
    }

    public void handleEnergy(TileEntity te, EnumFacing facing, int amount) {
        if (te.hasCapability(CapabilityEnergy.ENERGY, facing)) {
            IEnergyStorage cap = te.getCapability(CapabilityEnergy.ENERGY, facing);
            if (cap != null) {
                if (cap.canReceive()) {
                    if(storage.getEnergyStored() - amount >= 0)  {
                        storage.extractEnergyInternal(amount, false);
                        cap.receiveEnergy(amount, false);
                    }
                }
                if(cap.canExtract()) {
                    if(storage.getEnergyStored() + amount <= storage.getMaxEnergyStored()) {
                        this.storage.receiveEnergyInternal(amount, false);
                        cap.extractEnergy(amount, false);
                    }
                }
            }
        }
    }

    public void validateList() {
        if (energyUsers != null && energyUsers.size() != 0) {
            for (TileEntity te : energyUsers) {
                if(te != null) {
                    if (world.getTileEntity(te.getPos()) == null) {
                        energyUsers.remove(te);
                    }
                }
            }
        }
    }

    @Override
    public IEnergyStorage getEnergyStorage(EnumFacing facing) {
        return storage;
    }

    @Override
    public int getEnergyToSplitShare() {
        return storage.getEnergyStored();
    }

    @Override
    public boolean doesShareEnergy() {
        return true;
    }

    @Override
    public EnumFacing[] getEnergyShareSides() {
        return EnumFacing.VALUES;
    }

    @Override
    public boolean canShareTo(TileEntity tile) {
        return true;
    }
}

 

Here is the crash:

net.minecraft.util.ReportedException: Ticking block entity
at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:800) ~[MinecraftServer.class:?]
at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:698) ~[MinecraftServer.class:?]
at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:156) ~[integratedServer.class:?]
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:547) [MinecraftServer.class:?]
at java.lang.Thread.run(Thread.java:745) [?:1.8.0_91]
Caused by: java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901) ~[?:1.8.0_91]
at java.util.ArrayList$Itr.next(ArrayList.java:851) ~[?:1.8.0_91]
at com.lambda.plentifulutilities.block.tile.TileEntityNetworkTethers.validateList(TileEntityNetworkTethers.java:95) ~[TileEntityNetworkTethers.class:?]
at com.lambda.plentifulutilities.block.tile.TileEntityNetworkTethers.updateEntity(TileEntityNetworkTethers.java:64) ~[TileEntityNetworkTethers.class:?]
at com.lambda.plentifulutilities.block.tile.TileEntityBase.update(TileEntityBase.java:171) ~[TileEntityBase.class:?]
at net.minecraft.world.World.updateEntities(World.java:1942) ~[World.class:?]
at net.minecraft.world.WorldServer.updateEntities(WorldServer.java:647) ~[WorldServer.class:?]
at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:794) ~[MinecraftServer.class:?]
... 4 more
[14:53:56] [server thread/ERROR]: This crash report has been saved to: F:\Minecraft Workspace\PlentifulUtilities\PlentifulUtilities\run\.\crash-reports\crash-2017-01-06_14.53.56-server.txt
[14:53:56] [server thread/INFO]: Stopping server
[14:53:56] [server thread/INFO]: Saving players
[14:53:56] [Client thread/INFO] [sTDOUT]: [net.minecraft.init.Bootstrap:printToSYSOUT:600]: ---- Minecraft Crash Report ----
// Uh... Did I do that?

 

Where its happening:

                            public void validateList() {
        if (energyUsers != null && energyUsers.size() != 0) {
            for (TileEntity te : energyUsers) {
                if(te != null) {
                    if (world.getTileEntity(te.getPos()) == null) {
                        energyUsers.remove(te); //--------HERE--------
                    }
                }
            }
        }
    }

 

Maybe there is a better way to store a TE other than an list? A map wont work due to them not being able to store duplicate keys.

 

Thanks,

[shadowfacts]

Well of course there's a ConcurrentModificationException, you're trying to remove something from a list you're currently iterating over. You can manually use the list's Iterator so you have access to the Iterator.remove function:

 

Iterator<TileEntity> iterator = energyUsers.iterator();
while (iterator.hasNext()) {
    TileEntity te = iterator.next();
    if (te != null && world.getTileEntity(te.getPos()) == null) {
        iterator.remove();
    }
}

 

Additionally, you shouldn't need that

te != null

check and you probably shouldn't be storing

null

in your list.

 

Also you could probably use TileEntity.isInvalid instead of the weird null-check stuff you're currently doing.

[Lambda]

Thanks.