[1.7.10] Concurrent Modification Exception occuring randomly

[Thornack]

Anyone know what would cause this here is the error log. I keep getting this exception when running a dedicated server and it happens sometimes during gameplay. I cannot seem to get it to occur on a consistent basis

 

 

[20:31:49] [Netty IO #1/ERROR] [FML]: NetworkDispatcher exception

io.netty.handler.codec.EncoderException: java.util.ConcurrentModificationException

at io.netty.handler.codec.MessageToByteEncoder.write(MessageToByteEncoder.java:129) ~[MessageToByteEncoder.class:?]

at io.netty.channel.DefaultChannelHandlerContext.invokeWrite(DefaultChannelHandlerContext.java:644) ~[DefaultChannelHandlerContext.class:?]

at io.netty.channel.DefaultChannelHandlerContext.write(DefaultChannelHandlerContext.java:698) ~[DefaultChannelHandlerContext.class:?]

at io.netty.channel.DefaultChannelHandlerContext.write(DefaultChannelHandlerContext.java:637) ~[DefaultChannelHandlerContext.class:?]

at cpw.mods.fml.common.network.handshake.NetworkDispatcher.write(NetworkDispatcher.java:423) ~[NetworkDispatcher.class:?]

at io.netty.channel.DefaultChannelHandlerContext.invokeWrite(DefaultChannelHandlerContext.java:644) ~[DefaultChannelHandlerContext.class:?]

at io.netty.channel.DefaultChannelHandlerContext.write(DefaultChannelHandlerContext.java:698) ~[DefaultChannelHandlerContext.class:?]

at io.netty.channel.DefaultChannelHandlerContext.writeAndFlush(DefaultChannelHandlerContext.java:688) ~[DefaultChannelHandlerContext.class:?]

at io.netty.channel.DefaultChannelHandlerContext.writeAndFlush(DefaultChannelHandlerContext.java:717) ~[DefaultChannelHandlerContext.class:?]

at io.netty.channel.DefaultChannelPipeline.writeAndFlush(DefaultChannelPipeline.java:893) ~[DefaultChannelPipeline.class:?]

at io.netty.channel.AbstractChannel.writeAndFlush(AbstractChannel.java:239) ~[AbstractChannel.class:?]

at net.minecraft.network.NetworkManager$1.run(NetworkManager.java:197) [NetworkManager$1.class:?]

at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:354) [singleThreadEventExecutor.class:?]

at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:348) [NioEventLoop.class:?]

at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:101) [singleThreadEventExecutor$2.class:?]

at java.lang.Thread.run(Unknown Source) [?:1.7.0_25]

Caused by: java.util.ConcurrentModificationException

at java.util.HashMap$HashIterator.nextEntry(Unknown Source) ~[?:1.7.0_25]

at java.util.HashMap$KeyIterator.next(Unknown Source) ~[?:1.7.0_25]

at net.minecraft.nbt.NBTTagCompound.write(NBTTagCompound.java:33) ~[NBTTagCompound.class:?]

at net.minecraft.nbt.NBTTagCompound.func_150298_a(NBTTagCompound.java:472) ~[NBTTagCompound.class:?]

at net.minecraft.nbt.NBTTagCompound.write(NBTTagCompound.java:35) ~[NBTTagCompound.class:?]

at net.minecraft.nbt.CompressedStreamTools.func_150663_a(CompressedStreamTools.java:158) ~[CompressedStreamTools.class:?]

at net.minecraft.nbt.CompressedStreamTools.write(CompressedStreamTools.java:148) ~[CompressedStreamTools.class:?]

at net.minecraft.nbt.CompressedStreamTools.compress(CompressedStreamTools.java:88) ~[CompressedStreamTools.class:?]

at net.minecraft.network.PacketBuffer.writeNBTTagCompoundToBuffer(PacketBuffer.java:94) ~[PacketBuffer.class:?]

at net.minecraft.network.PacketBuffer.writeItemStackToBuffer(PacketBuffer.java:140) ~[PacketBuffer.class:?]

at net.minecraft.entity.DataWatcher.writeWatchableObjectToPacketBuffer(DataWatcher.java:289) ~[DataWatcher.class:?]

at net.minecraft.entity.DataWatcher.writeWatchedListToPacketBuffer(DataWatcher.java:186) ~[DataWatcher.class:?]

at net.minecraft.network.play.server.S1CPacketEntityMetadata.writePacketData(S1CPacketEntityMetadata.java:50) ~[s1CPacketEntityMetadata.class:?]

at net.minecraft.util.MessageSerializer.encode(MessageSerializer.java:46) ~[MessageSerializer.class:?]

at net.minecraft.util.MessageSerializer.encode(MessageSerializer.java:53) ~[MessageSerializer.class:?]

at io.netty.handler.codec.MessageToByteEncoder.write(MessageToByteEncoder.java:111) ~[MessageToByteEncoder.class:?]

[coolAlias]

CMEs typically occur when dealing with Collections, usually when one thread is iterating over one and another thread is removing items to that same Collection.

 

From your log, it looks as though you have an entity that might be doing some Collections processing when reading/writing NBT, specifically writeWatchedListToPacketBuffer.

 

Putting that section of code within a synchronized block will probably fix it, or by using Iterators to traverse your list when you are removing entries.

[Thornack]

I think I know what the issue is. How would you add a pickup delay for an EntityItem. I think this will fix the issue

[coolAlias]

entityitem#delayBeforeCanPickup = x; // changes to setter in 1.8