java.util.ConcurrentModificationException

What is ConcurrentModificationException?

The java.util.ConcurrentModificationException occurs when a thread attempts to modify a collection (such as a list or map) while another process is actively iterating over it. In the context of a Minecraft server, this usually indicates that a plugin or mod is trying to change data in a way that conflicts with the server's main tick loop.

Common Causes

• Incompatible Plugins: Two or more plugins attempting to modify the same player data or entity list simultaneously.
• Outdated Software: Using a plugin version that is not compatible with your current server software version.
• Asynchronous Tasks: A plugin trying to modify server objects from an asynchronous thread instead of the main server thread.

How to fix it

On AwakeNode

1. Use the File Manager: Navigate to your server's plugins folder via the AwakeNode File Manager to identify recently added plugins.
2. Isolate the Cause: Remove or disable suspected plugins one by one. Restart your server after each change to see if the error persists in the console.
3. Contact Support: If the error continues after removing plugins, open a ticket with our support team. We can review your crash logs and server environment to determine if a specific startup flag or configuration adjustment is required.

On other hosts / manually

1. Check Logs: Access your latest.log or crash-reports via SFTP. Look for the stack trace immediately following the ConcurrentModificationException to identify which plugin or mod is triggering the conflict.
2. Update or Remove: Ensure all plugins and mods are updated to the latest stable release. If the error persists, remove the plugin identified in the stack trace.
3. Adjust Startup Flags: If the error is caused by improper memory handling or threading issues, you may need to edit your startup command. Locate your server's startup script and ensure your -Xmx and -Xms flags are set correctly for your RAM allocation. If you are unsure how to configure these, consult your host's documentation.