# Concurrent Modification Exception when executing workflow
**URL:** https://community.temporal.io/t/concurrent-modification-exception-when-executing-workflow/12479
**Category:** Community Support
**Tags:** java-sdk
**Created:** [June 12, 2024, 2:06pm UTC](https://community.temporal.io/t/concurrent-modification-exception-when-executing-workflow/12479 "2024-06-12T14:06:37Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@rvr](https://community.temporal.io/u/rvr)
#### Post date: [June 12, 2024, 2:06pm UTC](https://community.temporal.io/t/concurrent-modification-exception-when-executing-workflow/12479/1 "2024-06-12T14:06:37Z")
Hello,
I am getting the following error in the logs of my Java application which uses Temporal Java SDK:
```auto
java.util.ConcurrentModificationException: null
at java.base/java.util.HashMap$HashIterator.nextNode(HashMap.java:1605)
at java.base/java.util.HashMap$KeyIterator.next(HashMap.java:1628)
at io.temporal.internal.replay.ReplayWorkflowRunTaskHandler$LocalActivityMeteringHelper.newWFTStarting(ReplayWorkflowRunTaskHandler.java:431)
at io.temporal.internal.replay.ReplayWorkflowRunTaskHandler$LocalActivityMeteringHelper.access$200(ReplayWorkflowRunTaskHandler.java:425)
at io.temporal.internal.replay.ReplayWorkflowRunTaskHandler.handleWorkflowTask(ReplayWorkflowRunTaskHandler.java:143)
at io.temporal.internal.replay.ReplayWorkflowTaskHandler.handleWorkflowTaskWithQuery(ReplayWorkflowTaskHandler.java:133)
at io.temporal.internal.replay.ReplayWorkflowTaskHandler.handleWorkflowTask(ReplayWorkflowTaskHandler.java:98)
at io.temporal.internal.worker.WorkflowWorker$TaskHandlerImpl.handleTask(WorkflowWorker.java:413)
at io.temporal.internal.worker.WorkflowWorker$TaskHandlerImpl.handle(WorkflowWorker.java:320)
at io.temporal.internal.worker.WorkflowWorker$TaskHandlerImpl.handle(WorkflowWorker.java:261)
at io.temporal.internal.worker.PollTaskExecutor.lambda$process$0(PollTaskExecutor.java:105)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
at java.base/java.lang.Thread.run(Thread.java:1583)
```
Most of the time (but not always) the workflow gets stuck on this, but still it gets printed to the logs every few seconds.
In my workflow I am using two lists to keep track of the state. I have a few local activities that run in a loop until the processing is done.
I am using SDK version 1.22.3.
Do you know what might be causing this? Could it be a configuration issue on my side?
Thanks!
---
### Author:  [@maxim](https://community.temporal.io/u/maxim)
#### Post date: [June 12, 2024, 6:52pm UTC](https://community.temporal.io/t/concurrent-modification-exception-when-executing-workflow/12479/2 "2024-06-12T18:52:28Z")
We are looking into this.
---
### Author:  [@Quinn\_Klassen](https://community.temporal.io/u/Quinn_Klassen)
#### Post date: [June 12, 2024, 9:25pm UTC](https://community.temporal.io/t/concurrent-modification-exception-when-executing-workflow/12479/3 "2024-06-12T21:25:36Z")
> [@rvr](#):
>
> ```auto
> java.util.ConcurrentModificationException: null
> at java.base/java.util.HashMap$HashIterator.nextNode(HashMap.java:1605)
> at java.base/java.util.HashMap$KeyIterator.next(HashMap.java:1628)
> at io.temporal.internal.replay.ReplayWorkflowRunTaskHandler$LocalActivityMeteringHelper.newWFTStarting(ReplayWorkflowRunTaskHandler.java:431)
> at io.temporal.internal.replay.ReplayWorkflowRunTaskHandler$LocalActivityMeteringHelper.access$200(ReplayWorkflowRunTaskHandler.java:425)
> at io.temporal.internal.replay.ReplayWorkflowRunTaskHandler.handleWorkflowTask(ReplayWorkflowRunTaskHandler.java:143)
> at io.temporal.internal.replay.ReplayWorkflowTaskHandler.handleWorkflowTaskWithQuery(ReplayWorkflowTaskHandler.java:133)
> at io.temporal.internal.replay.ReplayWorkflowTaskHandler.handleWorkflowTask(ReplayWorkflowTaskHandler.java:98)
> at io.temporal.internal.worker.WorkflowWorker$TaskHandlerImpl.handleTask(WorkflowWorker.java:413)
> at io.temporal.internal.worker.WorkflowWorker$TaskHandlerImpl.handle(WorkflowWorker.java:320)
> at io.temporal.internal.worker.WorkflowWorker$TaskHandlerImpl.handle(WorkflowWorker.java:261)
> at io.temporal.internal.worker.PollTaskExecutor.lambda$process$0(PollTaskExecutor.java:105)
> at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
> at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
> at java.base/java.lang.Thread.run(Thread.java:1583)
>
> ```
Confirmed this is a bug in the Java SDK. We have opened an issue and it should be resolved for the next Java SDK release that we are targeting for next week.
>
>
> \## Issue
>
> When executing workflow tasks with local activities \`LocalActivityMe…teringHelper\` may attempt to make illegal modifications to its underlying data structure when calling \`newWFTStarting\` causing a \`ConcurrentModificationException\`
>
> \## Example:
> \`\`\`
> java.util.ConcurrentModificationException: null
> at java.base/java.util.HashMap$HashIterator.nextNode(HashMap.java:1605)
> at java.base/java.util.HashMap$KeyIterator.next(HashMap.java:1628)
> at io.temporal.internal.replay.ReplayWorkflowRunTaskHandler$LocalActivityMeteringHelper.newWFTStarting(ReplayWorkflowRunTaskHandler.java:431)
> at io.temporal.internal.replay.ReplayWorkflowRunTaskHandler$LocalActivityMeteringHelper.access$200(ReplayWorkflowRunTaskHandler.java:425)
> at io.temporal.internal.replay.ReplayWorkflowRunTaskHandler.handleWorkflowTask(ReplayWorkflowRunTaskHandler.java:143)
> at io.temporal.internal.replay.ReplayWorkflowTaskHandler.handleWorkflowTaskWithQuery(ReplayWorkflowTaskHandler.java:133)
> at io.temporal.internal.replay.ReplayWorkflowTaskHandler.handleWorkflowTask(ReplayWorkflowTaskHandler.java:98)
> at io.temporal.internal.worker.WorkflowWorker$TaskHandlerImpl.handleTask(WorkflowWorker.java:413)
> at io.temporal.internal.worker.WorkflowWorker$TaskHandlerImpl.handle(WorkflowWorker.java:320)
> at io.temporal.internal.worker.WorkflowWorker$TaskHandlerImpl.handle(WorkflowWorker.java:261)
> at io.temporal.internal.worker.PollTaskExecutor.lambda$process$0(PollTaskExecutor.java:105)
> at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
> at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
> at java.base/java.lang.Thread.run(Thread.java:1583)
> \`\`\`
>
> https://community.temporal.io/t/concurrent-modification-exception-when-executing-workflow/12479/1
>
> \## Specifications
>
> - Platform: 1.23.1
---
### Author:  [@rvr](https://community.temporal.io/u/rvr)
#### Post date: [June 13, 2024, 7:10am UTC](https://community.temporal.io/t/concurrent-modification-exception-when-executing-workflow/12479/4 "2024-06-13T07:10:43Z")
Thank you for your quick response!