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Posted to dev@poi.apache.org by "PJ Fanning (Jira)" <ji...@apache.org> on 2026/10/04 12:06:00 UTC
[jira] [Closed] (XMLBEANS-676) ThreadLocals in NamespaceContext are sometimes left over and cause a memory leak
[ https://issues.apache.org/jira/browse/XMLBEANS-676?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
PJ Fanning closed XMLBEANS-676.
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Resolution: Fixed
> ThreadLocals in NamespaceContext are sometimes left over and cause a memory leak
> --------------------------------------------------------------------------------
>
> Key: XMLBEANS-676
> URL: https://issues.apache.org/jira/browse/XMLBEANS-676
> Project: XMLBeans
> Issue Type: Bug
> Affects Versions: 5.4.1
> Reporter: Dominik Stadler
> Priority: Major
> Fix For: 5.5.0
>
> Attachments: image-2026-10-04-10-19-21-146.png, image-2026-10-04-10-20-36-513.png
>
>
> When running the large regression test-suite for Apache POI, I saw that over time, more and more memory is allocated by thread-locals in NamespaceContext and is not freed any more.
> The test-application reads millions of documents in multiple threads. It re-uses the threads for multiple documents.
> Looking at memory dumps, it seems the thread-local in NamespaceContext keeps considerable amounts of memory from being freed in at least two threads.
> It seems sometimes the pushed elements are not pop()ed from the stack properly.
> A quick look at the code did not show how this can happen, it seems calls to "push()" are always followed by a "pop()" in a try-finally block. So elements should always be removed again.
> Also pop()ing the last item should always clear the thread-local, but one of the two threads has an empty stack with "current" still holding onto a large portion of memory.
> The application is using Thread.stop() in some cases, but this should cause the thread to be re-created by the executor and thus thread-locals to be freed. The application also triggers all sorts of exceptions, including OOMs as part of processing files.
>
> As a result, the regression testing application now runs very slowly as it constantly causes OOMs as lots of memory is used by the thread-locals.
>
> Thread holding onto memory in "current" inside the thread-local:
> !image-2026-10-04-10-19-21-146.png!
>
> Thread holding onto memory via a large number of elements remaining in the stack:
> !image-2026-10-04-10-20-36-513.png!
>
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