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https://issues.apache.org/jira/browse/PDFBOX-5731?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17796052#comment-17796052
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Axel Howind commented on PDFBOX-5731:
-------------------------------------
[~lycheng] I have created a patch for current trunk. Could you please try it
out?
What it does: I replaced nameMap and commonNameMap by a Map that holds
WeakReference instances to values (we cannot use a WeakHashMap since that one
holds weak keys instead). The clearResources() method is automatically invoked
every time a new COSName instance is created (that is, if it is not yet present
in the cache). This step is necessary, because the problem with unused COSName
instances is that they hold a reference to their key. That means, the bulk of
memory can only be released, if the string used as key can also be GCed.
Using a WeakHashMap would not help here because weak references to keys would
not become stale unless the value is removed, which will not happen before the
key is removed etc.
I have confirmed that unused entries are removed automatically. The instances
that were stored in the commonNameMap before are also retained because their
references never become stale (because they are defined as constants in
COSName).
* Calling clearResources manually is still possible but should not be
necessary.
* I also have tried to call clearResources only every 100th time the nameMap
is changed but I could see no measurable performance impact, so I removed that
code again.
* I think there should no extra synchronisation be necessary when calling
clearResources as IMHO the worst that could happen is that we end up with a
couple of extra COSName instances. But this probably needs some more testing.
Please let me know if this solves your problem.
Added patch
"attempted_fix_for_PDFBOX-5731__clear_out_unused_COSName_instances_automatically.patch".
> org.apache.pdfbox.cos.COSName#nameMap There is a memory leak problem.
> ---------------------------------------------------------------------
>
> Key: PDFBOX-5731
> URL: https://issues.apache.org/jira/browse/PDFBOX-5731
> Project: PDFBox
> Issue Type: Bug
> Affects Versions: 2.0.30, 3.0.1 PDFBox
> Reporter: liu
> Priority: Major
> Attachments:
> attempted_fix_for_PDFBOX-5731__clear_out_unused_COSName_instances_automatically.patch,
> image-2023-12-08-16-02-12-293.png, screenshot-1.png, screenshot-2.png,
> screenshot-3.png, screenshot-4.png, screenshot-5.png
>
>
> !image-2023-12-08-16-02-12-293.png!
> !screenshot-1.png!
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