Ben Manes created PDFBOX-4396:
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Summary: Memory leak due to soft reference caching
Key: PDFBOX-4396
URL: https://issues.apache.org/jira/browse/PDFBOX-4396
Project: PDFBox
Issue Type: Bug
Affects Versions: 2.0.12
Environment: JDK10; G1
Reporter: Ben Manes
Attachments: memory leak 2.png, memory leak.png
In a heap dump, it appears that DefaultResourceCache is retaining 5.3 GB of
memory due to buffered images (via PDImageXObject). I suspect that G1 is not
collecting soft references across all regions before it out-of-memory errors.
In PDFBOX-4389, I discovered very slow PDDocument#load times due to a JDK10 I/O
bug. Previously I was loading the document to render each page, but this took
1.5 minutes. To work around that bug I reused the document instance across
pages. This seems to have fail because the pages were cached and not cleared by
the GC.
The DefaultResourceCache does not prune its cache entries when the soft
references are collected. Like WeakHashMap, it should use a ReferenceQueue,
poll it on every access, and prune accordingly.
Thankfully PDDocument#setResourceCache exists. For now I am going to reset the
cache to a new instance after a page has been rendered. The entries should no
longer be reachable and be GC'd more aggressively. If that doesn't work, I'll
either replace the cache (e.g. with Caffeine) or disable it by setting the
instance to null.
I think the desired fix is to prune the DefaultResourceCache and, ideally,
reconsider usage of soft references (as they tend to be poor in practice).
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