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https://issues.apache.org/jira/browse/PDFBOX-4963?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17624321#comment-17624321
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Kenichi Suzuki commented on PDFBOX-4963:
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Thank you for your prompt reply.
I was able to confirm that GC works and finalize() runs a lot, but it is
leaking.
We worked around this by changing the processing sequence so that the font
object is static and can be used around.
If it is not released, the idea is to make it resident. (It's tentative, with
an anti-pattern.)
I will also consider overriding the finalize() method.
Thank you very much.
> TTF file leakage in font cache
> ------------------------------
>
> Key: PDFBOX-4963
> URL: https://issues.apache.org/jira/browse/PDFBOX-4963
> Project: PDFBox
> Issue Type: Bug
> Components: PDModel
> Affects Versions: 2.0.21
> Reporter: Maison
> Priority: Major
>
> We observe many TTF opened files in our production server, which result in
> exhausting file descriptors.
> We have checked and rechecked that every PDDocument is properly closed (try
> with resource everywhere).
> By looking at pdfbox source code, I suspect 2 problems in FontCache and in
> FileSystemFontProvider
> 1 - FontCache
> In FontCache, a map keeps SoftReference<FontBoxFont> as values.
> IIUC for TTF fonts, the values are instances of
> org.apache.fontbox.ttf.TrueTypeFont. Such instances have a TTFDataStream
> member, which is RAFDataStream (so there is an opened file).
> Problem is that if the soft reference is cleared by GC, we can suppose the
> TrueTypeFont objects are GCed (is that guaranteed?) ; but what about the
> RAFDataStream sub-object ? There is no RAFDataStream.close() in TrueTypeFont
> finalizer
> 2 - FileSystemFontProvider
> There seems to be a TOCTOU-like race condition when a font is needed. Code
> looks like below (simplified) :
> @Override
> public FontBoxFont getFont()
> {
> FontBoxFont cached = parent.cache.getFont(this);
> if (cached != null) {
> return cached;
> }
> FontBoxFont font = ... // instantiate font
> parent.cache.addFont(this, font); // <--- not thread safe ?
> return font;
> }
> The font, if not in cache, is instantiated and added into cache. But two
> threads can do that at the same time, and the last addFont() wins. So the
> first SoftReference<FontBoxFont> object is now eligible to GC; but the
> FontBoxFont has not been closed.
> This problem is probably less frequent.
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