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From Dominik Stadler <dominik.stad...@dynatrace.com>
Subject Keeping memory usage low when FOP is not running and avoid open file handles after FOP is run
Date Mon, 19 Jul 2010 08:53:04 GMT

my use-case is to have FOP integrated into a larger server application, where FOP is only
executed sporadically.

We already evaluated running FOP externally, but had severe trouble doing so for various reasons.
Therefore we need to try to keep memory usage of FOP as low as possible when it is not running,
I already had to do some workarounds to keep FOP from storing memory in caches or in thread
locals, partly also the XML implementation from Sun interferes and keeps the whole FOP SAX
Handler as thread local. Also any intermediate files need to be removed when FOP is finished
rendering, something that caused me a bit of headache last week.

I have one final item that I just found and would like to get input if there is a better solution:
The FOUserAgent holds an element "imageSessionContext" which holds SoftReferences to Source/ImageSource
elements via AbstractImageSessionContext.sessionSources. The memory for these items is cleaned
correctly when we un-reference the FOUserAgent object, however the Source-items still hold
a file-handle via the InputStream that is included in StreamSource/ImageStreamSource object.
The effect is that I cannot remove intermediate image files that are used during PDF generation,
but would like to delete after the PDF is created.

Currently I employ an ugly hack where I remember the file-names and afterwards use FOUserAgent.getImageSessionContext().getSource()
to retrieve the Source and do the "close()" on the item manually.

-          Is this a bug, as file handles are kept open this way and are only given up, when
the SoftReference is collected? So this can easily cause "out of handle" type of errors if
a lot of memory is available and thus SoftReferences are not collected for a long time.
-          Is there a way to not keep these references in the first run? I use different images
throughout the document, so image caching is not very useful for me anyway.

Thanks... Dominik.

Dominik Stadler, Team Lead
F +43 732 210100008 | E dominik.stadler@dynatrace.com<mailto:dominik.stadler@dynatrace.com>
| Skype: stadler.dominik
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