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From "Torsten Kuhnhenne (JIRA)" <j...@apache.org>
Subject [jira] [Created] (XGC-117) ConcurrentModificationException in ImageCache / ImageCache not thread-safe
Date Tue, 11 Dec 2018 07:41:00 GMT
Torsten Kuhnhenne created XGC-117:
-------------------------------------

             Summary: ConcurrentModificationException in ImageCache / ImageCache not thread-safe
                 Key: XGC-117
                 URL: https://issues.apache.org/jira/browse/XGC-117
             Project: XMLGraphicsCommons
          Issue Type: Bug
          Components: general
    Affects Versions: 2.3
            Reporter: Torsten Kuhnhenne


When using a single {{FopFactory}} to create multiple {{Fop}} instances that are used in different
threads I get an {{ConcurrentModificationException}} in {{ImageCache#doInvalidURIHouseKeeping}}
in line 294.

 

Source of the problem is the that new HashSet(this.invalidURIs.keySet()) internaly iterates
over the key-set that is backed by the {{HashMap}} and when another thread changes the {{HashMap}}
the {{ConcurrentModificationException}} occurs.

 

In my opinion there must be synchronized-blocks around each access of the {{invalidURIs}}
map  to solve this problem. The use of a synchronized map can not solve this problem.

 

Stacktrace:
{code:java}
Caused by: java.util.ConcurrentModificationException: null
at java.util.HashMap$HashIterator.nextNode(HashMap.java:1437)
at java.util.HashMap$KeyIterator.next(HashMap.java:1461)
at java.util.AbstractCollection.addAll(AbstractCollection.java:343)
at java.util.HashSet.<init>(HashSet.java:119)
at org.apache.xmlgraphics.image.loader.cache.ImageCache.doInvalidURIHouseKeeping(ImageCache.java:294)
at org.apache.xmlgraphics.image.loader.cache.ImageCache.doHouseKeeping(ImageCache.java:290)
at org.apache.xmlgraphics.image.loader.cache.ImageCache.considerHouseKeeping(ImageCache.java:280)
at org.apache.xmlgraphics.image.loader.cache.ImageCache.registerInvalidURI(ImageCache.java:209)
at org.apache.xmlgraphics.image.loader.cache.ImageCache.needImageInfo(ImageCache.java:130)
at org.apache.xmlgraphics.image.loader.ImageManager.getImageInfo(ImageManager.java:123)
at org.apache.fop.fo.flow.ExternalGraphic.bind(ExternalGraphic.java:81)
at org.apache.fop.fo.FObj.processNode(FObj.java:126)
at org.apache.fop.fo.FOTreeBuilder$MainFOHandler.startElement(FOTreeBuilder.java:291)
at org.apache.fop.fo.FOTreeBuilder.startElement(FOTreeBuilder.java:179)
{code}
The issue XGC-30 sounds similiar but does not solve the problem.



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