Possible ConcurrentModificationException while accessing Metadata produced by
ParsingReader
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Key: TIKA-885
URL: https://issues.apache.org/jira/browse/TIKA-885
Project: Tika
Issue Type: Improvement
Components: metadata, parser
Affects Versions: 1.0
Environment: jre 1.6_25 x64 and Windows7 Enterprise x64
Reporter: Luis Filipe Nassif
Priority: Minor
Oracle PipedReader and PipedWriter classes have a bug that do not allow them to
execute concurrently, because they notify each other only when the pipe is full
or empty, and do not after a char is read or written to the pipe. So i modified
ParsingReader to use modified versions of PipedReader and PipedWriter, similar
to gnu versions of them, that work concurrently. However, sometimes and with
certain files, i am getting the following error:
java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
at java.util.HashMap$KeyIterator.next(Unknown Source)
at java.util.AbstractCollection.toArray(Unknown Source)
at org.apache.tika.metadata.Metadata.names(Metadata.java:146)
It is because the ParsingReader.ParsingTask thread is writing metadata while it
is being read by the ParsingReader thread, with files containing metadata
beyond its initial bytes. It will not occur with the current implementation,
because java PipedReader and PipedWriter block each other, what is a
performance bug that affect ParsingReader, but they could be fixed in a future
java release. I think it would be a defensive approach to turn access to the
private Metadata.metadata Map synchronized, what could avoid a possible future
problem using ParsingReader.
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