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From "Luis Filipe Nassif (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (TIKA-885) Possible ConcurrentModificationException while accessing Metadata produced by ParsingReader
Date Tue, 16 Oct 2012 12:47:04 GMT

    [ https://issues.apache.org/jira/browse/TIKA-885?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13475865#comment-13475865
] 

Luis Filipe Nassif edited comment on TIKA-885 at 10/16/12 12:46 PM:
--------------------------------------------------------------------

Ok, I got the idea. I think it will solve the problem. Setting a flag on metadata changes
and testing for it on reads and writes would save unnecessarily copies and synchronization.

I will open a new issue describing the improvement on PipedReader and PipedWriter to use with
ParsingReader.
                
      was (Author: lfcnassif):
    Ok, I got the idea. I think it will solve the problem. Setting a flag on metadata changes
and testing for it on reads and writes would save unnecessarily copies and synchronization.

I have opened a new issue TIKA-1007 describing the improvement on PipedReader and PipedWriter
to use with ParsingReader.
                  
> Possible ConcurrentModificationException while accessing Metadata produced by ParsingReader
> -------------------------------------------------------------------------------------------
>
>                 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
>              Labels: patch
>
> 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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