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https://issues.apache.org/jira/browse/TIKA-885?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13426842#comment-13426842
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Jukka Zitting commented on TIKA-885:
------------------------------------
What I had in mind was something like a {{Metadata.copyFrom(Metadata)}} method
that would copy all metadata from one instance to another. We'd then have three
{{Metadata}} instances, one for the client, one for the parser and a shared one
for passing updates from the parser to the client. Each {{write()}} in the
background parser would do something like:
{code}
synchronized (sharedMetadata) {
sharedMetadata.copyFrom(parserMetadata);
}
{code}
... and each {{read()}} by the client would do:
{code}
synchronized (sharedMetadata) {
clientMetadata.copyFrom(sharedMetadata);
}
{code}
It's not terribly elegant, but should avoid the need to make all {{Metadata}}
instances thread-safe.
bq. customized versions of PipedReader and PipedWriter classes that work
concurrently
I'm not sure I understand. Perhaps you could describe the idea in more detail
either on the dev@ list or in a separate improvement issue.
> 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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