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From "Christoph Ludwig (JIRA)" <>
Subject [jira] [Created] (COMPRESS-446) Resource Leak in ParallelScatterZipCreator#writeTo(ZipArchiveOutputStream)
Date Sat, 17 Mar 2018 20:25:00 GMT
Christoph Ludwig created COMPRESS-446:

             Summary: Resource Leak in ParallelScatterZipCreator#writeTo(ZipArchiveOutputStream)
                 Key: COMPRESS-446
             Project: Commons Compress
          Issue Type: Bug
          Components: Archivers
    Affects Versions: 1.16.1
         Environment: The application was running inside a Docker container, the JVM had about
1.7 GByte heap space.
            Reporter: Christoph Ludwig

Before it does anything else, {{ParallelScatterZipCreator#writeTo(ZipArchiveOutputStream)}}
loops over all futures returned by the creator`s executor service and calls {{Future#get()}}.
This will block until the future's computation is completed, respectively - i.e., until all
entries have been written to the thread-local scatter streams.

However, if the computation of a future fails, then {{Future#get()}} can also throw an exception.
This exception escapes {{ParallelScatterZipCreator#writeTo(ZipArchiveOutputStream)}} before
the executor service is shut down. The latter means that also the thread-local variables in
the executor service's threads and all objects referenced by them continue to exist and cannot
be reclaimed by the GC.

I encountered this situation when - while processing an archive with 130,000 documents - the
JVM threw an {{OutOfMemoryError}}. The application was not able to recover from this OOM error
because most of the heap was occupied by objects reachable from the executor service's threads.

Of course, the OOM is mostly the fault of my own code; I will be able to work around the "leaked"
executor service because I supply it in the first place and can therefore shut it down if
I detect an error situation.  

The effect would be the same, though, if, say, {{Future#get()}} throws an {{InterruptedException}}.
Therefore, {{ParallelScatterZipCreator#writeTo(ZipArchiveOutputStream)}}  should either shut
down and release all resources if it cannot complete its task due to an Exception thrown by
a future or it should offer a reasonable recovery strategy. 

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