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From "Sebb (JIRA)" <>
Subject [jira] [Commented] (COMPRESS-357) BZip2CompressorOutputStream can affect output stream incorrectly
Date Fri, 10 Jun 2016 23:33:21 GMT


Sebb commented on COMPRESS-357:

As mentioned on the mailing list, it's tricky to get finalize working properly.

Rather than try to fix up bad code, maybe the finalize method should just report if it detects
failure to close the resource.
[It should report unclosed resources anyway.]

Also, are there any use-cases where the app code deliberately does not want to close the resource?

> BZip2CompressorOutputStream can affect output stream incorrectly
> ----------------------------------------------------------------
>                 Key: COMPRESS-357
>                 URL:
>             Project: Commons Compress
>          Issue Type: Bug
>          Components: Compressors
>    Affects Versions: 1.9, 1.11
>         Environment: multithreaded
>            Reporter: Richard Shapiro
>              Labels: easyfix
>             Fix For: 1.12
>   Original Estimate: 1h
>  Remaining Estimate: 1h
> BZip2CompressorOutputStream has an unsynchronized finished() method, and an unsynchronized
finalize method. Finish checks to see if the output stream is null, and if it is not it calls
various methods, some of which write to the output stream. 
> Now, consider something like this sequence.
> BZip2OutputStream s = ...
> ...
> s.close();
> s = null;
> After the s = null, the stream is garbage. At some point the garbage collector call finalize(),
which calls finish(). But, since the GC may be on a different thread, there is no guarantee
that the assignment this.out = null in finish() has actually been made visible to the GC thread,
which results in bad data in the output stream.
> This is not a theoretical problem; In a part of a large project I'm working on, this
happens about 2% of the time. 
> The fixes are simple
> 1) synchronize finish() or
> 2) don't call finish from finalize().
> A workaround is to derive a class and override the finalize() method. 

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