[jira] [Created] (COMPRESS-357) BZip2CompressorOutputStream can affect output stream incorrectly

["Richard Shapiro (JIRA)" <ji...@apache.org>]

Richard Shapiro created COMPRESS-357:
----------------------------------------

             Summary: BZip2CompressorOutputStream can affect output stream incorrectly
                 Key: COMPRESS-357
                 URL: https://issues.apache.org/jira/browse/COMPRESS-357
             Project: Commons Compress
          Issue Type: Bug
          Components: Compressors
    Affects Versions: 1.11, 1.9
         Environment: multithreaded
            Reporter: Richard Shapiro


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. 





--
This message was sent by Atlassian JIRA
(v6.3.4#6332)