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From "Jesse Wilson (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HARMONY-6312) Concurrency problems in NIO
Date Mon, 28 Sep 2009 19:50:15 GMT

    [ https://issues.apache.org/jira/browse/HARMONY-6312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12760360#action_12760360
] 

Jesse Wilson commented on HARMONY-6312:
---------------------------------------



>From a quick glance, this microbenchmark doesn't appear to test changes to
the selected keys set. Since that's the reason for maintaining the indices,
it doesn't feel like a representative benchmark.

That said, the benchmark does show that iterating the full keyset has its
cost.



There's only one other caller, so I'd prefer to just fix that.




Cool, and I agree that compartmentalized changes are good. Applying and
diffing six patches just seemed labour-intensive for what I think of as one
logical change.


> Concurrency problems in NIO
> ---------------------------
>
>                 Key: HARMONY-6312
>                 URL: https://issues.apache.org/jira/browse/HARMONY-6312
>             Project: Harmony
>          Issue Type: Bug
>          Components: Classlib
>         Environment: SVN Revision: 801399
>            Reporter: Jesse Wilson
>            Assignee: Regis Xu
>         Attachments: cancelledkey.diff, harmony_svn.html, harmony_svn_plus_patch_2009-08-19.html,
NIO_Concurrency_issues.patch, ri.html, selector.zip, SelectorBenchmark.java
>
>   Original Estimate: 72h
>  Remaining Estimate: 72h
>
> There's several potential concurrency problems in our NIO implementation...
>  - Charset#isSupported isn't synchronized, but it accesses mutable member cachedCharsetTable.
>  - In SelectionKeyImpl, stHash++ is a non-atomic operation so multiple SelectionKey instances
may receive the same hash code. (Why not use the default hash code?)
>  - In SelectorImpl, the unmodifiableKeys member is never synchronized on. But the documentation
specifies that clients can synchronize on that set to guard against changes
> These are the obvious problems; I suspect there are more subtle concurrency defects at
play here. I'll prepare a patch to address the major issues, and we should consider a rigorous
approach (Findbugs?) to discover concurrency problems.
> #Android

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