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From "Aaron T. Myers (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-7888) TestFailoverProxy fails intermittently on trunk
Date Wed, 07 Dec 2011 21:42:40 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7888?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13164735#comment-13164735
] 

Aaron T. Myers commented on HADOOP-7888:
----------------------------------------

Thanks a lot for tracking down this issue and providing a patch, Jason.

A question for you about testing - given that this test would only fail intermittently before,
have you tried running this test in a loop with and without the patch applied to *ensure*
that the patch addresses the issue? I believe it should fix it, but just want to make sure.
Also, can you comment on the frequency with which you'd observe this spurious test failure
without the patch?

The patch looks good to me. I'll commit it once Jason comments on the above question.
                
> TestFailoverProxy fails intermittently on trunk
> -----------------------------------------------
>
>                 Key: HADOOP-7888
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7888
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: test
>    Affects Versions: 0.24.0
>            Reporter: Jason Lowe
>            Assignee: Jason Lowe
>         Attachments: hadoop-7888.patch
>
>
> TestFailoverProxy can fail intermittently with the failures occurring in testConcurrentMethodFailures().
 The test has a race condition where the two threads may be sequentially invoking the unreliable
interface rather than concurrently.  Currently the proxy provider's getProxy() method contains
the thread synchronization to enforce a concurrent invocation, but examining the source to
RetryInvocationHandler.invoke() shows that the call to getProxy() during failover is too late
to enforce a truly concurrent invocation.
> For this particular test, one thread could race ahead and block on the CountDownLatch
in getProxy() before the other thread even enters RetryInvocationHandler.invoke().  If that
happens the second thread will cache the newly updated value for proxyProviderFailoverCount,
since the failover has mostly been processed by the original thread.  Therefore the second
thread ends up assuming no other thread is present, performs a failover, and the test fails
because two failovers occurred instead of one.

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