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From "Ramkumar Vadali (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1257) Race condition introduced by HADOOP-5124
Date Wed, 23 Jun 2010 21:21:51 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1257?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12881884#action_12881884
] 

Ramkumar Vadali commented on HDFS-1257:
---------------------------------------

I am quite sure it is not a case of modifying while iterating over the collection. ConcurrentModificationException
is typically seen when a collection is modified while iterating on it,but that is not the
case here. This is a case of two threads actually performing read/write without protection.
The collection is not guaranteed to catch the multi-threaded case, but I have seen it happen.


> Race condition introduced by HADOOP-5124
> ----------------------------------------
>
>                 Key: HDFS-1257
>                 URL: https://issues.apache.org/jira/browse/HDFS-1257
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: name-node
>            Reporter: Ramkumar Vadali
>
> HADOOP-5124 provided some improvements to FSNamesystem#recentInvalidateSets. But it introduced
unprotected access to the data structure recentInvalidateSets. Specifically, FSNamesystem.computeInvalidateWork
accesses recentInvalidateSets without read-lock protection. If there is concurrent activity
(like reducing replication on a file) that adds to recentInvalidateSets, the name-node crashes
with a ConcurrentModificationException.

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