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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4522) LightWeightGSet expects incrementing a volatile to be atomic
Date Wed, 27 Feb 2013 21:17:13 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4522?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13588769#comment-13588769
] 

Hadoop QA commented on HDFS-4522:
---------------------------------

{color:red}-1 overall{color}.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12571252/HDFS-4522.002.patch
  against trunk revision .

    {color:green}+1 @author{color}.  The patch does not contain any @author tags.

    {color:red}-1 tests included{color}.  The patch doesn't appear to include any new or modified
tests.
                        Please justify why no new tests are needed for this patch.
                        Also please list what manual steps were performed to verify this patch.

    {color:green}+1 javac{color}.  The applied patch does not increase the total number of
javac compiler warnings.

    {color:green}+1 javadoc{color}.  The javadoc tool did not generate any warning messages.

    {color:green}+1 eclipse:eclipse{color}.  The patch built with eclipse:eclipse.

    {color:green}+1 findbugs{color}.  The patch does not introduce any new Findbugs (version
1.3.9) warnings.

    {color:green}+1 release audit{color}.  The applied patch does not increase the total number
of release audit warnings.

    {color:green}+1 core tests{color}.  The patch passed unit tests in hadoop-hdfs-project/hadoop-hdfs.

    {color:green}+1 contrib tests{color}.  The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-HDFS-Build/4013//testReport/
Console output: https://builds.apache.org/job/PreCommit-HDFS-Build/4013//console

This message is automatically generated.
                
> LightWeightGSet expects incrementing a volatile to be atomic
> ------------------------------------------------------------
>
>                 Key: HDFS-4522
>                 URL: https://issues.apache.org/jira/browse/HDFS-4522
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 2.0.4-beta
>            Reporter: Colin Patrick McCabe
>            Assignee: Colin Patrick McCabe
>            Priority: Minor
>         Attachments: HDFS-4522.001.patch, HDFS-4522.002.patch
>
>
> LightWeightGSet uses a volatile integer to track the current modification number (kind
of an epoch number).
> Unfortunately, it includes code like this, that increments this volatile int:
> {code}
>      //insert the element to the head of the linked list
>      modification++;
>      size++;
> {code}
> The bug here is that in between reading the value of modification, incrementing it, and
storing it back in the variable, another thread may have modified it.  This could lead to
lost updates.
> We should use {{AtomicInteger}} for these cases.

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