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https://issues.apache.org/jira/browse/HADOOP-5859?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12713180#action_12713180
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Kan Zhang edited comment on HADOOP-5859 at 5/26/09 11:24 AM:
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> Unless the variable is declared as "volatile", right?

I just checked, the JDK6 implementation of LinkedList didn't declare the "size" 
variable volatile. So Todd is right, a second thread may see a stale cached 
value (does anyone know how long the value will be cached by a thread, I hope 
it's not forever :)). In any case, this is a non-issue after my refactoring. In 
the refactored code, all accesses to dataQueue or ackQueue are sync'ed on 
dataQueue lock. 

      was (Author: kzhang):
    > Unless the variable is declared as "volatile", right?

I just checked, the JDK6 implementation of LinkedList didn't declare the "size" 
variable volatile. So Todd is right, a second thread may see a stale cached 
value (does anyone know how long the value will be cached a thread, I hope it's 
not forever :). In any case, this is a non-issue after my refactoring. In the 
refactored code, all accesses to dataQueue or ackQueue are sync'ed on dataQueue 
lock. 
  
> FindBugs : fix "wait() or sleep() with locks held" warnings in hdfs
> -------------------------------------------------------------------
>
>                 Key: HADOOP-5859
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5859
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>            Reporter: Kan Zhang
>            Assignee: Kan Zhang
>         Attachments: 5859-21.patch, 5859-22.patch, 5859-26.patch, 
> 5859-4.patch, 5859-5.patch, 5859-8.patch
>
>
> This JIRA fixes the following warnings:
> SWL   org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.closeInternal() calls 
> Thread.sleep() with a lock held
> TLW   wait() with two locks held in 
> org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.flushInternal()
> TLW   wait() with two locks held in 
> org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.flushInternal()
> TLW   wait() with two locks held in 
> org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.writeChunk(byte[], int, int, 
> byte[])

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