[jira] Commented: (HADOOP-5933) Make it harder to accidentally close a shared DFSClient

["Steve Loughran (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-5933?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12714027#action_12714027 ] 

Steve Loughran commented on HADOOP-5933:
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Some options
# if the log is at debug level, generate an exception in close() and save it until the next checkOpen() call is reached -and use that exception as the nested cause of the exception that is raised there.
# some complicated reference count mechanism with its own leakage problems
# add the ability to reopen things if they were in cache and got purged. 

I've done the first one of these to track down problems, and while I now know where I shouldn't be calling close(), there's a risk that my code will now leak filesystem clients. 

> Make it harder to accidentally close a shared DFSClient
> -------------------------------------------------------
>
>                 Key: HADOOP-5933
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5933
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: fs
>    Affects Versions: 0.21.0
>            Reporter: Steve Loughran
>            Priority: Minor
>
> Every so often I get stack traces telling me that DFSClient is closed, usually in {{org.apache.hadoop.hdfs.DFSClient.checkOpen() }} . The root cause of this is usually that one thread has closed a shared fsclient while another thread still has a reference to it. If the other thread then asks for a new client it will get one -and the cache repopulated- but if has one already, then I get to see a stack trace. 
> It's effectively a race condition between clients in different threads. 

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