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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3818) Not possible to access a FileSystem from within a ShutdownHook
Date Mon, 28 Jul 2008 17:13:32 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3818?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12617477#action_12617477
] 

Tsz Wo (Nicholas), SZE commented on HADOOP-3818:
------------------------------------------------

> What we want to do here is simply close our output stream before exiting so that data
isn't lost. 

We already have automatic files closing during shutdown.  It is done by the FileSystem shutdown
hook.

> Not possible to access a FileSystem from within a ShutdownHook
> --------------------------------------------------------------
>
>                 Key: HADOOP-3818
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3818
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: fs
>    Affects Versions: 0.17.1
>            Reporter: Rowan Nairn
>            Priority: Minor
>
> FileSystem uses addShutdownHook to close all FileSystems at exit.  This makes it impossible
to access a FileSystem from within your own ShutdownHook threads, say for deleting incomplete
output.  Using a pre-existing FileSystem object is unsafe since it may be closed by the time
the thread executes.  Using FileSystem.get(...) results in an exception:
> Exception in thread "Thread-10" java.lang.IllegalStateException: Shutdown in progress
> 	at java.lang.Shutdown.add(Shutdown.java:81)
> 	at java.lang.Runtime.addShutdownHook(Runtime.java:190)
> 	at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:1293)
> 	at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:203)
> 	at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:108)

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