[jira] Commented: (HADOOP-3818) Not possible to access a FileSystem from within a ShutdownHook

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

    [ https://issues.apache.org/jira/browse/HADOOP-3818?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12616356#action_12616356 ] 

Ankur commented on HADOOP-3818:
-------------------------------

We faced the same issue and the workaround that we did was to register a SIGNAL handler in the application code that would re
cieve a the TERM signal before shutdown hooks are invoked. However this introduces a dependency on Sun's misc package which generates a compiler warning stating the package might be de-supported in Sun's JDK.

I think a better solution would be for FileSystem to expose an API to register application cleanup code and guarantee that the code is invoked ahead of the code in 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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