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From "Josh Elser (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-1292) Tablet constructor can hang on vfs classloader, preventing tablets from loading
Date Thu, 22 Jan 2015 02:46:34 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-1292?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14286846#comment-14286846
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Josh Elser commented on ACCUMULO-1292:
--------------------------------------

Giving it a quick look (not nearly in the depth/context necessary):

Why the need to use a new thread to rebuild the classloader in either patch? It's possible
that I'm not understanding the problem entirely, though.

If you have multiple callers coming in that want to reload the classloader, you only want
one to do that reload, and then have the other callers use the result from the single caller
which actually updated the classloader. All of the callers try to race to reinitialize the
classloader, one wins and updates it, while the others wait for it to finish. In other words,
the ReadWriteLock and marking the VFSClassLoader as volatile or wrapping it in an AtomicReference
seems to me to provide all the concurrency control that you need. Did I misinterpret the problem?

> Tablet constructor can hang on vfs classloader, preventing tablets from loading
> -------------------------------------------------------------------------------
>
>                 Key: ACCUMULO-1292
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-1292
>             Project: Accumulo
>          Issue Type: Bug
>          Components: tserver
>    Affects Versions: 1.5.0, 1.6.0, 1.6.1
>            Reporter: John Vines
>            Assignee: Eric Newton
>             Fix For: 1.7.0, 1.6.3
>
>         Attachments: ACCUMULO-1292-using-locks.patch, ACCUMULO-1292.patch
>
>
> Taken from TODO from r1424106 regarding ACCUMULO-867. This is something that we should
at least look into more before 1.5 is released.



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