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From "Eric Tschetter (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (CURATOR-21) PathChildrenCache consumes an entire thread all the time no matter what
Date Fri, 03 May 2013 16:46:15 GMT

     [ https://issues.apache.org/jira/browse/CURATOR-21?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Eric Tschetter updated CURATOR-21:
----------------------------------

    Attachment: CURATOR-21-Fix_watcher_race.patch

Attaching another patch to fix a slight bug with the changes introduced here.

Allowing the executor to queue up tasks has introduced a race condition in which.  Specifically,
if the PathChildrenCache is set to watch for data changes, after the PathChildrenCache has
been closed the dataWatcher will stay registered on the various paths ('cause ZK is awesome
like that) and, when changes happen to those paths, the watcher will fire and try to submit
Runnables to the closed ExecutorService.  This results in RejectedExecutionExceptions showing
up in the logs, there is actually nothing functionally wrong with this other than that it
scares people who don't know what is going on.

This patch fixes it so that it will not generate those exceptions anymore.
                
> PathChildrenCache consumes an entire thread all the time no matter what
> -----------------------------------------------------------------------
>
>                 Key: CURATOR-21
>                 URL: https://issues.apache.org/jira/browse/CURATOR-21
>             Project: Apache Curator
>          Issue Type: Bug
>          Components: Recipes
>    Affects Versions: 2.0.0
>            Reporter: Eric Tschetter
>            Assignee: Jordan Zimmerman
>         Attachments: CURATOR-21-docs.patch, CURATOR-21-Fix_watcher_race.patch, CURATOR-21.patch
>
>
> PathChildrenCache currently takes an Executor, but only to fire off a Runnable that does
a blocking while loop waiting for work.  This means that you must have one thread per PathChildrenCache,
which is not that great.
> PathChildrenCache should just use the Executor's work queuing mechanism to enqueue work
items instead of maintaining its own work queue mechanism.

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