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Date: Mon, 7 Jul 2008 06:39:31 -0700 (PDT)
From: "Steve Loughran (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Updated: (HADOOP-3415) JobEndNotifier isnt synchronized,
 doesnt check state before acting
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     [ https://issues.apache.org/jira/browse/HADOOP-3415?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Steve Loughran updated HADOOP-3415:
-----------------------------------

    Attachment: hadoop-3415.patch

simple patch to fix a basic problem: the fact that a thread ref may be null during shutdown.

> JobEndNotifier isnt synchronized, doesnt check state before acting
> ------------------------------------------------------------------
>
>                 Key: HADOOP-3415
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3415
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>    Affects Versions: 0.19.0
>            Reporter: Steve Loughran
>            Priority: Minor
>         Attachments: hadoop-3415.patch
>
>
> JobEndNotifier is pretty hazardous inside.
> 1. the static startNotifier isnt synchronized, and doesnt check for being already running before it creates a new worker thread. It should be sycnhronized and a no-op if there is a live thread.
> 2. stopNotifier() should be a no-op if already stopped. It MUST NOT call thread.interrupt() in such a state, as thread may be null. 
> 3. the registerNotification method also assumes that the static queue is non null.
> Things would be a lot safer by making this class part of a JobTracker, not a singleton with static methods, as then you could more safely make assumptions about object state. This would not only eliminate a lot of reentrancy problems, but tie the life of the notifier to that of its owner, the JobTracker.

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