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Date: Tue, 21 Dec 2010 17:18:01 -0500 (EST)
From: "tom pierce (JIRA)" <jira@apache.org>
To: common-issues@hadoop.apache.org
Subject: [jira] Updated: (HADOOP-7021) MapWritable NullPointerException
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     [ https://issues.apache.org/jira/browse/HADOOP-7021?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

tom pierce updated HADOOP-7021:
-------------------------------

    Attachment: HADOOP-7021.patch

I tidied the new test a bit, putting it into the current TestMapWritable class and using UTF8 as the "foreign class" instead of a one-off example Writable.

Hopefully Hudson will find this patch more digestible; I followed the submission guidelines except for building the tar, which proved cumbersome on CentOS.  

> MapWritable NullPointerException
> --------------------------------
>
>                 Key: HADOOP-7021
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7021
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: io
>    Affects Versions: 0.20.1
>         Environment: Hadoop 0.20.1, Centos
>            Reporter: John Lee
>            Priority: Minor
>             Fix For: 0.20.1
>
>         Attachments: AbstractMapWritable.diff, AbstractMapWritable.java, HADOOP-7021.patch, TestMapWritableNPE.java
>
>
> We have encountered a NullPointerException when we use MapWritable with custom Writable objects.
> The root cause is the counter newClasses in AbstractMapWritable is allowed to get out of sync with the id to class mapping tables when addToMap(Class) is called.  We have a patch to AbstractMapWritable.addToMap(Class) that handles the case when newClasses gets out of sync with the id to class mapping tables and adds a serialization optimization to minimize the number of class names to write out per MapWritable object.

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