[jira] [Commented] (HADOOP-15639) Classloader issue with hadoop cmd -libjars option

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

    [ https://issues.apache.org/jira/browse/HADOOP-15639?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16597575#comment-16597575 ] 

Qinghui Xu commented on HADOOP-15639:
-------------------------------------

Here is a patch to fix it: https://github.com/criteo-forks/hadoop-common/pull/87/commits/da6fdfa53410906068383550b6214b7a81344083

> Classloader issue with hadoop cmd -libjars option 
> --------------------------------------------------
>
>                 Key: HADOOP-15639
>                 URL: https://issues.apache.org/jira/browse/HADOOP-15639
>             Project: Hadoop Common
>          Issue Type: Bug
>            Reporter: Qinghui Xu
>            Priority: Major
>
> '-libjars' option gives the possibility to add extra libraries in a hadoop command by providing a custom URLClassLoader to fetch jars regarding to the option.
> The classloader is provided to both hadoop Configuration and the main thread's context classloader, so that when calling Configuration#getClass or using Class.forName the class can be loaded by the URLClassLoader.
> But two instances of URLClassLoader are provided to Configuration and to thread context classloader respectively, which makes a same class possible to be loaded twice by two classloaders. And class loaded by different classloaders is considered different.
> So the following assertion will fail:
> {code:java}
> // CustomFileSystem is provided by -libjars option
> Class<?> clazz1 = conf.getClass("CustomFileSystem");
> Class<?> clazz2 = Class.forName("CustomFileSystem");
> // The two classes are different
> assert clazz1 == clazz2{code}



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