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

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

Qinghui Xu created HADOOP-15639:
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             Summary: 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


'-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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