Github user dlmarion commented on the issue:
https://github.com/apache/accumulo/pull/113
@madrob Here is what is basically what's happening:
The ServiceLoader thread looks in the classpath for services files for
classes implementing the KeywordExecutable interface. When it finds them, it
tries to load the class, using Class.forName. Since the classloader is the
VFSClassLoader and the files are in HDFS, it uses the DFS client code to
retrieve the associated object. The DFS client, in another thread, is
performing RPC calls to retrieve the object. During the processing of a
response (1st call stack in the JIRA), it attempts to load some classes, using
Class.forName. Class.forName acquires a lock on the ClassLoader, which is the
root of the problem. The solution here is to attempt to preload the classes
that the DFS Client is going to load.
I will clean up the code, address the findbugs issues, and try to backport
to 1.7.2 tomorrow.
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