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http://issues.apache.org/jira/browse/HADOOP-217?page=comments#action_12413905 ]
Doug Cutting commented on HADOOP-217:
-------------------------------------
I think this has been fixed, no?
The problem is that, when we modified Hadoop to use a classloader the writable
factory stuff partially broke. In particular, one can now obtain a reference
to a Class instance when the static initializers of that class have not yet
been run. In particular, the RPC code calls something like
'WritableFactories.newInstance(ClassLoader.findClass("foo.bar.Baz")), and
foo.bar.Baz's static initializer, which registers the writable factory, has not
yet run, and the call to newInstance fails as above. The work-around we've
been using thus far is to, in the RPC client code, add a 'static { new Baz();
}' to force the static initializers of Baz to run. Long-term we should find a
better solution.
We'd like to be able to pass objects in RPCs that are not public classes. This
means that the RPC code needs to be able to construct an instance. The
WritableFactory mechanism was created to solve this, but, as described above,
it mysteriously broke when we stopped using the bootstrap classloader.
> IllegalAcessException when creating a Block object via WritableFactories
> ------------------------------------------------------------------------
>
> Key: HADOOP-217
> URL: http://issues.apache.org/jira/browse/HADOOP-217
> Project: Hadoop
> Type: Bug
> Components: dfs
> Versions: 0.3
> Reporter: Hairong Kuang
> Assignee: Hairong Kuang
> Fix For: 0.4
> Attachments: access.patch
>
> When I ran the dfs namenode, I received an error message listed below.
> Changing Block class to be public will be able to fix the problem.
> java.lang.RuntimeException: java.lang.IllegalAccessException: Class
> org.apache.hadoop.io.WritableFactories can not access a member of class
> org.apache.hadoop.dfs.Block with modifiers "public"
> java.lang.RuntimeException: java.lang.IllegalAccessException: Class
> org.apache.hadoop.io.WritableFactories can not access a member of class
> org.apache.hadoop.dfs.Block with modifiers "public"
> at
> org.apache.hadoop.io.WritableFactories.newInstance(WritableFactories.java:49)
> at
> org.apache.hadoop.io.ObjectWritable.readObject(ObjectWritable.java:226)
> at
> org.apache.hadoop.io.ObjectWritable.readObject(ObjectWritable.java:163)
> at
> org.apache.hadoop.io.ObjectWritable.readObject(ObjectWritable.java:211)
> at org.apache.hadoop.ipc.RPC$Invocation.readFields(RPC.java:88)
> at org.apache.hadoop.ipc.Server$Connection.run(Server.java:154)
> Caused by: java.lang.IllegalAccessException: Class
> org.apache.hadoop.io.WritableFactories can not access a member of class
> org.apache.hadoop.dfs.Block with modifiers "public"
> at sun.reflect.Reflection.ensureMemberAccess(Reflection.java:65)
> at java.lang.Class.newInstance0(Class.java:344)
> at java.lang.Class.newInstance(Class.java:303)
> at
> org.apache.hadoop.io.WritableFactories.newInstance(WritableFactories.java:45)
> ... 5 more
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