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https://issues.apache.org/jira/browse/HADOOP-7607?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13116916#comment-13116916
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Aaron T. Myers commented on HADOOP-7607:
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OK, I've looked into this issue quite a bit. The thing that surprised me about
Uma's description of the problem is that the proxy object (like all Objects)
should have an implementation of {{toString()}}, so I was surprised that
anything would throw a {{noSuchMethodException}}. For that matter, note that
the last line of the stack trace Uma posted references
{{RetryInvocationHandler.java:70}}, which is inside a catch clause which only
gets reached if the method invocation fails. I was obviously surprised that a
call to {{toString()}} would throw an exception. :)
Turns out this happens because {{RetryInvocationHandler.invoke}} assumes that
the interface implemented by the proxy declares all the methods which get
invoked on it. This is done to check for the {{@Idempotent}} annotation on the
method, and this is what throws the {{NoSuchMethodException}}. The reason the
call to {{toString()}} throws an exception is because the underlying
{{WritableRpcEngine}} checks for the declaring class's ({{Object}}'s)
{{versionID}} field, which obviously doesn't exist on {{Object}}.
So, this patch doesn't really introduce the issue, except to cause
{{toString()}} to be potentially called on an implementation of
{{ClientProtocol}}. Ideally we would do something to allow the calling of
{{toString()}} on RPC proxy objects without weird exceptions, but that seems
like it's beyond the scope of this JIRA. I'll file a separate one to address
the issue of calling {{toString}} on a proxy object. The patch Uma supplied
won't quite work as-is, since the {{proxy}} and {{invocationHandler}} objects
can't be assumed to be non-null, but it's close. I'll file a separate JIRA to
get this addressed as well.
> Simplify the RPC proxy cleanup process
> --------------------------------------
>
> Key: HADOOP-7607
> URL: https://issues.apache.org/jira/browse/HADOOP-7607
> Project: Hadoop Common
> Issue Type: Improvement
> Components: ipc
> Affects Versions: 0.24.0
> Reporter: Aaron T. Myers
> Assignee: Aaron T. Myers
> Fix For: 0.24.0
>
> Attachments: HADOOP-7607.2.patch, hadoop-7607.0.patch,
> hadoop-7607.1.patch
>
>
> The process to clean up an RPC proxy object is to call RPC.stopProxy, which
> looks up the RPCEngine previously associated with the interface which that
> proxy object provides and calls RPCEngine.stopProxy passing in the proxy
> object. Every concrete implementation of RPCEngine.stopProxy then looks up
> the invocation handler associated with the proxy object and calls close() on
> that invocation handler.
> This process can be simplified by cutting out the steps of looking up the
> previously-registered RPCEngine, and instead just having RPC.stopProxy
> directly look up the invocation handler for the proxy object and call close()
> on it.
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