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https://issues.apache.org/jira/browse/HADOOP-12909?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15203039#comment-15203039
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Tsz Wo Nicholas Sze commented on HADOOP-12909:
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> ... Is there any cleaner way to do it?
The reason of being implemented using ThreadLocal is that there are no easy
ways to get the ipc.Client object from the caller, say DFSClient. The
ipc.Client object is hidden very deep by Java
[Proxy|http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Proxy.html]
and the RpcEngine layer. If you could find some better ways to do it, please
kindly let us know.
> Change ipc.Client to support asynchronous calls
> -----------------------------------------------
>
> Key: HADOOP-12909
> URL: https://issues.apache.org/jira/browse/HADOOP-12909
> Project: Hadoop Common
> Issue Type: New Feature
> Components: ipc
> Reporter: Tsz Wo Nicholas Sze
> Assignee: Xiaobing Zhou
> Attachments: HADOOP-12909-HDFS-9924.000.patch,
> HADOOP-12909-HDFS-9924.001.patch, HADOOP-12909-HDFS-9924.002.patch,
> HADOOP-12909-HDFS-9924.003.patch
>
>
> In ipc.Client, the underlying mechanism is already supporting asynchronous
> calls -- the calls shares a connection, the call requests are sent using a
> thread pool and the responses can be out of order. Indeed, synchronous call
> is implemented by invoking wait() in the caller thread in order to wait for
> the server response.
> In this JIRA, we change ipc.Client to support asynchronous mode. In
> asynchronous mode, it return once the request has been sent out but not wait
> for the response from the server.
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