HADOOP-10389, you made a comment that we should set call id rather than just using 0 everywhere. I implemented this in version #5 of this patch.
I think the comment was this:
1. to my understanding, rpc client should have a map<callid, call> to record all unfinished calls, but I could not find any code assigning callids(only make them 0) and manage unfinished calls, could you help me located those logic?
We don't need a map here, since we can only have one call ID in flight at once (the server doesn't yet support this). In the future, this might change, but for now, it's OK just to check that the call ID we got in the response was the same as the call ID we made in the request.