end of 17/03
finish coding and tested Test2
starting with sync for calls : ensure, no matter how many threads on client, a connection sends calls sync; recv res sync.
change connection.calls from queue to map
end of 24 Mar. To figure out the slowness
a single client process, when connect to a server, it will queue calls to that server from all threads. there is a single queue for a connection. each client process has only 1 client obj, stored in ClientCache