private void closeSocket() {
    IOUtils.closeStream(out);
    IOUtils.closeStream(in);
    IOUtils.closeSocket(socket);
    out = null;
    in = null;
    socket = null;
  }
Initiates a call by sending the parameter to the remote server. Note: this is not called from
the Connection thread, but by other threads.
@see #readResponse()
hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/BlockingRpcConnection.java