private void closeConn(IOException e) {
    if (thread == null) {
      return;
    }
    thread.interrupt();
    thread = null;
    closeSocket();
    if (callSender != null) {
      callSender.cleanup(e);
    }
    for (Call call : calls.values()) {
      call.setException(e);
    }
    calls.clear();
  }
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