@Override
  protected void doCall() {
    ClientService.Interface stub;
    try {
      stub = this.conn.getRegionServerStub(serverName);
    } catch (IOException e) {
      onError(e, () -> "Get async admin stub to " + serverName + " failed", err -> {
      });
      return;
    }
    resetCallTimeout();
    addListener(callable.call(controller, stub), (result, error) -> {
      if (error != null) {
        onError(error, () -> "Call to admin stub failed", err -> {
        });
        return;
      }
      future.complete(result);
    });
  }
Retry caller for a request call to region server. Now only used for coprocessor call to region
server.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncServerRequestRpcRetryingCaller.java