code: def _install_signal_handler(self, signal_number, signal_name):
      
      old_signal_handler = None  # set below
      def handler(handled_signal_number, frame):
        # In case we catch this signal again while running atexit
        # handlers, take the hint and actually die.
        signal.signal(signal_number, signal.SIG_DFL)
        sys.stderr.write("TensorBoard caught %s; exiting...\n" % signal_name)
        # The main thread is the only non-daemon thread, so it suffices to
        # exit hence.
        if old_signal_handler not in (signal.SIG_IGN, signal.SIG_DFL):
          old_signal_handler(handled_signal_number, frame)
        sys.exit(0)
      old_signal_handler = signal.signal(signal_number, handler)
docs: Set a signal handler to gracefully exit on the given signal.
  
      When this process receives the given signal, it will run `atexit`
      handlers and then exit with `0`.
  
      Args:
        signal_number: The numeric code for the signal to handle, like
          `signal.SIGTERM`.
        signal_name: The human-readable signal name.