class_docstr: Monitor a given trial inside a thread, updating its heartbeat
  at a given interval of time.
  
  Parameters
  ----------
  exp: Experiment
      The current Experiment.
docstr: Stop monitoring.
docstr_tok: ["Stop","monitoring","."]
code: def stop(self):
      """Stop monitoring."""
      self.stopped.set()
      self.join()
  
imports: import threading
label_desc: Use image node_id 2 for calling the TrialPacemaker obj's underlying member method code with example usage: obj.stop() without return types