svoid cancelThread(Thread t) {
  if (t == null) ret;
  ping();
  ifndef LeanMode
  
  ifdef PingV3
    var ps = pingSource(t);
    if (ps == null)
      warn("No ping source for thread " + t + ", can't cancel");
    else
      ps.cancel();
  endifdef
  
  ifndef PingV3
    synchronized(ping_actions) {
      ping_actions.put(t, "cancelled");
      ping_anyActions = true;
    }
  endifndef
  
  endifndef
}