svoid cancelForeignThread(Thread t) {
  if (t == null) ret;
  O mc = getMainClassForThread(t);
  if (mc == null) ret with print("Can't find main class for thread " + t);
  ping();
  Map ping_actions = cast get(mc, 'ping_actions);
  if (ping_actions == null) ret with print("No ping_actions");
  synchronized(ping_actions) {
    ping_actions.put(t, "cancelled");
    set(mc, ping_anyActions := true);
    print("Cancelled foreign thread: " + t);
  }
}

svoid cancelForeignThread(long threadID) {
  cancelForeignThread(getThreadByID(threadID));
}

Began life as a copy of #1004549