#vulnerable code 
                              void stop() {
    if (stopped.compareAndSet(false, true)) {
      stopChildren();

//      suspended.reset();

//      stowage.reset();

      mailbox.close();
    }
  } 
                            #location 3 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                              void addChild(final Actor child) {
    children.add(child);
  }