code: synchronized public void notifyFrameThreadExit(FrameThread ft) {
      frameThreadMap.remove(ft);
      inactiveFrameThreads.add(ft);
      startFrameThreads();
    }
docs: Notify this manager that a FrameThread has ended it's run() method,
  returning the FrameThread object to the manager for use in future Threads.
  
  @param ft FrameThread object which is ending.