* execution of tasks will stop until a call to this method is made.
   */
  @Override
  public void execute(Runnable task) {
    checkNotNull(task);
    Runnable submittedTask;
    long oldRunCount;
    synchronized (queue) {
      // If the worker is already running (or execute() on the delegate returned successfully, and
      // the worker has yet to start) then we don't need to start the worker.