}

    void execute() {
      try {
        executor.execute(command);
      } catch (RuntimeException e) {
        log.log(
            Level.SEVERE,
            "RuntimeException while executing runnable " + command + " with executor " + executor,
            e);
      }
    }
  }

  private final class SetFuture implements Runnable {
    final ListenableFuture<? extends V> delegate;

  private void removeWaiter(Waiter node) {
    node.thread = null; // mark as 'deleted'
    restart:
    while (true) {
      Waiter pred = null;
      Waiter curr = waiters;
      if (curr == Waiter.TOMBSTONE) {
        return; // give up if someone is calling complete
      }
      Waiter succ;
      while (curr != null) {
        succ = curr.next;