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;
        if (curr.thread != null) { // we aren't unlinking this node, update pred.
          pred = curr;
        } else if (pred != null) { // We are unlinking this node and it has a predecessor.

    checkNotNull(future);

    // If this future is already cancelled, cancel the delegate.
    // TODO(cpovirk): Should we do this at the end of the method, as in the server version?
    // TODO(cpovirk): Use maybePropagateCancellationTo?
    if (isCancelled()) {
      future.cancel(mayInterruptIfRunning);
    }

    if (!state.permitsPublicUserToTransitionTo(State.DELEGATED)) {
      return false;