newHead.execute();
          return;
        }
        // Try to make newHead the new head of the stack at runnables.
        newHead.next = oldHead;
      } while (!UNSAFE.compareAndSwapObject(this, HEAD_OFFSET, oldHead, newHead));
    }

    public void execute() {
      RunnableExecutorPair stack;
      do {
        stack = head;
        if (stack == null) {

          newHead.execute();
          return;
        }
        // Try to make newHead the new head of the stack at runnables.
        newHead.next = oldHead;
      } while (!UNSAFE.compareAndSwapObject(this, HEAD_OFFSET, oldHead, newHead));
    }

    public void execute() {
      RunnableExecutorPair stack;
      do {
        stack = head;
        if (stack == null) {

      return UNSAFE.compareAndSwapObject(future, WAITERS_OFFSET, expect, update);
    }

    /** Performs a CAS operation on the {@link #listeners} field. */
    @Override
    boolean casListeners(AbstractFuture<?> future, @CheckForNull Listener expect, Listener update) {
      return UNSAFE.compareAndSwapObject(future, LISTENERS_OFFSET, expect, update);
    }