}
          oldHead = waitersField; // re-read and loop.
        } while (oldHead != Waiter.TOMBSTONE);
      }
      // re-read valueField, if we get here then we must have observed a TOMBSTONE while trying to
      // add a waiter.
      // requireNonNull is safe because valueField is always set before TOMBSTONE.
      return getDoneValue(requireNonNull(valueField));
    }

          }
          oldHead = waitersField; // re-read and loop.
        } while (oldHead != Waiter.TOMBSTONE);
      }
      // re-read valueField, if we get here then we must have observed a TOMBSTONE while trying to
      // add a waiter.
      // requireNonNull is safe because valueField is always set before TOMBSTONE.
      return getDoneValue(requireNonNull(valueField));
    }

  void setUp() throws Exception {
    if (state != State.NOT_DONE && (numListeners != 0 || numThreads != 0)) {
      throw new SkipThisScenarioException();
    }
  }

  // This exclusion doesn't exclude the TOMBSTONE objects we set. So 'done' NEW futures will look
  // larger than they are.
  @SuppressWarnings("FutureReturnValueIgnored")
  @Footprint(exclude = {Runnable.class, Executor.class, Thread.class, Exception.class})