"Expected state to be %s, but it was %s",
        oldState,
        newState);
  }

  private boolean compareAndUpdateState(State oldState, State newState) {
    return state.compareAndSet(oldState, newState);
  }

  // TODO(dpb): Should we use a pair of ArrayLists instead of an IdentityHashMap?
  private static final class CloseableList extends IdentityHashMap<AutoCloseable, Executor>