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>
      implements Closeable {
    private final DeferredCloser closer = new DeferredCloser(this);
    private volatile boolean closed;

    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>
      implements Closeable {
    private final DeferredCloser closer = new DeferredCloser(this);
    private volatile boolean closed;