}
        return null;
      }

      @Override
      public @Nullable V remove(@Nullable Object key) {
        V value = get(key);
        if (value != null) {
          // it's definitely in the map, so the cast and requireNonNull are safe
          @SuppressWarnings("unchecked")
          Range<K> range = (Range<K>) requireNonNull(key);
          TreeRangeMap.this.remove(range);
          return value;

    // all values are lower or higher than centerFloor, in which case we find the two highest or
    // lowest respectively). If centerFloor is in allRequired, we will definitely find it. If not,
    // but centerFloor + 1 is, we'll definitely find that. The closest value to the true (unrounded)
    // center will be at either low or high.
    int low = requiredFrom;
    int high = requiredTo;
    while (high > low + 1) {

    return file(new File(first), more);
  }

  /** Returns a {@code File} object for the given path parts. */
  private static File file(File first, String... more) {
    // not very efficient, but should definitely be correct
    File file = first;
    for (String name : more) {
      file = new File(file, name);
    }
    return file;
  }

    return file(new File(first), more);
  }

  /** Returns a {@code File} object for the given path parts. */
  private static File file(File first, String... more) {
    // not very efficient, but should definitely be correct
    File file = first;
    for (String name : more) {
      file = new File(file, name);
    }
    return file;
  }

          // getDeclaredField to throw a NoSuchFieldException when the field is definitely there.
          // For these users fallback to a suboptimal implementation, based on synchronized. This
          // will be a definite performance hit to those users.
          thrownAtomicReferenceFieldUpdaterFailure = atomicReferenceFieldUpdaterFailure;

          // getDeclaredField to throw a NoSuchFieldException when the field is definitely there.
          // For these users fallback to a suboptimal implementation, based on synchronized. This
          // will be a definite performance hit to those users.
          thrownAtomicReferenceFieldUpdaterFailure = atomicReferenceFieldUpdaterFailure;

        return false;
      }
    }

    @Override
    int indexOf(@Nullable Object target) {
      if (contains(target)) {
        @SuppressWarnings("unchecked") // if it's contained, it's definitely a C
        C c = (C) requireNonNull(target);
        long total = 0;
        for (Range<C> range : ranges) {
          if (range.contains(c)) {

   * isn't guaranteed to expose the issue, but it is at least likely to become flaky if the race
   * sneaks back in, and in this case flaky means something is definitely wrong.
   *
   * <p>Before the bug was fixed this test would fail at least 30% of the time.
   */
  public void testTransitionRace() throws TimeoutException {
    for (int k = 0; k < 1000; k++) {

  //    (hypothetical) unsafe read by our caller. Note: adding 'volatile' does not fix this issue,
  //    it would just add an edge such that if done() observed non-null, then it would also
  //    definitely observe all earlier writes, but we still have no guarantee that done() would see
  //    the initial write (just stronger guarantees if it does).
  //

           */
          for (int i = 2; i <= k; i++, n--) {
            if (numeratorBits + nBits < Long.SIZE - 1) {
              // It's definitely safe to multiply into numerator and denominator.
              numerator *= n;
              denominator *= i;
              numeratorBits += nBits;
            } else {