code: private void checkInUseChunk(long p) {
      if (VALIDATING) {
        checkAnyChunk(p);
        if (!isInUse(p))
          throw new AssertionError("Chunk at " + p + " is not in use");
        if (!nextPreviousInUse(p))
          throw new AssertionError("Chunk after " + p + " does not see this chunk as in use");
        /* If not pinuse previous chunk has OK offset */
        if (!previousInUse(p) && nextChunk(prevChunk(p)) != p)
          throw new AssertionError("Previous chunk to " + p + " is marked free but has an incorrect next pointer");
      }
    }
docs: /* Check properties of inuse chunks