code: private String hashKeyForDisk(LoaderRequest request) {
          String key = request.getCacheKey();
  
          // We don't except to have a lot of threads
          // so it's okay to synchronize access
          synchronized (hasher) {
              return hasher.hash(key);
          }
      }
docs: A hashing method that changes a string (like a URL) into a hash suitable
  for using as a disk filename.