code: Path getCache(Path hdfsPath) {
      CacheEntry c = cacheMap.get(hdfsPath);
      localMetrics.numGetAttempts++;
      if (c != null) {
        // update the accessTime before returning to caller
        c.setGenstamp(globalStamp.incrementAndGet());
        localMetrics.numGetHits++;
        return c.localPath;
      }
      return null; // not in cache
    }
docs: Maps the hdfs pathname to a local pathname. Returns null
  if this is not found in the cache.