code: func (t *TimestampCollector) Collect(ch chan<- prometheus.Metric) {
  	// New map to dedup filenames.
  	uniqueFiles := make(map[string]float64)
  	t.lock.RLock()
  	for fileSD := range t.discoverers {
  		fileSD.lock.RLock()
  		for filename, timestamp := range fileSD.timestamps {
  			uniqueFiles[filename] = timestamp
  		}
  		fileSD.lock.RUnlock()
  	}
  	t.lock.RUnlock()
  	for filename, timestamp := range uniqueFiles {
  		ch <- prometheus.MustNewConstMetric(
  			t.Description,
  			prometheus.GaugeValue,
  			timestamp,
  			filename,
  		)
  	}
  }
docs: // Collect creates constant metrics for each file with last modified time of the file.