Pinterest: Upgrading Java Operational Metrics 3

gauges.java

// Unoptimized
// list will not be garbage collected
// cumbersome instantiation
List<Integer> list = someList();
Stats.addGauge("metric_name", new Function0<Object>() {
  List<Integer> listRef = list;
  @Override
  public Double apply() {
    return (double) listRef.size();
  }
});

// Optimized
// Weak reference to the list is maintained
// list is returned from the gauge call, removes need for anonymous class
List<Object> list = Stats.gauge("metric_name", new ArrayList<>, l -> l.size());