Counter

See Counter for the concept.

Counters are created using the Registry, which will be set up as part of application initialization. For example:

public class Queue {

  private final Counter insertCounter;
  private final Counter removeCounter;
  private final QueueImpl impl;

  @Inject
  public Queue(Registry registry) {
    insertCounter = registry.counter("queue.insert");
    removeCounter = registry.counter("queue.remove");
    impl = new QueueImpl();
  }

Then call increment when an event occurs:

  public void insert(Object obj) {
    insertCounter.increment();
    impl.insert(obj);
  }

  public Object remove() {
    if (impl.nonEmpty()) {
      removeCounter.increment();
      return impl.remove();
    } else {
      return null;
    }
  }

Optionally, an amount can be passed in when calling increment. This is useful when a collection of events happen together.

  public void insertAll(Collection<Object> objs) {
    insertCounter.increment(objs.size());
    impl.insertAll(objs);
  }
}

Batch Updates

For very high-volume updates within a single thread, Counter exposes a batchUpdater that buffers updates and flushes them as a single operation. The trade-off is that updates are delayed by up to batchSize events before they appear on the underlying counter.

try (Counter.BatchUpdater updater = insertCounter.batchUpdater(1000)) {
  for (Object obj : objs) {
    impl.insert(obj);
    updater.increment();
  }
}

The updater is AutoCloseable; the try-with-resources block guarantees a final flush. See Performance Tips for the cross-cutting guidance.