code: package io.ray.runtime.metric;
  
  import com.google.common.base.Preconditions;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  import java.util.Map;
  import java.util.stream.Collectors;
  
  /**
   * Histogram measurement is mapped to histogram object in stats. In order to reduce JNI calls
   * overhead, a memory historical window is used for storing transient value and we assume its max
   * size is 100.
   */
  public class Histogram extends Metric {
  
    private List<Double> histogramWindow;
    public static final int HISTOGRAM_WINDOW_SIZE = 100;
  
    @Deprecated
    public Histogram(
        String name,
        String description,
        String unit,
        List<Double> boundaries,
        Map<TagKey, String> tags) {
      super(name, tags);
      metricNativePointer =
          NativeMetric.registerHistogramNative(
              name,
              description,
              unit,
              boundaries.stream().mapToDouble(Double::doubleValue).toArray(),
              tags.keySet().stream().map(TagKey::getTagKey).collect(Collectors.toList()));
      Preconditions.checkState(metricNativePointer != 0, "Histogram native pointer must not be 0.");
      histogramWindow = Collections.synchronizedList(new ArrayList<>());
    }
  
    public Histogram(
        String name, String description, List<Double> boundaries, Map<String, String> tags) {
      this(name, description, "", boundaries, TagKey.tagsFromMap(tags));
    }
  
    private void updateForWindow(double value) {
      if (histogramWindow.size() == HISTOGRAM_WINDOW_SIZE) {
        histogramWindow.remove(0);
      }
      histogramWindow.add(value);
    }
  
    @Override
    public void update(double value) {
      updateForWindow(value);
      this.value.set(value);
    }
  
    @Override
    protected double getAndReset() {
      histogramWindow.clear();
      return value.doubleValue();
    }
  
    public List<Double> getHistogramWindow() {
      return histogramWindow;
    }
  
    public double getValue() {
      return value.get();
    }
  }
  