import org.apache.hadoop.metrics2.util.Quantile; //导入依赖的package包/类
/**
 * Asserts that the NumOps and quantiles for a metric have been changed at
 * some point to a non-zero value.
 * 
 * @param prefix of the metric
 * @param rb MetricsRecordBuilder with the metric
 */
public static void assertQuantileGauges(String prefix, 
    MetricsRecordBuilder rb) {
  verify(rb).addGauge(eqName(info(prefix + "NumOps", "")), geq(0l));
  for (Quantile q : MutableQuantiles.quantiles) {
    String nameTemplate = prefix + "%dthPercentileLatency";
    int percentile = (int) (100 * q.quantile);
    verify(rb).addGauge(
        eqName(info(String.format(nameTemplate, percentile), "")),
        geq(0l));
  }
}
 

import org.apache.hadoop.metrics2.util.Quantile; //导入依赖的package包/类
/**
 * Ensure that quantile estimates from {@link MutableQuantiles} are within
 * specified error bounds.
 */
@Test(timeout = 30000)
public void testMutableQuantilesError() throws Exception {
  MetricsRecordBuilder mb = mockMetricsRecordBuilder();
  MetricsRegistry registry = new MetricsRegistry("test");
  // Use a 5s rollover period
  MutableQuantiles quantiles = registry.newQuantiles("foo", "stat", "Ops",
      "Latency", 5);
  // Push some values in and wait for it to publish
  long start = System.nanoTime() / 1000000;
  for (long i = 1; i <= 1000; i++) {
    quantiles.add(i);
    quantiles.add(1001 - i);
  }
  long end = System.nanoTime() / 1000000;

  Thread.sleep(6000 - (end - start));

  registry.snapshot(mb, false);

  // Print out the snapshot
  Map<Quantile, Long> previousSnapshot = quantiles.previousSnapshot;
  for (Entry<Quantile, Long> item : previousSnapshot.entrySet()) {
    System.out.println(String.format("Quantile %.2f has value %d",
        item.getKey().quantile, item.getValue()));
  }

  // Verify the results are within our requirements
  verify(mb).addGauge(
      info("FooNumOps", "Number of ops for stat with 5s interval"),
      (long) 2000);
  Quantile[] quants = MutableQuantiles.quantiles;
  String name = "Foo%dthPercentileLatency";
  String desc = "%d percentile latency with 5 second interval for stat";
  for (Quantile q : quants) {
    int percentile = (int) (100 * q.quantile);
    int error = (int) (1000 * q.error);
    String n = String.format(name, percentile);
    String d = String.format(desc, percentile);
    long expected = (long) (q.quantile * 1000);
    verify(mb).addGauge(eq(info(n, d)), leq(expected + error));
    verify(mb).addGauge(eq(info(n, d)), geq(expected - error));
  }
}