@DataProvider(value = {
    "42     |   DAYS",
    "123    |   SECONDS",
    "999    |   MILLISECONDS",
    "3      |   HOURS"
}, splitBy = "\\|")
@Test
public void RollingWindowTimerBuilder_newMetric_creates_new_timer_with_SlidingTimeWindowArrayReservoir_with_expected_values(
    long amount, TimeUnit timeUnit
) {
    // given
    RollingWindowTimerBuilder rwtb = new RollingWindowTimerBuilder(amount, timeUnit);

    // when
    Timer timer = rwtb.newMetric();

    // then
    Histogram histogram = (Histogram) getInternalState(timer, "histogram");
    Reservoir reservoir = (Reservoir) getInternalState(histogram, "reservoir");
    assertThat(reservoir).isInstanceOf(SlidingTimeWindowArrayReservoir.class);
    // The expected value here comes from logic in the SlidingTimeWindowArrayReservoir constructor.
    assertThat(getInternalState(reservoir, "window")).isEqualTo(timeUnit.toNanos(amount) * 256);
}
 

@DataProvider(value = {
    "42     |   DAYS",
    "123    |   SECONDS",
    "999    |   MILLISECONDS",
    "3      |   HOURS"
}, splitBy = "\\|")
@Test
public void RollingWindowHistogramBuilder_newMetric_creates_new_histogram_with_SlidingTimeWindowArrayReservoir_with_expected_values(
    long amount, TimeUnit timeUnit
) {
    // given
    RollingWindowHistogramBuilder rwhb = new RollingWindowHistogramBuilder(amount, timeUnit);

    // when
    Histogram histogram = rwhb.newMetric();

    // then
    Reservoir reservoir = (Reservoir) getInternalState(histogram, "reservoir");
    assertThat(reservoir).isInstanceOf(SlidingTimeWindowArrayReservoir.class);
    // The expected value here comes from logic in the SlidingTimeWindowArrayReservoir constructor.
    assertThat(getInternalState(reservoir, "window")).isEqualTo(timeUnit.toNanos(amount) * 256);
}
 

@Test
public void testCustomReservoir() throws Exception {
  System.setProperty("timer.reservoir", UniformReservoir.class.getName());
  System.setProperty("histogram.size", "2048");
  System.setProperty("histogram.window", "600");
  System.setProperty("histogram.reservoir", SlidingTimeWindowReservoir.class.getName());
  NodeConfig cfg = loadNodeConfig();
  SolrMetricManager mgr = new SolrMetricManager(cfg.getSolrResourceLoader(), cfg.getMetricsConfig());
  assertTrue(mgr.getCounterSupplier() instanceof MetricSuppliers.DefaultCounterSupplier);
  assertTrue(mgr.getMeterSupplier() instanceof MetricSuppliers.DefaultMeterSupplier);
  assertTrue(mgr.getTimerSupplier() instanceof MetricSuppliers.DefaultTimerSupplier);
  assertTrue(mgr.getHistogramSupplier() instanceof MetricSuppliers.DefaultHistogramSupplier);
  Reservoir rsv = ((MetricSuppliers.DefaultTimerSupplier)mgr.getTimerSupplier()).getReservoir();
  assertTrue(rsv instanceof UniformReservoir);
  rsv = ((MetricSuppliers.DefaultHistogramSupplier)mgr.getHistogramSupplier()).getReservoir();
  assertTrue(rsv instanceof SlidingTimeWindowReservoir);
}
 

@Test
public void shouldCacheSnapshot() {
    Reservoir reservoir = new HdrBuilder().neverResetReservoir().buildReservoir();

    reservoir.update(10);
    reservoir.update(20);
    Snapshot firstSnapshot = reservoir.getSnapshot();

    reservoir.update(30);
    reservoir.update(40);
    Snapshot secondSnapshot = reservoir.getSnapshot();
    assertNotSame(firstSnapshot, secondSnapshot);
    assertEquals(10, secondSnapshot.getMin());
    assertEquals(40, secondSnapshot.getMax());

    reservoir.update(9);
    reservoir.update(60);
    Snapshot thirdSnapshot = reservoir.getSnapshot();
    assertNotSame(secondSnapshot, thirdSnapshot);
    assertEquals(9, thirdSnapshot.getMin());
    assertEquals(60, thirdSnapshot.getMax());
}
 

@Test
public void shouldCacheSnapshot() {
    Reservoir reservoir = new HdrBuilder().resetReservoirOnSnapshot().buildReservoir();

    reservoir.update(10);
    reservoir.update(20);
    Snapshot firstSnapshot = reservoir.getSnapshot();

    reservoir.update(30);
    reservoir.update(40);
    Snapshot secondSnapshot = reservoir.getSnapshot();
    assertNotSame(firstSnapshot, secondSnapshot);
    assertEquals(30, secondSnapshot.getMin());
    assertEquals(40, secondSnapshot.getMax());

    reservoir.update(50);
    reservoir.update(60);
    Snapshot thirdSnapshot = reservoir.getSnapshot();
    assertNotSame(secondSnapshot, thirdSnapshot);
    assertEquals(50, thirdSnapshot.getMin());
    assertEquals(60, thirdSnapshot.getMax());
}
 

@Test
public void testSkipBigValues() {
    Reservoir reservoir = new HdrBuilder().withHighestTrackableValue(100, OverflowResolver.SKIP).buildReservoir();

    reservoir.update(101);
    Snapshot snapshot = reservoir.getSnapshot();
    assertEquals(0, snapshot.getMax());

    reservoir.update(100);
    snapshot = reservoir.getSnapshot();
    assertEquals(100, snapshot.getMax());

    reservoir.update(99);
    snapshot = reservoir.getSnapshot();
    assertEquals(99, snapshot.getMin());
}
 

@Test
public void testReduceBigValuesToMax() {
    Reservoir reservoir = new HdrBuilder().withHighestTrackableValue(100, OverflowResolver.REDUCE_TO_HIGHEST_TRACKABLE).buildReservoir();

    reservoir.update(101);
    Snapshot snapshot = reservoir.getSnapshot();
    assertEquals(100, snapshot.getMax());

    reservoir.update(100);
    snapshot = reservoir.getSnapshot();
    assertEquals(100, snapshot.getMax());

    reservoir.update(99);
    snapshot = reservoir.getSnapshot();
    assertEquals(99, snapshot.getMin());
}
 

private void registerMetrics(Class<?> bean, Executable executable) {
    MetricResolver.Of<Counted> counted = resolver.counted(bean, executable);
    if (counted.isPresent())
        registry.counter(counted.metricName());

    MetricResolver.Of<ExceptionMetered> exceptionMetered = resolver.exceptionMetered(bean, executable);
    if (exceptionMetered.isPresent())
        registry.meter(exceptionMetered.metricName());

    MetricResolver.Of<Metered> metered = resolver.metered(bean, executable);
    if (metered.isPresent())
        registry.meter(metered.metricName());

    MetricResolver.Of<Timed> timed = resolver.timed(bean, executable);
    if (timed.isPresent()) {
        extension.<BiFunction<String, Class<? extends Metric>, Optional<Reservoir>>>getParameter(ReservoirFunction)
            .flatMap(function -> function.apply(timed.metricName(), Timer.class))
            .map(reservoir -> registry.timer(timed.metricName(), () -> new Timer(reservoir)))
            .orElseGet(() -> registry.timer(timed.metricName()));
    }
}
 

@Test
public void testBasic() throws Exception {
  double maxDelta = 0.00000000001;
  Reservoir reservoir = new TDigestReservoir();
  assertEquals(0, reservoir.size());
  reservoir.update(100);
  reservoir.update(101);
  reservoir.update(300);
  assertEquals(3, reservoir.size());
  assertEquals(3, reservoir.getSnapshot().size());    
  assertEquals(100, reservoir.getSnapshot().getMin());    
  assertEquals(300, reservoir.getSnapshot().getMax());    
  assertEquals(101, reservoir.getSnapshot().getMedian(), maxDelta);    
  assertEquals(101, reservoir.getSnapshot().getValue(0.5), maxDelta);    
  assertEquals(501.0 / 3, reservoir.getSnapshot().getMean(), maxDelta);    
}
 

public SemanticMetricRegistry(
    final ConcurrentMap<MetricId, Metric> metrics,
    final Supplier<Reservoir> defaultReservoirSupplier
) {
    this.metrics = metrics;
    this.listeners = new CopyOnWriteArrayList<SemanticMetricRegistryListener>();
    this.defaultReservoirSupplier = defaultReservoirSupplier;
}
 

public ReservoirWithTtl(
    final Reservoir delegate,
    final int ttlSeconds,
    final int minimumRate,
    final Supplier<Instant> now) {
    this.delegate = delegate;
    this.now = now;
    this.ttlSeconds = ttlSeconds;
    final int bufferSize = ttlSeconds * minimumRate;
    this.valueBuffer = new OverwritingFixedConcurrentRingBuffer<>(DUMMY, bufferSize);
}
 

public static SemanticMetricBuilder<Timer> timerWithReservoir(
    final Supplier<Reservoir> reservoirSupplier) {
    return new SemanticMetricBuilder<Timer>() {
        @Override
        public Timer newMetric() {
            return new Timer(reservoirSupplier.get());
        }

        @Override
        public boolean isInstance(final Metric metric) {
            return Timer.class.isInstance(metric);
        }
    };
}
 

public static SemanticMetricBuilder<Histogram> histogramWithReservoir(
    final Supplier<Reservoir> reservoirSupplier) {
    return new SemanticMetricBuilder<Histogram>() {
        @Override
        public Histogram newMetric() {
            return new Histogram(reservoirSupplier.get());
        }

        @Override
        public boolean isInstance(final Metric metric) {
            return Histogram.class.isInstance(metric);
        }
    };
}
 

@Test
public void testDefaults() throws Exception {
  NodeConfig cfg = loadNodeConfig();
  SolrMetricManager mgr = new SolrMetricManager(cfg.getSolrResourceLoader(), cfg.getMetricsConfig());
  assertTrue(mgr.getCounterSupplier() instanceof MetricSuppliers.DefaultCounterSupplier);
  assertTrue(mgr.getMeterSupplier() instanceof MetricSuppliers.DefaultMeterSupplier);
  assertTrue(mgr.getTimerSupplier() instanceof MetricSuppliers.DefaultTimerSupplier);
  assertTrue(mgr.getHistogramSupplier() instanceof MetricSuppliers.DefaultHistogramSupplier);
  Clock clk = ((MetricSuppliers.DefaultTimerSupplier)mgr.getTimerSupplier()).clk;
  assertTrue(clk instanceof Clock.UserTimeClock);
  Reservoir rsv = ((MetricSuppliers.DefaultTimerSupplier)mgr.getTimerSupplier()).getReservoir();
  assertTrue(rsv instanceof ExponentiallyDecayingReservoir);
}
 

@Test(timeout = 32000)
public void testThatConcurrentThreadsNotHung() throws InterruptedException {
    Reservoir reservoir = new HdrBuilder()
            .resetReservoirPeriodically(Duration.ofSeconds(1))
            .buildReservoir();

    HistogramUtil.runInParallel(reservoir, TimeUnit.SECONDS.toMillis(30));
}
 

@Test(timeout = 32000)
public void testThatConcurrentThreadsNotHungWithThreeChunks() throws InterruptedException {
    Reservoir reservoir = new HdrBuilder()
            .resetReservoirPeriodicallyByChunks(Duration.ofSeconds(3), 3)
            .buildReservoir();

    HistogramUtil.runInParallel(reservoir, TimeUnit.SECONDS.toMillis(30));
}
 

public static void runInParallel(Reservoir reservoir, long durationMillis) throws InterruptedException {
    AtomicReference<Throwable> errorRef = new AtomicReference<>();

    Thread[] threads = new Thread[Runtime.getRuntime().availableProcessors() * 2];
    long start = System.currentTimeMillis();
    final CountDownLatch latch = new CountDownLatch(threads.length);
    for (int i = 0; i < threads.length; i++) {
        threads[i] = new Thread(() -> {
            try {
                // update reservoir 100 times and take snapshot on each cycle
                while (errorRef.get() == null && System.currentTimeMillis() - start < durationMillis) {
                    for (int j = 1; j <= 10; j++) {
                        reservoir.update(ThreadLocalRandom.current().nextInt(j));
                    }
                    reservoir.getSnapshot();
                }
            } catch (Exception e){
                e.printStackTrace();
                errorRef.set(e);
            } finally {
                latch.countDown();
            }
        });
        threads[i].start();
    }
    latch.await();
    //latch.await(duration.toMillis() + 4000, TimeUnit.MILLISECONDS);
    if (latch.getCount() > 0) {
        throw new IllegalStateException("" + latch.getCount() + " was not completed");
    }
    if (errorRef.get() != null) {
        throw new RuntimeException(errorRef.get());
    }
}
 

@Test
public void testSmartSnapshotCalculation() {
    double[] predefinedPercentiles = {0.5, 0.6, 0.75, 0.9, 0.95, 0.98, 0.99, 0.999};
    Reservoir reservoir = new HdrBuilder().withPredefinedPercentiles(predefinedPercentiles).buildReservoir();
    Snapshot snapshot = snapshotTaker.apply(reservoir);

    Histogram hdrHistogram = createEquivalentHistogram();
    assertEquals(hdrHistogram.getStdDeviation(), snapshot.getStdDev());
    assertEquals(hdrHistogram.getMinValue(), snapshot.getMin());
    assertEquals(hdrHistogram.getMean(), snapshot.getMean());
    assertEquals(hdrHistogram.getValueAtPercentile(50.0), (long) snapshot.getValue(0.42)); // do not defined percentile should be rounded up to first defined
    assertEquals(hdrHistogram.getValueAtPercentile(50.0), (long) snapshot.getMedian());
    assertEquals(hdrHistogram.getMaxValue(), snapshot.getMax());
    assertEquals(hdrHistogram.getValueAtPercentile(60.0), (long) snapshot.getValue(0.6));
    assertEquals(hdrHistogram.getValueAtPercentile(75.0), (long) snapshot.get75thPercentile());
    assertEquals(hdrHistogram.getValueAtPercentile(90.0), (long) snapshot.getValue(0.8)); // do not defined percentile should be rounded up to first defined
    assertEquals(hdrHistogram.getValueAtPercentile(90.0), (long) snapshot.getValue(0.9));
    assertEquals(hdrHistogram.getValueAtPercentile(95.0), (long) snapshot.getValue(0.94)); // do not defined percentile should be rounded up to first defined
    assertEquals(hdrHistogram.getValueAtPercentile(95.0), (long) snapshot.get95thPercentile());
    assertEquals(hdrHistogram.getValueAtPercentile(98.0), (long) snapshot.get98thPercentile());
    assertEquals(hdrHistogram.getValueAtPercentile(99.0), (long) snapshot.get99thPercentile());
    assertEquals(hdrHistogram.getValueAtPercentile(99.9), (long) snapshot.get999thPercentile());
    assertEquals(hdrHistogram.getMaxValue(), (long) snapshot.getValue(0.9999));

    assertEquals(predefinedPercentiles.length, snapshot.size());

    assertTrue(Arrays.equals(
            snapshot.getValues(),
            new long[] {
                    hdrHistogram.getValueAtPercentile(50.0),
                    hdrHistogram.getValueAtPercentile(60.0),
                    hdrHistogram.getValueAtPercentile(75.0),
                    hdrHistogram.getValueAtPercentile(90.0),
                    hdrHistogram.getValueAtPercentile(95.0),
                    hdrHistogram.getValueAtPercentile(98.0),
                    hdrHistogram.getValueAtPercentile(99.0),
                    hdrHistogram.getValueAtPercentile(99.9),
            }
    ));
}
 

@Test
public void testFullSnapshotCalculation() {
    Reservoir reservoir = new HdrBuilder().withoutSnapshotOptimization().buildReservoir();
    Snapshot snapshot = snapshotTaker.apply(reservoir);

    Histogram hdrHistogram = createEquivalentHistogram();
    assertEquals(hdrHistogram.getStdDeviation(), snapshot.getStdDev());
    assertEquals(hdrHistogram.getMinValue(), snapshot.getMin());
    assertEquals(hdrHistogram.getMean(), snapshot.getMean());
    assertEquals(hdrHistogram.getValueAtPercentile(50.0), (long) snapshot.getMedian());
    assertEquals(hdrHistogram.getMaxValue(), snapshot.getMax());
    assertEquals(hdrHistogram.getValueAtPercentile(60.0), (long) snapshot.getValue(0.6));
    assertEquals(hdrHistogram.getValueAtPercentile(75.0), (long) snapshot.get75thPercentile());
    assertEquals(hdrHistogram.getValueAtPercentile(80.0), (long) snapshot.getValue(0.8));
    assertEquals(hdrHistogram.getValueAtPercentile(90.0), (long) snapshot.getValue(0.9));
    assertEquals(hdrHistogram.getValueAtPercentile(94.0), (long) snapshot.getValue(0.94));
    assertEquals(hdrHistogram.getValueAtPercentile(95.0), (long) snapshot.get95thPercentile());
    assertEquals(hdrHistogram.getValueAtPercentile(98.0), (long) snapshot.get98thPercentile());
    assertEquals(hdrHistogram.getValueAtPercentile(99.0), (long) snapshot.get99thPercentile());
    assertEquals(hdrHistogram.getValueAtPercentile(99.9), (long) snapshot.get999thPercentile());

    assertEquals(hdrHistogram.getTotalCount(), snapshot.size());

    int i = 0;
    long[] values = snapshot.getValues();
    for (HistogramIterationValue value : hdrHistogram.recordedValues()) {
        assertEquals(value.getValueIteratedTo(), values[i++]);
    }
}
 

@Test
public void testPassThruBigValues2() {
    Reservoir reservoir = new HdrBuilder()
            .withHighestTrackableValue(100, OverflowResolver.PASS_THRU)
            .buildReservoir();
    reservoir.update(101);
    Snapshot snapshot = reservoir.getSnapshot();
    assertEquals(101, snapshot.getMax());
}
 

@Test
public void testSmartSnapshotPrinting() {
    Reservoir reservoir = new HdrBuilder().buildReservoir();
    Snapshot snapshot = snapshotTaker.apply(reservoir);

    System.out.println(snapshot);
    snapshot.dump(new ByteArrayOutputStream());
}
 

@Test
public void testFullSnapshotPrinting() {
    Reservoir reservoir = new HdrBuilder().withoutSnapshotOptimization().buildReservoir();
    Snapshot snapshot = snapshotTaker.apply(reservoir);

    System.out.println(snapshot);
    snapshot.dump(new ByteArrayOutputStream());
}
 

@Test
public void testGetTaggedHistogram() {
	tags.put("a", "b");
	tags.put("c", "d");
	String name = "foo";
	TaggedHistogram counter = registry.taggedHistogram(mock(Reservoir.class), name, tags);
	
	Map<String, String> searchTags = new HashMap<String, String>();
	searchTags.put("a", "b");
	TaggedHistogram actual = registry.getTaggedHistogram("foo", searchTags);
	assertEquals(counter, actual);
}
 

@Test
public void testTaggedHistogram() {
	tags.put("a", "b");
	String name = "foo";
	TaggedHistogram counter = registry.taggedHistogram(mock(Reservoir.class), name, tags);
	assertEquals(1, registry.getHistograms().size());
	String expected = name + TaggedMetricRegistry.delimiter + tags.hashCode();
	for(Map.Entry<String, Histogram> entry : registry.getHistograms().entrySet()) {
		assertEquals(expected, entry.getKey());
		assertEquals(counter, entry.getValue());
		TaggedHistogram actual = (TaggedHistogram) entry.getValue();
		assertEquals(tags, actual.getTags());
	}
}
 

/**
 * Create a new {@link com.codahale.metrics.Histogram} instance. These constructors are
 * not public in 2.2.0, so we use reflection to find them.
 */
public static Histogram newHistogram(Reservoir sample) {
  try {
    Constructor<?> ctor =
        Histogram.class.getDeclaredConstructor(Reservoir.class);
    ctor.setAccessible(true);
    return (Histogram) ctor.newInstance(sample);
  } catch (Exception e) {
    throw new RuntimeException(e);
  }
}
 

@Test
public void testBuilder() {
    final MetricRegistry metricRegistry = Mockito.mock(MetricRegistry.class);

    DataSource dataSource = Mockito.mock(DataSource.class);
    PoolAdapterFactory<DataSource> poolAdapterFactory = Mockito.mock(PoolAdapterFactory.class);
    ConnectionProxyFactory connectionProxyFactory = Mockito.mock(ConnectionProxyFactory.class);
    Metrics metrics = Mockito.mock(Metrics.class);
    PoolAdapter poolAdapter = Mockito.mock(PoolAdapter.class);
    when(poolAdapterFactory.newInstance(any(ConfigurationProperties.class))).thenReturn(poolAdapter);
    Configuration<DataSource> configuration = new Configuration.Builder<DataSource>(
            "unique", dataSource, poolAdapterFactory)
            .setConnectionProxyFactory(connectionProxyFactory)
            .setJmxAutoStart(true)
            .setJmxEnabled(true)
            .setMetricLogReporterMillis(120)
            .setMetricsFactory(new MetricsFactory() {
                @Override
                public Metrics newInstance(ConfigurationProperties configurationProperties) {
                    return new DropwizardMetrics(configurationProperties, metricRegistry, new ReservoirFactory() {
                        @Override
                        public Reservoir newInstance(Class<? extends Metric> metricClass, String metricName) {
                            return new ExponentiallyDecayingReservoir();
                        }
                    });
                }
            })
            .build();
    assertSame("unique", configuration.getUniqueName());
    assertSame(connectionProxyFactory, configuration.getConnectionProxyFactory());
    assertTrue(configuration.isJmxAutoStart());
    assertTrue(configuration.isJmxEnabled());
    assertEquals(120, configuration.getMetricLogReporterMillis());
    assertSame(poolAdapter, configuration.getPoolAdapter());
    assertSame(dataSource, configuration.getTargetDataSource());
}
 

@Test
public void testBuilder() {
    final MetricRegistry metricRegistry = Mockito.mock(MetricRegistry.class);

    DataSource dataSource = Mockito.mock(DataSource.class);
    PoolAdapterFactory<DataSource> poolAdapterFactory = Mockito.mock(PoolAdapterFactory.class);
    ConnectionProxyFactory connectionProxyFactory = Mockito.mock(ConnectionProxyFactory.class);
    Metrics metrics = Mockito.mock(Metrics.class);
    PoolAdapter poolAdapter = Mockito.mock(PoolAdapter.class);
    when(poolAdapterFactory.newInstance(any(ConfigurationProperties.class))).thenReturn(poolAdapter);
    Configuration<DataSource> configuration = new Configuration.Builder<DataSource>(
            "unique", dataSource, poolAdapterFactory)
            .setConnectionProxyFactory(connectionProxyFactory)
            .setJmxAutoStart(true)
            .setJmxEnabled(true)
            .setMetricLogReporterMillis(120)
            .setMetricsFactory(new MetricsFactory() {
                @Override
                public Metrics newInstance(ConfigurationProperties configurationProperties) {
                    return new CodahaleMetrics(configurationProperties, metricRegistry, new ReservoirFactory() {
                        @Override
                        public Reservoir newInstance(Class<? extends Metric> metricClass, String metricName) {
                            return new ExponentiallyDecayingReservoir();
                        }
                    });
                }
            })
            .build();
    assertSame("unique", configuration.getUniqueName());
    assertSame(connectionProxyFactory, configuration.getConnectionProxyFactory());
    assertTrue(configuration.isJmxAutoStart());
    assertTrue(configuration.isJmxEnabled());
    assertEquals(120, configuration.getMetricLogReporterMillis());
    assertSame(poolAdapter, configuration.getPoolAdapter());
    assertSame(dataSource, configuration.getTargetDataSource());
}
 

public static Reservoir getConfiguredReservoir(FluoConfiguration config) {
  String clazz = config.getString(FluoConfigurationImpl.METRICS_RESERVOIR_PROP,
      HdrHistogramResetOnSnapshotReservoir.class.getName());
  try {
    return Class.forName(clazz).asSubclass(Reservoir.class).newInstance();
  } catch (InstantiationException | IllegalAccessException | ClassNotFoundException e) {
    throw new IllegalStateException(e);
  }
}
 

/**
 * Exposed for testing.
 * @param clock the {@link Clock} to use for the {@link CachedGauge}.
 * @param reservoir the {@link Reservoir} to use for the histogram.
 * @param timeoutMs the timeout for the value stored in the cache in milliseconds. After this time has passed, a new
 *                  value of the histogram at {@code quantile} will be calculated.
 * @param quantile the quantile of the histogram to cache.
 */
CachedHistogram(Clock clock, Reservoir reservoir, long timeoutMs, double quantile) {
  super(reservoir);
  cache = new CachedGauge<Double>(clock, timeoutMs, TimeUnit.MILLISECONDS) {
    @Override
    protected Double loadValue() {
      return getSnapshot().getValue(quantile);
    }
  };
}
 

/**
 * Test caching behavior.
 */
@Test
public void testCache() {
  AtomicInteger snapshotCalls = new AtomicInteger(0);
  MockClock clock = new MockClock();
  Reservoir reservoir = new ExponentiallyDecayingReservoir();
  CachedHistogram histogram = new CachedHistogram(clock, reservoir, TimeUnit.SECONDS.toMillis(1), 0.50) {
    @Override
    public Snapshot getSnapshot() {
      // count number of calls to test caching
      snapshotCalls.getAndIncrement();
      return super.getSnapshot();
    }
  };
  long value = 2;
  double epsilon = 0.01;
  histogram.update(value);
  // getSnapshot should be called the first time
  assertEquals(value, histogram.getCachedValue(), epsilon);
  assertEquals(1, snapshotCalls.get());
  // the cached value should be used and getSnapshot should not be called.
  assertEquals(value, histogram.getCachedValue(), epsilon);
  assertEquals(1, snapshotCalls.get());
  // after progressing time, the cached value should expire and getSnapshot should be called
  clock.tick(1);
  assertEquals(value, histogram.getCachedValue(), epsilon);
  assertEquals(2, snapshotCalls.get());
}