Add the EventMetric metric type

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=132345599

java/google/registry/monitoring/metrics/AbstractMetric.java

@@ -19,7 +19,6 @@ import com.google.common.base.MoreObjects;
 import com.google.common.collect.ImmutableSet;
 import google.registry.monitoring.metrics.MetricSchema.Kind;
 
-//TODO(shikhman): implement HistogramMetrics.
 abstract class AbstractMetric<V> implements Metric<V> {
 
   private final Class<V> valueClass;

java/google/registry/monitoring/metrics/EventMetric.java

@@ -0,0 +1,223 @@
+// Copyright 2016 The Domain Registry Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.monitoring.metrics;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Ordering;
+import com.google.common.util.concurrent.Striped;
+import google.registry.monitoring.metrics.MetricSchema.Kind;
+import java.util.Map.Entry;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.locks.Lock;
+import org.joda.time.Instant;
+
+/**
+ * A metric which stores {@link Distribution} values. The values are stateful and meant to be
+ * updated incrementally via the {@link EventMetric#record(double, String...)} method.
+ *
+ * <p>This metric class is generally suitable for recording aggregations of data about a
+ * quantitative aspect of an event. For example, this metric would be suitable for recording the
+ * latency distribution for a request over the network.
+ *
+ * <p>The {@link MutableDistribution} values tracked by this metric can be reset with {@link
+ * EventMetric#reset()}.
+ */
+public final class EventMetric extends AbstractMetric<Distribution> {
+
+  /**
+   * The below constants replicate the default initial capacity, load factor, and concurrency level
+   * for {@link ConcurrentHashMap} as of Java SE 7. They are hardcoded here so that the concurrency
+   * level in {@code valueLocks} below can be set identically.
+   */
+  private static final int HASHMAP_INITIAL_CAPACITY = 16;
+
+  private static final float HASHMAP_LOAD_FACTOR = 0.75f;
+  private static final int HASHMAP_CONCURRENCY_LEVEL = 16;
+
+  private final ConcurrentHashMap<ImmutableList<String>, Instant> valueStartTimestamps =
+      new ConcurrentHashMap<>(
+          HASHMAP_INITIAL_CAPACITY, HASHMAP_LOAD_FACTOR, HASHMAP_CONCURRENCY_LEVEL);
+  private final ConcurrentHashMap<ImmutableList<String>, MutableDistribution> values =
+      new ConcurrentHashMap<>(
+          HASHMAP_INITIAL_CAPACITY, HASHMAP_LOAD_FACTOR, HASHMAP_CONCURRENCY_LEVEL);
+
+  private final DistributionFitter distributionFitter;
+
+  /**
+   * A fine-grained lock to ensure that {@code values} and {@code valueStartTimestamps} are modified
+   * and read in a critical section. The initialization parameter is the concurrency level, set to
+   * match the default concurrency level of {@link ConcurrentHashMap}.
+   *
+   * @see Striped
+   */
+  private final Striped<Lock> valueLocks = Striped.lock(HASHMAP_CONCURRENCY_LEVEL);
+
+  EventMetric(
+      String name,
+      String description,
+      String valueDisplayName,
+      DistributionFitter distributionFitter,
+      ImmutableSet<LabelDescriptor> labels) {
+    super(name, description, valueDisplayName, Kind.CUMULATIVE, labels, Distribution.class);
+
+    this.distributionFitter = distributionFitter;
+  }
+
+  @Override
+  public final int getCardinality() {
+    return values.size();
+  }
+
+  @Override
+  public final ImmutableList<MetricPoint<Distribution>> getTimestampedValues() {
+    return getTimestampedValues(Instant.now());
+  }
+
+  @VisibleForTesting
+  final ImmutableList<MetricPoint<Distribution>> getTimestampedValues(Instant endTimestamp) {
+    ImmutableList.Builder<MetricPoint<Distribution>> timestampedValues =
+        new ImmutableList.Builder<>();
+
+    for (Entry<ImmutableList<String>, MutableDistribution> entry : values.entrySet()) {
+      ImmutableList<String> labelValues = entry.getKey();
+      Lock lock = valueLocks.get(labelValues);
+      lock.lock();
+
+      Instant startTimestamp;
+      ImmutableDistribution distribution;
+      try {
+        startTimestamp = valueStartTimestamps.get(labelValues);
+        distribution = ImmutableDistribution.copyOf(entry.getValue());
+      } finally {
+        lock.unlock();
+      }
+
+      // There is an opportunity for endTimestamp to be less than startTimestamp if
+      // one of the modification methods is called on a value before the lock for that value is
+      // acquired but after getTimestampedValues has been invoked. Just set endTimestamp equal to
+      // startTimestamp if that happens.
+      endTimestamp = Ordering.natural().max(startTimestamp, endTimestamp);
+
+      timestampedValues.add(
+          MetricPoint.create(this, labelValues, startTimestamp, endTimestamp, distribution));
+    }
+
+    return timestampedValues.build();
+  }
+
+  /**
+   * Adds the given {@code sample} to the {@link Distribution} for the given {@code labelValues}.
+   *
+   * <p>If the metric is undefined for given label values, this method will autovivify the {@link
+   * Distribution}.
+   *
+   * <p>The count of {@code labelValues} must be equal to the underlying metric's count of labels.
+   */
+  public final void record(double sample, String... labelValues) {
+    MetricsUtils.checkLabelValuesLength(this, labelValues);
+
+    recordMultiple(sample, 1, Instant.now(), ImmutableList.copyOf(labelValues));
+  }
+
+  /**
+   * Adds {@code count} of the given {@code sample} to the {@link Distribution} for the given {@code
+   * labelValues}.
+   *
+   * <p>If the metric is undefined for given label values, this method will autovivify the {@link
+   * Distribution}.
+   *
+   * <p>The count of {@code labelValues} must be equal to the underlying metric's count of labels.
+   */
+  public final void record(double sample, int count, String... labelValues) {
+    MetricsUtils.checkLabelValuesLength(this, labelValues);
+
+    recordMultiple(sample, count, Instant.now(), ImmutableList.copyOf(labelValues));
+  }
+
+  @VisibleForTesting
+  final void recordMultiple(
+      double sample, int count, Instant startTimestamp, ImmutableList<String> labelValues) {
+    Lock lock = valueLocks.get(labelValues);
+    lock.lock();
+
+    try {
+      if (!values.containsKey(labelValues)) {
+        values.put(labelValues, new MutableDistribution(distributionFitter));
+      }
+
+      values.get(labelValues).add(sample, count);
+      valueStartTimestamps.putIfAbsent(labelValues, startTimestamp);
+    } finally {
+      lock.unlock();
+    }
+  }
+
+  /**
+   * Atomically resets the value and start timestamp of the metric for all label values.
+   *
+   * <p>This is useful if the metric is tracking values that are reset as part of a retrying
+   * transaction, for example.
+   */
+  public void reset() {
+    reset(Instant.now());
+  }
+
+  @VisibleForTesting
+  final void reset(Instant startTime) {
+    // Lock the entire set of values so that all existing values will have a consistent timestamp
+    // after this call, without the possibility of interleaving with another reset() call.
+    for (int i = 0; i < valueLocks.size(); i++) {
+      valueLocks.getAt(i).lock();
+    }
+
+    try {
+      for (ImmutableList<String> labelValues : values.keySet()) {
+        this.values.put(labelValues, new MutableDistribution(distributionFitter));
+        this.valueStartTimestamps.put(labelValues, startTime);
+      }
+    } finally {
+      for (int i = 0; i < valueLocks.size(); i++) {
+        valueLocks.getAt(i).unlock();
+      }
+    }
+  }
+
+  /**
+   * Resets the value and start timestamp of the metric for the given label values.
+   *
+   * <p>This is useful if the metric is tracking a value that is reset as part of a retrying
+   * transaction, for example.
+   */
+  public void reset(String... labelValues) {
+    MetricsUtils.checkLabelValuesLength(this, labelValues);
+
+    reset(Instant.now(), ImmutableList.copyOf(labelValues));
+  }
+
+  @VisibleForTesting
+  final void reset(Instant startTimestamp, ImmutableList<String> labelValues) {
+    Lock lock = valueLocks.get(labelValues);
+    lock.lock();
+
+    try {
+      this.values.put(labelValues, new MutableDistribution(distributionFitter));
+      this.valueStartTimestamps.put(labelValues, startTimestamp);
+    } finally {
+      lock.unlock();
+    }
+  }
+}

java/google/registry/monitoring/metrics/ImmutableDistribution.java

@@ -14,7 +14,11 @@
 
 package google.registry.monitoring.metrics;
 
+import static com.google.common.base.Preconditions.checkArgument;
+import static google.registry.monitoring.metrics.MetricsUtils.checkDouble;
+
 import com.google.auto.value.AutoValue;
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableRangeMap;
 import javax.annotation.concurrent.ThreadSafe;
 
@@ -37,6 +41,21 @@ public abstract class ImmutableDistribution implements Distribution {
         distribution.distributionFitter());
   }
 
+  @VisibleForTesting
+  static ImmutableDistribution create(
+      double mean,
+      double sumOfSquaredDeviation,
+      long count,
+      ImmutableRangeMap<Double, Long> intervalCounts,
+      DistributionFitter distributionFitter) {
+    checkDouble(mean);
+    checkDouble(sumOfSquaredDeviation);
+    checkArgument(count >= 0);
+
+    return new AutoValue_ImmutableDistribution(
+        mean, sumOfSquaredDeviation, count, intervalCounts, distributionFitter);
+  }
+
   @Override
   public abstract double mean();