Add StackDriver implementation, in monitoring/metrics package

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=130287319

java/google/registry/monitoring/metrics/MetricRegistryImpl.java

@@ -0,0 +1,118 @@
+// 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 static com.google.common.base.Preconditions.checkState;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Supplier;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.ImmutableSet;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.logging.Logger;
+import javax.annotation.concurrent.ThreadSafe;
+
+/** A singleton registry of {@link Metric}s. */
+@ThreadSafe
+public final class MetricRegistryImpl implements MetricRegistry {
+
+  private static final Logger logger = Logger.getLogger(MetricRegistryImpl.class.getName());
+  private static final MetricRegistryImpl INSTANCE = new MetricRegistryImpl();
+
+  /** The canonical registry for metrics. The map key is the metric name. */
+  private final ConcurrentHashMap<String, Metric<?>> registeredMetrics = new ConcurrentHashMap<>();
+
+  private MetricRegistryImpl() {}
+
+  public static MetricRegistryImpl getDefault() {
+    return INSTANCE;
+  }
+
+  @Override
+  @CanIgnoreReturnValue
+  public <V> Metric<V> newGauge(
+      String name,
+      String description,
+      String valueDisplayName,
+      ImmutableSet<LabelDescriptor> labels,
+      Supplier<ImmutableMap<ImmutableList<String>, V>> metricCallback,
+      Class<V> valueClass) {
+    VirtualMetric<V> metric =
+        new VirtualMetric<>(
+            name, description, valueDisplayName, labels, metricCallback, valueClass);
+    registerMetric(name, metric);
+    logger.info("Registered new callback metric: " + name);
+
+    return metric;
+  }
+
+  @Override
+  public <V> SettableMetric<V> newSettableMetric(
+      String name,
+      String description,
+      String valueDisplayName,
+      ImmutableSet<LabelDescriptor> labels,
+      Class<V> valueClass) {
+    StoredMetric<V> metric =
+        new StoredMetric<>(name, description, valueDisplayName, labels, valueClass);
+    registerMetric(name, metric);
+    logger.info("Registered new stored metric: " + name);
+
+    return metric;
+  }
+
+  @Override
+  public IncrementableMetric newIncrementableMetric(
+      String name,
+      String description,
+      String valueDisplayName,
+      ImmutableSet<LabelDescriptor> labels) {
+
+    Counter metric = new Counter(name, description, valueDisplayName, labels);
+    registerMetric(name, metric);
+    logger.info("Registered new counter: " + name);
+
+    return metric;
+  }
+
+  @Override
+  public ImmutableList<Metric<?>> getRegisteredMetrics() {
+    return ImmutableList.copyOf(registeredMetrics.values());
+  }
+
+  /**
+   * Unregisters a metric.
+   *
+   * <p>This is a no-op if the metric is not already registered.
+   *
+   * <p>{@link MetricWriter} implementations should not send unregistered metrics on subsequent
+   * write intervals.
+   */
+  @VisibleForTesting
+  void unregisterMetric(String name) {
+    registeredMetrics.remove(name);
+    logger.info("Unregistered metric: " + name);
+  }
+
+  /** Registers a metric. */
+  @VisibleForTesting
+  void registerMetric(String name, Metric<?> metric) {
+    Metric<?> previousMetric = registeredMetrics.putIfAbsent(name, metric);
+
+    checkState(previousMetric == null, "Duplicate metric of same name: %s", name);
+  }
+}