Gauge API : Add DoubleGauge Support (Part2) (#1496)

* Gauge API : Add DoubleGauge Support (Part2)

* Fix review comments

2 files changed, 180 insertions, 7 deletions

diff --git a/impl_core/src/main/java/io/opencensus/implcore/metrics/DoubleGaugeImpl.java b/impl_core/src/main/java/io/opencensus/implcore/metrics/DoubleGaugeImpl.java
new file mode 100644
index 00000000..d329091e
--- /dev/null
+++ b/impl_core/src/main/java/io/opencensus/implcore/metrics/DoubleGaugeImpl.java
@@ -0,0 +1,174 @@
+/*
+ * Copyright 2018, OpenCensus Authors
+ *
+ * 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 io.opencensus.implcore.metrics;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.util.concurrent.AtomicDouble;
+import io.opencensus.common.Clock;
+import io.opencensus.implcore.internal.Utils;
+import io.opencensus.metrics.DoubleGauge;
+import io.opencensus.metrics.LabelKey;
+import io.opencensus.metrics.LabelValue;
+import io.opencensus.metrics.export.Metric;
+import io.opencensus.metrics.export.MetricDescriptor;
+import io.opencensus.metrics.export.MetricDescriptor.Type;
+import io.opencensus.metrics.export.Point;
+import io.opencensus.metrics.export.TimeSeries;
+import io.opencensus.metrics.export.Value;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import javax.annotation.Nullable;
+
+/** Implementation of {@link DoubleGauge}. */
+public final class DoubleGaugeImpl extends DoubleGauge implements Meter {
+  @VisibleForTesting static final LabelValue UNSET_VALUE = LabelValue.create(null);
+
+  private final MetricDescriptor metricDescriptor;
+  private volatile Map<List<LabelValue>, PointImpl> registeredPoints = Collections.emptyMap();
+  private final int labelKeysSize;
+  private final List<LabelValue> defaultLabelValues;
+
+  DoubleGaugeImpl(String name, String description, String unit, List<LabelKey> labelKeys) {
+    labelKeysSize = labelKeys.size();
+    this.metricDescriptor =
+        MetricDescriptor.create(name, description, unit, Type.GAUGE_DOUBLE, labelKeys);
+
+    // initialize defaultLabelValues
+    defaultLabelValues = new ArrayList<LabelValue>(labelKeysSize);
+    for (int i = 0; i < labelKeysSize; i++) {
+      defaultLabelValues.add(UNSET_VALUE);
+    }
+  }
+
+  @Override
+  public DoublePoint getOrCreateTimeSeries(List<LabelValue> labelValues) {
+    // lock free point retrieval, if it is present
+    PointImpl existingPoint = registeredPoints.get(labelValues);
+    if (existingPoint != null) {
+      return existingPoint;
+    }
+
+    List<LabelValue> labelValuesCopy =
+        Collections.unmodifiableList(
+            new ArrayList<LabelValue>(
+                checkNotNull(labelValues, "labelValues should not be null.")));
+    return registerTimeSeries(labelValuesCopy);
+  }
+
+  @Override
+  public DoublePoint getDefaultTimeSeries() {
+    // lock free default point retrieval, if it is present
+    PointImpl existingPoint = registeredPoints.get(defaultLabelValues);
+    if (existingPoint != null) {
+      return existingPoint;
+    }
+    return registerTimeSeries(Collections.unmodifiableList(defaultLabelValues));
+  }
+
+  @Override
+  public synchronized void removeTimeSeries(List<LabelValue> labelValues) {
+    checkNotNull(labelValues, "labelValues should not be null.");
+
+    Map<List<LabelValue>, PointImpl> registeredPointsCopy =
+        new LinkedHashMap<List<LabelValue>, PointImpl>(registeredPoints);
+    if (registeredPointsCopy.remove(labelValues) == null) {
+      // The element not present, no need to update the current map of points.
+      return;
+    }
+    registeredPoints = Collections.unmodifiableMap(registeredPointsCopy);
+  }
+
+  @Override
+  public synchronized void clear() {
+    registeredPoints = Collections.emptyMap();
+  }
+
+  private synchronized DoublePoint registerTimeSeries(List<LabelValue> labelValues) {
+    PointImpl existingPoint = registeredPoints.get(labelValues);
+    if (existingPoint != null) {
+      // Return a Point that are already registered. This can happen if a multiple threads
+      // concurrently try to register the same {@code TimeSeries}.
+      return existingPoint;
+    }
+
+    checkArgument(labelKeysSize == labelValues.size(), "Incorrect number of labels.");
+    Utils.checkListElementNotNull(labelValues, "labelValues element should not be null.");
+
+    PointImpl newPoint = new PointImpl(labelValues);
+    // Updating the map of points happens under a lock to avoid multiple add operations
+    // to happen in the same time.
+    Map<List<LabelValue>, PointImpl> registeredPointsCopy =
+        new LinkedHashMap<List<LabelValue>, PointImpl>(registeredPoints);
+    registeredPointsCopy.put(labelValues, newPoint);
+    registeredPoints = Collections.unmodifiableMap(registeredPointsCopy);
+
+    return newPoint;
+  }
+
+  @Nullable
+  @Override
+  public Metric getMetric(Clock clock) {
+    Map<List<LabelValue>, PointImpl> currentRegisteredPoints = registeredPoints;
+    if (currentRegisteredPoints.isEmpty()) {
+      return null;
+    }
+
+    if (currentRegisteredPoints.size() == 1) {
+      PointImpl point = currentRegisteredPoints.values().iterator().next();
+      return Metric.createWithOneTimeSeries(metricDescriptor, point.getTimeSeries(clock));
+    }
+
+    List<TimeSeries> timeSeriesList = new ArrayList<TimeSeries>(currentRegisteredPoints.size());
+    for (Map.Entry<List<LabelValue>, PointImpl> entry : currentRegisteredPoints.entrySet()) {
+      timeSeriesList.add(entry.getValue().getTimeSeries(clock));
+    }
+    return Metric.create(metricDescriptor, timeSeriesList);
+  }
+
+  /** Implementation of {@link DoubleGauge.DoublePoint}. */
+  public static final class PointImpl extends DoublePoint {
+
+    // TODO(mayurkale): Consider to use DoubleAdder here, once we upgrade to Java8.
+    private final AtomicDouble value = new AtomicDouble(0);
+    private final List<LabelValue> labelValues;
+
+    PointImpl(List<LabelValue> labelValues) {
+      this.labelValues = labelValues;
+    }
+
+    @Override
+    public void add(double amt) {
+      value.addAndGet(amt);
+    }
+
+    @Override
+    public void set(double val) {
+      value.set(val);
+    }
+
+    private TimeSeries getTimeSeries(Clock clock) {
+      return TimeSeries.createWithOnePoint(
+          labelValues, Point.create(Value.doubleValue(value.get()), clock.now()), null);
+    }
+  }
+}
diff --git a/impl_core/src/main/java/io/opencensus/implcore/metrics/LongGaugeImpl.java b/impl_core/src/main/java/io/opencensus/implcore/metrics/LongGaugeImpl.java
index a7f84347..64cb3200 100644
--- a/impl_core/src/main/java/io/opencensus/implcore/metrics/LongGaugeImpl.java
+++ b/impl_core/src/main/java/io/opencensus/implcore/metrics/LongGaugeImpl.java
@@ -33,7 +33,7 @@ import io.opencensus.metrics.export.TimeSeries;
 import io.opencensus.metrics.export.Value;
 import java.util.ArrayList;
 import java.util.Collections;
-import java.util.HashMap;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.atomic.AtomicLong;
@@ -82,7 +82,7 @@ public final class LongGaugeImpl extends LongGauge implements Meter {
     if (existingPoint != null) {
       return existingPoint;
     }
-    return registerTimeSeries(defaultLabelValues);
+    return registerTimeSeries(Collections.unmodifiableList(defaultLabelValues));
   }
 
   @Override
@@ -90,7 +90,7 @@ public final class LongGaugeImpl extends LongGauge implements Meter {
     checkNotNull(labelValues, "labelValues should not be null.");
 
     Map<List<LabelValue>, PointImpl> registeredPointsCopy =
-        new HashMap<List<LabelValue>, PointImpl>(registeredPoints);
+        new LinkedHashMap<List<LabelValue>, PointImpl>(registeredPoints);
     if (registeredPointsCopy.remove(labelValues) == null) {
       // The element not present, no need to update the current map of points.
       return;
@@ -118,7 +118,7 @@ public final class LongGaugeImpl extends LongGauge implements Meter {
     // Updating the map of points happens under a lock to avoid multiple add operations
     // to happen in the same time.
     Map<List<LabelValue>, PointImpl> registeredPointsCopy =
-        new HashMap<List<LabelValue>, PointImpl>(registeredPoints);
+        new LinkedHashMap<List<LabelValue>, PointImpl>(registeredPoints);
     registeredPointsCopy.put(labelValues, newPoint);
     registeredPoints = Collections.unmodifiableMap(registeredPointsCopy);
 
@@ -133,13 +133,12 @@ public final class LongGaugeImpl extends LongGauge implements Meter {
       return null;
     }
 
-    int pointCount = currentRegisteredPoints.size();
-    if (pointCount == 1) {
+    if (currentRegisteredPoints.size() == 1) {
       PointImpl point = currentRegisteredPoints.values().iterator().next();
       return Metric.createWithOneTimeSeries(metricDescriptor, point.getTimeSeries(clock));
     }
 
-    List<TimeSeries> timeSeriesList = new ArrayList<TimeSeries>(pointCount);
+    List<TimeSeries> timeSeriesList = new ArrayList<TimeSeries>(currentRegisteredPoints.size());
     for (Map.Entry<List<LabelValue>, PointImpl> entry : currentRegisteredPoints.entrySet()) {
       timeSeriesList.add(entry.getValue().getTimeSeries(clock));
     }