Gauge API : Add support for DerivedDoubleGauge (#1504)

* Add support for DerivedDoubleGauge

* Fix review comments

* Fix reviews

4 files changed, 168 insertions, 10 deletions

diff --git a/impl_core/src/main/java/io/opencensus/implcore/metrics/DerivedDoubleGaugeImpl.java b/impl_core/src/main/java/io/opencensus/implcore/metrics/DerivedDoubleGaugeImpl.java
new file mode 100644
index 00000000..b7104c9b
--- /dev/null
+++ b/impl_core/src/main/java/io/opencensus/implcore/metrics/DerivedDoubleGaugeImpl.java
@@ -0,0 +1,155 @@
+/*
+ * 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 io.opencensus.common.Clock;
+import io.opencensus.common.ToDoubleFunction;
+import io.opencensus.implcore.internal.Utils;
+import io.opencensus.metrics.DerivedDoubleGauge;
+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.lang.ref.WeakReference;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
+/*>>>
+import org.checkerframework.checker.nullness.qual.Nullable;
+*/
+
+/** Implementation of {@link DerivedDoubleGauge}. */
+public final class DerivedDoubleGaugeImpl extends DerivedDoubleGauge implements Meter {
+  private final MetricDescriptor metricDescriptor;
+  private final int labelKeysSize;
+
+  @SuppressWarnings("rawtypes")
+  private volatile Map<List<LabelValue>, PointWithFunction> registeredPoints =
+      Collections.<List<LabelValue>, PointWithFunction>emptyMap();
+
+  DerivedDoubleGaugeImpl(String name, String description, String unit, List<LabelKey> labelKeys) {
+    labelKeysSize = labelKeys.size();
+    this.metricDescriptor =
+        MetricDescriptor.create(name, description, unit, Type.GAUGE_DOUBLE, labelKeys);
+  }
+
+  @Override
+  @SuppressWarnings("rawtypes")
+  public synchronized <T> void createTimeSeries(
+      List<LabelValue> labelValues,
+      /*@Nullable*/ T obj,
+      ToDoubleFunction</*@Nullable*/ T> function) {
+    Utils.checkListElementNotNull(
+        checkNotNull(labelValues, "labelValues"), "labelValue element should not be null.");
+    checkArgument(labelKeysSize == labelValues.size(), "Incorrect number of labels.");
+    checkNotNull(function, "function");
+
+    List<LabelValue> labelValuesCopy =
+        Collections.<LabelValue>unmodifiableList(new ArrayList<LabelValue>(labelValues));
+
+    PointWithFunction existingPoint = registeredPoints.get(labelValuesCopy);
+    if (existingPoint != null) {
+      throw new IllegalArgumentException(
+          "A different time series with the same labels already exists.");
+    }
+
+    PointWithFunction newPoint = new PointWithFunction<T>(labelValuesCopy, obj, function);
+    // Updating the map of time series happens under a lock to avoid multiple add operations
+    // to happen in the same time.
+    Map<List<LabelValue>, PointWithFunction> registeredPointsCopy =
+        new LinkedHashMap<List<LabelValue>, PointWithFunction>(registeredPoints);
+    registeredPointsCopy.put(labelValuesCopy, newPoint);
+    registeredPoints = Collections.unmodifiableMap(registeredPointsCopy);
+  }
+
+  @Override
+  @SuppressWarnings("rawtypes")
+  public synchronized void removeTimeSeries(List<LabelValue> labelValues) {
+    checkNotNull(labelValues, "labelValues");
+
+    Map<List<LabelValue>, PointWithFunction> registeredPointsCopy =
+        new LinkedHashMap<List<LabelValue>, PointWithFunction>(registeredPoints);
+    if (registeredPointsCopy.remove(labelValues) == null) {
+      // The element not present, no need to update the current map of time series.
+      return;
+    }
+    registeredPoints = Collections.unmodifiableMap(registeredPointsCopy);
+  }
+
+  @Override
+  @SuppressWarnings("rawtypes")
+  public synchronized void clear() {
+    registeredPoints = Collections.<List<LabelValue>, PointWithFunction>emptyMap();
+  }
+
+  /*@Nullable*/
+  @Override
+  @SuppressWarnings("rawtypes")
+  public Metric getMetric(Clock clock) {
+    Map<List<LabelValue>, PointWithFunction> currentRegisteredPoints = registeredPoints;
+    if (currentRegisteredPoints.isEmpty()) {
+      return null;
+    }
+
+    if (currentRegisteredPoints.size() == 1) {
+      PointWithFunction 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>, PointWithFunction> entry :
+        currentRegisteredPoints.entrySet()) {
+      timeSeriesList.add(entry.getValue().getTimeSeries(clock));
+    }
+    return Metric.create(metricDescriptor, timeSeriesList);
+  }
+
+  /** Implementation of {@link PointWithFunction} with an object and a callback function. */
+  public static final class PointWithFunction<T> {
+    private final List<LabelValue> labelValues;
+    @javax.annotation.Nullable private final WeakReference<T> ref;
+    private final ToDoubleFunction</*@Nullable*/ T> function;
+
+    PointWithFunction(
+        List<LabelValue> labelValues,
+        /*@Nullable*/ T obj,
+        ToDoubleFunction</*@Nullable*/ T> function) {
+      this.labelValues = labelValues;
+      ref = obj != null ? new WeakReference<T>(obj) : null;
+      this.function = function;
+    }
+
+    private TimeSeries getTimeSeries(Clock clock) {
+      final T obj = ref != null ? ref.get() : null;
+      double value = function.applyAsDouble(obj);
+
+      // TODO(mayurkale): OPTIMIZATION: Avoid re-evaluate the labelValues all the time (issue#1490).
+      return TimeSeries.createWithOnePoint(
+          labelValues, Point.create(Value.doubleValue(value), clock.now()), null);
+    }
+  }
+}
diff --git a/impl_core/src/main/java/io/opencensus/implcore/metrics/DerivedLongGaugeImpl.java b/impl_core/src/main/java/io/opencensus/implcore/metrics/DerivedLongGaugeImpl.java
index b325b163..90e3e706 100644
--- a/impl_core/src/main/java/io/opencensus/implcore/metrics/DerivedLongGaugeImpl.java
+++ b/impl_core/src/main/java/io/opencensus/implcore/metrics/DerivedLongGaugeImpl.java
@@ -49,7 +49,7 @@ public final class DerivedLongGaugeImpl extends DerivedLongGauge implements Mete
 
   @SuppressWarnings("rawtypes")
   private volatile Map<List<LabelValue>, PointWithFunction> registeredPoints =
-      Collections.emptyMap();
+      Collections.<List<LabelValue>, PointWithFunction>emptyMap();
 
   DerivedLongGaugeImpl(String name, String description, String unit, List<LabelKey> labelKeys) {
     labelKeysSize = labelKeys.size();
@@ -99,11 +99,12 @@ public final class DerivedLongGaugeImpl extends DerivedLongGauge implements Mete
   }
 
   @Override
+  @SuppressWarnings("rawtypes")
   public synchronized void clear() {
-    registeredPoints = Collections.emptyMap();
+    registeredPoints = Collections.<List<LabelValue>, PointWithFunction>emptyMap();
   }
 
-  @javax.annotation.Nullable
+  /*@Nullable*/
   @Override
   @SuppressWarnings("rawtypes")
   public Metric getMetric(Clock clock) {
@@ -125,15 +126,15 @@ public final class DerivedLongGaugeImpl extends DerivedLongGauge implements Mete
     return Metric.create(metricDescriptor, timeSeriesList);
   }
 
-  /** Implementation of {@link PointWithFunction} with a obj and a callback function. */
+  /** Implementation of {@link PointWithFunction} with an object and a callback function. */
   public static final class PointWithFunction<T> {
     private final List<LabelValue> labelValues;
     @javax.annotation.Nullable private final WeakReference<T> ref;
     private final ToLongFunction</*@Nullable*/ T> function;
 
     PointWithFunction(
-        List<LabelValue> labelValues, /*@Nullable*/
-        T obj,
+        List<LabelValue> labelValues,
+        /*@Nullable*/ T obj,
         ToLongFunction</*@Nullable*/ T> function) {
       this.labelValues = labelValues;
       ref = obj != null ? new WeakReference<T>(obj) : null;
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
index 86b3512d..c314e980 100644
--- a/impl_core/src/main/java/io/opencensus/implcore/metrics/DoubleGaugeImpl.java
+++ b/impl_core/src/main/java/io/opencensus/implcore/metrics/DoubleGaugeImpl.java
@@ -44,7 +44,8 @@ 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 volatile Map<List<LabelValue>, PointImpl> registeredPoints =
+      Collections.<List<LabelValue>, PointImpl>emptyMap();
   private final int labelKeysSize;
   private final List<LabelValue> defaultLabelValues;
 
@@ -99,7 +100,7 @@ public final class DoubleGaugeImpl extends DoubleGauge implements Meter {
 
   @Override
   public synchronized void clear() {
-    registeredPoints = Collections.emptyMap();
+    registeredPoints = Collections.<List<LabelValue>, PointImpl>emptyMap();
   }
 
   private synchronized DoublePoint registerTimeSeries(List<LabelValue> labelValues) {
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 f158e656..3460d7a4 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
@@ -44,7 +44,8 @@ public final class LongGaugeImpl extends LongGauge 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 volatile Map<List<LabelValue>, PointImpl> registeredPoints =
+      Collections.<List<LabelValue>, PointImpl>emptyMap();
   private final int labelKeysSize;
   private final List<LabelValue> defaultLabelValues;
 
@@ -99,7 +100,7 @@ public final class LongGaugeImpl extends LongGauge implements Meter {
 
   @Override
   public synchronized void clear() {
-    registeredPoints = Collections.emptyMap();
+    registeredPoints = Collections.<List<LabelValue>, PointImpl>emptyMap();
   }
 
   private synchronized LongPoint registerTimeSeries(List<LabelValue> labelValues) {