Gauge API : Add DoubleGauge Support (Part2) (#1496)upstream-master

* Gauge API : Add DoubleGauge Support (Part2)

* Fix review comments

7 files changed, 795 insertions, 27 deletions

diff --git a/api/src/main/java/io/opencensus/metrics/DoubleGauge.java b/api/src/main/java/io/opencensus/metrics/DoubleGauge.java
new file mode 100644
index 00000000..91e131ec
--- /dev/null
+++ b/api/src/main/java/io/opencensus/metrics/DoubleGauge.java
@@ -0,0 +1,214 @@
+/*
+ * 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.metrics;
+
+import io.opencensus.internal.Utils;
+import java.util.List;
+import javax.annotation.concurrent.ThreadSafe;
+
+/**
+ * Double Gauge metric, to report instantaneous measurement of a double value. Gauges can go both up
+ * and down. The gauges values can be negative.
+ *
+ * <p>Example 1: Create a Gauge with default labels.
+ *
+ * <pre>{@code
+ * class YourClass {
+ *
+ *   private static final MetricRegistry metricRegistry = Metrics.getMetricRegistry();
+ *
+ *   List<LabelKey> labelKeys = Arrays.asList(LabelKey.create("Name", "desc"));
+ *   // TODO(mayurkale): Plugs-in the DoubleGauge into the registry.
+ *   DoubleGauge gauge = metricRegistry.addDoubleGauge("queue_size",
+ *                       "Pending jobs", "1", labelKeys);
+ *
+ *   // It is recommended to keep a reference of a point for manual operations.
+ *   DoublePoint defaultPoint = gauge.getDefaultTimeSeries();
+ *
+ *   void doWork() {
+ *      // Your code here.
+ *      defaultPoint.add(10);
+ *   }
+ *
+ * }
+ * }</pre>
+ *
+ * <p>Example 2: You can also use labels(keys and values) to track different types of metric.
+ *
+ * <pre>{@code
+ * class YourClass {
+ *
+ *   private static final MetricRegistry metricRegistry = Metrics.getMetricRegistry();
+ *
+ *   List<LabelKey> labelKeys = Arrays.asList(LabelKey.create("Name", "desc"));
+ *   List<LabelValue> labelValues = Arrays.asList(LabelValue.create("Inbound"));
+ *
+ *   // TODO(mayurkale): Plugs-in the DoubleGauge into the registry.
+ *   DoubleGauge gauge = metricRegistry.addDoubleGauge("queue_size",
+ *                       "Pending jobs", "1", labelKeys);
+ *
+ *   // It is recommended to keep a reference of a point for manual operations.
+ *   DoublePoint inboundPoint = gauge.getOrCreateTimeSeries(labelValues);
+ *
+ *   void doSomeWork() {
+ *      // Your code here.
+ *      inboundPoint.set(15);
+ *   }
+ *
+ * }
+ * }</pre>
+ *
+ * @since 0.17
+ */
+@ThreadSafe
+public abstract class DoubleGauge {
+
+  /**
+   * Creates a {@code TimeSeries} and returns a {@code DoublePoint} if the specified {@code
+   * labelValues} is not already associated with this gauge, else returns an existing {@code
+   * DoublePoint}.
+   *
+   * <p>It is recommended to keep a reference to the DoublePoint instead of always calling this
+   * method for manual operations.
+   *
+   * @param labelValues the list of label values. The number of label values must be the same to
+   *     that of the label keys passed to {@link MetricRegistry#addDoubleGauge}.
+   * @return a {@code DoublePoint} the value of single gauge.
+   * @throws NullPointerException if {@code labelValues} is null OR any element of {@code
+   *     labelValues} is null.
+   * @throws IllegalArgumentException if number of {@code labelValues}s are not equal to the label
+   *     keys passed to {@link MetricRegistry#addDoubleGauge}.
+   * @since 0.17
+   */
+  public abstract DoublePoint getOrCreateTimeSeries(List<LabelValue> labelValues);
+
+  /**
+   * Returns a {@code DoublePoint} for a gauge with all labels not set, or default labels.
+   *
+   * @return a {@code DoublePoint} for a gauge with all labels not set, or default labels.
+   * @since 0.17
+   */
+  public abstract DoublePoint getDefaultTimeSeries();
+
+  /**
+   * Removes the {@code TimeSeries} from the gauge metric, if it is present. i.e. references to
+   * previous {@code DoublePoint} objects are invalid (not part of the metric).
+   *
+   * @param labelValues the list of label values.
+   * @throws NullPointerException if {@code labelValues} is null or any element of {@code
+   *     labelValues} is null.
+   * @since 0.17
+   */
+  public abstract void removeTimeSeries(List<LabelValue> labelValues);
+
+  /**
+   * Removes all {@code TimeSeries} from the gauge metric. i.e. references to all previous {@code
+   * DoublePoint} objects are invalid (not part of the metric).
+   *
+   * @since 0.17
+   */
+  public abstract void clear();
+
+  /**
+   * Returns the no-op implementation of the {@code DoubleGauge}.
+   *
+   * @return the no-op implementation of the {@code DoubleGauge}.
+   * @since 0.17
+   */
+  static DoubleGauge newNoopDoubleGauge(
+      String name, String description, String unit, List<LabelKey> labelKeys) {
+    return NoopDoubleGauge.create(name, description, unit, labelKeys);
+  }
+
+  /**
+   * The value of a single point in the Gauge.TimeSeries.
+   *
+   * @since 0.17
+   */
+  public abstract static class DoublePoint {
+
+    /**
+     * Adds the given value to the current value. The values can be negative.
+     *
+     * @param amt the value to add
+     * @since 0.17
+     */
+    public abstract void add(double amt);
+
+    /**
+     * Sets the given value.
+     *
+     * @param val the new value.
+     * @since 0.17
+     */
+    public abstract void set(double val);
+  }
+
+  /** No-op implementations of DoubleGauge class. */
+  private static final class NoopDoubleGauge extends DoubleGauge {
+    private final int labelKeysSize;
+
+    static NoopDoubleGauge create(
+        String name, String description, String unit, List<LabelKey> labelKeys) {
+      return new NoopDoubleGauge(name, description, unit, labelKeys);
+    }
+
+    /** Creates a new {@code NoopDoublePoint}. */
+    NoopDoubleGauge(String name, String description, String unit, List<LabelKey> labelKeys) {
+      Utils.checkNotNull(name, "name");
+      Utils.checkNotNull(description, "description");
+      Utils.checkNotNull(unit, "unit");
+      Utils.checkNotNull(labelKeys, "labelKeys should not be null.");
+      Utils.checkListElementNotNull(labelKeys, "labelKeys element should not be null.");
+      labelKeysSize = labelKeys.size();
+    }
+
+    @Override
+    public NoopDoublePoint getOrCreateTimeSeries(List<LabelValue> labelValues) {
+      Utils.checkNotNull(labelValues, "labelValues should not be null.");
+      Utils.checkListElementNotNull(labelValues, "labelValues element should not be null.");
+      Utils.checkArgument(labelKeysSize == labelValues.size(), "Incorrect number of labels.");
+      return NoopDoublePoint.INSTANCE;
+    }
+
+    @Override
+    public NoopDoublePoint getDefaultTimeSeries() {
+      return NoopDoublePoint.INSTANCE;
+    }
+
+    @Override
+    public void removeTimeSeries(List<LabelValue> labelValues) {
+      Utils.checkNotNull(labelValues, "labelValues should not be null.");
+    }
+
+    @Override
+    public void clear() {}
+
+    /** No-op implementations of DoublePoint class. */
+    private static final class NoopDoublePoint extends DoublePoint {
+      private static final NoopDoublePoint INSTANCE = new NoopDoublePoint();
+
+      private NoopDoublePoint() {}
+
+      @Override
+      public void add(double amt) {}
+
+      @Override
+      public void set(double val) {}
+    }
+  }
+}
diff --git a/api/src/main/java/io/opencensus/metrics/LongGauge.java b/api/src/main/java/io/opencensus/metrics/LongGauge.java
index 2294f0cf..42951d50 100644
--- a/api/src/main/java/io/opencensus/metrics/LongGauge.java
+++ b/api/src/main/java/io/opencensus/metrics/LongGauge.java
@@ -77,7 +77,7 @@ public abstract class LongGauge {
 
   /**
    * Creates a {@code TimeSeries} and returns a {@code LongPoint} if the specified {@code
-   * labelValues} is not already associated with this gauge, else returns a existing {@code
+   * labelValues} is not already associated with this gauge, else returns an existing {@code
    * LongPoint}.
    *
    * <p>It is recommended to keep a reference to the LongPoint instead of always calling this method
@@ -97,7 +97,7 @@ public abstract class LongGauge {
   /**
    * Returns a {@code LongPoint} for a gauge with all labels not set, or default labels.
    *
-   * @return a {@code LongPoint} the value of default gauge.
+   * @return a {@code LongPoint} for a gauge with all labels not set, or default labels.
    * @since 0.17
    */
   public abstract LongPoint getDefaultTimeSeries();
@@ -114,7 +114,8 @@ public abstract class LongGauge {
   public abstract void removeTimeSeries(List<LabelValue> labelValues);
 
   /**
-   * References to all previous {@code LongPoint} objects are invalid (not part of the metric).
+   * Removes all {@code TimeSeries} from the gauge metric. i.e. references to all previous {@code
+   * LongPoint} objects are invalid (not part of the metric).
    *
    * @since 0.17
    */
diff --git a/api/src/test/java/io/opencensus/metrics/DoubleGaugeTest.java b/api/src/test/java/io/opencensus/metrics/DoubleGaugeTest.java
new file mode 100644
index 00000000..5690bd44
--- /dev/null
+++ b/api/src/test/java/io/opencensus/metrics/DoubleGaugeTest.java
@@ -0,0 +1,88 @@
+/*
+ * 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.metrics;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Unit tests for {@link DoubleGauge}. */
+@RunWith(JUnit4.class)
+public class DoubleGaugeTest {
+  @Rule public ExpectedException thrown = ExpectedException.none();
+
+  private static final String NAME = "name";
+  private static final String DESCRIPTION = "description";
+  private static final String UNIT = "1";
+  private static final List<LabelKey> LABEL_KEY =
+      Collections.singletonList(LabelKey.create("key", "key description"));
+  private static final List<LabelValue> LABEL_VALUES =
+      Collections.singletonList(LabelValue.create("value"));
+  private static final List<LabelKey> EMPTY_LABEL_KEYS = new ArrayList<LabelKey>();
+  private static final List<LabelValue> EMPTY_LABEL_VALUES = new ArrayList<LabelValue>();
+
+  // TODO(mayurkale): Add more tests, once DoubleGauge plugs-in into the registry.
+
+  @Test
+  public void noopGetOrCreateTimeSeries_WithNullLabelValues() {
+    DoubleGauge doubleGauge =
+        DoubleGauge.newNoopDoubleGauge(NAME, DESCRIPTION, UNIT, EMPTY_LABEL_KEYS);
+    thrown.expect(NullPointerException.class);
+    thrown.expectMessage("labelValues should not be null.");
+    doubleGauge.getOrCreateTimeSeries(null);
+  }
+
+  @Test
+  public void noopGetOrCreateTimeSeries_WithNullElement() {
+    List<LabelValue> labelValues = Collections.singletonList(null);
+    DoubleGauge doubleGauge = DoubleGauge.newNoopDoubleGauge(NAME, DESCRIPTION, UNIT, LABEL_KEY);
+    thrown.expect(NullPointerException.class);
+    thrown.expectMessage("labelValues element should not be null.");
+    doubleGauge.getOrCreateTimeSeries(labelValues);
+  }
+
+  @Test
+  public void noopGetOrCreateTimeSeries_WithInvalidLabelSize() {
+    DoubleGauge doubleGauge = DoubleGauge.newNoopDoubleGauge(NAME, DESCRIPTION, UNIT, LABEL_KEY);
+    thrown.expect(IllegalArgumentException.class);
+    thrown.expectMessage("Incorrect number of labels.");
+    doubleGauge.getOrCreateTimeSeries(EMPTY_LABEL_VALUES);
+  }
+
+  @Test
+  public void noopRemoveTimeSeries_WithNullLabelValues() {
+    DoubleGauge doubleGauge = DoubleGauge.newNoopDoubleGauge(NAME, DESCRIPTION, UNIT, LABEL_KEY);
+    thrown.expect(NullPointerException.class);
+    thrown.expectMessage("labelValues should not be null.");
+    doubleGauge.removeTimeSeries(null);
+  }
+
+  @Test
+  public void noopSameAs() {
+    DoubleGauge doubleGauge = DoubleGauge.newNoopDoubleGauge(NAME, DESCRIPTION, UNIT, LABEL_KEY);
+    assertThat(doubleGauge.getDefaultTimeSeries()).isSameAs(doubleGauge.getDefaultTimeSeries());
+    assertThat(doubleGauge.getDefaultTimeSeries())
+        .isSameAs(doubleGauge.getOrCreateTimeSeries(LABEL_VALUES));
+  }
+}
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));
     }
diff --git a/impl_core/src/test/java/io/opencensus/implcore/metrics/DoubleGaugeImplTest.java b/impl_core/src/test/java/io/opencensus/implcore/metrics/DoubleGaugeImplTest.java
new file mode 100644
index 00000000..61de77b6
--- /dev/null
+++ b/impl_core/src/test/java/io/opencensus/implcore/metrics/DoubleGaugeImplTest.java
@@ -0,0 +1,292 @@
+/*
+ * 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.truth.Truth.assertThat;
+import static io.opencensus.implcore.metrics.DoubleGaugeImpl.UNSET_VALUE;
+
+import com.google.common.testing.EqualsTester;
+import io.opencensus.common.Timestamp;
+import io.opencensus.metrics.DoubleGauge.DoublePoint;
+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 io.opencensus.testing.common.TestClock;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Unit tests for {@link DoubleGaugeImpl}. */
+@RunWith(JUnit4.class)
+public class DoubleGaugeImplTest {
+  @Rule public ExpectedException thrown = ExpectedException.none();
+
+  private static final String METRIC_NAME = "name";
+  private static final String METRIC_DESCRIPTION = "description";
+  private static final String METRIC_UNIT = "1";
+  private static final List<LabelKey> LABEL_KEY =
+      Collections.singletonList(LabelKey.create("key", "key description"));
+  private static final List<LabelValue> LABEL_VALUES =
+      Collections.singletonList(LabelValue.create("value"));
+  private static final List<LabelValue> LABEL_VALUES1 =
+      Collections.singletonList(LabelValue.create("value1"));
+  private static final List<LabelValue> DEFAULT_LABEL_VALUES =
+      Collections.singletonList(UNSET_VALUE);
+
+  private static final Timestamp TEST_TIME = Timestamp.create(1234, 123);
+  private final TestClock testClock = TestClock.create(TEST_TIME);
+  private static final MetricDescriptor METRIC_DESCRIPTOR =
+      MetricDescriptor.create(
+          METRIC_NAME, METRIC_DESCRIPTION, METRIC_UNIT, Type.GAUGE_DOUBLE, LABEL_KEY);
+  private final DoubleGaugeImpl doubleGauge =
+      new DoubleGaugeImpl(METRIC_NAME, METRIC_DESCRIPTION, METRIC_UNIT, LABEL_KEY);
+
+  @Test
+  public void getOrCreateTimeSeries_WithNullLabelValues() {
+    thrown.expect(NullPointerException.class);
+    thrown.expectMessage("labelValues should not be null.");
+    doubleGauge.getOrCreateTimeSeries(null);
+  }
+
+  @Test
+  public void getOrCreateTimeSeries_WithNullElement() {
+    List<LabelKey> labelKeys =
+        Arrays.asList(LabelKey.create("key1", "desc"), LabelKey.create("key2", "desc"));
+    List<LabelValue> labelValues = Arrays.asList(LabelValue.create("value1"), null);
+
+    DoubleGaugeImpl doubleGauge =
+        new DoubleGaugeImpl(METRIC_NAME, METRIC_DESCRIPTION, METRIC_UNIT, labelKeys);
+    thrown.expect(NullPointerException.class);
+    thrown.expectMessage("labelValues element should not be null.");
+    doubleGauge.getOrCreateTimeSeries(labelValues);
+  }
+
+  @Test
+  public void getOrCreateTimeSeries_WithInvalidLabelSize() {
+    List<LabelValue> labelValues =
+        Arrays.asList(LabelValue.create("value1"), LabelValue.create("value2"));
+
+    thrown.expect(IllegalArgumentException.class);
+    thrown.expectMessage("Incorrect number of labels.");
+    doubleGauge.getOrCreateTimeSeries(labelValues);
+  }
+
+  @Test
+  public void getOrCreateTimeSeries() {
+    DoublePoint point = doubleGauge.getOrCreateTimeSeries(LABEL_VALUES);
+    point.add(100);
+    DoublePoint point1 = doubleGauge.getOrCreateTimeSeries(LABEL_VALUES);
+    point1.set(500);
+
+    Metric metric = doubleGauge.getMetric(testClock);
+    assertThat(metric).isNotNull();
+    assertThat(metric)
+        .isEqualTo(
+            Metric.create(
+                METRIC_DESCRIPTOR,
+                Collections.singletonList(
+                    TimeSeries.createWithOnePoint(
+                        LABEL_VALUES, Point.create(Value.doubleValue(500), TEST_TIME), null))));
+    assertThat(point).isSameAs(point1);
+  }
+
+  @Test
+  public void getOrCreateTimeSeries_WithNegativePointValues() {
+    DoublePoint point = doubleGauge.getOrCreateTimeSeries(LABEL_VALUES);
+    point.add(-100);
+    point.add(-33);
+
+    Metric metric = doubleGauge.getMetric(testClock);
+    assertThat(metric).isNotNull();
+    assertThat(metric.getMetricDescriptor()).isEqualTo(METRIC_DESCRIPTOR);
+    assertThat(metric.getTimeSeriesList().size()).isEqualTo(1);
+    assertThat(metric.getTimeSeriesList().get(0).getPoints().size()).isEqualTo(1);
+    assertThat(metric.getTimeSeriesList().get(0).getPoints().get(0).getValue())
+        .isEqualTo(Value.doubleValue(-133));
+    assertThat(metric.getTimeSeriesList().get(0).getPoints().get(0).getTimestamp())
+        .isEqualTo(TEST_TIME);
+    assertThat(metric.getTimeSeriesList().get(0).getStartTimestamp()).isNull();
+  }
+
+  @Test
+  public void getDefaultTimeSeries() {
+    DoublePoint point = doubleGauge.getDefaultTimeSeries();
+    point.add(100);
+    point.set(500);
+
+    DoublePoint point1 = doubleGauge.getDefaultTimeSeries();
+    point1.add(-100);
+
+    Metric metric = doubleGauge.getMetric(testClock);
+    assertThat(metric).isNotNull();
+    assertThat(metric)
+        .isEqualTo(
+            Metric.create(
+                METRIC_DESCRIPTOR,
+                Collections.singletonList(
+                    TimeSeries.createWithOnePoint(
+                        DEFAULT_LABEL_VALUES,
+                        Point.create(Value.doubleValue(400), TEST_TIME),
+                        null))));
+    assertThat(point).isSameAs(point1);
+  }
+
+  @Test
+  public void removeTimeSeries() {
+    doubleGauge.getOrCreateTimeSeries(LABEL_VALUES);
+    assertThat(doubleGauge.getMetric(testClock))
+        .isEqualTo(
+            Metric.create(
+                METRIC_DESCRIPTOR,
+                Collections.singletonList(
+                    TimeSeries.createWithOnePoint(
+                        LABEL_VALUES, Point.create(Value.doubleValue(0), TEST_TIME), null))));
+
+    doubleGauge.removeTimeSeries(LABEL_VALUES);
+    assertThat(doubleGauge.getMetric(testClock)).isNull();
+  }
+
+  @Test
+  public void removeTimeSeries_WithNullLabelValues() {
+    thrown.expect(NullPointerException.class);
+    thrown.expectMessage("labelValues should not be null.");
+    doubleGauge.removeTimeSeries(null);
+  }
+
+  @Test
+  public void clear() {
+    DoublePoint doublePoint = doubleGauge.getOrCreateTimeSeries(LABEL_VALUES);
+    doublePoint.add(-11);
+    DoublePoint defaultPoint = doubleGauge.getDefaultTimeSeries();
+    defaultPoint.set(100);
+
+    Metric metric = doubleGauge.getMetric(testClock);
+    assertThat(metric).isNotNull();
+    assertThat(metric.getMetricDescriptor()).isEqualTo(METRIC_DESCRIPTOR);
+    assertThat(metric.getTimeSeriesList().size()).isEqualTo(2);
+
+    doubleGauge.clear();
+    assertThat(doubleGauge.getMetric(testClock)).isNull();
+  }
+
+  @Test
+  public void setDefaultLabelValues() {
+    List<LabelKey> labelKeys =
+        Arrays.asList(LabelKey.create("key1", "desc"), LabelKey.create("key2", "desc"));
+    DoubleGaugeImpl doubleGauge =
+        new DoubleGaugeImpl(METRIC_NAME, METRIC_DESCRIPTION, METRIC_UNIT, labelKeys);
+    DoublePoint defaultPoint = doubleGauge.getDefaultTimeSeries();
+    defaultPoint.set(-230);
+
+    Metric metric = doubleGauge.getMetric(testClock);
+    assertThat(metric).isNotNull();
+    assertThat(metric.getTimeSeriesList().size()).isEqualTo(1);
+    assertThat(metric.getTimeSeriesList().get(0).getLabelValues().size()).isEqualTo(2);
+    assertThat(metric.getTimeSeriesList().get(0).getLabelValues().get(0)).isEqualTo(UNSET_VALUE);
+    assertThat(metric.getTimeSeriesList().get(0).getLabelValues().get(1)).isEqualTo(UNSET_VALUE);
+  }
+
+  @Test
+  public void pointImpl_InstanceOf() {
+    DoublePoint doublePoint = doubleGauge.getOrCreateTimeSeries(LABEL_VALUES);
+    assertThat(doublePoint).isInstanceOf(DoubleGaugeImpl.PointImpl.class);
+  }
+
+  @Test
+  public void multipleMetrics_GetMetric() {
+    DoublePoint doublePoint = doubleGauge.getOrCreateTimeSeries(LABEL_VALUES);
+    doublePoint.add(1);
+    doublePoint.add(2);
+
+    DoublePoint defaultPoint = doubleGauge.getDefaultTimeSeries();
+    defaultPoint.set(100);
+
+    DoublePoint doublePoint1 = doubleGauge.getOrCreateTimeSeries(LABEL_VALUES1);
+    doublePoint1.add(-100);
+    doublePoint1.add(-20);
+
+    List<TimeSeries> expectedTimeSeriesList = new ArrayList<TimeSeries>();
+    expectedTimeSeriesList.add(
+        TimeSeries.createWithOnePoint(
+            LABEL_VALUES, Point.create(Value.doubleValue(3), TEST_TIME), null));
+    expectedTimeSeriesList.add(
+        TimeSeries.createWithOnePoint(
+            DEFAULT_LABEL_VALUES, Point.create(Value.doubleValue(100), TEST_TIME), null));
+    expectedTimeSeriesList.add(
+        TimeSeries.createWithOnePoint(
+            LABEL_VALUES1, Point.create(Value.doubleValue(-120), TEST_TIME), null));
+
+    Metric metric = doubleGauge.getMetric(testClock);
+    assertThat(metric).isNotNull();
+    assertThat(metric.getMetricDescriptor()).isEqualTo(METRIC_DESCRIPTOR);
+    assertThat(metric.getTimeSeriesList().size()).isEqualTo(3);
+    assertThat(metric.getTimeSeriesList()).containsExactlyElementsIn(expectedTimeSeriesList);
+  }
+
+  @Test
+  public void empty_GetMetrics() {
+    assertThat(doubleGauge.getMetric(testClock)).isNull();
+  }
+
+  @Test
+  public void testEquals() {
+    List<LabelKey> labelKeys =
+        Arrays.asList(LabelKey.create("key1", "desc"), LabelKey.create("key2", "desc"));
+    List<LabelValue> labelValues =
+        Arrays.asList(LabelValue.create("value1"), LabelValue.create("value2"));
+
+    DoubleGaugeImpl doubleGauge =
+        new DoubleGaugeImpl(METRIC_NAME, METRIC_DESCRIPTION, METRIC_UNIT, labelKeys);
+
+    DoublePoint defaultPoint1 = doubleGauge.getDefaultTimeSeries();
+    DoublePoint defaultPoint2 = doubleGauge.getDefaultTimeSeries();
+    DoublePoint doublePoint1 = doubleGauge.getOrCreateTimeSeries(labelValues);
+    DoublePoint doublePoint2 = doubleGauge.getOrCreateTimeSeries(labelValues);
+
+    new EqualsTester()
+        .addEqualityGroup(defaultPoint1, defaultPoint2)
+        .addEqualityGroup(doublePoint1, doublePoint2)
+        .testEquals();
+
+    doubleGauge.clear();
+
+    DoublePoint newDefaultPointAfterClear = doubleGauge.getDefaultTimeSeries();
+    DoublePoint newDoublePointAfterClear = doubleGauge.getOrCreateTimeSeries(labelValues);
+
+    doubleGauge.removeTimeSeries(labelValues);
+    DoublePoint newDoublePointAfterRemove = doubleGauge.getOrCreateTimeSeries(labelValues);
+
+    new EqualsTester()
+        .addEqualityGroup(defaultPoint1, defaultPoint2)
+        .addEqualityGroup(doublePoint1, doublePoint2)
+        .addEqualityGroup(newDefaultPointAfterClear)
+        .addEqualityGroup(newDoublePointAfterClear)
+        .addEqualityGroup(newDoublePointAfterRemove)
+        .testEquals();
+  }
+}
diff --git a/impl_core/src/test/java/io/opencensus/implcore/metrics/LongGaugeImplTest.java b/impl_core/src/test/java/io/opencensus/implcore/metrics/LongGaugeImplTest.java
index 81637c61..25797cff 100644
--- a/impl_core/src/test/java/io/opencensus/implcore/metrics/LongGaugeImplTest.java
+++ b/impl_core/src/test/java/io/opencensus/implcore/metrics/LongGaugeImplTest.java
@@ -104,14 +104,14 @@ public class LongGaugeImplTest {
     point1.set(500);
 
     Metric metric = longGaugeMetric.getMetric(testClock);
-    assertThat(metric).isNotEqualTo(null);
+    assertThat(metric).isNotNull();
     assertThat(metric)
         .isEqualTo(
             Metric.createWithOneTimeSeries(
                 METRIC_DESCRIPTOR,
                 TimeSeries.createWithOnePoint(
                     LABEL_VALUES, Point.create(Value.longValue(500), TEST_TIME), null)));
-    new EqualsTester().addEqualityGroup(point, point1).testEquals();
+    assertThat(point).isSameAs(point1);
   }
 
   @Test
@@ -121,7 +121,7 @@ public class LongGaugeImplTest {
     point.add(-33);
 
     Metric metric = longGaugeMetric.getMetric(testClock);
-    assertThat(metric).isNotEqualTo(null);
+    assertThat(metric).isNotNull();
     assertThat(metric.getMetricDescriptor()).isEqualTo(METRIC_DESCRIPTOR);
     assertThat(metric.getTimeSeriesList().size()).isEqualTo(1);
     assertThat(metric.getTimeSeriesList().get(0).getPoints().size()).isEqualTo(1);
@@ -129,7 +129,7 @@ public class LongGaugeImplTest {
         .isEqualTo(Value.longValue(-133));
     assertThat(metric.getTimeSeriesList().get(0).getPoints().get(0).getTimestamp())
         .isEqualTo(TEST_TIME);
-    assertThat(metric.getTimeSeriesList().get(0).getStartTimestamp()).isEqualTo(null);
+    assertThat(metric.getTimeSeriesList().get(0).getStartTimestamp()).isNull();
   }
 
   @Test
@@ -142,14 +142,14 @@ public class LongGaugeImplTest {
     point1.add(-100);
 
     Metric metric = longGaugeMetric.getMetric(testClock);
-    assertThat(metric).isNotEqualTo(null);
+    assertThat(metric).isNotNull();
     assertThat(metric)
         .isEqualTo(
             Metric.createWithOneTimeSeries(
                 METRIC_DESCRIPTOR,
                 TimeSeries.createWithOnePoint(
                     DEFAULT_LABEL_VALUES, Point.create(Value.longValue(400), TEST_TIME), null)));
-    new EqualsTester().addEqualityGroup(point, point1).testEquals();
+    assertThat(point).isSameAs(point1);
   }
 
   @Test
@@ -163,7 +163,7 @@ public class LongGaugeImplTest {
                     LABEL_VALUES, Point.create(Value.longValue(0), TEST_TIME), null)));
 
     longGaugeMetric.removeTimeSeries(LABEL_VALUES);
-    assertThat(longGaugeMetric.getMetric(testClock)).isEqualTo(null);
+    assertThat(longGaugeMetric.getMetric(testClock)).isNull();
   }
 
   @Test
@@ -181,12 +181,12 @@ public class LongGaugeImplTest {
     defaultPoint.set(100);
 
     Metric metric = longGaugeMetric.getMetric(testClock);
-    assertThat(metric).isNotEqualTo(null);
+    assertThat(metric).isNotNull();
     assertThat(metric.getMetricDescriptor()).isEqualTo(METRIC_DESCRIPTOR);
     assertThat(metric.getTimeSeriesList().size()).isEqualTo(2);
 
     longGaugeMetric.clear();
-    assertThat(longGaugeMetric.getMetric(testClock)).isEqualTo(null);
+    assertThat(longGaugeMetric.getMetric(testClock)).isNull();
   }
 
   @Test
@@ -199,7 +199,7 @@ public class LongGaugeImplTest {
     defaultPoint.set(-230);
 
     Metric metric = longGauge.getMetric(testClock);
-    assertThat(metric).isNotEqualTo(null);
+    assertThat(metric).isNotNull();
     assertThat(metric.getTimeSeriesList().size()).isEqualTo(1);
     assertThat(metric.getTimeSeriesList().get(0).getLabelValues().size()).isEqualTo(2);
     assertThat(metric.getTimeSeriesList().get(0).getLabelValues().get(0)).isEqualTo(UNSET_VALUE);
@@ -225,27 +225,27 @@ public class LongGaugeImplTest {
     longPoint1.add(-100);
     longPoint1.add(-20);
 
-    List<TimeSeries> timeSeriesList = new ArrayList<TimeSeries>();
-    timeSeriesList.add(
+    List<TimeSeries> expectedTimeSeriesList = new ArrayList<TimeSeries>();
+    expectedTimeSeriesList.add(
         TimeSeries.createWithOnePoint(
             LABEL_VALUES, Point.create(Value.longValue(3), TEST_TIME), null));
-    timeSeriesList.add(
+    expectedTimeSeriesList.add(
         TimeSeries.createWithOnePoint(
             DEFAULT_LABEL_VALUES, Point.create(Value.longValue(100), TEST_TIME), null));
-    timeSeriesList.add(
+    expectedTimeSeriesList.add(
         TimeSeries.createWithOnePoint(
             LABEL_VALUES1, Point.create(Value.longValue(-120), TEST_TIME), null));
 
     Metric metric = longGaugeMetric.getMetric(testClock);
-    assertThat(metric).isNotEqualTo(null);
+    assertThat(metric).isNotNull();
     assertThat(metric.getMetricDescriptor()).isEqualTo(METRIC_DESCRIPTOR);
     assertThat(metric.getTimeSeriesList().size()).isEqualTo(3);
-    assertThat(metric.getTimeSeriesList()).containsExactlyElementsIn(timeSeriesList);
+    assertThat(metric.getTimeSeriesList()).containsExactlyElementsIn(expectedTimeSeriesList);
   }
 
   @Test
   public void empty_GetMetrics() {
-    assertThat(longGaugeMetric.getMetric(testClock)).isEqualTo(null);
+    assertThat(longGaugeMetric.getMetric(testClock)).isNull();
   }
 
   @Test