Add support for recording Gauges. (#1344)

* Add support for Gauges in OpenCensus.

* Minor comment fix.

10 files changed, 415 insertions, 5 deletions

diff --git a/api/src/main/java/io/opencensus/common/ToDoubleFunction.java b/api/src/main/java/io/opencensus/common/ToDoubleFunction.java
new file mode 100644
index 00000000..479270f1
--- /dev/null
+++ b/api/src/main/java/io/opencensus/common/ToDoubleFunction.java
@@ -0,0 +1,39 @@
+/*
+ * 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.common;
+
+// TODO(bdrutu): Change @code to @link when metrics is moved in the API.
+
+/**
+ * Represents a function that produces a double-valued result. See {@code
+ * io.opencensus.metrics.MetricRegistry} for an example of its use.
+ *
+ * <p>Note: This class is based on the java.util.ToDoubleFunction class added in Java 1.8. We cannot
+ * use the Function from Java 1.8 because this library is Java 1.6 compatible.
+ *
+ * @since 0.16
+ */
+public interface ToDoubleFunction<T> {
+
+  /**
+   * Applies this function to the given argument.
+   *
+   * @param value the function argument.
+   * @return the function result.
+   */
+  double applyAsDouble(T value);
+}
diff --git a/api/src/main/java/io/opencensus/common/ToLongFunction.java b/api/src/main/java/io/opencensus/common/ToLongFunction.java
new file mode 100644
index 00000000..9a6e9b19
--- /dev/null
+++ b/api/src/main/java/io/opencensus/common/ToLongFunction.java
@@ -0,0 +1,38 @@
+/*
+ * 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.common;
+
+// TODO(bdrutu): Change @code to @link when metrics is moved in the API.
+
+/**
+ * Represents a function that produces a long-valued result. See {@code
+ * io.opencensus.metrics.MetricRegistry} for an example of its use.
+ *
+ * <p>Note: This class is based on the java.util.ToLongFunction class added in Java 1.8. We cannot
+ * use the Function from Java 1.8 because this library is Java 1.6 compatible.
+ *
+ * @since 0.16
+ */
+public interface ToLongFunction<T> {
+  /**
+   * Applies this function to the given argument.
+   *
+   * @param value the function argument.
+   * @return the function result.
+   */
+  long applyAsLong(T value);
+}
diff --git a/metrics/src/main/java/io/opencensus/metrics/export/MetricProducer.java b/metrics/src/main/java/io/opencensus/metrics/MetricProducer.java
index a6658ac1..38b5d571 100644
--- a/metrics/src/main/java/io/opencensus/metrics/export/MetricProducer.java
+++ b/metrics/src/main/java/io/opencensus/metrics/MetricProducer.java
@@ -14,14 +14,14 @@
  * limitations under the License.
  */
 
-package io.opencensus.metrics.export;
+package io.opencensus.metrics;
 
 import io.opencensus.common.ExperimentalApi;
-import io.opencensus.metrics.Metric;
+import io.opencensus.metrics.export.MetricProducerManager;
 import java.util.Collection;
 
 /**
- * A {@link Metric} producer that can be registered for exporting using {@link
+ * A {@link io.opencensus.metrics.Metric} producer that can be registered for exporting using {@link
  * MetricProducerManager}.
  *
  * <p>All implementation MUST be thread-safe.
@@ -30,9 +30,9 @@ import java.util.Collection;
 public abstract class MetricProducer {
 
   /**
-   * Returns a collection of produced {@link Metric}s to be exported.
+   * Returns a collection of produced {@link io.opencensus.metrics.Metric}s to be exported.
    *
-   * @return a collection of produced {@link Metric}s to be exported.
+   * @return a collection of produced {@link io.opencensus.metrics.Metric}s to be exported.
    */
   public abstract Collection<Metric> getMetrics();
 }
diff --git a/metrics/src/main/java/io/opencensus/metrics/MetricRegistry.java b/metrics/src/main/java/io/opencensus/metrics/MetricRegistry.java
new file mode 100644
index 00000000..ae4d90b0
--- /dev/null
+++ b/metrics/src/main/java/io/opencensus/metrics/MetricRegistry.java
@@ -0,0 +1,117 @@
+/*
+ * 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.common.ExperimentalApi;
+import io.opencensus.common.ToDoubleFunction;
+import io.opencensus.common.ToLongFunction;
+import io.opencensus.internal.Utils;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+
+/**
+ * Creates and manages your application's set of metrics. Exporters use the metric registry to
+ * iterate over the set of metrics instrumenting your application, and then further export each
+ * metric to the backend of choice.
+ *
+ * @since 0.16
+ */
+@ExperimentalApi
+public abstract class MetricRegistry extends MetricProducer {
+  /**
+   * Build a new long gauge to be added to the registry.
+   *
+   * <p>Must be called only once.
+   *
+   * @param name the name of the metric.
+   * @param description the description of the metric.
+   * @param unit the unit of the metric.
+   * @param obj the function argument.
+   * @param function the function to be called.
+   * @since 0.16 @ExperimentalApi
+   */
+  public abstract <T> void addLongGauge(
+      String name,
+      String description,
+      String unit,
+      LinkedHashMap<LabelKey, LabelValue> labels,
+      T obj,
+      ToLongFunction<T> function);
+
+  /**
+   * Build a new double gauge to be added to the registry.
+   *
+   * <p>Must be called only once.
+   *
+   * @param name the name of the metric.
+   * @param description the description of the metric.
+   * @param unit the unit of the metric.
+   * @param obj the function argument.
+   * @param function the function to be called.
+   * @since 0.16 @ExperimentalApi
+   */
+  public abstract <T> void addDoubleGauge(
+      String name,
+      String description,
+      String unit,
+      LinkedHashMap<LabelKey, LabelValue> labels,
+      T obj,
+      ToDoubleFunction<T> function);
+
+  static MetricRegistry newNoopMetricRegistry() {
+    return new NoopMetricRegistry();
+  }
+
+  private static final class NoopMetricRegistry extends MetricRegistry {
+
+    @Override
+    public <T> void addLongGauge(
+        String name,
+        String description,
+        String unit,
+        LinkedHashMap<LabelKey, LabelValue> labels,
+        T obj,
+        ToLongFunction<T> function) {
+      Utils.checkNotNull(name, "name");
+      Utils.checkNotNull(description, "description");
+      Utils.checkNotNull(unit, "unit");
+      Utils.checkNotNull(labels, "labels");
+      Utils.checkNotNull(function, "function");
+    }
+
+    @Override
+    public <T> void addDoubleGauge(
+        String name,
+        String description,
+        String unit,
+        LinkedHashMap<LabelKey, LabelValue> labels,
+        T obj,
+        ToDoubleFunction<T> function) {
+      Utils.checkNotNull(name, "name");
+      Utils.checkNotNull(description, "description");
+      Utils.checkNotNull(unit, "unit");
+      Utils.checkNotNull(labels, "labels");
+      Utils.checkNotNull(function, "function");
+    }
+
+    @Override
+    public Collection<Metric> getMetrics() {
+      return Collections.emptyList();
+    }
+  }
+}
diff --git a/metrics/src/main/java/io/opencensus/metrics/Metrics.java b/metrics/src/main/java/io/opencensus/metrics/Metrics.java
index e36bc4e1..ed7d6716 100644
--- a/metrics/src/main/java/io/opencensus/metrics/Metrics.java
+++ b/metrics/src/main/java/io/opencensus/metrics/Metrics.java
@@ -40,6 +40,19 @@ public final class Metrics {
     return metricsComponent.getExportComponent();
   }
 
+  /**
+   * Returns the global {@link MetricRegistry}.
+   *
+   * <p>This {@code MetricRegistry} is already added to the global {@link
+   * io.opencensus.metrics.export.MetricProducerManager}.
+   *
+   * @return the global {@code MetricRegistry}.
+   * @since 0.16
+   */
+  public static MetricRegistry getMetricRegistry() {
+    return metricsComponent.getMetricRegistry();
+  }
+
   // Any provider that may be used for MetricsComponent can be added here.
   @DefaultVisibilityForTesting
   static MetricsComponent loadMetricsComponent(@Nullable ClassLoader classLoader) {
diff --git a/metrics/src/main/java/io/opencensus/metrics/MetricsComponent.java b/metrics/src/main/java/io/opencensus/metrics/MetricsComponent.java
index df6d4aec..08d954ef 100644
--- a/metrics/src/main/java/io/opencensus/metrics/MetricsComponent.java
+++ b/metrics/src/main/java/io/opencensus/metrics/MetricsComponent.java
@@ -37,6 +37,14 @@ public abstract class MetricsComponent {
   public abstract ExportComponent getExportComponent();
 
   /**
+   * Returns the {@link MetricRegistry} with the provided implementation.
+   *
+   * @return the {@link MetricRegistry} implementation.
+   * @since 0.16
+   */
+  public abstract MetricRegistry getMetricRegistry();
+
+  /**
    * Returns an instance that contains no-op implementations for all the instances.
    *
    * @return an instance that contains no-op implementations for all the instances.
@@ -48,10 +56,16 @@ public abstract class MetricsComponent {
   private static final class NoopMetricsComponent extends MetricsComponent {
     private static final ExportComponent EXPORT_COMPONENT =
         ExportComponent.newNoopExportComponent();
+    private static final MetricRegistry METRIC_REGISTRY = MetricRegistry.newNoopMetricRegistry();
 
     @Override
     public ExportComponent getExportComponent() {
       return EXPORT_COMPONENT;
     }
+
+    @Override
+    public MetricRegistry getMetricRegistry() {
+      return METRIC_REGISTRY;
+    }
   }
 }
diff --git a/metrics/src/main/java/io/opencensus/metrics/export/MetricProducerManager.java b/metrics/src/main/java/io/opencensus/metrics/export/MetricProducerManager.java
index ae744635..9600a023 100644
--- a/metrics/src/main/java/io/opencensus/metrics/export/MetricProducerManager.java
+++ b/metrics/src/main/java/io/opencensus/metrics/export/MetricProducerManager.java
@@ -18,6 +18,7 @@ package io.opencensus.metrics.export;
 
 import io.opencensus.common.ExperimentalApi;
 import io.opencensus.internal.Utils;
+import io.opencensus.metrics.MetricProducer;
 import java.util.Collections;
 import java.util.LinkedHashSet;
 import java.util.Set;
diff --git a/metrics/src/test/java/io/opencensus/metrics/MetricRegistryTest.java b/metrics/src/test/java/io/opencensus/metrics/MetricRegistryTest.java
new file mode 100644
index 00000000..0e467dc8
--- /dev/null
+++ b/metrics/src/test/java/io/opencensus/metrics/MetricRegistryTest.java
@@ -0,0 +1,181 @@
+/*
+ * 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.common.ToDoubleFunction;
+import io.opencensus.common.ToLongFunction;
+import java.util.LinkedHashMap;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+public class MetricRegistryTest {
+  @Rule public ExpectedException thrown = ExpectedException.none();
+
+  private final MetricRegistry metricRegistry =
+      MetricsComponent.newNoopMetricsComponent().getMetricRegistry();
+
+  @Test
+  public void addDoubleGauge_NullName() {
+    thrown.expect(NullPointerException.class);
+    metricRegistry.addDoubleGauge(
+        null,
+        "description",
+        "1",
+        new LinkedHashMap<LabelKey, LabelValue>(),
+        null,
+        new ToDoubleFunction<Object>() {
+          @Override
+          public double applyAsDouble(Object value) {
+            return 5.0;
+          }
+        });
+  }
+
+  @Test
+  public void addDoubleGauge_NullDescription() {
+    thrown.expect(NullPointerException.class);
+    metricRegistry.addDoubleGauge(
+        "name",
+        null,
+        "1",
+        new LinkedHashMap<LabelKey, LabelValue>(),
+        null,
+        new ToDoubleFunction<Object>() {
+          @Override
+          public double applyAsDouble(Object value) {
+            return 5.0;
+          }
+        });
+  }
+
+  @Test
+  public void addDoubleGauge_NullUnit() {
+    thrown.expect(NullPointerException.class);
+    metricRegistry.addDoubleGauge(
+        "name",
+        "description",
+        null,
+        new LinkedHashMap<LabelKey, LabelValue>(),
+        null,
+        new ToDoubleFunction<Object>() {
+          @Override
+          public double applyAsDouble(Object value) {
+            return 5.0;
+          }
+        });
+  }
+
+  @Test
+  public void addDoubleGauge_NullLabels() {
+    thrown.expect(NullPointerException.class);
+    metricRegistry.addDoubleGauge(
+        "name",
+        "description",
+        "1",
+        null,
+        null,
+        new ToDoubleFunction<Object>() {
+          @Override
+          public double applyAsDouble(Object value) {
+            return 5.0;
+          }
+        });
+  }
+
+  @Test
+  public void addDoubleGauge_NullFunction() {
+    thrown.expect(NullPointerException.class);
+    metricRegistry.addDoubleGauge(
+        "name", "description", "1", new LinkedHashMap<LabelKey, LabelValue>(), null, null);
+  }
+
+  @Test
+  public void addLongGauge_NullName() {
+    thrown.expect(NullPointerException.class);
+    metricRegistry.addLongGauge(
+        null,
+        "description",
+        "1",
+        new LinkedHashMap<LabelKey, LabelValue>(),
+        null,
+        new ToLongFunction<Object>() {
+          @Override
+          public long applyAsLong(Object value) {
+            return 5;
+          }
+        });
+  }
+
+  @Test
+  public void addLongGauge_NullDescription() {
+    thrown.expect(NullPointerException.class);
+    metricRegistry.addLongGauge(
+        "name",
+        null,
+        "1",
+        new LinkedHashMap<LabelKey, LabelValue>(),
+        null,
+        new ToLongFunction<Object>() {
+          @Override
+          public long applyAsLong(Object value) {
+            return 5;
+          }
+        });
+  }
+
+  @Test
+  public void addLongGauge_NullUnit() {
+    thrown.expect(NullPointerException.class);
+    metricRegistry.addLongGauge(
+        "name",
+        "description",
+        null,
+        new LinkedHashMap<LabelKey, LabelValue>(),
+        null,
+        new ToLongFunction<Object>() {
+          @Override
+          public long applyAsLong(Object value) {
+            return 5;
+          }
+        });
+  }
+
+  @Test
+  public void addLongGauge_NullLabels() {
+    thrown.expect(NullPointerException.class);
+    metricRegistry.addLongGauge(
+        "name",
+        "description",
+        "1",
+        null,
+        null,
+        new ToLongFunction<Object>() {
+          @Override
+          public long applyAsLong(Object value) {
+            return 5;
+          }
+        });
+  }
+
+  @Test
+  public void addLongGauge_NullFunction() {
+    thrown.expect(NullPointerException.class);
+    metricRegistry.addLongGauge(
+        "name", "description", "1", new LinkedHashMap<LabelKey, LabelValue>(), null, null);
+  }
+}
diff --git a/metrics/src/test/java/io/opencensus/metrics/MetricsComponentTest.java b/metrics/src/test/java/io/opencensus/metrics/MetricsComponentTest.java
index 0a3ceb14..1c4e70f7 100644
--- a/metrics/src/test/java/io/opencensus/metrics/MetricsComponentTest.java
+++ b/metrics/src/test/java/io/opencensus/metrics/MetricsComponentTest.java
@@ -31,4 +31,10 @@ public class MetricsComponentTest {
     assertThat(MetricsComponent.newNoopMetricsComponent().getExportComponent())
         .isInstanceOf(ExportComponent.newNoopExportComponent().getClass());
   }
+
+  @Test
+  public void defaultMetricRegistry() {
+    assertThat(MetricsComponent.newNoopMetricsComponent().getMetricRegistry())
+        .isInstanceOf(MetricRegistry.newNoopMetricRegistry().getClass());
+  }
 }
diff --git a/metrics/src/test/java/io/opencensus/metrics/export/MetricProducerManagerTest.java b/metrics/src/test/java/io/opencensus/metrics/export/MetricProducerManagerTest.java
index 2d4e7c9c..b79de213 100644
--- a/metrics/src/test/java/io/opencensus/metrics/export/MetricProducerManagerTest.java
+++ b/metrics/src/test/java/io/opencensus/metrics/export/MetricProducerManagerTest.java
@@ -18,6 +18,7 @@ package io.opencensus.metrics.export;
 
 import static com.google.common.truth.Truth.assertThat;
 
+import io.opencensus.metrics.MetricProducer;
 import java.util.Set;
 import org.junit.Before;
 import org.junit.Rule;