Split the public metrics API from the data model. (#1477)

* Split the public API from the data model.

* Small comment added about registration of the MetricProducer.

6 files changed, 72 insertions, 42 deletions

diff --git a/api/src/main/java/io/opencensus/metrics/MetricProducer.java b/api/src/main/java/io/opencensus/metrics/MetricProducer.java
index 38b5d571..2a78b989 100644
--- a/api/src/main/java/io/opencensus/metrics/MetricProducer.java
+++ b/api/src/main/java/io/opencensus/metrics/MetricProducer.java
@@ -21,18 +21,20 @@ import io.opencensus.metrics.export.MetricProducerManager;
 import java.util.Collection;
 
 /**
- * A {@link io.opencensus.metrics.Metric} producer that can be registered for exporting using {@link
+ * A {@link Metric} producer that can be registered for exporting using {@link
  * MetricProducerManager}.
  *
  * <p>All implementation MUST be thread-safe.
+ *
+ * @since 0.17
  */
 @ExperimentalApi
 public abstract class MetricProducer {
 
   /**
-   * Returns a collection of produced {@link io.opencensus.metrics.Metric}s to be exported.
+   * Returns a collection of produced {@link Metric}s to be exported.
    *
-   * @return a collection of produced {@link io.opencensus.metrics.Metric}s to be exported.
+   * @return a collection of produced {@link Metric}s to be exported.
    */
   public abstract Collection<Metric> getMetrics();
 }
diff --git a/api/src/main/java/io/opencensus/metrics/MetricRegistry.java b/api/src/main/java/io/opencensus/metrics/MetricRegistry.java
index ae4d90b0..c249d47b 100644
--- a/api/src/main/java/io/opencensus/metrics/MetricRegistry.java
+++ b/api/src/main/java/io/opencensus/metrics/MetricRegistry.java
@@ -20,19 +20,17 @@ 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.
+ * Creates and manages your application's set of metrics. The default implementation of this creates
+ * a {@link MetricProducer} and registers it to the global {@link
+ * io.opencensus.metrics.export.MetricProducerManager}.
  *
- * @since 0.16
+ * @since 0.17
  */
 @ExperimentalApi
-public abstract class MetricRegistry extends MetricProducer {
+public abstract class MetricRegistry {
   /**
    * Build a new long gauge to be added to the registry.
    *
@@ -43,7 +41,7 @@ public abstract class MetricRegistry extends MetricProducer {
    * @param unit the unit of the metric.
    * @param obj the function argument.
    * @param function the function to be called.
-   * @since 0.16 @ExperimentalApi
+   * @since 0.17
    */
   public abstract <T> void addLongGauge(
       String name,
@@ -63,7 +61,7 @@ public abstract class MetricRegistry extends MetricProducer {
    * @param unit the unit of the metric.
    * @param obj the function argument.
    * @param function the function to be called.
-   * @since 0.16 @ExperimentalApi
+   * @since 0.17
    */
   public abstract <T> void addDoubleGauge(
       String name,
@@ -108,10 +106,5 @@ public abstract class MetricRegistry extends MetricProducer {
       Utils.checkNotNull(labels, "labels");
       Utils.checkNotNull(function, "function");
     }
-
-    @Override
-    public Collection<Metric> getMetrics() {
-      return Collections.emptyList();
-    }
   }
 }
diff --git a/impl_core/src/main/java/io/opencensus/implcore/metrics/MetricRegistryImpl.java b/impl_core/src/main/java/io/opencensus/implcore/metrics/MetricRegistryImpl.java
index f3daaef7..642a9515 100644
--- a/impl_core/src/main/java/io/opencensus/implcore/metrics/MetricRegistryImpl.java
+++ b/impl_core/src/main/java/io/opencensus/implcore/metrics/MetricRegistryImpl.java
@@ -26,6 +26,7 @@ import io.opencensus.implcore.metrics.Gauge.LongGauge;
 import io.opencensus.metrics.LabelKey;
 import io.opencensus.metrics.LabelValue;
 import io.opencensus.metrics.Metric;
+import io.opencensus.metrics.MetricProducer;
 import io.opencensus.metrics.MetricRegistry;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -36,11 +37,12 @@ import java.util.Set;
 
 /** Implementation of {@link MetricRegistry}. */
 public final class MetricRegistryImpl extends MetricRegistry {
-  private final Clock clock;
-  private volatile Set<Gauge> registeredGauges = Collections.emptySet();
+  private final RegisteredMeters registeredMeters;
+  private final MetricProducer metricProducer;
 
   MetricRegistryImpl(Clock clock) {
-    this.clock = clock;
+    registeredMeters = new RegisteredMeters();
+    metricProducer = new MetricProducerForRegistry(registeredMeters, clock);
   }
 
   @Override
@@ -52,7 +54,7 @@ public final class MetricRegistryImpl extends MetricRegistry {
       T obj,
       ToLongFunction<T> function) {
     checkNotNull(labels, "labels");
-    registerGauge(
+    registeredMeters.registerMeter(
         new LongGauge<T>(
             checkNotNull(name, "name"),
             checkNotNull(description, "description"),
@@ -72,7 +74,7 @@ public final class MetricRegistryImpl extends MetricRegistry {
       T obj,
       ToDoubleFunction<T> function) {
     checkNotNull(labels, "labels");
-    registerGauge(
+    registeredMeters.registerMeter(
         new DoubleGauge<T>(
             checkNotNull(name, "name"),
             checkNotNull(description, "description"),
@@ -83,23 +85,45 @@ public final class MetricRegistryImpl extends MetricRegistry {
             checkNotNull(function, "function")));
   }
 
-  @Override
-  public Collection<Metric> getMetrics() {
-    // Get a snapshot of the current registered gauges.
-    Set<Gauge> gaguges = registeredGauges;
-    if (gaguges.isEmpty()) {
-      return Collections.emptyList();
+  private static final class RegisteredMeters {
+    private volatile Set<Gauge> registeredGauges = Collections.emptySet();
+
+    private Set<Gauge> getRegisteredMeters() {
+      return registeredGauges;
     }
-    ArrayList<Metric> metrics = new ArrayList<Metric>();
-    for (Gauge gauge : gaguges) {
-      metrics.add(gauge.getMetric(clock));
+
+    private synchronized void registerMeter(Gauge gauge) {
+      Set<Gauge> newGaguesList = new LinkedHashSet<Gauge>(registeredGauges);
+      newGaguesList.add(gauge);
+      registeredGauges = Collections.unmodifiableSet(newGaguesList);
+    }
+  }
+
+  private static final class MetricProducerForRegistry extends MetricProducer {
+    private final RegisteredMeters registeredMeters;
+    private final Clock clock;
+
+    private MetricProducerForRegistry(RegisteredMeters registeredMeters, Clock clock) {
+      this.registeredMeters = registeredMeters;
+      this.clock = clock;
+    }
+
+    @Override
+    public Collection<Metric> getMetrics() {
+      // Get a snapshot of the current registered gauges.
+      Set<Gauge> gaguges = registeredMeters.getRegisteredMeters();
+      if (gaguges.isEmpty()) {
+        return Collections.emptyList();
+      }
+      ArrayList<Metric> metrics = new ArrayList<Metric>();
+      for (Gauge gauge : gaguges) {
+        metrics.add(gauge.getMetric(clock));
+      }
+      return metrics;
     }
-    return metrics;
   }
 
-  private synchronized void registerGauge(Gauge gauge) {
-    Set<Gauge> newGaguesList = new LinkedHashSet<Gauge>(registeredGauges);
-    newGaguesList.add(gauge);
-    registeredGauges = Collections.unmodifiableSet(newGaguesList);
+  MetricProducer getMetricProducer() {
+    return metricProducer;
   }
 }
diff --git a/impl_core/src/main/java/io/opencensus/implcore/metrics/MetricsComponentImplBase.java b/impl_core/src/main/java/io/opencensus/implcore/metrics/MetricsComponentImplBase.java
index 46ad028c..1aef6727 100644
--- a/impl_core/src/main/java/io/opencensus/implcore/metrics/MetricsComponentImplBase.java
+++ b/impl_core/src/main/java/io/opencensus/implcore/metrics/MetricsComponentImplBase.java
@@ -18,7 +18,6 @@ package io.opencensus.implcore.metrics;
 
 import io.opencensus.common.Clock;
 import io.opencensus.implcore.metrics.export.ExportComponentImpl;
-import io.opencensus.metrics.MetricRegistry;
 import io.opencensus.metrics.MetricsComponent;
 
 /** Implementation of {@link MetricsComponent}. */
@@ -33,12 +32,14 @@ public class MetricsComponentImplBase extends MetricsComponent {
   }
 
   @Override
-  public MetricRegistry getMetricRegistry() {
+  public MetricRegistryImpl getMetricRegistry() {
     return metricRegistry;
   }
 
   protected MetricsComponentImplBase(Clock clock) {
     exportComponent = new ExportComponentImpl();
     metricRegistry = new MetricRegistryImpl(clock);
+    // Register the MetricRegistry's MetricProducer to the global MetricProducerManager.
+    exportComponent.getMetricProducerManager().add(metricRegistry.getMetricProducer());
   }
 }
diff --git a/impl_core/src/test/java/io/opencensus/implcore/metrics/MetricRegistryImplTest.java b/impl_core/src/test/java/io/opencensus/implcore/metrics/MetricRegistryImplTest.java
index 769efab2..0b75a6e0 100644
--- a/impl_core/src/test/java/io/opencensus/implcore/metrics/MetricRegistryImplTest.java
+++ b/impl_core/src/test/java/io/opencensus/implcore/metrics/MetricRegistryImplTest.java
@@ -149,7 +149,7 @@ public class MetricRegistryImplTest {
             return 5.0;
           }
         });
-    assertThat(metricRegistry.getMetrics())
+    assertThat(metricRegistry.getMetricProducer().getMetrics())
         .containsExactly(
             Metric.create(
                 MetricDescriptor.create(
@@ -253,7 +253,7 @@ public class MetricRegistryImplTest {
             return 7;
           }
         });
-    assertThat(metricRegistry.getMetrics())
+    assertThat(metricRegistry.getMetricProducer().getMetrics())
         .containsExactly(
             Metric.create(
                 MetricDescriptor.create(
@@ -295,7 +295,7 @@ public class MetricRegistryImplTest {
             return 5.0;
           }
         });
-    assertThat(metricRegistry.getMetrics())
+    assertThat(metricRegistry.getMetricProducer().getMetrics())
         .containsExactly(
             Metric.create(
                 MetricDescriptor.create(
@@ -325,6 +325,6 @@ public class MetricRegistryImplTest {
 
   @Test
   public void empty_GetMetrics() {
-    assertThat(metricRegistry.getMetrics()).isEmpty();
+    assertThat(metricRegistry.getMetricProducer().getMetrics()).isEmpty();
   }
 }
diff --git a/impl_core/src/test/java/io/opencensus/implcore/metrics/MetricsComponentImplBaseTest.java b/impl_core/src/test/java/io/opencensus/implcore/metrics/MetricsComponentImplBaseTest.java
index 5050625b..7f8515d3 100644
--- a/impl_core/src/test/java/io/opencensus/implcore/metrics/MetricsComponentImplBaseTest.java
+++ b/impl_core/src/test/java/io/opencensus/implcore/metrics/MetricsComponentImplBaseTest.java
@@ -40,4 +40,14 @@ public class MetricsComponentImplBaseTest {
   public void getMetricRegistry() {
     assertThat(metricsComponentImplBase.getMetricRegistry()).isInstanceOf(MetricRegistryImpl.class);
   }
+
+  @Test
+  public void metricRegistry_InstalledToMetricProducerManger() {
+    assertThat(
+            metricsComponentImplBase
+                .getExportComponent()
+                .getMetricProducerManager()
+                .getAllMetricProducer())
+        .containsExactly(metricsComponentImplBase.getMetricRegistry().getMetricProducer());
+  }
 }