Add ViewManager.getAllExportedViews().

This method currently returns all registered cumulative views.  We could add a
way to specify which views should be exported later.  The API is currently
needed for the StackDriver exporter.

The NoopViewManager also returns all cumulative views.  However, the exporter
could choose to not export data when stats collection isn't enabled.

3 files changed, 91 insertions, 0 deletions

diff --git a/api/src/main/java/io/opencensus/stats/NoopStats.java b/api/src/main/java/io/opencensus/stats/NoopStats.java
index 55c424c7..c087a19f 100644
--- a/api/src/main/java/io/opencensus/stats/NoopStats.java
+++ b/api/src/main/java/io/opencensus/stats/NoopStats.java
@@ -22,10 +22,12 @@ import static com.google.common.base.Preconditions.checkState;
 
 import com.google.common.base.Preconditions;
 import com.google.common.collect.Maps;
+import com.google.common.collect.Sets;
 import io.opencensus.common.Functions;
 import io.opencensus.common.Timestamp;
 import io.opencensus.stats.Measure.MeasureDouble;
 import io.opencensus.stats.Measure.MeasureLong;
+import io.opencensus.stats.View.AggregationWindow;
 import io.opencensus.stats.ViewData.AggregationWindowData;
 import io.opencensus.stats.ViewData.AggregationWindowData.CumulativeData;
 import io.opencensus.stats.ViewData.AggregationWindowData.IntervalData;
@@ -34,6 +36,7 @@ import io.opencensus.tags.TagValue;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.GuardedBy;
 import javax.annotation.concurrent.Immutable;
@@ -187,5 +190,18 @@ final class NoopStats {
         }
       }
     }
+
+    @Override
+    public Set<View> getAllExportedViews() {
+      synchronized (views) {
+        Set<View> exportedViews = Sets.newHashSet();
+        for (View view : views.values()) {
+          if (view.getWindow() instanceof AggregationWindow.Cumulative) {
+            exportedViews.add(view);
+          }
+        }
+        return Collections.unmodifiableSet(exportedViews);
+      }
+    }
   }
 }
diff --git a/api/src/main/java/io/opencensus/stats/ViewManager.java b/api/src/main/java/io/opencensus/stats/ViewManager.java
index f98e8058..a6e18b89 100644
--- a/api/src/main/java/io/opencensus/stats/ViewManager.java
+++ b/api/src/main/java/io/opencensus/stats/ViewManager.java
@@ -16,6 +16,7 @@
 
 package io.opencensus.stats;
 
+import java.util.Set;
 import javax.annotation.Nullable;
 
 /**
@@ -42,4 +43,15 @@ public abstract class ViewManager {
    */
   @Nullable
   public abstract ViewData getView(View.Name view);
+
+  /**
+   * Returns all registered views that should be exported.
+   *
+   * <p>This method should be used by any stats exporter that automatically exports data for views
+   * registered with the {@link ViewManager}.
+   *
+   * @return all registered views that should be exported.
+   * @since 0.9
+   */
+  public abstract Set<View> getAllExportedViews();
 }
diff --git a/api/src/test/java/io/opencensus/stats/NoopViewManagerTest.java b/api/src/test/java/io/opencensus/stats/NoopViewManagerTest.java
index 24d1b14a..4aaa60dc 100644
--- a/api/src/test/java/io/opencensus/stats/NoopViewManagerTest.java
+++ b/api/src/test/java/io/opencensus/stats/NoopViewManagerTest.java
@@ -29,6 +29,7 @@ import io.opencensus.stats.ViewData.AggregationWindowData.CumulativeData;
 import io.opencensus.stats.ViewData.AggregationWindowData.IntervalData;
 import io.opencensus.tags.TagKey;
 import java.util.Arrays;
+import java.util.Set;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
@@ -128,4 +129,66 @@ public final class NoopViewManagerTest {
     thrown.expect(NullPointerException.class);
     viewManager.getView(null);
   }
+
+  @Test
+  public void getAllExportedViews() {
+    ViewManager viewManager = NoopStats.newNoopViewManager();
+    assertThat(viewManager.getAllExportedViews()).isEmpty();
+    View cumulativeView1 =
+        View.create(
+            View.Name.create("View 1"),
+            VIEW_DESCRIPTION,
+            MEASURE,
+            AGGREGATION,
+            Arrays.asList(KEY),
+            CUMULATIVE);
+    View cumulativeView2 =
+        View.create(
+            View.Name.create("View 2"),
+            VIEW_DESCRIPTION,
+            MEASURE,
+            AGGREGATION,
+            Arrays.asList(KEY),
+            CUMULATIVE);
+    View intervalView =
+        View.create(
+            View.Name.create("View 3"),
+            VIEW_DESCRIPTION,
+            MEASURE,
+            AGGREGATION,
+            Arrays.asList(KEY),
+            INTERVAL);
+    viewManager.registerView(cumulativeView1);
+    viewManager.registerView(cumulativeView2);
+    viewManager.registerView(intervalView);
+
+    // Only cumulative views should be exported.
+    assertThat(viewManager.getAllExportedViews()).containsExactly(cumulativeView1, cumulativeView2);
+  }
+
+  @Test
+  public void getAllExportedViews_ResultIsUnmodifiable() {
+    ViewManager viewManager = NoopStats.newNoopViewManager();
+    View view1 =
+        View.create(
+            View.Name.create("View 1"),
+            VIEW_DESCRIPTION,
+            MEASURE,
+            AGGREGATION,
+            Arrays.asList(KEY),
+            CUMULATIVE);
+    viewManager.registerView(view1);
+    Set<View> exported = viewManager.getAllExportedViews();
+
+    View view2 =
+        View.create(
+            View.Name.create("View 2"),
+            VIEW_DESCRIPTION,
+            MEASURE,
+            AGGREGATION,
+            Arrays.asList(KEY),
+            CUMULATIVE);
+    thrown.expect(UnsupportedOperationException.class);
+    exported.add(view2);
+  }
 }