gRPC RealTimeMetrics values not populated

Please answer these questions before submitting a bug report.

What version of OpenCensus are you using?

0.28.0

What JVM are you using (`java -version`)?

openjdk version "11.0.2" 2019-01-15

What did you do?

Use RpcViews.registerRealTimeMetricsViews() with https://github.com/grpc/grpc-java/tree/v1.39.0/examples

I cloned the above repo, and applied this patch

diff --git a/examples/pom.xml b/examples/pom.xml
index 156b11fb7..571b49c5c 100644
--- a/examples/pom.xml
+++ b/examples/pom.xml
@@ -18,6 +18,7 @@
     <!-- required for jdk9 -->
     <maven.compiler.source>1.7</maven.compiler.source>
     <maven.compiler.target>1.7</maven.compiler.target>
+    <opencensus.version>0.28.0</opencensus.version>
   </properties>

   <dependencyManagement>
@@ -46,6 +47,40 @@
       <groupId>io.grpc</groupId>
       <artifactId>grpc-stub</artifactId>
     </dependency>
+
+<!--    Census -->
+    <dependency>
+      <groupId>io.grpc</groupId>
+      <artifactId>grpc-census</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>io.opencensus</groupId>
+      <artifactId>opencensus-exporter-stats-prometheus</artifactId>
+      <version>${opencensus.version}</version>
+    </dependency>
+    <dependency>
+      <groupId>io.opencensus</groupId>
+      <artifactId>opencensus-api</artifactId>
+      <version>${opencensus.version}</version>
+    </dependency>
+    <dependency>
+      <groupId>io.opencensus</groupId>
+      <artifactId>opencensus-contrib-grpc-metrics</artifactId>
+      <version>${opencensus.version}</version>
+    </dependency>
+    <dependency>
+      <groupId>io.opencensus</groupId>
+      <artifactId>opencensus-impl</artifactId>
+      <version>${opencensus.version}</version>
+      <scope>runtime</scope>
+    </dependency>
+    <dependency>
+      <groupId>io.prometheus</groupId>
+      <artifactId>simpleclient_httpserver</artifactId>
+      <version>0.3.0</version>
+    </dependency>
+<!--    -->
+
     <dependency>
       <groupId>com.google.protobuf</groupId>
       <artifactId>protobuf-java-util</artifactId>
diff --git a/examples/src/main/java/io/grpc/examples/routeguide/RouteGuideServer.java b/examples/src/main/java/io/grpc/examples/routeguide/RouteGuideServer.java
index c91544ae4..cd7a3b1ee 100644
--- a/examples/src/main/java/io/grpc/examples/routeguide/RouteGuideServer.java
+++ b/examples/src/main/java/io/grpc/examples/routeguide/RouteGuideServer.java
@@ -28,6 +28,10 @@ import static java.util.concurrent.TimeUnit.NANOSECONDS;
 import io.grpc.Server;
 import io.grpc.ServerBuilder;
 import io.grpc.stub.StreamObserver;
+import io.opencensus.contrib.grpc.metrics.RpcViews;
+import io.opencensus.exporter.stats.prometheus.PrometheusStatsCollector;
+import io.prometheus.client.exporter.HTTPServer;
+
 import java.io.IOException;
 import java.net.URL;
 import java.util.ArrayList;
@@ -49,6 +53,17 @@ public class RouteGuideServer {
   private final int port;
   private final Server server;

+  static {
+      RpcViews.registerServerGrpcViews();
+      RpcViews.registerRealTimeMetricsViews();
+      PrometheusStatsCollector.createAndRegister();
+      try {
+          HTTPServer s = new HTTPServer("localhost", 8888, true);
+      } catch (IOException e) {
+          throw new RuntimeException(e);
+      }
+  }
+
   public RouteGuideServer(int port) throws IOException {
     this(port, RouteGuideUtil.getDefaultFeaturesFile());
   }
-- 
2.24.3 (Apple Git-128)

Started the server with

mvn exec:java -Dexec.mainClass=io.grpc.examples.routeguide.RouteGuideServer

Then the client

mvn exec:java -Dexec.mainClass=io.grpc.examples.routeguide.RouteGuideClient

Curled the prometheus endpoint

curl localhost:8888

What did you expect to see?

The counter grpc_io_server_received_messages_per_method having some value for the client-streaming / server-streaming methods.

What did you see instead?

The *_per_method counters are empty / no value. Only the #HELP... and #TYPE... shows up.

$ curl -s localhost:8888 | grep per_method
# HELP grpc_io_client_sent_bytes_per_method Sent bytes per method
# TYPE grpc_io_client_sent_bytes_per_method counter
# HELP grpc_io_client_received_bytes_per_method Received bytes per method
# TYPE grpc_io_client_received_bytes_per_method counter
# HELP grpc_io_client_sent_messages_per_method Number of messages sent
# TYPE grpc_io_client_sent_messages_per_method counter
# HELP grpc_io_client_received_messages_per_method Number of messages received
# TYPE grpc_io_client_received_messages_per_method counter
# HELP grpc_io_server_sent_bytes_per_method Sent bytes per method
# TYPE grpc_io_server_sent_bytes_per_method counter
# HELP grpc_io_server_received_bytes_per_method Received bytes per method
# TYPE grpc_io_server_received_bytes_per_method counter
# HELP grpc_io_server_sent_messages_per_method Number of messages sent
# TYPE grpc_io_server_sent_messages_per_method counter
# HELP grpc_io_server_received_messages_per_method Number of messages received
# TYPE grpc_io_server_received_messages_per_method counter

All other grpc_io_server_* metrics show up and have values.

$ curl -s localhost:8888 | grep grpc_io_server_received_messages_per_rpc_count
grpc_io_server_received_messages_per_rpc_count{grpc_server_method="routeguide.RouteGuide/ListFeatures",} 1.0
grpc_io_server_received_messages_per_rpc_count{grpc_server_method="routeguide.RouteGuide/RouteChat",} 1.0
grpc_io_server_received_messages_per_rpc_count{grpc_server_method="routeguide.RouteGuide/GetFeature",} 2.0
grpc_io_server_received_messages_per_rpc_count{grpc_server_method="routeguide.RouteGuide/RecordRoute",} 1.0

Additional context

N/A

census-instrumentation / opencensus-java