core: use new OpenCensus stats/tagging API. (grpc#3647)

This commit updates gRPC core to use io.opencensus:opencensus-api and
io.opencensus:opencensus-contrib-grpc-metrics instead of
com.google.instrumentation:instrumentation-api for stats and tagging. The gRPC
Monitoring Service continues to use instrumentation-api.

The main changes affecting gRPC:

- The StatsContextFactory is replaced by three objects, StatsRecorder, Tagger,
  and TagContextBinarySerializer.

- The StatsRecorder, Tagger, and TagContextBinarySerializer are never null,
  but the objects are no-ops when the OpenCensus implementation is not
  available.

This commit includes changes written by @songy23 and @sebright.

build.gradle

@@ -192,6 +192,7 @@ subprojects {
                 okhttp: 'com.squareup.okhttp:okhttp:2.5.0',
                 okio: 'com.squareup.okio:okio:1.6.0',
                 opencensus_api: 'io.opencensus:opencensus-api:0.8.0',
+                opencensus_contrib_grpc_metrics: 'io.opencensus:opencensus-contrib-grpc-metrics:0.8.0',
                 opencensus_impl: 'io.opencensus:opencensus-impl:0.8.0',
                 instrumentation_api: 'com.google.instrumentation:instrumentation-api:0.4.3',
                 protobuf: "com.google.protobuf:protobuf-java:${protobufVersion}",

core/build.gradle

@@ -19,6 +19,12 @@ dependencies {
         // we'll always be more up-to-date
         exclude group: 'io.grpc', module: 'grpc-context'
     }
+    compile (libraries.opencensus_contrib_grpc_metrics) {
+        // prefer 3.0.0 from libraries instead of 3.0.1
+        exclude group: 'com.google.code.findbugs', module: 'jsr305'
+        // we'll always be more up-to-date
+        exclude group: 'io.grpc', module: 'grpc-context'
+    }
 
     testCompile project(':grpc-testing')
 

core/src/main/java/io/grpc/internal/AbstractManagedChannelImplBuilder.java

@@ -21,8 +21,6 @@
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
 import com.google.common.util.concurrent.MoreExecutors;
-import com.google.instrumentation.stats.Stats;
-import com.google.instrumentation.stats.StatsContextFactory;
 import io.grpc.Attributes;
 import io.grpc.ClientInterceptor;
 import io.grpc.CompressorRegistry;
@@ -152,7 +150,7 @@ protected final int maxInboundMessageSize() {
   private boolean tracingEnabled = true;
 
   @Nullable
-  private StatsContextFactory statsFactory;
+  private CensusStatsModule censusStatsOverride;
 
   protected AbstractManagedChannelImplBuilder(String target) {
     this.target = Preconditions.checkNotNull(target, "target");
@@ -287,8 +285,8 @@ public final T idleTimeout(long value, TimeUnit unit) {
    * Override the default stats implementation.
    */
   @VisibleForTesting
-  protected final T statsContextFactory(StatsContextFactory statsFactory) {
-    this.statsFactory = statsFactory;
+  protected final T overrideCensusStatsModule(CensusStatsModule censusStats) {
+    this.censusStatsOverride = censusStats;
     return thisT();
   }
 
@@ -346,15 +344,13 @@ final List<ClientInterceptor> getEffectiveInterceptors() {
     List<ClientInterceptor> effectiveInterceptors =
         new ArrayList<ClientInterceptor>(this.interceptors);
     if (statsEnabled) {
-      StatsContextFactory statsCtxFactory =
-          this.statsFactory != null ? this.statsFactory : Stats.getStatsContextFactory();
-      if (statsCtxFactory != null) {
-        CensusStatsModule censusStats =
-            new CensusStatsModule(statsCtxFactory, GrpcUtil.STOPWATCH_SUPPLIER, true, recordStats);
-        // First interceptor runs last (see ClientInterceptors.intercept()), so that no
-        // other interceptor can override the tracer factory we set in CallOptions.
-        effectiveInterceptors.add(0, censusStats.getClientInterceptor());
+      CensusStatsModule censusStats = this.censusStatsOverride;
+      if (censusStats == null) {
+        censusStats = new CensusStatsModule(GrpcUtil.STOPWATCH_SUPPLIER, true);
       }
+      // First interceptor runs last (see ClientInterceptors.intercept()), so that no
+      // other interceptor can override the tracer factory we set in CallOptions.
+      effectiveInterceptors.add(0, censusStats.getClientInterceptor(recordStats));
     }
     if (tracingEnabled) {
       CensusTracingModule censusTracing =

core/src/main/java/io/grpc/internal/AbstractServerImplBuilder.java

@@ -20,8 +20,6 @@
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.util.concurrent.MoreExecutors;
-import com.google.instrumentation.stats.Stats;
-import com.google.instrumentation.stats.StatsContextFactory;
 import io.grpc.BindableService;
 import io.grpc.CompressorRegistry;
 import io.grpc.Context;
@@ -97,7 +95,7 @@ public List<ServerServiceDefinition> getServices() {
   CompressorRegistry compressorRegistry = DEFAULT_COMPRESSOR_REGISTRY;
 
   @Nullable
-  private StatsContextFactory statsFactory;
+  private CensusStatsModule censusStatsOverride;
 
   private boolean statsEnabled = true;
   private boolean recordStats = true;
@@ -184,8 +182,8 @@ public final T compressorRegistry(CompressorRegistry registry) {
    * Override the default stats implementation.
    */
   @VisibleForTesting
-  protected T statsContextFactory(StatsContextFactory statsFactory) {
-    this.statsFactory = statsFactory;
+  protected T overrideCensusStatsModule(CensusStatsModule censusStats) {
+    this.censusStatsOverride = censusStats;
     return thisT();
   }
 
@@ -228,13 +226,11 @@ final List<ServerStreamTracer.Factory> getTracerFactories() {
     ArrayList<ServerStreamTracer.Factory> tracerFactories =
         new ArrayList<ServerStreamTracer.Factory>();
     if (statsEnabled) {
-      StatsContextFactory statsFactory =
-          this.statsFactory != null ? this.statsFactory : Stats.getStatsContextFactory();
-      if (statsFactory != null) {
-        CensusStatsModule censusStats =
-            new CensusStatsModule(statsFactory, GrpcUtil.STOPWATCH_SUPPLIER, true, recordStats);
-        tracerFactories.add(censusStats.getServerTracerFactory());
+      CensusStatsModule censusStats = this.censusStatsOverride;
+      if (censusStats == null) {
+        censusStats = new CensusStatsModule(GrpcUtil.STOPWATCH_SUPPLIER, true);
       }
+      tracerFactories.add(censusStats.getServerTracerFactory(recordStats));
     }
     if (tracingEnabled) {
       CensusTracingModule censusTracing =