From e1865b565d63aafc412bcb4975da9b5200d2b8ac Mon Sep 17 00:00:00 2001
From: ZHANG Dapeng <zdapeng@google.com>
Date: Mon, 23 Jul 2018 14:30:38 -0700
Subject: [PATCH] core: channel tracing log only when number of backends
 changed between zeor and nonzero

This is to implement one of changes made in the spec
https://github.com/grpc/proposal/pull/89/files
---
 .../io/grpc/internal/ManagedChannelImpl.java  |  7 ++--
 .../grpc/internal/ManagedChannelImplTest.java | 34 +++++++++++++++++++
 2 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/core/src/main/java/io/grpc/internal/ManagedChannelImpl.java b/core/src/main/java/io/grpc/internal/ManagedChannelImpl.java
index 1ee538a836..ff46cca638 100644
--- a/core/src/main/java/io/grpc/internal/ManagedChannelImpl.java
+++ b/core/src/main/java/io/grpc/internal/ManagedChannelImpl.java
@@ -211,6 +211,7 @@ final class ManagedChannelImpl extends ManagedChannel implements Instrumented<Ch
   @CheckForNull
   private final ChannelTracer channelTracer;
   private final Channelz channelz;
+  private Boolean zeroBackends; // a flag for doing channel tracing when flipped
 
   // One instance per channel.
   private final ChannelBufferMeter channelBufferUsed = new ChannelBufferMeter();
@@ -1249,12 +1250,13 @@ final class ManagedChannelImpl extends ManagedChannel implements Instrumented<Ch
             new Object[]{getLogId(), servers, config});
       }
 
-      if (channelTracer != null) {
+      if (channelTracer != null && (zeroBackends == null || zeroBackends)) {
         channelTracer.reportEvent(new ChannelTrace.Event.Builder()
             .setDescription("Address resolved: " + servers)
             .setSeverity(ChannelTrace.Event.Severity.CT_INFO)
             .setTimestampNanos(timeProvider.currentTimeNanos())
             .build());
+        zeroBackends = false;
       }
 
       final class NamesResolved implements Runnable {
@@ -1295,12 +1297,13 @@ final class ManagedChannelImpl extends ManagedChannel implements Instrumented<Ch
       checkArgument(!error.isOk(), "the error status must not be OK");
       logger.log(Level.WARNING, "[{0}] Failed to resolve name. status={1}",
           new Object[] {getLogId(), error});
-      if (channelTracer != null) {
+      if (channelTracer != null && (zeroBackends == null || !zeroBackends)) {
         channelTracer.reportEvent(new ChannelTrace.Event.Builder()
             .setDescription("Failed to resolve name")
             .setSeverity(ChannelTrace.Event.Severity.CT_WARNING)
             .setTimestampNanos(timeProvider.currentTimeNanos())
             .build());
+        zeroBackends = true;
       }
       channelExecutor
           .executeLater(
diff --git a/core/src/test/java/io/grpc/internal/ManagedChannelImplTest.java b/core/src/test/java/io/grpc/internal/ManagedChannelImplTest.java
index 69eb1a6931..f8e72e63c3 100644
--- a/core/src/test/java/io/grpc/internal/ManagedChannelImplTest.java
+++ b/core/src/test/java/io/grpc/internal/ManagedChannelImplTest.java
@@ -2182,6 +2182,40 @@ public class ManagedChannelImplTest {
         .build());
   }
 
+  @Test
+  public void channelTracing_nameResolvedEvent_zeorAndNonzeroBackends() throws Exception {
+    timer.forwardNanos(1234);
+    channelBuilder.maxTraceEvents(10);
+    List<EquivalentAddressGroup> servers = new ArrayList<EquivalentAddressGroup>();
+    servers.add(new EquivalentAddressGroup(socketAddress));
+    FakeNameResolverFactory nameResolverFactory =
+        new FakeNameResolverFactory.Builder(expectedUri).setServers(servers).build();
+    channelBuilder.nameResolverFactory(nameResolverFactory);
+    createChannel();
+
+    int prevSize = getStats(channel).channelTrace.events.size();
+    nameResolverFactory.resolvers.get(0).listener.onAddresses(
+        Collections.singletonList(new EquivalentAddressGroup(
+            Arrays.asList(new SocketAddress() {}, new SocketAddress() {}))),
+        Attributes.EMPTY);
+    assertThat(getStats(channel).channelTrace.events).hasSize(prevSize);
+
+    prevSize = getStats(channel).channelTrace.events.size();
+    nameResolverFactory.resolvers.get(0).listener.onError(Status.INTERNAL);
+    assertThat(getStats(channel).channelTrace.events).hasSize(prevSize + 1);
+
+    prevSize = getStats(channel).channelTrace.events.size();
+    nameResolverFactory.resolvers.get(0).listener.onError(Status.INTERNAL);
+    assertThat(getStats(channel).channelTrace.events).hasSize(prevSize);
+
+    prevSize = getStats(channel).channelTrace.events.size();
+    nameResolverFactory.resolvers.get(0).listener.onAddresses(
+        Collections.singletonList(new EquivalentAddressGroup(
+            Arrays.asList(new SocketAddress() {}, new SocketAddress() {}))),
+        Attributes.EMPTY);
+    assertThat(getStats(channel).channelTrace.events).hasSize(prevSize + 1);
+  }
+
   @Test
   public void channelTracing_stateChangeEvent() throws Exception {
     channelBuilder.maxTraceEvents(10);