core: fix a channel panic bug caused by calling NameResolver.refresh() when it's not started (#5223)

Resolves #5222

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

@@ -308,16 +308,20 @@ final class ManagedChannelImpl extends ManagedChannel implements
   }
 
   // Must be called from syncContext
-  private void shutdownNameResolverAndLoadBalancer(boolean verifyActive) {
-    if (verifyActive) {
-      checkState(nameResolver != null, "nameResolver is null");
+  private void shutdownNameResolverAndLoadBalancer(boolean channelIsActive) {
+    if (channelIsActive) {
+      checkState(nameResolverStarted, "nameResolver is not started");
       checkState(lbHelper != null, "lbHelper is null");
     }
     if (nameResolver != null) {
       cancelNameResolverBackoff();
       nameResolver.shutdown();
-      nameResolver = null;
       nameResolverStarted = false;
+      if (channelIsActive) {
+        nameResolver = getNameResolver(target, nameResolverFactory, nameResolverParams);
+      } else {
+        nameResolver = null;
+      }
     }
     if (lbHelper != null) {
       lbHelper.lb.shutdown();
@@ -372,7 +376,6 @@ final class ManagedChannelImpl extends ManagedChannel implements
     // which are bugs.
     shutdownNameResolverAndLoadBalancer(true);
     delayedTransport.reprocess(null);
-    nameResolver = getNameResolver(target, nameResolverFactory, nameResolverParams);
     channelLogger.log(ChannelLogLevel.INFO, "Entering IDLE state");
     channelStateManager.gotoState(IDLE);
     if (inUseStateAggregator.isInUse()) {
@@ -399,9 +402,7 @@ final class ManagedChannelImpl extends ManagedChannel implements
     @Override
     public void run() {
       scheduledNameResolverRefresh = null;
-      if (nameResolver != null) {
-        nameResolver.refresh();
-      }
+      refreshNameResolution();
     }
   }
 
@@ -421,11 +422,19 @@ final class ManagedChannelImpl extends ManagedChannel implements
     }
   }
 
-  // Must be run from syncContext
-  private void refreshNameResolutionNow() {
+  /**
+   * Force name resolution refresh to happen immediately and reset refresh back-off. Must be run
+   * from syncContext.
+   */
+  private void refreshAndResetNameResolution() {
     syncContext.throwIfNotInThisSynchronizationContext();
     cancelNameResolverBackoff();
-    if (nameResolver != null) {
+    refreshNameResolution();
+  }
+
+  private void refreshNameResolution() {
+    syncContext.throwIfNotInThisSynchronizationContext();
+    if (nameResolverStarted) {
       nameResolver.refresh();
     }
   }
@@ -871,7 +880,7 @@ final class ManagedChannelImpl extends ManagedChannel implements
         }
         if (scheduledNameResolverRefresh != null && scheduledNameResolverRefresh.isPending()) {
           checkState(nameResolverStarted, "name resolver must be started");
-          refreshNameResolutionNow();
+          refreshAndResetNameResolution();
         }
         for (InternalSubchannel subchannel : subchannels) {
           subchannel.resetConnectBackoff();
@@ -990,7 +999,7 @@ final class ManagedChannelImpl extends ManagedChannel implements
     // Must be called from syncContext
     private void handleInternalSubchannelState(ConnectivityStateInfo newState) {
       if (newState.getState() == TRANSIENT_FAILURE || newState.getState() == IDLE) {
-        refreshNameResolutionNow();
+        refreshAndResetNameResolution();
       }
     }
 
@@ -1122,7 +1131,7 @@ final class ManagedChannelImpl extends ManagedChannel implements
       final class LoadBalancerRefreshNameResolution implements Runnable {
         @Override
         public void run() {
-          refreshNameResolutionNow();
+          refreshAndResetNameResolution();
         }
       }
 

core/src/test/java/io/grpc/internal/ManagedChannelImplTest.java

@@ -1612,24 +1612,33 @@ public class ManagedChannelImplTest {
   }
 
   @Test
-  public void refreshNameResolutionWhenSubchannelConnectionFailed() {
-    subtestRefreshNameResolutionWhenConnectionFailed(false);
+  public void refreshNameResolution_whenSubchannelConnectionFailed_notIdle() {
+    subtestNameResolutionRefreshWhenConnectionFailed(false, false);
   }
 
   @Test
-  public void refreshNameResolutionWhenOobChannelConnectionFailed() {
-    subtestRefreshNameResolutionWhenConnectionFailed(true);
+  public void refreshNameResolution_whenOobChannelConnectionFailed_notIdle() {
+    subtestNameResolutionRefreshWhenConnectionFailed(true, false);
   }
 
-  private void subtestRefreshNameResolutionWhenConnectionFailed(boolean isOobChannel) {
+  @Test
+  public void notRefreshNameResolution_whenSubchannelConnectionFailed_idle() {
+    subtestNameResolutionRefreshWhenConnectionFailed(false, true);
+  }
+
+  @Test
+  public void notRefreshNameResolution_whenOobChannelConnectionFailed_idle() {
+    subtestNameResolutionRefreshWhenConnectionFailed(true, true);
+  }
+
+  private void subtestNameResolutionRefreshWhenConnectionFailed(
+      boolean isOobChannel, boolean isIdle) {
     FakeNameResolverFactory nameResolverFactory =
         new FakeNameResolverFactory.Builder(expectedUri)
             .setServers(Collections.singletonList(new EquivalentAddressGroup(socketAddress)))
             .build();
     channelBuilder.nameResolverFactory(nameResolverFactory);
     createChannel();
-    FakeNameResolverFactory.FakeNameResolver resolver = nameResolverFactory.resolvers.get(0);
-
     if (isOobChannel) {
       OobChannel oobChannel = (OobChannel) helper.createOobChannel(addressGroup, "oobAuthority");
       oobChannel.getSubchannel().requestConnection();
@@ -1641,10 +1650,26 @@ public class ManagedChannelImplTest {
     MockClientTransportInfo transportInfo = transports.poll();
     assertNotNull(transportInfo);
 
+    FakeNameResolverFactory.FakeNameResolver resolver = nameResolverFactory.resolvers.remove(0);
+
+    if (isIdle) {
+      channel.enterIdle();
+      // Entering idle mode will result in a new resolver
+      resolver = nameResolverFactory.resolvers.remove(0);
+    }
+
+    assertEquals(0, nameResolverFactory.resolvers.size());
+
+    int expectedRefreshCount = 0;
+
     // Transport closed when connecting
-    assertEquals(0, resolver.refreshCalled);
+    assertEquals(expectedRefreshCount, resolver.refreshCalled);
     transportInfo.listener.transportShutdown(Status.UNAVAILABLE);
-    assertEquals(1, resolver.refreshCalled);
+    // When channel enters idle, new resolver is created but not started.
+    if (!isIdle) {
+      expectedRefreshCount++;
+    }
+    assertEquals(expectedRefreshCount, resolver.refreshCalled);
 
     timer.forwardNanos(RECONNECT_BACKOFF_INTERVAL_NANOS);
     transportInfo = transports.poll();
@@ -1653,9 +1678,13 @@ public class ManagedChannelImplTest {
     transportInfo.listener.transportReady();
 
     // Transport closed when ready
-    assertEquals(1, resolver.refreshCalled);
+    assertEquals(expectedRefreshCount, resolver.refreshCalled);
     transportInfo.listener.transportShutdown(Status.UNAVAILABLE);
-    assertEquals(2, resolver.refreshCalled);
+    // When channel enters idle, new resolver is created but not started.
+    if (!isIdle) {
+      expectedRefreshCount++;
+    }
+    assertEquals(expectedRefreshCount, resolver.refreshCalled);
   }
 
   @Test
@@ -3316,7 +3345,6 @@ public class ManagedChannelImplTest {
       }
 
       @Override public void refresh() {
-        assertNotNull(listener);
         refreshCalled++;
         resolved();
       }