client: ensure resolver operations are handled in order

clientconn.go

@@ -286,19 +286,14 @@ func DialContext(ctx context.Context, target string, opts ...DialOption) (conn *
 	}
 
 	// Build the resolver.
-	cc.resolverWrapper, err = newCCResolverWrapper(cc)
+	rWrapper, err := newCCResolverWrapper(cc)
 	if err != nil {
 		return nil, fmt.Errorf("failed to build resolver: %v", err)
 	}
-	// Start the resolver wrapper goroutine after resolverWrapper is created.
-	//
-	// If the goroutine is started before resolverWrapper is ready, the
-	// following may happen: The goroutine sends updates to cc. cc forwards
-	// those to balancer. Balancer creates new addrConn. addrConn fails to
-	// connect, and calls resolveNow(). resolveNow() tries to use the non-ready
-	// resolverWrapper.
-	cc.resolverWrapper.start()
 
+	cc.mu.Lock()
+	cc.resolverWrapper = rWrapper
+	cc.mu.Unlock()
 	// A blocking dial blocks until the clientConn is ready.
 	if cc.dopts.block {
 		for {
@@ -387,13 +382,13 @@ type ClientConn struct {
 	csMgr        *connectivityStateManager
 
 	balancerBuildOpts balancer.BuildOptions
-	resolverWrapper   *ccResolverWrapper
 	blockingpicker    *pickerWrapper
 
-	mu    sync.RWMutex
-	sc    ServiceConfig
-	scRaw string
-	conns map[*addrConn]struct{}
+	mu              sync.RWMutex
+	resolverWrapper *ccResolverWrapper
+	sc              ServiceConfig
+	scRaw           string
+	conns           map[*addrConn]struct{}
 	// Keepalive parameter can be updated if a GoAway is received.
 	mkp             keepalive.ClientParameters
 	curBalancerName string

resolver_conn_wrapper.go

@@ -93,47 +93,6 @@ func newCCResolverWrapper(cc *ClientConn) (*ccResolverWrapper, error) {
 	return ccr, nil
 }
 
-func (ccr *ccResolverWrapper) start() {
-	go ccr.watcher()
-}
-
-// watcher processes address updates and service config updates sequentially.
-// Otherwise, we need to resolve possible races between address and service
-// config (e.g. they specify different balancer types).
-func (ccr *ccResolverWrapper) watcher() {
-	for {
-		select {
-		case <-ccr.done:
-			return
-		default:
-		}
-
-		select {
-		case addrs := <-ccr.addrCh:
-			select {
-			case <-ccr.done:
-				return
-			default:
-			}
-			grpclog.Infof("ccResolverWrapper: sending new addresses to cc: %v", addrs)
-			if channelz.IsOn() {
-				ccr.addChannelzTraceEvent(addrs)
-			}
-			ccr.cc.handleResolvedAddrs(addrs, nil)
-		case sc := <-ccr.scCh:
-			select {
-			case <-ccr.done:
-				return
-			default:
-			}
-			grpclog.Infof("ccResolverWrapper: got new service config: %v", sc)
-			ccr.cc.handleServiceConfig(sc)
-		case <-ccr.done:
-			return
-		}
-	}
-}
-
 func (ccr *ccResolverWrapper) resolveNow(o resolver.ResolveNowOption) {
 	ccr.resolver.ResolveNow(o)
 }
@@ -146,20 +105,27 @@ func (ccr *ccResolverWrapper) close() {
 // NewAddress is called by the resolver implemenetion to send addresses to gRPC.
 func (ccr *ccResolverWrapper) NewAddress(addrs []resolver.Address) {
 	select {
-	case <-ccr.addrCh:
+	case <-ccr.done:
+		return
 	default:
 	}
-	ccr.addrCh <- addrs
+	grpclog.Infof("ccResolverWrapper: sending new addresses to cc: %v", addrs)
+	if channelz.IsOn() {
+		ccr.addChannelzTraceEvent(addrs)
+	}
+	ccr.cc.handleResolvedAddrs(addrs, nil)
 }
 
 // NewServiceConfig is called by the resolver implemenetion to send service
 // configs to gRPC.
 func (ccr *ccResolverWrapper) NewServiceConfig(sc string) {
 	select {
-	case <-ccr.scCh:
+	case <-ccr.done:
+		return
 	default:
 	}
-	ccr.scCh <- sc
+	grpclog.Infof("ccResolverWrapper: got new service config: %v", sc)
+	ccr.cc.handleServiceConfig(sc)
 }
 
 func (ccr *ccResolverWrapper) addChannelzTraceEvent(addrs []resolver.Address) {