[pickfirst_check_addrs] do it in pickfirst?

pickfirst.go

@@ -24,6 +24,7 @@ import (
 
 	"google.golang.org/grpc/balancer"
 	"google.golang.org/grpc/connectivity"
+	"google.golang.org/grpc/resolver"
 )
 
 // PickFirstBalancerName is the name of the pick_first balancer.
@@ -47,6 +48,7 @@ type pickfirstBalancer struct {
 	state   connectivity.State
 	cc      balancer.ClientConn
 	subConn balancer.SubConn
+	addrs   []resolver.Address
 }
 
 func (b *pickfirstBalancer) ResolverError(err error) {
@@ -68,6 +70,18 @@ func (b *pickfirstBalancer) ResolverError(err error) {
 	})
 }
 
+func equalAddresses(a, b []resolver.Address) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i, v := range a {
+		if !v.Equal(b[i]) {
+			return false
+		}
+	}
+	return true
+}
+
 func (b *pickfirstBalancer) UpdateClientConnState(state balancer.ClientConnState) error {
 	if len(state.ResolverState.Addresses) == 0 {
 		// The resolver reported an empty address list. Treat it like an error by
@@ -82,6 +96,21 @@ func (b *pickfirstBalancer) UpdateClientConnState(state balancer.ClientConnState
 		return balancer.ErrBadResolverState
 	}
 
+	if equalAddresses(b.addrs, state.ResolverState.Addresses) {
+		// Avoid updating SubConn addresses if the addresses are the same.
+		//
+		// Usually SubConns can compare the new addresses with the address in
+		// use, and will not recreate the connection if not necessary.
+		//
+		// A special case is if the SubConn is in Connecting (so it's still
+		// trying to connect the addresses, and there's no address in use).
+		// Calling update addresses, even with the same set of Addresses, cause
+		// the SubConn to stop connecting, and retry with the new (same) set of
+		// addresses.
+		return nil
+	}
+	b.addrs = state.ResolverState.Addresses
+
 	if b.subConn != nil {
 		b.cc.UpdateAddresses(b.subConn, state.ResolverState.Addresses)
 		return nil