balancer: Move metrics recorder from BuildOptions to ClientConn

balancer/balancer.go

@@ -175,6 +175,12 @@ type ClientConn interface {
 	// Deprecated: Use the Target field in the BuildOptions instead.
 	Target() string
 
+	// MetricsRecorder provides the metrics recorder that balancers can use to
+	// record metrics. Balancer implementations which do not register metrics on
+	// metrics registry and record on them can ignore this method. The returned
+	// MetricsRecorder is guaranteed to never be nil.
+	MetricsRecorder() estats.MetricsRecorder
+
 	// EnforceClientConnEmbedding is included to force implementers to embed
 	// another implementation of this interface, allowing gRPC to add methods
 	// without breaking users.
@@ -210,10 +216,6 @@ type BuildOptions struct {
 	// same resolver.Target as passed to the resolver. See the documentation for
 	// the resolver.Target type for details about what it contains.
 	Target resolver.Target
-	// MetricsRecorder is the metrics recorder that balancers can use to record
-	// metrics. Balancer implementations which do not register metrics on
-	// metrics registry and record on them can ignore this field.
-	MetricsRecorder estats.MetricsRecorder
 }
 
 // Builder creates a balancer.

balancer/pickfirst/pickfirst_test.go

@@ -29,7 +29,6 @@ import (
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/internal/grpctest"
 	"google.golang.org/grpc/internal/testutils"
-	"google.golang.org/grpc/internal/testutils/stats"
 	"google.golang.org/grpc/resolver"
 )
 
@@ -56,7 +55,7 @@ func (s) TestPickFirst_InitialResolverError(t *testing.T) {
 	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
 	defer cancel()
 	cc := testutils.NewBalancerClientConn(t)
-	bal := balancer.Get(Name).Build(cc, balancer.BuildOptions{MetricsRecorder: &stats.NoopMetricsRecorder{}})
+	bal := balancer.Get(Name).Build(cc, balancer.BuildOptions{})
 	defer bal.Close()
 	bal.ResolverError(errors.New("resolution failed: test error"))
 
@@ -89,7 +88,7 @@ func (s) TestPickFirst_ResolverErrorinTF(t *testing.T) {
 	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
 	defer cancel()
 	cc := testutils.NewBalancerClientConn(t)
-	bal := balancer.Get(Name).Build(cc, balancer.BuildOptions{MetricsRecorder: &stats.NoopMetricsRecorder{}})
+	bal := balancer.Get(Name).Build(cc, balancer.BuildOptions{})
 	defer bal.Close()
 
 	// After sending a valid update, the LB policy should report CONNECTING.

balancer/pickfirst/pickfirstleaf/pickfirstleaf.go

@@ -120,7 +120,7 @@ func (pickfirstBuilder) Build(cc balancer.ClientConn, bo balancer.BuildOptions)
 	b := &pickfirstBalancer{
 		cc:              cc,
 		target:          bo.Target.String(),
-		metricsRecorder: bo.MetricsRecorder, // ClientConn will always create a Metrics Recorder.
+		metricsRecorder: cc.MetricsRecorder(),
 
 		subConns:              resolver.NewAddressMap(),
 		state:                 connectivity.Connecting,

balancer/pickfirst/pickfirstleaf/pickfirstleaf_ext_test.go

@@ -1099,7 +1099,7 @@ func (s) TestPickFirstLeaf_InterleavingIPV4Preffered(t *testing.T) {
 	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
 	defer cancel()
 	cc := testutils.NewBalancerClientConn(t)
-	bal := balancer.Get(pickfirstleaf.Name).Build(cc, balancer.BuildOptions{MetricsRecorder: &stats.NoopMetricsRecorder{}})
+	bal := balancer.Get(pickfirstleaf.Name).Build(cc, balancer.BuildOptions{})
 	defer bal.Close()
 	ccState := balancer.ClientConnState{
 		ResolverState: resolver.State{
@@ -1145,7 +1145,7 @@ func (s) TestPickFirstLeaf_InterleavingIPv6Preffered(t *testing.T) {
 	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
 	defer cancel()
 	cc := testutils.NewBalancerClientConn(t)
-	bal := balancer.Get(pickfirstleaf.Name).Build(cc, balancer.BuildOptions{MetricsRecorder: &stats.NoopMetricsRecorder{}})
+	bal := balancer.Get(pickfirstleaf.Name).Build(cc, balancer.BuildOptions{})
 	defer bal.Close()
 	ccState := balancer.ClientConnState{
 		ResolverState: resolver.State{
@@ -1189,7 +1189,7 @@ func (s) TestPickFirstLeaf_InterleavingUnknownPreffered(t *testing.T) {
 	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
 	defer cancel()
 	cc := testutils.NewBalancerClientConn(t)
-	bal := balancer.Get(pickfirstleaf.Name).Build(cc, balancer.BuildOptions{MetricsRecorder: &stats.NoopMetricsRecorder{}})
+	bal := balancer.Get(pickfirstleaf.Name).Build(cc, balancer.BuildOptions{})
 	defer bal.Close()
 	ccState := balancer.ClientConnState{
 		ResolverState: resolver.State{

balancer/pickfirst/pickfirstleaf/pickfirstleaf_test.go

@@ -29,7 +29,6 @@ import (
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/internal/grpctest"
 	"google.golang.org/grpc/internal/testutils"
-	"google.golang.org/grpc/internal/testutils/stats"
 	"google.golang.org/grpc/resolver"
 )
 
@@ -196,7 +195,7 @@ func (s) TestPickFirstLeaf_TFPickerUpdate(t *testing.T) {
 	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
 	defer cancel()
 	cc := testutils.NewBalancerClientConn(t)
-	bal := pickfirstBuilder{}.Build(cc, balancer.BuildOptions{MetricsRecorder: &stats.NoopMetricsRecorder{}})
+	bal := pickfirstBuilder{}.Build(cc, balancer.BuildOptions{})
 	defer bal.Close()
 	ccState := balancer.ClientConnState{
 		ResolverState: resolver.State{

balancer/rls/balancer.go

@@ -140,7 +140,7 @@ func (rlsBB) Build(cc balancer.ClientConn, opts balancer.BuildOptions) balancer.
 		updateCh:           buffer.NewUnbounded(),
 	}
 	lb.logger = internalgrpclog.NewPrefixLogger(logger, fmt.Sprintf("[rls-experimental-lb %p] ", lb))
-	lb.dataCache = newDataCache(maxCacheSize, lb.logger, opts.MetricsRecorder, opts.Target.String())
+	lb.dataCache = newDataCache(maxCacheSize, lb.logger, cc.MetricsRecorder(), opts.Target.String())
 	lb.bg = balancergroup.New(balancergroup.Options{
 		CC:                      cc,
 		BuildOpts:               opts,
@@ -539,7 +539,7 @@ func (b *rlsBalancer) sendNewPickerLocked() {
 		bg:              b.bg,
 		rlsServerTarget: b.lbCfg.lookupService,
 		grpcTarget:      b.bopts.Target.String(),
-		metricsRecorder: b.bopts.MetricsRecorder,
+		metricsRecorder: b.cc.MetricsRecorder(),
 	}
 	picker.logger = internalgrpclog.NewPrefixLogger(logger, fmt.Sprintf("[rls-picker %p] ", picker))
 	state := balancer.State{

balancer/weightedroundrobin/balancer.go

@@ -94,7 +94,7 @@ func (bb) Build(cc balancer.ClientConn, bOpts balancer.BuildOptions) balancer.Ba
 	b := &wrrBalancer{
 		ClientConn:       cc,
 		target:           bOpts.Target.String(),
-		metricsRecorder:  bOpts.MetricsRecorder,
+		metricsRecorder:  cc.MetricsRecorder(),
 		addressWeights:   resolver.NewAddressMap(),
 		endpointToWeight: resolver.NewEndpointMap(),
 		scToWeight:       make(map[balancer.SubConn]*endpointWeight),

balancer_wrapper.go

@@ -26,6 +26,7 @@ import (
 	"google.golang.org/grpc/balancer"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/connectivity"
+	"google.golang.org/grpc/experimental/stats"
 	"google.golang.org/grpc/internal"
 	"google.golang.org/grpc/internal/balancer/gracefulswitch"
 	"google.golang.org/grpc/internal/channelz"
@@ -93,7 +94,6 @@ func newCCBalancerWrapper(cc *ClientConn) *ccBalancerWrapper {
 			CustomUserAgent: cc.dopts.copts.UserAgent,
 			ChannelzParent:  cc.channelz,
 			Target:          cc.parsedTarget,
-			MetricsRecorder: cc.metricsRecorderList,
 		},
 		serializer:       grpcsync.NewCallbackSerializer(ctx),
 		serializerCancel: cancel,
@@ -102,6 +102,10 @@ func newCCBalancerWrapper(cc *ClientConn) *ccBalancerWrapper {
 	return ccb
 }
 
+func (ccb *ccBalancerWrapper) MetricsRecorder() stats.MetricsRecorder {
+	return ccb.cc.metricsRecorderList
+}
+
 // updateClientConnState is invoked by grpc to push a ClientConnState update to
 // the underlying balancer.  This is always executed from the serializer, so
 // it is safe to call into the balancer here.

internal/balancergroup/balancergroup_test.go

@@ -33,7 +33,6 @@ import (
 	"google.golang.org/grpc/internal/channelz"
 	"google.golang.org/grpc/internal/grpctest"
 	"google.golang.org/grpc/internal/testutils"
-	"google.golang.org/grpc/internal/testutils/stats"
 	"google.golang.org/grpc/resolver"
 )
 
@@ -604,7 +603,6 @@ func (s) TestBalancerGracefulSwitch(t *testing.T) {
 	childPolicyName := t.Name()
 	stub.Register(childPolicyName, stub.BalancerFuncs{
 		Init: func(bd *stub.BalancerData) {
-			bd.BuildOptions.MetricsRecorder = &stats.NoopMetricsRecorder{}
 			bd.Data = balancer.Get(pickfirst.Name).Build(bd.ClientConn, bd.BuildOptions)
 		},
 		Close: func(bd *stub.BalancerData) {

internal/stats/metrics_recorder_list_test.go

@@ -110,11 +110,11 @@ func (recordingLoadBalancerBuilder) Name() string {
 }
 
 func (recordingLoadBalancerBuilder) Build(cc balancer.ClientConn, bOpts balancer.BuildOptions) balancer.Balancer {
-	intCountHandle.Record(bOpts.MetricsRecorder, 1, "int counter label val", "int counter optional label val")
-	floatCountHandle.Record(bOpts.MetricsRecorder, 2, "float counter label val", "float counter optional label val")
-	intHistoHandle.Record(bOpts.MetricsRecorder, 3, "int histo label val", "int histo optional label val")
-	floatHistoHandle.Record(bOpts.MetricsRecorder, 4, "float histo label val", "float histo optional label val")
-	intGaugeHandle.Record(bOpts.MetricsRecorder, 5, "int gauge label val", "int gauge optional label val")
+	intCountHandle.Record(cc.MetricsRecorder(), 1, "int counter label val", "int counter optional label val")
+	floatCountHandle.Record(cc.MetricsRecorder(), 2, "float counter label val", "float counter optional label val")
+	intHistoHandle.Record(cc.MetricsRecorder(), 3, "int histo label val", "int histo optional label val")
+	floatHistoHandle.Record(cc.MetricsRecorder(), 4, "float histo label val", "float histo optional label val")
+	intGaugeHandle.Record(cc.MetricsRecorder(), 5, "int gauge label val", "int gauge optional label val")
 
 	return &recordingLoadBalancer{
 		Balancer: balancer.Get(pickfirst.Name).Build(cc, bOpts),

internal/testutils/balancer.go

@@ -26,9 +26,12 @@ import (
 
 	"google.golang.org/grpc/balancer"
 	"google.golang.org/grpc/connectivity"
+	"google.golang.org/grpc/experimental/stats"
 	"google.golang.org/grpc/internal"
 	"google.golang.org/grpc/internal/grpcsync"
 	"google.golang.org/grpc/resolver"
+
+	istats "google.golang.org/grpc/internal/stats"
 )
 
 // TestSubConn implements the SubConn interface, to be used in tests.
@@ -155,6 +158,11 @@ func (tcc *BalancerClientConn) NewSubConn(a []resolver.Address, o balancer.NewSu
 	return sc, nil
 }
 
+// MetricsRecorder returns an empty MetricsRecorderList.
+func (*BalancerClientConn) MetricsRecorder() stats.MetricsRecorder {
+	return istats.NewMetricsRecorderList(nil)
+}
+
 // RemoveSubConn is a nop; tests should all be updated to use sc.Shutdown()
 // instead.
 func (tcc *BalancerClientConn) RemoveSubConn(sc balancer.SubConn) {

xds/internal/balancer/clustermanager/clustermanager_test.go

@@ -34,7 +34,6 @@ import (
 	"google.golang.org/grpc/internal/grpctest"
 	"google.golang.org/grpc/internal/hierarchy"
 	"google.golang.org/grpc/internal/testutils"
-	"google.golang.org/grpc/internal/testutils/stats"
 	"google.golang.org/grpc/resolver"
 	"google.golang.org/grpc/status"
 )
@@ -644,7 +643,6 @@ func TestClusterGracefulSwitch(t *testing.T) {
 	childPolicyName := t.Name()
 	stub.Register(childPolicyName, stub.BalancerFuncs{
 		Init: func(bd *stub.BalancerData) {
-			bd.BuildOptions.MetricsRecorder = &stats.NoopMetricsRecorder{}
 			bd.Data = balancer.Get(pickfirst.Name).Build(bd.ClientConn, bd.BuildOptions)
 		},
 		Close: func(bd *stub.BalancerData) {