internal/stats: Add metrics recorder list and usage in ClientConn

balancer/balancer.go

@@ -30,6 +30,7 @@ import (
 	"google.golang.org/grpc/channelz"
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/credentials"
+	estats "google.golang.org/grpc/experimental/stats"
 	"google.golang.org/grpc/grpclog"
 	"google.golang.org/grpc/internal"
 	"google.golang.org/grpc/metadata"
@@ -256,6 +257,10 @@ 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_wrapper.go

@@ -82,6 +82,7 @@ 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,

clientconn.go

@@ -40,6 +40,7 @@ import (
 	"google.golang.org/grpc/internal/grpcsync"
 	"google.golang.org/grpc/internal/idle"
 	iresolver "google.golang.org/grpc/internal/resolver"
+	"google.golang.org/grpc/internal/stats"
 	"google.golang.org/grpc/internal/transport"
 	"google.golang.org/grpc/keepalive"
 	"google.golang.org/grpc/resolver"
@@ -195,8 +196,11 @@ func NewClient(target string, opts ...DialOption) (conn *ClientConn, err error)
 	cc.csMgr = newConnectivityStateManager(cc.ctx, cc.channelz)
 	cc.pickerWrapper = newPickerWrapper(cc.dopts.copts.StatsHandlers)
 
+	cc.metricsRecorderList = stats.NewMetricsRecorderList(cc.dopts.copts.StatsHandlers)
+
 	cc.initIdleStateLocked() // Safe to call without the lock, since nothing else has a reference to cc.
 	cc.idlenessMgr = idle.NewManager((*idler)(cc), cc.dopts.idleTimeout)
+
 	return cc, nil
 }
 
@@ -591,13 +595,14 @@ type ClientConn struct {
 	cancel context.CancelFunc // Cancelled on close.
 
 	// The following are initialized at dial time, and are read-only after that.
-	target          string            // User's dial target.
-	parsedTarget    resolver.Target   // See initParsedTargetAndResolverBuilder().
-	authority       string            // See initAuthority().
-	dopts           dialOptions       // Default and user specified dial options.
-	channelz        *channelz.Channel // Channelz object.
-	resolverBuilder resolver.Builder  // See initParsedTargetAndResolverBuilder().
-	idlenessMgr     *idle.Manager
+	target              string            // User's dial target.
+	parsedTarget        resolver.Target   // See initParsedTargetAndResolverBuilder().
+	authority           string            // See initAuthority().
+	dopts               dialOptions       // Default and user specified dial options.
+	channelz            *channelz.Channel // Channelz object.
+	resolverBuilder     resolver.Builder  // See initParsedTargetAndResolverBuilder().
+	idlenessMgr         *idle.Manager
+	metricsRecorderList *stats.MetricsRecorderList
 
 	// The following provide their own synchronization, and therefore don't
 	// require cc.mu to be held to access them.

internal/stats/metrics_recorder_list.go

@@ -0,0 +1,96 @@
+/*
+ * Copyright 2024 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package stats
+
+import (
+	estats "google.golang.org/grpc/experimental/stats"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/stats"
+)
+
+var logger = grpclog.Component("metrics-recorder-list")
+
+// MetricsRecorderList forwards Record calls to all of it's metricsRecorders.
+//
+// It eats any record calls where the label values provided do not match the
+// number of label keys.
+type MetricsRecorderList struct {
+	// metricsRecorders are the metrics recorders this list will forward to.
+	metricsRecorders []estats.MetricsRecorder
+}
+
+// NewMetricsRecorderList creates a new metric recorder list with all the stats
+// handlers provided which implement the MetricsRecorder interface.
+// If no stats handlers provided implement the MetricsRecorder interface,
+// the MetricsRecorder list returned is a no-op.
+func NewMetricsRecorderList(shs []stats.Handler) *MetricsRecorderList {
+	var mrs []estats.MetricsRecorder
+	for _, sh := range shs {
+		if mr, ok := sh.(estats.MetricsRecorder); ok {
+			mrs = append(mrs, mr)
+		}
+	}
+	return &MetricsRecorderList{
+		metricsRecorders: mrs,
+	}
+}
+
+func verifyLabels(labels []string, optionalLabels []string, labelsRecv ...string) {
+	if got, want := len(labelsRecv), len(labels)+len(optionalLabels); got != want {
+		logger.Fatalf("Length of labels passed to Record incorrect, got: %v, want: %v.", got, want)
+	}
+}
+
+func (l *MetricsRecorderList) RecordInt64Count(handle *estats.Int64CountHandle, incr int64, labels ...string) {
+	verifyLabels(handle.Labels, handle.OptionalLabels, labels...)
+
+	for _, metricRecorder := range l.metricsRecorders {
+		metricRecorder.RecordInt64Count(handle, incr, labels...)
+	}
+}
+
+func (l *MetricsRecorderList) RecordFloat64Count(handle *estats.Float64CountHandle, incr float64, labels ...string) {
+	verifyLabels(handle.Labels, handle.OptionalLabels, labels...)
+
+	for _, metricRecorder := range l.metricsRecorders {
+		metricRecorder.RecordFloat64Count(handle, incr, labels...)
+	}
+}
+
+func (l *MetricsRecorderList) RecordInt64Histo(handle *estats.Int64HistoHandle, incr int64, labels ...string) {
+	verifyLabels(handle.Labels, handle.OptionalLabels, labels...)
+
+	for _, metricRecorder := range l.metricsRecorders {
+		metricRecorder.RecordInt64Histo(handle, incr, labels...)
+	}
+}
+
+func (l *MetricsRecorderList) RecordFloat64Histo(handle *estats.Float64HistoHandle, incr float64, labels ...string) {
+	verifyLabels(handle.Labels, handle.OptionalLabels, labels...)
+
+	for _, metricRecorder := range l.metricsRecorders {
+		metricRecorder.RecordFloat64Histo(handle, incr, labels...)
+	}
+}
+
+func (l *MetricsRecorderList) RecordInt64Gauge(handle *estats.Int64GaugeHandle, incr int64, labels ...string) {
+	verifyLabels(handle.Labels, handle.OptionalLabels, labels...)
+
+	for _, metricRecorder := range l.metricsRecorders {
+		metricRecorder.RecordInt64Gauge(handle, incr, labels...)
+	}
+}