Add Metric Producer as a new interface, which returns scope metrics

CHANGELOG.md

@@ -12,6 +12,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - The deprecated `go.opentelemetry.io/otel/sdk/metric/view` package is removed. (#3520)
 
+### Added
+
+- Add `Producer` interface and `Reader.RegisterProducer(Producer)` to `go.opentelemetry.io/otel/sdk/metric` to enable external metric Producers. (#3524)
+
 ## [1.11.2/0.34.0] 2022-12-05
 
 ### Added

sdk/metric/config.go

@@ -54,14 +54,19 @@ func unify(funcs []func(context.Context) error) func(context.Context) error {
 				errs = append(errs, err)
 			}
 		}
-		switch len(errs) {
-		case 0:
-			return nil
-		case 1:
-			return errs[0]
-		default:
-			return fmt.Errorf("%v", errs)
-		}
+		return unifyErrors(errs)
+	}
+}
+
+// unifyErrors combines multiple errors into a single error
+func unifyErrors(errs []error) error {
+	switch len(errs) {
+	case 0:
+		return nil
+	case 1:
+		return errs[0]
+	default:
+		return fmt.Errorf("%v", errs)
 	}
 }
 

sdk/metric/config_test.go

@@ -28,12 +28,13 @@ import (
 )
 
 type reader struct {
-	producer        producer
-	temporalityFunc TemporalitySelector
-	aggregationFunc AggregationSelector
-	collectFunc     func(context.Context) (metricdata.ResourceMetrics, error)
-	forceFlushFunc  func(context.Context) error
-	shutdownFunc    func(context.Context) error
+	producer          sdkProducer
+	externalProducers []Producer
+	temporalityFunc   TemporalitySelector
+	aggregationFunc   AggregationSelector
+	collectFunc       func(context.Context) (metricdata.ResourceMetrics, error)
+	forceFlushFunc    func(context.Context) error
+	shutdownFunc      func(context.Context) error
 }
 
 var _ Reader = (*reader)(nil)
@@ -42,7 +43,8 @@ func (r *reader) aggregation(kind InstrumentKind) aggregation.Aggregation { // n
 	return r.aggregationFunc(kind)
 }
 
-func (r *reader) register(p producer) { r.producer = p }
+func (r *reader) register(p sdkProducer)      { r.producer = p }
+func (r *reader) RegisterProducer(p Producer) { r.externalProducers = append(r.externalProducers, p) }
 func (r *reader) temporality(kind InstrumentKind) metricdata.Temporality {
 	return r.temporalityFunc(kind)
 }

sdk/metric/manual_reader.go

@@ -28,9 +28,12 @@ import (
 // manualReader is a simple Reader that allows an application to
 // read metrics on demand.
 type manualReader struct {
-	producer     atomic.Value
+	sdkProducer  atomic.Value
 	shutdownOnce sync.Once
 
+	mu                sync.Mutex
+	externalProducers atomic.Value
+
 	temporalitySelector TemporalitySelector
 	aggregationSelector AggregationSelector
 }
@@ -41,22 +44,36 @@ var _ = map[Reader]struct{}{&manualReader{}: {}}
 // NewManualReader returns a Reader which is directly called to collect metrics.
 func NewManualReader(opts ...ManualReaderOption) Reader {
 	cfg := newManualReaderConfig(opts)
-	return &manualReader{
+	r := &manualReader{
 		temporalitySelector: cfg.temporalitySelector,
 		aggregationSelector: cfg.aggregationSelector,
 	}
+	r.externalProducers.Store([]Producer{})
+	return r
 }
 
-// register stores the Producer which enables the caller to read
-// metrics on demand.
-func (mr *manualReader) register(p producer) {
+// register stores the sdkProducer which enables the caller
+// to read metrics from the SDK on demand.
+func (mr *manualReader) register(p sdkProducer) {
 	// Only register once. If producer is already set, do nothing.
-	if !mr.producer.CompareAndSwap(nil, produceHolder{produce: p.produce}) {
+	if !mr.sdkProducer.CompareAndSwap(nil, produceHolder{produce: p.produce}) {
 		msg := "did not register manual reader"
 		global.Error(errDuplicateRegister, msg)
 	}
 }
 
+// RegisterProducer stores the external Producer which enables the caller
+// to read metrics on demand.
+func (mr *manualReader) RegisterProducer(p Producer) {
+	mr.mu.Lock()
+	defer mr.mu.Unlock()
+	currentProducers := mr.externalProducers.Load().([]Producer)
+	newProducers := []Producer{}
+	newProducers = append(newProducers, currentProducers...)
+	newProducers = append(newProducers, p)
+	mr.externalProducers.Store(newProducers)
+}
+
 // temporality reports the Temporality for the instrument kind provided.
 func (mr *manualReader) temporality(kind InstrumentKind) metricdata.Temporality {
 	return mr.temporalitySelector(kind)
@@ -77,18 +94,18 @@ func (mr *manualReader) Shutdown(context.Context) error {
 	err := ErrReaderShutdown
 	mr.shutdownOnce.Do(func() {
 		// Any future call to Collect will now return ErrReaderShutdown.
-		mr.producer.Store(produceHolder{
+		mr.sdkProducer.Store(produceHolder{
 			produce: shutdownProducer{}.produce,
 		})
 		err = nil
 	})
 	return err
 }
 
-// Collect gathers all metrics from the SDK, calling any callbacks necessary.
-// Collect will return an error if called after shutdown.
+// Collect gathers all metrics from the SDK and other Producers, calling any
+// callbacks necessary. Collect will return an error if called after shutdown.
 func (mr *manualReader) Collect(ctx context.Context) (metricdata.ResourceMetrics, error) {
-	p := mr.producer.Load()
+	p := mr.sdkProducer.Load()
 	if p == nil {
 		return metricdata.ResourceMetrics{}, ErrReaderNotRegistered
 	}
@@ -103,7 +120,19 @@ func (mr *manualReader) Collect(ctx context.Context) (metricdata.ResourceMetrics
 		return metricdata.ResourceMetrics{}, err
 	}
 
-	return ph.produce(ctx)
+	rm, err := ph.produce(ctx)
+	if err != nil {
+		return metricdata.ResourceMetrics{}, err
+	}
+	var errs []error
+	for _, producer := range mr.externalProducers.Load().([]Producer) {
+		externalMetrics, err := producer.Produce(ctx)
+		if err != nil {
+			errs = append(errs, err)
+		}
+		rm.ScopeMetrics = append(rm.ScopeMetrics, externalMetrics...)
+	}
+	return rm, unifyErrors(errs)
 }
 
 // manualReaderConfig contains configuration options for a ManualReader.

sdk/metric/periodic_reader.go

@@ -114,6 +114,7 @@ func NewPeriodicReader(exporter Exporter, options ...PeriodicReaderOption) Reade
 		cancel:   cancel,
 		done:     make(chan struct{}),
 	}
+	r.externalProducers.Store([]Producer{})
 
 	go func() {
 		defer func() { close(r.done) }()
@@ -126,7 +127,10 @@ func NewPeriodicReader(exporter Exporter, options ...PeriodicReaderOption) Reade
 // periodicReader is a Reader that continuously collects and exports metric
 // data at a set interval.
 type periodicReader struct {
-	producer atomic.Value
+	sdkProducer atomic.Value
+
+	mu                sync.Mutex
+	externalProducers atomic.Value
 
 	timeout  time.Duration
 	exporter Exporter
@@ -166,14 +170,25 @@ func (r *periodicReader) run(ctx context.Context, interval time.Duration) {
 }
 
 // register registers p as the producer of this reader.
-func (r *periodicReader) register(p producer) {
+func (r *periodicReader) register(p sdkProducer) {
 	// Only register once. If producer is already set, do nothing.
-	if !r.producer.CompareAndSwap(nil, produceHolder{produce: p.produce}) {
+	if !r.sdkProducer.CompareAndSwap(nil, produceHolder{produce: p.produce}) {
 		msg := "did not register periodic reader"
 		global.Error(errDuplicateRegister, msg)
 	}
 }
 
+// RegisterProducer registers p as an external Producer of this reader.
+func (r *periodicReader) RegisterProducer(p Producer) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	currentProducers := r.externalProducers.Load().([]Producer)
+	newProducers := []Producer{}
+	newProducers = append(newProducers, currentProducers...)
+	newProducers = append(newProducers, p)
+	r.externalProducers.Store(newProducers)
+}
+
 // temporality reports the Temporality for the instrument kind provided.
 func (r *periodicReader) temporality(kind InstrumentKind) metricdata.Temporality {
 	return r.exporter.Temporality(kind)
@@ -195,12 +210,13 @@ func (r *periodicReader) collectAndExport(ctx context.Context) error {
 }
 
 // Collect gathers and returns all metric data related to the Reader from
-// the SDK. The returned metric data is not exported to the configured
-// exporter, it is left to the caller to handle that if desired.
+// the SDK and other Producers. The returned metric data is not exported
+// to the configured exporter, it is left to the caller to handle that if
+// desired.
 //
 // An error is returned if this is called after Shutdown.
 func (r *periodicReader) Collect(ctx context.Context) (metricdata.ResourceMetrics, error) {
-	return r.collect(ctx, r.producer.Load())
+	return r.collect(ctx, r.sdkProducer.Load())
 }
 
 // collect unwraps p as a produceHolder and returns its produce results.
@@ -218,7 +234,20 @@ func (r *periodicReader) collect(ctx context.Context, p interface{}) (metricdata
 		err := fmt.Errorf("periodic reader: invalid producer: %T", p)
 		return metricdata.ResourceMetrics{}, err
 	}
-	return ph.produce(ctx)
+
+	rm, err := ph.produce(ctx)
+	if err != nil {
+		return metricdata.ResourceMetrics{}, err
+	}
+	var errs []error
+	for _, producer := range r.externalProducers.Load().([]Producer) {
+		externalMetrics, err := producer.Produce(ctx)
+		if err != nil {
+			errs = append(errs, err)
+		}
+		rm.ScopeMetrics = append(rm.ScopeMetrics, externalMetrics...)
+	}
+	return rm, unifyErrors(errs)
 }
 
 // export exports metric data m using r's exporter.
@@ -259,7 +288,7 @@ func (r *periodicReader) Shutdown(ctx context.Context) error {
 		<-r.done
 
 		// Any future call to Collect will now return ErrReaderShutdown.
-		ph := r.producer.Swap(produceHolder{
+		ph := r.sdkProducer.Swap(produceHolder{
 			produce: shutdownProducer{}.produce,
 		})
 

sdk/metric/periodic_reader_test.go

@@ -114,7 +114,8 @@ func (ts *periodicReaderTestSuite) SetupTest() {
 	}
 
 	ts.ErrReader = NewPeriodicReader(e)
-	ts.ErrReader.register(testProducer{})
+	ts.ErrReader.register(testSDKProducer{})
+	ts.ErrReader.RegisterProducer(testExternalProducer{})
 }
 
 func (ts *periodicReaderTestSuite) TearDownTest() {
@@ -186,14 +187,15 @@ func TestPeriodicReaderRun(t *testing.T) {
 
 	exp := &fnExporter{
 		exportFunc: func(_ context.Context, m metricdata.ResourceMetrics) error {
-			// The testProducer produces testMetrics.
-			assert.Equal(t, testMetrics, m)
+			// The testSDKProducer produces testResourceMetricsAB.
+			assert.Equal(t, testResourceMetricsAB, m)
 			return assert.AnError
 		},
 	}
 
 	r := NewPeriodicReader(exp)
-	r.register(testProducer{})
+	r.register(testSDKProducer{})
+	r.RegisterProducer(testExternalProducer{})
 	trigger <- time.Now()
 	assert.Equal(t, assert.AnError, <-eh.Err)
 
@@ -210,8 +212,8 @@ func TestPeriodicReaderFlushesPending(t *testing.T) {
 		called = new(bool)
 		return &fnExporter{
 			exportFunc: func(_ context.Context, m metricdata.ResourceMetrics) error {
-				// The testProducer produces testMetrics.
-				assert.Equal(t, testMetrics, m)
+				// The testSDKProducer produces testResourceMetricsA.
+				assert.Equal(t, testResourceMetricsAB, m)
 				*called = true
 				return assert.AnError
 			},
@@ -221,7 +223,8 @@ func TestPeriodicReaderFlushesPending(t *testing.T) {
 	t.Run("ForceFlush", func(t *testing.T) {
 		exp, called := expFunc(t)
 		r := NewPeriodicReader(exp)
-		r.register(testProducer{})
+		r.register(testSDKProducer{})
+		r.RegisterProducer(testExternalProducer{})
 		assert.Equal(t, assert.AnError, r.ForceFlush(context.Background()), "export error not returned")
 		assert.True(t, *called, "exporter Export method not called, pending telemetry not flushed")
 
@@ -232,7 +235,8 @@ func TestPeriodicReaderFlushesPending(t *testing.T) {
 	t.Run("Shutdown", func(t *testing.T) {
 		exp, called := expFunc(t)
 		r := NewPeriodicReader(exp)
-		r.register(testProducer{})
+		r.register(testSDKProducer{})
+		r.RegisterProducer(testExternalProducer{})
 		assert.Equal(t, assert.AnError, r.Shutdown(context.Background()), "export error not returned")
 		assert.True(t, *called, "exporter Export method not called, pending telemetry not flushed")
 	})

sdk/metric/reader.go

@@ -51,7 +51,12 @@ type Reader interface {
 	// register registers a Reader with a MeterProvider.
 	// The producer argument allows the Reader to signal the sdk to collect
 	// and send aggregated metric measurements.
-	register(producer)
+	register(sdkProducer)
+
+	// RegisterProducer registers a an external Producer with this Reader.
+	// The Producer is used as a source of aggregated metric data which is
+	// incorporated into metrics collected from the SDK.
+	RegisterProducer(Producer)
 
 	// temporality reports the Temporality for the instrument kind provided.
 	temporality(InstrumentKind) metricdata.Temporality
@@ -84,14 +89,22 @@ type Reader interface {
 	Shutdown(context.Context) error
 }
 
-// producer produces metrics for a Reader.
-type producer interface {
+// sdkProducer produces metrics for a Reader.
+type sdkProducer interface {
 	// produce returns aggregated metrics from a single collection.
 	//
 	// This method is safe to call concurrently.
 	produce(context.Context) (metricdata.ResourceMetrics, error)
 }
 
+// Producer produces metrics for a Reader from an external source.
+type Producer interface {
+	// Produce returns aggregated metrics from an external source.
+	//
+	// This method should be safe to call concurrently.
+	Produce(context.Context) ([]metricdata.ScopeMetrics, error)
+}
+
 // produceHolder is used as an atomic.Value to wrap the non-concrete producer
 // type.
 type produceHolder struct {