feat: sdk/trace: span processed metric for simple span processor

CHANGELOG.md

@@ -61,6 +61,8 @@ The next release will require at least [Go 1.24].
 - The `go.opentelemetry.io/otel/semconv/v1.37.0` package.
   The package contains semantic conventions from the `v1.37.0` version of the OpenTelemetry Semantic Conventions.
   See the [migration documentation](./semconv/v1.37.0/MIGRATION.md) for information on how to upgrade from `go.opentelemetry.io/otel/semconv/v1.36.0.`(#7254)
+- Add experimental self-observability simple span processor metrics in `go.opentelemetry.io/otel/sdk/trace`.
+  Check the `go.opentelemetry.io/otel/sdk/trace/internal/x` package documentation for more information. (#7162)
 
 ### Changed
 

sdk/trace/internal/x/README.md

@@ -20,6 +20,7 @@ When enabled, the SDK will create the following metrics using the global `MeterP
 
 - `otel.sdk.span.live`
 - `otel.sdk.span.started`
+- `otel.sdk.processor.span.processed` (only for simple span processor)
 
 Please see the [Semantic conventions for OpenTelemetry SDK metrics] documentation for more details on these metrics.
 

sdk/trace/simple_span_processor.go

@@ -5,18 +5,42 @@ package trace // import "go.opentelemetry.io/otel/sdk/trace"
 
 import (
 	"context"
+	"fmt"
 	"sync"
+	"sync/atomic"
 
 	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/internal/global"
+	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/sdk"
+	"go.opentelemetry.io/otel/sdk/trace/internal/x"
+	semconv "go.opentelemetry.io/otel/semconv/v1.36.0"
+	"go.opentelemetry.io/otel/semconv/v1.36.0/otelconv"
+	"go.opentelemetry.io/otel/trace"
 )
 
+var measureAttrsPool = sync.Pool{
+	New: func() any {
+		// "component.name" + "component.type" + "error.type"
+		const n = 1 + 1 + 1
+		s := make([]attribute.KeyValue, 0, n)
+		// Return a pointer to a slice instead of a slice itself
+		// to avoid allocations on every call.
+		return &s
+	},
+}
+
 // simpleSpanProcessor is a SpanProcessor that synchronously sends all
 // completed Spans to a trace.Exporter immediately.
 type simpleSpanProcessor struct {
 	exporterMu sync.Mutex
 	exporter   SpanExporter
 	stopOnce   sync.Once
+
+	selfObservabilityEnabled bool
+	componentNameAttr        attribute.KeyValue
+	spansProcessedCounter    otelconv.SDKProcessorSpanProcessed
 }
 
 var _ SpanProcessor = (*simpleSpanProcessor)(nil)
@@ -31,13 +55,46 @@ var _ SpanProcessor = (*simpleSpanProcessor)(nil)
 // use instead.
 func NewSimpleSpanProcessor(exporter SpanExporter) SpanProcessor {
 	ssp := &simpleSpanProcessor{
-		exporter: exporter,
+		exporter:                 exporter,
+		selfObservabilityEnabled: x.SelfObservability.Enabled(),
+	}
+
+	if ssp.selfObservabilityEnabled {
+		ssp.componentNameAttr = semconv.OTelComponentName(
+			fmt.Sprintf("%s/%d", otelconv.ComponentTypeSimpleSpanProcessor, nextSimpleProcessorID()))
+
+		var err error
+		ssp.spansProcessedCounter, err = newSpanProcessedInst()
+		if err != nil {
+			msg := "failed to create self-observability metrics for simple span processor: %w"
+			err := fmt.Errorf(msg, err)
+			otel.Handle(err)
+		}
 	}
+
 	global.Warn("SimpleSpanProcessor is not recommended for production use, consider using BatchSpanProcessor instead.")
 
 	return ssp
 }
 
+var simpleProcessorIDCounter atomic.Int64
+
+// nextSimpleProcessorID returns an identifier for this simple span processor,
+// starting with 0 and incrementing by 1 each time it is called.
+func nextSimpleProcessorID() int64 {
+	return simpleProcessorIDCounter.Add(1) - 1
+}
+
+func newSpanProcessedInst() (otelconv.SDKProcessorSpanProcessed, error) {
+	meter := otel.GetMeterProvider().Meter(
+		selfObsScopeName,
+		metric.WithInstrumentationVersion(sdk.Version()),
+		metric.WithSchemaURL(semconv.SchemaURL),
+	)
+	spansProcessedCounter, err := otelconv.NewSDKProcessorSpanProcessed(meter)
+	return spansProcessedCounter, err
+}
+
 // OnStart does nothing.
 func (*simpleSpanProcessor) OnStart(context.Context, ReadWriteSpan) {}
 
@@ -47,8 +104,25 @@ func (ssp *simpleSpanProcessor) OnEnd(s ReadOnlySpan) {
 	defer ssp.exporterMu.Unlock()
 
 	if ssp.exporter != nil && s.SpanContext().TraceFlags().IsSampled() {
-		if err := ssp.exporter.ExportSpans(context.Background(), []ReadOnlySpan{s}); err != nil {
+		attrs := measureAttrsPool.Get().(*[]attribute.KeyValue)
+		defer func() {
+			*attrs = (*attrs)[:0] // reset the slice for reuse
+			measureAttrsPool.Put(attrs)
+		}()
+		*attrs = append(*attrs,
+			ssp.componentNameAttr,
+			ssp.spansProcessedCounter.AttrComponentType(otelconv.ComponentTypeSimpleSpanProcessor))
+
+		err := ssp.exporter.ExportSpans(context.Background(), []ReadOnlySpan{s})
+		if err != nil {
 			otel.Handle(err)
+			*attrs = append(*attrs, semconv.ErrorType(err))
+		}
+		if ssp.selfObservabilityEnabled {
+			// Add the span to the context to ensure the metric is recorded
+			// with the correct span context.
+			ctx := trace.ContextWithSpanContext(context.Background(), s.SpanContext())
+			ssp.spansProcessedCounter.Add(ctx, 1, *attrs...)
 		}
 	}
 }

sdk/trace/simple_span_processor_test.go

@@ -6,11 +6,23 @@ package trace
 import (
 	"context"
 	"errors"
+	"strconv"
 	"sync"
 	"testing"
 	"time"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/sdk"
+	"go.opentelemetry.io/otel/sdk/instrumentation"
+	"go.opentelemetry.io/otel/sdk/metric"
+	"go.opentelemetry.io/otel/sdk/metric/metricdata"
+	"go.opentelemetry.io/otel/sdk/metric/metricdata/metricdatatest"
+	semconv "go.opentelemetry.io/otel/semconv/v1.36.0"
+	"go.opentelemetry.io/otel/semconv/v1.36.0/otelconv"
 )
 
 type simpleTestExporter struct {
@@ -34,6 +46,17 @@ func (t *simpleTestExporter) Shutdown(ctx context.Context) error {
 	}
 }
 
+var _ SpanExporter = (*failingTestExporter)(nil)
+
+type failingTestExporter struct {
+	simpleTestExporter
+}
+
+func (f *failingTestExporter) ExportSpans(ctx context.Context, spans []ReadOnlySpan) error {
+	_ = f.simpleTestExporter.ExportSpans(ctx, spans)
+	return errors.New("failed to export spans")
+}
+
 var _ SpanExporter = (*simpleTestExporter)(nil)
 
 func TestNewSimpleSpanProcessor(t *testing.T) {
@@ -168,3 +191,140 @@ func TestSimpleSpanProcessorShutdownHonorsContextCancel(t *testing.T) {
 		t.Errorf("SimpleSpanProcessor.Shutdown did not return %v, got %v", want, got)
 	}
 }
+
+func TestSimpleSpanProcessorSelfObservability(t *testing.T) {
+	tests := []struct {
+		name          string
+		enabled       bool
+		exporter      SpanExporter
+		assertMetrics func(t *testing.T, rm metricdata.ResourceMetrics)
+	}{
+		{
+			name:     "Disabled",
+			enabled:  false,
+			exporter: &simpleTestExporter{},
+			assertMetrics: func(t *testing.T, rm metricdata.ResourceMetrics) {
+				assert.Empty(t, rm.ScopeMetrics)
+			},
+		},
+		{
+			name:     "Enabled",
+			enabled:  true,
+			exporter: &simpleTestExporter{},
+			assertMetrics: func(t *testing.T, rm metricdata.ResourceMetrics) {
+				assert.Len(t, rm.ScopeMetrics, 1)
+				sm := rm.ScopeMetrics[0]
+
+				want := metricdata.ScopeMetrics{
+					Scope: instrumentation.Scope{
+						Name:      "go.opentelemetry.io/otel/sdk/trace",
+						Version:   sdk.Version(),
+						SchemaURL: semconv.SchemaURL,
+					},
+					Metrics: []metricdata.Metrics{
+						{
+							Name:        otelconv.SDKProcessorSpanProcessed{}.Name(),
+							Description: otelconv.SDKProcessorSpanProcessed{}.Description(),
+							Unit:        otelconv.SDKProcessorSpanProcessed{}.Unit(),
+							Data: metricdata.Sum[int64]{
+								DataPoints: []metricdata.DataPoint[int64]{
+									{
+										Value: 1,
+										Attributes: attribute.NewSet(
+											semconv.OTelComponentName("simple_span_processor/0"),
+											semconv.OTelComponentTypeKey.String("simple_span_processor"),
+										),
+									},
+								},
+								Temporality: metricdata.CumulativeTemporality,
+								IsMonotonic: true,
+							},
+						},
+					},
+				}
+
+				metricdatatest.AssertEqual(
+					t,
+					want,
+					sm,
+					metricdatatest.IgnoreTimestamp(),
+					metricdatatest.IgnoreExemplars(),
+				)
+			},
+		},
+		{
+			name:    "Enabled, Exporter error",
+			enabled: true,
+			exporter: &failingTestExporter{
+				simpleTestExporter: simpleTestExporter{},
+			},
+			assertMetrics: func(t *testing.T, rm metricdata.ResourceMetrics) {
+				assert.Len(t, rm.ScopeMetrics, 1)
+				sm := rm.ScopeMetrics[0]
+
+				want := metricdata.ScopeMetrics{
+					Scope: instrumentation.Scope{
+						Name:      "go.opentelemetry.io/otel/sdk/trace",
+						Version:   sdk.Version(),
+						SchemaURL: semconv.SchemaURL,
+					},
+					Metrics: []metricdata.Metrics{
+						{
+							Name:        otelconv.SDKProcessorSpanProcessed{}.Name(),
+							Description: otelconv.SDKProcessorSpanProcessed{}.Description(),
+							Unit:        otelconv.SDKProcessorSpanProcessed{}.Unit(),
+							Data: metricdata.Sum[int64]{
+								DataPoints: []metricdata.DataPoint[int64]{
+									{
+										Value: 1,
+										Attributes: attribute.NewSet(
+											semconv.OTelComponentName("simple_span_processor/0"),
+											semconv.OTelComponentTypeKey.String("simple_span_processor"),
+											semconv.ErrorTypeKey.String("*errors.errorString"),
+										),
+									},
+								},
+								Temporality: metricdata.CumulativeTemporality,
+								IsMonotonic: true,
+							},
+						},
+					},
+				}
+
+				metricdatatest.AssertEqual(
+					t,
+					want,
+					sm,
+					metricdatatest.IgnoreTimestamp(),
+					metricdatatest.IgnoreExemplars(),
+				)
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			t.Setenv("OTEL_GO_X_SELF_OBSERVABILITY", strconv.FormatBool(test.enabled))
+
+			original := otel.GetMeterProvider()
+			t.Cleanup(func() { otel.SetMeterProvider(original) })
+
+			r := metric.NewManualReader()
+			mp := metric.NewMeterProvider(
+				metric.WithReader(r),
+				metric.WithView(dropSpanMetricsView),
+			)
+			otel.SetMeterProvider(mp)
+
+			ssp := NewSimpleSpanProcessor(test.exporter)
+			tp := basicTracerProvider(t)
+			tp.RegisterSpanProcessor(ssp)
+			startSpan(tp, test.name).End()
+
+			var rm metricdata.ResourceMetrics
+			require.NoError(t, r.Collect(context.Background(), &rm))
+			test.assertMetrics(t, rm)
+			simpleProcessorIDCounter.Store(0) // reset simpleProcessorIDCounter
+		})
+	}
+}