Test duplicate Reader registration

sdk/metric/go.mod

@@ -4,6 +4,7 @@ go 1.16
 
 require (
 	github.com/stretchr/testify v1.7.1
+	go.opentelemetry.io/otel v1.6.3
 	go.opentelemetry.io/otel/metric v0.0.0-00010101000000-000000000000
 )
 

sdk/metric/go.sum

@@ -1,7 +1,9 @@
 github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/go-logr/logr v1.2.2/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
+github.com/go-logr/logr v1.2.3 h1:2DntVwHkVopvECVRSlL5PSo9eG+cAkDCuckLubN+rq0=
 github.com/go-logr/logr v1.2.3/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
+github.com/go-logr/stdr v1.2.2 h1:hSWxHoqTgW2S2qGc0LTAI563KZ5YKYRhT3MFKZMbjag=
 github.com/go-logr/stdr v1.2.2/go.mod h1:mMo/vtBO5dYbehREoey6XUKy/eSumjCCveDpRre4VKE=
 github.com/google/go-cmp v0.5.7 h1:81/ik6ipDQS2aGcBfIN5dHDB36BwrStyeAQquSYCV4o=
 github.com/google/go-cmp v0.5.7/go.mod h1:n+brtR0CgQNWTVd5ZUFpTBC8YFBDLK/h/bpaJ8/DtOE=

sdk/metric/manual_reader.go

@@ -19,6 +19,7 @@ import (
 	"fmt"
 	"sync"
 
+	"go.opentelemetry.io/otel/internal/global"
 	"go.opentelemetry.io/otel/sdk/metric/export"
 )
 
@@ -43,6 +44,11 @@ func NewManualReader() Reader {
 func (mr *manualReader) register(p producer) {
 	mr.lock.Lock()
 	defer mr.lock.Unlock()
+	if mr.producer != nil {
+		msg := "did not register manualReader"
+		global.Error(errDuplicateRegister, msg)
+		return
+	}
 	mr.producer = p
 }
 

sdk/metric/reader.go

@@ -16,10 +16,15 @@ package metric // import "go.opentelemetry.io/otel/sdk/metric"
 
 import (
 	"context"
+	"fmt"
 
 	"go.opentelemetry.io/otel/sdk/metric/export"
 )
 
+// errDuplicateRegister is logged by a Reader when an attempt to registered it
+// more than once occurs.
+var errDuplicateRegister = fmt.Errorf("duplicate reader registration")
+
 // Reader is the interface used between the SDK and an
 // exporter.  Control flow is bi-directional through the
 // Reader, since the SDK initiates ForceFlush and Shutdown

sdk/metric/reader_test.go

@@ -79,14 +79,42 @@ func testReaderHarness(t *testing.T, f readerFactory) {
 		// Ensure Reader is allowed clean up attempt.
 		_ = r.Shutdown(ctx)
 	})
+
+	t.Run("MultipleRegister", func(t *testing.T) {
+		p0 := testProducer{
+			produceFunc: func(ctx context.Context) (export.Metrics, error) {
+				// Differentiate this producer from the second by returning an
+				// error.
+				return testMetrics, assert.AnError
+			},
+		}
+		p1 := testProducer{}
+
+		r := f()
+		r.register(p0)
+		// This should be ignored.
+		r.register(p1)
+
+		ctx := context.Background()
+		_, err := r.Collect(ctx)
+		assert.Equal(t, assert.AnError, err)
+
+		// Ensure Reader is allowed clean up attempt.
+		_ = r.Shutdown(ctx)
+	})
 }
 
 var testMetrics = export.Metrics{
 	// TODO: test with actual data.
 }
 
-type testProducer struct{}
+type testProducer struct {
+	produceFunc func(context.Context) (export.Metrics, error)
+}
 
-func (p testProducer) produce(context.Context) (export.Metrics, error) {
+func (p testProducer) produce(ctx context.Context) (export.Metrics, error) {
+	if p.produceFunc != nil {
+		return p.produceFunc(ctx)
+	}
 	return testMetrics, nil
 }