SetMeterProvider might miss the delegation for instruments and registries (#5780)

Closes #5757

This PR fixes an issue where `SetMeterProvider` might miss the
delegation for instruments and registries. This bug brings a concurrent
issue that could possibly make instruments and registries unable to
operate correctly, such as recording, after using the `SetMeterProvider`
method. The data put on these instruments and registries might be lost.

CHANGELOG.md

@@ -18,6 +18,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Fix memory leak in the global `MeterProvider` when identical instruments are repeatedly created. (#5754)
 - Fix panic instruments creation when setting meter provider. (#5758)
+- Fix an issue where `SetMeterProvider` in `go.opentelemetry.io/otel` might miss the delegation for instruments and registries. (#5780)
 
 ### Removed
 

internal/global/meter.go

@@ -7,7 +7,6 @@ import (
 	"container/list"
 	"reflect"
 	"sync"
-	"sync/atomic"
 
 	"go.opentelemetry.io/otel/metric"
 	"go.opentelemetry.io/otel/metric/embedded"
@@ -97,7 +96,7 @@ type meter struct {
 
 	registry list.List
 
-	delegate atomic.Value // metric.Meter
+	delegate metric.Meter
 }
 
 type delegatedInstrument interface {
@@ -123,12 +122,12 @@ type instID struct {
 //
 // It is guaranteed by the caller that this happens only once.
 func (m *meter) setDelegate(provider metric.MeterProvider) {
-	meter := provider.Meter(m.name, m.opts...)
-	m.delegate.Store(meter)
-
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
 
+	meter := provider.Meter(m.name, m.opts...)
+	m.delegate = meter
+
 	for _, inst := range m.instruments {
 		inst.setDelegate(meter)
 	}
@@ -141,16 +140,18 @@ func (m *meter) setDelegate(provider metric.MeterProvider) {
 		m.registry.Remove(e)
 	}
 
-	clear(m.instruments)
+	m.instruments = nil
 	m.registry.Init()
 }
 
 func (m *meter) Int64Counter(name string, options ...metric.Int64CounterOption) (metric.Int64Counter, error) {
-	if del, ok := m.delegate.Load().(metric.Meter); ok {
-		return del.Int64Counter(name, options...)
-	}
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
+
+	if m.delegate != nil {
+		return m.delegate.Int64Counter(name, options...)
+	}
+
 	i := &siCounter{name: name, opts: options}
 	cfg := metric.NewInt64CounterConfig(options...)
 	id := instID{
@@ -164,11 +165,13 @@ func (m *meter) Int64Counter(name string, options ...metric.Int64CounterOption)
 }
 
 func (m *meter) Int64UpDownCounter(name string, options ...metric.Int64UpDownCounterOption) (metric.Int64UpDownCounter, error) {
-	if del, ok := m.delegate.Load().(metric.Meter); ok {
-		return del.Int64UpDownCounter(name, options...)
-	}
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
+
+	if m.delegate != nil {
+		return m.delegate.Int64UpDownCounter(name, options...)
+	}
+
 	i := &siUpDownCounter{name: name, opts: options}
 	cfg := metric.NewInt64UpDownCounterConfig(options...)
 	id := instID{
@@ -182,11 +185,13 @@ func (m *meter) Int64UpDownCounter(name string, options ...metric.Int64UpDownCou
 }
 
 func (m *meter) Int64Histogram(name string, options ...metric.Int64HistogramOption) (metric.Int64Histogram, error) {
-	if del, ok := m.delegate.Load().(metric.Meter); ok {
-		return del.Int64Histogram(name, options...)
-	}
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
+
+	if m.delegate != nil {
+		return m.delegate.Int64Histogram(name, options...)
+	}
+
 	i := &siHistogram{name: name, opts: options}
 	cfg := metric.NewInt64HistogramConfig(options...)
 	id := instID{
@@ -200,11 +205,13 @@ func (m *meter) Int64Histogram(name string, options ...metric.Int64HistogramOpti
 }
 
 func (m *meter) Int64Gauge(name string, options ...metric.Int64GaugeOption) (metric.Int64Gauge, error) {
-	if del, ok := m.delegate.Load().(metric.Meter); ok {
-		return del.Int64Gauge(name, options...)
-	}
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
+
+	if m.delegate != nil {
+		return m.delegate.Int64Gauge(name, options...)
+	}
+
 	i := &siGauge{name: name, opts: options}
 	cfg := metric.NewInt64GaugeConfig(options...)
 	id := instID{
@@ -218,11 +225,13 @@ func (m *meter) Int64Gauge(name string, options ...metric.Int64GaugeOption) (met
 }
 
 func (m *meter) Int64ObservableCounter(name string, options ...metric.Int64ObservableCounterOption) (metric.Int64ObservableCounter, error) {
-	if del, ok := m.delegate.Load().(metric.Meter); ok {
-		return del.Int64ObservableCounter(name, options...)
-	}
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
+
+	if m.delegate != nil {
+		return m.delegate.Int64ObservableCounter(name, options...)
+	}
+
 	i := &aiCounter{name: name, opts: options}
 	cfg := metric.NewInt64ObservableCounterConfig(options...)
 	id := instID{
@@ -236,11 +245,13 @@ func (m *meter) Int64ObservableCounter(name string, options ...metric.Int64Obser
 }
 
 func (m *meter) Int64ObservableUpDownCounter(name string, options ...metric.Int64ObservableUpDownCounterOption) (metric.Int64ObservableUpDownCounter, error) {
-	if del, ok := m.delegate.Load().(metric.Meter); ok {
-		return del.Int64ObservableUpDownCounter(name, options...)
-	}
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
+
+	if m.delegate != nil {
+		return m.delegate.Int64ObservableUpDownCounter(name, options...)
+	}
+
 	i := &aiUpDownCounter{name: name, opts: options}
 	cfg := metric.NewInt64ObservableUpDownCounterConfig(options...)
 	id := instID{
@@ -254,11 +265,13 @@ func (m *meter) Int64ObservableUpDownCounter(name string, options ...metric.Int6
 }
 
 func (m *meter) Int64ObservableGauge(name string, options ...metric.Int64ObservableGaugeOption) (metric.Int64ObservableGauge, error) {
-	if del, ok := m.delegate.Load().(metric.Meter); ok {
-		return del.Int64ObservableGauge(name, options...)
-	}
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
+
+	if m.delegate != nil {
+		return m.delegate.Int64ObservableGauge(name, options...)
+	}
+
 	i := &aiGauge{name: name, opts: options}
 	cfg := metric.NewInt64ObservableGaugeConfig(options...)
 	id := instID{
@@ -272,11 +285,13 @@ func (m *meter) Int64ObservableGauge(name string, options ...metric.Int64Observa
 }
 
 func (m *meter) Float64Counter(name string, options ...metric.Float64CounterOption) (metric.Float64Counter, error) {
-	if del, ok := m.delegate.Load().(metric.Meter); ok {
-		return del.Float64Counter(name, options...)
-	}
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
+
+	if m.delegate != nil {
+		return m.delegate.Float64Counter(name, options...)
+	}
+
 	i := &sfCounter{name: name, opts: options}
 	cfg := metric.NewFloat64CounterConfig(options...)
 	id := instID{
@@ -290,11 +305,13 @@ func (m *meter) Float64Counter(name string, options ...metric.Float64CounterOpti
 }
 
 func (m *meter) Float64UpDownCounter(name string, options ...metric.Float64UpDownCounterOption) (metric.Float64UpDownCounter, error) {
-	if del, ok := m.delegate.Load().(metric.Meter); ok {
-		return del.Float64UpDownCounter(name, options...)
-	}
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
+
+	if m.delegate != nil {
+		return m.delegate.Float64UpDownCounter(name, options...)
+	}
+
 	i := &sfUpDownCounter{name: name, opts: options}
 	cfg := metric.NewFloat64UpDownCounterConfig(options...)
 	id := instID{
@@ -308,11 +325,13 @@ func (m *meter) Float64UpDownCounter(name string, options ...metric.Float64UpDow
 }
 
 func (m *meter) Float64Histogram(name string, options ...metric.Float64HistogramOption) (metric.Float64Histogram, error) {
-	if del, ok := m.delegate.Load().(metric.Meter); ok {
-		return del.Float64Histogram(name, options...)
-	}
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
+
+	if m.delegate != nil {
+		return m.delegate.Float64Histogram(name, options...)
+	}
+
 	i := &sfHistogram{name: name, opts: options}
 	cfg := metric.NewFloat64HistogramConfig(options...)
 	id := instID{
@@ -326,11 +345,13 @@ func (m *meter) Float64Histogram(name string, options ...metric.Float64Histogram
 }
 
 func (m *meter) Float64Gauge(name string, options ...metric.Float64GaugeOption) (metric.Float64Gauge, error) {
-	if del, ok := m.delegate.Load().(metric.Meter); ok {
-		return del.Float64Gauge(name, options...)
-	}
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
+
+	if m.delegate != nil {
+		return m.delegate.Float64Gauge(name, options...)
+	}
+
 	i := &sfGauge{name: name, opts: options}
 	cfg := metric.NewFloat64GaugeConfig(options...)
 	id := instID{
@@ -344,11 +365,13 @@ func (m *meter) Float64Gauge(name string, options ...metric.Float64GaugeOption)
 }
 
 func (m *meter) Float64ObservableCounter(name string, options ...metric.Float64ObservableCounterOption) (metric.Float64ObservableCounter, error) {
-	if del, ok := m.delegate.Load().(metric.Meter); ok {
-		return del.Float64ObservableCounter(name, options...)
-	}
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
+
+	if m.delegate != nil {
+		return m.delegate.Float64ObservableCounter(name, options...)
+	}
+
 	i := &afCounter{name: name, opts: options}
 	cfg := metric.NewFloat64ObservableCounterConfig(options...)
 	id := instID{
@@ -362,11 +385,13 @@ func (m *meter) Float64ObservableCounter(name string, options ...metric.Float64O
 }
 
 func (m *meter) Float64ObservableUpDownCounter(name string, options ...metric.Float64ObservableUpDownCounterOption) (metric.Float64ObservableUpDownCounter, error) {
-	if del, ok := m.delegate.Load().(metric.Meter); ok {
-		return del.Float64ObservableUpDownCounter(name, options...)
-	}
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
+
+	if m.delegate != nil {
+		return m.delegate.Float64ObservableUpDownCounter(name, options...)
+	}
+
 	i := &afUpDownCounter{name: name, opts: options}
 	cfg := metric.NewFloat64ObservableUpDownCounterConfig(options...)
 	id := instID{
@@ -380,11 +405,13 @@ func (m *meter) Float64ObservableUpDownCounter(name string, options ...metric.Fl
 }
 
 func (m *meter) Float64ObservableGauge(name string, options ...metric.Float64ObservableGaugeOption) (metric.Float64ObservableGauge, error) {
-	if del, ok := m.delegate.Load().(metric.Meter); ok {
-		return del.Float64ObservableGauge(name, options...)
-	}
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
+
+	if m.delegate != nil {
+		return m.delegate.Float64ObservableGauge(name, options...)
+	}
+
 	i := &afGauge{name: name, opts: options}
 	cfg := metric.NewFloat64ObservableGaugeConfig(options...)
 	id := instID{
@@ -399,14 +426,14 @@ func (m *meter) Float64ObservableGauge(name string, options ...metric.Float64Obs
 
 // RegisterCallback captures the function that will be called during Collect.
 func (m *meter) RegisterCallback(f metric.Callback, insts ...metric.Observable) (metric.Registration, error) {
-	if del, ok := m.delegate.Load().(metric.Meter); ok {
-		insts = unwrapInstruments(insts)
-		return del.RegisterCallback(f, insts...)
-	}
-
 	m.mtx.Lock()
 	defer m.mtx.Unlock()
 
+	if m.delegate != nil {
+		insts = unwrapInstruments(insts)
+		return m.delegate.RegisterCallback(f, insts...)
+	}
+
 	reg := &registration{instruments: insts, function: f}
 	e := m.registry.PushBack(reg)
 	reg.unreg = func() error {

internal/global/meter_test.go

@@ -83,6 +83,12 @@ func TestMeterConcurrentSafe(t *testing.T) {
 	mtr.setDelegate(noop.NewMeterProvider())
 	close(finish)
 	<-done
+
+	// No instruments should be left after the meter is replaced.
+	assert.Empty(t, mtr.instruments)
+
+	// No callbacks should be left after the meter is replaced.
+	assert.Zero(t, mtr.registry.Len())
 }
 
 func TestUnregisterConcurrentSafe(t *testing.T) {
@@ -162,8 +168,9 @@ func testSetupAllInstrumentTypes(t *testing.T, m metric.Meter) (metric.Float64Co
 // This is to emulate a read from an exporter.
 func testCollect(t *testing.T, m metric.Meter) {
 	if tMeter, ok := m.(*meter); ok {
-		m, ok = tMeter.delegate.Load().(metric.Meter)
-		if !ok {
+		// This changes the input m to the delegate.
+		m = tMeter.delegate
+		if m == nil {
 			t.Error("meter was not delegated")
 			return
 		}
@@ -261,7 +268,7 @@ func TestMeterDelegatesCalls(t *testing.T) {
 
 	// Calls to Meter methods after setDelegate() should be executed by the delegate
 	require.IsType(t, &meter{}, m)
-	tMeter := m.(*meter).delegate.Load().(*testMeter)
+	tMeter := m.(*meter).delegate.(*testMeter)
 	require.NotNil(t, tMeter)
 	assert.Equal(t, 1, tMeter.afCount)
 	assert.Equal(t, 1, tMeter.afUDCount)
@@ -309,7 +316,7 @@ func TestMeterDefersDelegations(t *testing.T) {
 
 	// Calls to Meter() before setDelegate() should be the delegated type
 	require.IsType(t, &meter{}, m)
-	tMeter := m.(*meter).delegate.Load().(*testMeter)
+	tMeter := m.(*meter).delegate.(*testMeter)
 	require.NotNil(t, tMeter)
 	assert.Equal(t, 1, tMeter.afCount)
 	assert.Equal(t, 1, tMeter.afUDCount)