metrics: remove use of reflect in metrics registration code (#31962)

Co-authored-by: Marius van der Wijden <m.vanderwijden@live.de>

metrics/counter.go

@@ -7,10 +7,7 @@ import (
 // GetOrRegisterCounter returns an existing Counter or constructs and registers
 // a new Counter.
 func GetOrRegisterCounter(name string, r Registry) *Counter {
-	if r == nil {
-		r = DefaultRegistry
-	}
-	return r.GetOrRegister(name, NewCounter).(*Counter)
+	return getOrRegister(name, NewCounter, r)
 }
 
 // NewCounter constructs a new Counter.

metrics/counter_float64.go

@@ -8,10 +8,7 @@ import (
 // GetOrRegisterCounterFloat64 returns an existing *CounterFloat64 or constructs and registers
 // a new CounterFloat64.
 func GetOrRegisterCounterFloat64(name string, r Registry) *CounterFloat64 {
-	if nil == r {
-		r = DefaultRegistry
-	}
-	return r.GetOrRegister(name, NewCounterFloat64).(*CounterFloat64)
+	return getOrRegister(name, NewCounterFloat64, r)
 }
 
 // NewCounterFloat64 constructs a new CounterFloat64.

metrics/gauge.go

@@ -11,10 +11,7 @@ func (g GaugeSnapshot) Value() int64 { return int64(g) }
 // GetOrRegisterGauge returns an existing Gauge or constructs and registers a
 // new Gauge.
 func GetOrRegisterGauge(name string, r Registry) *Gauge {
-	if r == nil {
-		r = DefaultRegistry
-	}
-	return r.GetOrRegister(name, NewGauge).(*Gauge)
+	return getOrRegister(name, NewGauge, r)
 }
 
 // NewGauge constructs a new Gauge.

metrics/gauge_float64.go

@@ -8,10 +8,7 @@ import (
 // GetOrRegisterGaugeFloat64 returns an existing GaugeFloat64 or constructs and registers a
 // new GaugeFloat64.
 func GetOrRegisterGaugeFloat64(name string, r Registry) *GaugeFloat64 {
-	if nil == r {
-		r = DefaultRegistry
-	}
-	return r.GetOrRegister(name, NewGaugeFloat64()).(*GaugeFloat64)
+	return getOrRegister(name, NewGaugeFloat64, r)
 }
 
 // GaugeFloat64Snapshot is a read-only copy of a GaugeFloat64.

metrics/gauge_info.go

@@ -16,10 +16,7 @@ func (val GaugeInfoValue) String() string {
 // GetOrRegisterGaugeInfo returns an existing GaugeInfo or constructs and registers a
 // new GaugeInfo.
 func GetOrRegisterGaugeInfo(name string, r Registry) *GaugeInfo {
-	if nil == r {
-		r = DefaultRegistry
-	}
-	return r.GetOrRegister(name, NewGaugeInfo()).(*GaugeInfo)
+	return getOrRegister(name, NewGaugeInfo, r)
 }
 
 // NewGaugeInfo constructs a new GaugeInfo.

metrics/histogram.go

@@ -23,19 +23,13 @@ type Histogram interface {
 // GetOrRegisterHistogram returns an existing Histogram or constructs and
 // registers a new StandardHistogram.
 func GetOrRegisterHistogram(name string, r Registry, s Sample) Histogram {
-	if nil == r {
-		r = DefaultRegistry
-	}
-	return r.GetOrRegister(name, func() Histogram { return NewHistogram(s) }).(Histogram)
+	return getOrRegister(name, func() Histogram { return NewHistogram(s) }, r)
 }
 
 // GetOrRegisterHistogramLazy returns an existing Histogram or constructs and
 // registers a new StandardHistogram.
 func GetOrRegisterHistogramLazy(name string, r Registry, s func() Sample) Histogram {
-	if nil == r {
-		r = DefaultRegistry
-	}
-	return r.GetOrRegister(name, func() Histogram { return NewHistogram(s()) }).(Histogram)
+	return getOrRegister(name, func() Histogram { return NewHistogram(s()) }, r)
 }
 
 // NewHistogram constructs a new StandardHistogram from a Sample.

metrics/meter.go

@@ -12,10 +12,7 @@ import (
 // Be sure to unregister the meter from the registry once it is of no use to
 // allow for garbage collection.
 func GetOrRegisterMeter(name string, r Registry) *Meter {
-	if r == nil {
-		r = DefaultRegistry
-	}
-	return r.GetOrRegister(name, NewMeter).(*Meter)
+	return getOrRegister(name, NewMeter, r)
 }
 
 // NewMeter constructs a new Meter and launches a goroutine.

metrics/registry.go

@@ -3,7 +3,6 @@ package metrics
 import (
 	"errors"
 	"fmt"
-	"reflect"
 	"sort"
 	"strings"
 	"sync"
@@ -30,10 +29,9 @@ type Registry interface {
 	// GetAll metrics in the Registry.
 	GetAll() map[string]map[string]interface{}
 
-	// GetOrRegister gets an existing metric or registers the given one.
-	// The interface can be the metric to register if not found in registry,
-	// or a function returning the metric for lazy instantiation.
-	GetOrRegister(string, interface{}) interface{}
+	// GetOrRegister returns an existing metric or registers the one returned
+	// by the given constructor.
+	GetOrRegister(string, func() interface{}) interface{}
 
 	// Register the given metric under the given name.
 	Register(string, interface{}) error
@@ -95,19 +93,13 @@ func (r *StandardRegistry) Get(name string) interface{} {
 // alternative to calling Get and Register on failure.
 // The interface can be the metric to register if not found in registry,
 // or a function returning the metric for lazy instantiation.
-func (r *StandardRegistry) GetOrRegister(name string, i interface{}) interface{} {
+func (r *StandardRegistry) GetOrRegister(name string, ctor func() interface{}) interface{} {
 	// fast path
 	cached, ok := r.metrics.Load(name)
 	if ok {
 		return cached
 	}
-	if v := reflect.ValueOf(i); v.Kind() == reflect.Func {
-		i = v.Call(nil)[0].Interface()
-	}
-	item, _, ok := r.loadOrRegister(name, i)
-	if !ok {
-		return i
-	}
+	item, _, _ := r.loadOrRegister(name, ctor())
 	return item
 }
 
@@ -120,9 +112,6 @@ func (r *StandardRegistry) Register(name string, i interface{}) error {
 		return fmt.Errorf("%w: %v", ErrDuplicateMetric, name)
 	}
 
-	if v := reflect.ValueOf(i); v.Kind() == reflect.Func {
-		i = v.Call(nil)[0].Interface()
-	}
 	_, loaded, _ := r.loadOrRegister(name, i)
 	if loaded {
 		return fmt.Errorf("%w: %v", ErrDuplicateMetric, name)
@@ -295,9 +284,9 @@ func (r *PrefixedRegistry) Get(name string) interface{} {
 // GetOrRegister gets an existing metric or registers the given one.
 // The interface can be the metric to register if not found in registry,
 // or a function returning the metric for lazy instantiation.
-func (r *PrefixedRegistry) GetOrRegister(name string, metric interface{}) interface{} {
+func (r *PrefixedRegistry) GetOrRegister(name string, ctor func() interface{}) interface{} {
 	realName := r.prefix + name
-	return r.underlying.GetOrRegister(realName, metric)
+	return r.underlying.GetOrRegister(realName, ctor)
 }
 
 // Register the given metric under the given name. The name will be prefixed.
@@ -338,10 +327,17 @@ func Get(name string) interface{} {
 
 // GetOrRegister gets an existing metric or creates and registers a new one. Threadsafe
 // alternative to calling Get and Register on failure.
-func GetOrRegister(name string, i interface{}) interface{} {
+func GetOrRegister(name string, i func() interface{}) interface{} {
 	return DefaultRegistry.GetOrRegister(name, i)
 }
 
+func getOrRegister[T any](name string, ctor func() T, r Registry) T {
+	if r == nil {
+		r = DefaultRegistry
+	}
+	return r.GetOrRegister(name, func() any { return ctor() }).(T)
+}
+
 // Register the given metric under the given name.  Returns a ErrDuplicateMetric
 // if a metric by the given name is already registered.
 func Register(name string, i interface{}) error {

metrics/registry_test.go

@@ -30,7 +30,7 @@ func benchmarkRegistryGetOrRegisterParallel(b *testing.B, amount int) {
 		wg.Add(1)
 		go func() {
 			for i := 0; i < b.N; i++ {
-				r.GetOrRegister("foo", NewMeter)
+				GetOrRegisterMeter("foo", r)
 			}
 			wg.Done()
 		}()
@@ -98,10 +98,10 @@ func TestRegistryGetOrRegister(t *testing.T) {
 	r := NewRegistry()
 
 	// First metric wins with GetOrRegister
-	_ = r.GetOrRegister("foo", NewCounter())
-	m := r.GetOrRegister("foo", NewGauge())
-	if _, ok := m.(*Counter); !ok {
-		t.Fatal(m)
+	c1 := GetOrRegisterCounter("foo", r)
+	c2 := GetOrRegisterCounter("foo", r)
+	if c1 != c2 {
+		t.Fatal("counters should've matched")
 	}
 
 	i := 0
@@ -123,10 +123,10 @@ func TestRegistryGetOrRegisterWithLazyInstantiation(t *testing.T) {
 	r := NewRegistry()
 
 	// First metric wins with GetOrRegister
-	_ = r.GetOrRegister("foo", NewCounter)
-	m := r.GetOrRegister("foo", NewGauge)
-	if _, ok := m.(*Counter); !ok {
-		t.Fatal(m)
+	c1 := GetOrRegisterCounter("foo", r)
+	c2 := GetOrRegisterCounter("foo", r)
+	if c1 != c2 {
+		t.Fatal("counters should've matched")
 	}
 
 	i := 0
@@ -165,7 +165,7 @@ func TestPrefixedChildRegistryGetOrRegister(t *testing.T) {
 	r := NewRegistry()
 	pr := NewPrefixedChildRegistry(r, "prefix.")
 
-	_ = pr.GetOrRegister("foo", NewCounter())
+	_ = GetOrRegisterCounter("foo", pr)
 
 	i := 0
 	r.Each(func(name string, m interface{}) {
@@ -182,7 +182,7 @@ func TestPrefixedChildRegistryGetOrRegister(t *testing.T) {
 func TestPrefixedRegistryGetOrRegister(t *testing.T) {
 	r := NewPrefixedRegistry("prefix.")
 
-	_ = r.GetOrRegister("foo", NewCounter())
+	_ = GetOrRegisterCounter("foo", r)
 
 	i := 0
 	r.Each(func(name string, m interface{}) {

metrics/resetting_timer.go

@@ -8,10 +8,7 @@ import (
 // GetOrRegisterResettingTimer returns an existing ResettingTimer or constructs and registers a
 // new ResettingTimer.
 func GetOrRegisterResettingTimer(name string, r Registry) *ResettingTimer {
-	if nil == r {
-		r = DefaultRegistry
-	}
-	return r.GetOrRegister(name, NewResettingTimer).(*ResettingTimer)
+	return getOrRegister(name, NewResettingTimer, r)
 }
 
 // NewRegisteredResettingTimer constructs and registers a new ResettingTimer.

metrics/runtimehistogram.go

@@ -8,11 +8,8 @@ import (
 )
 
 func getOrRegisterRuntimeHistogram(name string, scale float64, r Registry) *runtimeHistogram {
-	if r == nil {
-		r = DefaultRegistry
-	}
 	constructor := func() Histogram { return newRuntimeHistogram(scale) }
-	return r.GetOrRegister(name, constructor).(*runtimeHistogram)
+	return getOrRegister(name, constructor, r).(*runtimeHistogram)
 }
 
 // runtimeHistogram wraps a runtime/metrics histogram.

metrics/timer.go

@@ -10,10 +10,7 @@ import (
 // Be sure to unregister the meter from the registry once it is of no use to
 // allow for garbage collection.
 func GetOrRegisterTimer(name string, r Registry) *Timer {
-	if nil == r {
-		r = DefaultRegistry
-	}
-	return r.GetOrRegister(name, NewTimer).(*Timer)
+	return getOrRegister(name, NewTimer, r)
 }
 
 // NewCustomTimer constructs a new Timer from a Histogram and a Meter.