Make stats.{Int,Float}64 never return errors (#552)

Updates: #544

internal/readme/stats.go

@@ -34,11 +34,6 @@ func statsExamples() {
 		log.Fatal(err)
 	}
 
-	m := stats.FindMeasure("my.org/video_size")
-	if m == nil {
-		log.Fatalln("measure not found")
-	}
-
 	// START aggs
 	distAgg := view.Distribution(0, 1<<32, 2<<32, 3<<32)
 	countAgg := view.Count()

stats/measure.go

@@ -16,12 +16,8 @@
 package stats
 
 import (
-	"errors"
-	"fmt"
 	"sync"
 	"sync/atomic"
-
-	"go.opencensus.io/stats/internal"
 )
 
 // Measure represents a type of metric to be tracked and recorded.
@@ -38,69 +34,47 @@ type Measure interface {
 	Name() string
 	Description() string
 	Unit() string
-
-	subscribe()
-	subscribed() bool
 }
 
-type measure struct {
+// measureDescriptor is the untyped descriptor associated with each measure.
+// Int64Measure and Float64Measure wrap measureDescriptor to provide typed
+// recording APIs.
+// Two Measures with the same name will have the same measureDescriptor.
+type measureDescriptor struct {
 	subs int32 // access atomically
 
 	name        string
 	description string
 	unit        string
 }
 
-func (m *measure) subscribe() {
+func (m *measureDescriptor) subscribe() {
 	atomic.StoreInt32(&m.subs, 1)
 }
 
-func (m *measure) subscribed() bool {
+func (m *measureDescriptor) subscribed() bool {
 	return atomic.LoadInt32(&m.subs) == 1
 }
 
-// Name returns the name of the measure.
-func (m *measure) Name() string {
-	return m.name
-}
-
-// Description returns the description of the measure.
-func (m *measure) Description() string {
-	return m.description
-}
-
-// Unit returns the unit of the measure.
-func (m *measure) Unit() string {
-	return m.unit
-}
-
 var (
 	mu       sync.RWMutex
-	measures = make(map[string]Measure)
-)
-
-var (
-	errDuplicate          = errors.New("duplicate measure name")
-	errMeasureNameTooLong = fmt.Errorf("measure name cannot be longer than %v", internal.MaxNameLength)
+	measures = make(map[string]*measureDescriptor)
 )
 
-// FindMeasure finds the Measure instance, if any, associated with the given name.
-func FindMeasure(name string) Measure {
-	mu.RLock()
-	m := measures[name]
-	mu.RUnlock()
-	return m
-}
-
-func register(m Measure) (Measure, error) {
-	key := m.Name()
+func registerMeasureHandle(name, desc, unit string) *measureDescriptor {
 	mu.Lock()
 	defer mu.Unlock()
-	if stored, ok := measures[key]; ok {
-		return stored, errDuplicate
+
+	if stored, ok := measures[name]; ok {
+		return stored
+	}
+	m := &measureDescriptor{
+		name:        name,
+		description: desc,
+		unit:        unit,
 	}
-	measures[key] = m
-	return m, nil
+	measures[name] = m
+	return m
 }
 
 // Measurement is the numeric value measured when recording stats. Each measure
@@ -120,13 +94,3 @@ func (m Measurement) Value() float64 {
 func (m Measurement) Measure() Measure {
 	return m.m
 }
-
-func checkName(name string) error {
-	if len(name) > internal.MaxNameLength {
-		return errMeasureNameTooLong
-	}
-	if !internal.IsPrintable(name) {
-		return errors.New("measure name needs to be an ASCII string")
-	}
-	return nil
-}

stats/measure_float64.go

@@ -17,41 +17,36 @@ package stats
 
 // Float64Measure is a measure of type float64.
 type Float64Measure struct {
-	measure
+	md *measureDescriptor
 }
 
-func (m *Float64Measure) subscribe() {
-	m.measure.subscribe()
+// Name returns the name of the measure.
+func (m *Float64Measure) Name() string {
+	return m.md.name
 }
 
-func (m *Float64Measure) subscribed() bool {
-	return m.measure.subscribed()
+// Description returns the description of the measure.
+func (m *Float64Measure) Description() string {
+	return m.md.description
+}
+
+// Unit returns the unit of the measure.
+func (m *Float64Measure) Unit() string {
+	return m.md.unit
 }
 
 // M creates a new float64 measurement.
 // Use Record to record measurements.
 func (m *Float64Measure) M(v float64) Measurement {
-	if !m.subscribed() {
+	if !m.md.subscribed() {
 		return Measurement{}
 	}
 	return Measurement{m: m, v: v}
 }
 
-// Float64 creates a new measure of type Float64Measure. It returns
-// an error if a measure with the same name already exists.
+// Float64 creates a new measure of type Float64Measure.
+// It never returns an error.
 func Float64(name, description, unit string) (*Float64Measure, error) {
-	if err := checkName(name); err != nil {
-		return nil, err
-	}
-	m := &Float64Measure{
-		measure: measure{
-			name:        name,
-			description: description,
-			unit:        unit,
-		},
-	}
-	if _, err := register(m); err != nil {
-		return nil, err
-	}
-	return m, nil
+	mi := registerMeasureHandle(name, description, unit)
+	return &Float64Measure{mi}, nil
 }

stats/measure_int64.go

@@ -17,41 +17,36 @@ package stats
 
 // Int64Measure is a measure of type int64.
 type Int64Measure struct {
-	measure
+	md *measureDescriptor
 }
 
-func (m *Int64Measure) subscribe() {
-	m.measure.subscribe()
+// Name returns the name of the measure.
+func (m *Int64Measure) Name() string {
+	return m.md.name
 }
 
-func (m *Int64Measure) subscribed() bool {
-	return m.measure.subscribed()
+// Description returns the description of the measure.
+func (m *Int64Measure) Description() string {
+	return m.md.description
+}
+
+// Unit returns the unit of the measure.
+func (m *Int64Measure) Unit() string {
+	return m.md.unit
 }
 
 // M creates a new int64 measurement.
 // Use Record to record measurements.
 func (m *Int64Measure) M(v int64) Measurement {
-	if !m.subscribed() {
+	if !m.md.subscribed() {
 		return Measurement{}
 	}
 	return Measurement{m: m, v: float64(v)}
 }
 
-// Int64 creates a new measure of type Int64Measure. It returns an
-// error if a measure with the same name already exists.
+// Int64 creates a new measure of type Int64Measure.
+// It never returns an error.
 func Int64(name, description, unit string) (*Int64Measure, error) {
-	if err := checkName(name); err != nil {
-		return nil, err
-	}
-	m := &Int64Measure{
-		measure: measure{
-			name:        name,
-			description: description,
-			unit:        unit,
-		},
-	}
-	if _, err := register(m); err != nil {
-		return nil, err
-	}
-	return m, nil
+	mi := registerMeasureHandle(name, description, unit)
+	return &Int64Measure{mi}, nil
 }