Make tag.Map a concrete type. (#89)

This is to make tag.Map an immutable type, so it is safe to use
concurrently. The safety is not yet fully achieved because of the
functions returning contents of the map (Value and Foreach). The
functions give callers an access to core.Value objects, which contain
a byte slice, which has pointer like semantics. So to avoid accidental
changes, we will need to copy the value if it is of BYTES type.

Fixes #59

api/tag/context.go

@@ -16,8 +16,7 @@ package tag
 
 import (
 	"context"
-
-	"go.opentelemetry.io/api/core"
+	"runtime/pprof"
 )
 
 type ctxTagsType struct{}
@@ -26,56 +25,6 @@ var (
 	ctxTagsKey = &ctxTagsType{}
 )
 
-type MutatorOp int
-
-const (
-	INSERT MutatorOp = iota
-	UPDATE
-	UPSERT
-	DELETE
-)
-
-type Mutator struct {
-	MutatorOp
-	core.KeyValue
-	MeasureMetadata
-}
-
-type MeasureMetadata struct {
-	TTL int // -1 == infinite, 0 == do not propagate
-}
-
-func (m Mutator) WithTTL(hops int) Mutator {
-	m.TTL = hops
-	return m
-}
-
-type MapUpdate struct {
-	SingleKV      core.KeyValue
-	MultiKV       []core.KeyValue
-	SingleMutator Mutator
-	MultiMutator  []Mutator
-}
-
-type Map interface {
-	Apply(MapUpdate) Map
-
-	Value(core.Key) (core.Value, bool)
-	HasValue(core.Key) bool
-
-	Len() int
-
-	Foreach(func(kv core.KeyValue) bool)
-}
-
-func NewEmptyMap() Map {
-	return tagMap{}
-}
-
-func NewMap(update MapUpdate) Map {
-	return NewEmptyMap().Apply(update)
-}
-
 func WithMap(ctx context.Context, m Map) context.Context {
 	return context.WithValue(ctx, ctxTagsKey, m)
 }
@@ -90,5 +39,16 @@ func FromContext(ctx context.Context) Map {
 	if m, ok := ctx.Value(ctxTagsKey).(Map); ok {
 		return m
 	}
-	return tagMap{}
+	return NewEmptyMap()
+}
+
+// Note: the golang pprof.Do API forces this memory allocation, we
+// should file an issue about that.  (There's a TODO in the source.)
+func Do(ctx context.Context, f func(ctx context.Context)) {
+	m := FromContext(ctx)
+	keyvals := make([]string, 0, 2*len(m.m))
+	for k, v := range m.m {
+		keyvals = append(keyvals, k.Variable.Name, v.value.Emit())
+	}
+	pprof.Do(ctx, pprof.Labels(keyvals...), f)
 }

api/tag/map.go

@@ -15,64 +15,91 @@
 package tag
 
 import (
-	"context"
-	"runtime/pprof"
-
 	"go.opentelemetry.io/api/core"
 )
 
+type MeasureMetadata struct {
+	TTL int // -1 == infinite, 0 == do not propagate
+}
+
 type tagContent struct {
 	value core.Value
 	meta  MeasureMetadata
 }
 
-type tagMap map[core.Key]tagContent
+type rawMap map[core.Key]tagContent
 
-var _ Map = tagMap{}
+type Map struct {
+	m rawMap
+}
 
-func (t tagMap) Apply(update MapUpdate) Map {
-	m := make(tagMap, len(t)+len(update.MultiKV)+len(update.MultiMutator))
-	for k, v := range t {
-		m[k] = v
+type MapUpdate struct {
+	SingleKV      core.KeyValue
+	MultiKV       []core.KeyValue
+	SingleMutator Mutator
+	MultiMutator  []Mutator
+}
+
+func newMap(raw rawMap) Map {
+	return Map{
+		m: raw,
+	}
+}
+
+func NewEmptyMap() Map {
+	return newMap(nil)
+}
+
+func NewMap(update MapUpdate) Map {
+	return NewEmptyMap().Apply(update)
+}
+
+func (m Map) Apply(update MapUpdate) Map {
+	r := make(rawMap, len(m.m)+len(update.MultiKV)+len(update.MultiMutator))
+	for k, v := range m.m {
+		r[k] = v
 	}
 	if update.SingleKV.Key.Defined() {
-		m[update.SingleKV.Key] = tagContent{
+		r[update.SingleKV.Key] = tagContent{
 			value: update.SingleKV.Value,
 		}
 	}
 	for _, kv := range update.MultiKV {
-		m[kv.Key] = tagContent{
+		r[kv.Key] = tagContent{
 			value: kv.Value,
 		}
 	}
 	if update.SingleMutator.Key.Defined() {
-		m.apply(update.SingleMutator)
+		r.apply(update.SingleMutator)
 	}
 	for _, mutator := range update.MultiMutator {
-		m.apply(mutator)
+		r.apply(mutator)
 	}
-	return m
+	if len(r) == 0 {
+		r = nil
+	}
+	return newMap(r)
 }
 
-func (m tagMap) Value(k core.Key) (core.Value, bool) {
-	entry, ok := m[k]
+func (m Map) Value(k core.Key) (core.Value, bool) {
+	entry, ok := m.m[k]
 	if !ok {
 		entry.value.Type = core.INVALID
 	}
 	return entry.value, ok
 }
 
-func (m tagMap) HasValue(k core.Key) bool {
+func (m Map) HasValue(k core.Key) bool {
 	_, has := m.Value(k)
 	return has
 }
 
-func (m tagMap) Len() int {
-	return len(m)
+func (m Map) Len() int {
+	return len(m.m)
 }
 
-func (m tagMap) Foreach(f func(kv core.KeyValue) bool) {
-	for k, v := range m {
+func (m Map) Foreach(f func(kv core.KeyValue) bool) {
+	for k, v := range m.m {
 		if !f(core.KeyValue{
 			Key:   k,
 			Value: v.value,
@@ -82,10 +109,7 @@ func (m tagMap) Foreach(f func(kv core.KeyValue) bool) {
 	}
 }
 
-func (m tagMap) apply(mutator Mutator) {
-	if m == nil {
-		return
-	}
+func (r rawMap) apply(mutator Mutator) {
 	key := mutator.KeyValue.Key
 	content := tagContent{
 		value: mutator.KeyValue.Value,
@@ -93,57 +117,16 @@ func (m tagMap) apply(mutator Mutator) {
 	}
 	switch mutator.MutatorOp {
 	case INSERT:
-		if _, ok := m[key]; !ok {
-			m[key] = content
+		if _, ok := r[key]; !ok {
+			r[key] = content
 		}
 	case UPDATE:
-		if _, ok := m[key]; ok {
-			m[key] = content
+		if _, ok := r[key]; ok {
+			r[key] = content
 		}
 	case UPSERT:
-		m[key] = content
+		r[key] = content
 	case DELETE:
-		delete(m, key)
+		delete(r, key)
 	}
 }
-
-func Insert(kv core.KeyValue) Mutator {
-	return Mutator{
-		MutatorOp: INSERT,
-		KeyValue:  kv,
-	}
-}
-
-func Update(kv core.KeyValue) Mutator {
-	return Mutator{
-		MutatorOp: UPDATE,
-		KeyValue:  kv,
-	}
-}
-
-func Upsert(kv core.KeyValue) Mutator {
-	return Mutator{
-		MutatorOp: UPSERT,
-		KeyValue:  kv,
-	}
-}
-
-func Delete(k core.Key) Mutator {
-	return Mutator{
-		MutatorOp: DELETE,
-		KeyValue: core.KeyValue{
-			Key: k,
-		},
-	}
-}
-
-// Note: the golang pprof.Do API forces this memory allocation, we
-// should file an issue about that.  (There's a TODO in the source.)
-func Do(ctx context.Context, f func(ctx context.Context)) {
-	m := FromContext(ctx).(tagMap)
-	keyvals := make([]string, 0, 2*len(m))
-	for k, v := range m {
-		keyvals = append(keyvals, k.Variable.Name, v.value.Emit())
-	}
-	pprof.Do(ctx, pprof.Labels(keyvals...), f)
-}

api/tag/mutator.go

@@ -0,0 +1,69 @@
+// Copyright 2019, OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package tag
+
+import (
+	"go.opentelemetry.io/api/core"
+)
+
+type MutatorOp int
+
+const (
+	INSERT MutatorOp = iota
+	UPDATE
+	UPSERT
+	DELETE
+)
+
+type Mutator struct {
+	MutatorOp
+	core.KeyValue
+	MeasureMetadata
+}
+
+func (m Mutator) WithTTL(hops int) Mutator {
+	m.TTL = hops
+	return m
+}
+
+func Insert(kv core.KeyValue) Mutator {
+	return Mutator{
+		MutatorOp: INSERT,
+		KeyValue:  kv,
+	}
+}
+
+func Update(kv core.KeyValue) Mutator {
+	return Mutator{
+		MutatorOp: UPDATE,
+		KeyValue:  kv,
+	}
+}
+
+func Upsert(kv core.KeyValue) Mutator {
+	return Mutator{
+		MutatorOp: UPSERT,
+		KeyValue:  kv,
+	}
+}
+
+func Delete(k core.Key) Mutator {
+	return Mutator{
+		MutatorOp: DELETE,
+		KeyValue: core.KeyValue{
+			Key: k,
+		},
+	}
+}

experimental/streaming/exporter/reader/format/format.go

@@ -55,7 +55,7 @@ func AppendEvent(buf *strings.Builder, data reader.Event) {
 		} else {
 			buf.WriteString(" <")
 			f(false)(parentSpanIDKey.String(data.Parent.SpanIDString()))
-			if data.ParentAttributes != nil {
+			if data.ParentAttributes.Len() > 0 {
 				data.ParentAttributes.Foreach(f(false))
 			}
 			buf.WriteString(" >")
@@ -113,10 +113,10 @@ func AppendEvent(buf *strings.Builder, data reader.Event) {
 
 	// Attach the scope (span) attributes and context tags.
 	buf.WriteString(" [")
-	if data.Attributes != nil {
+	if data.Attributes.Len() > 0 {
 		data.Attributes.Foreach(f(false))
 	}
-	if data.Tags != nil {
+	if data.Tags.Len() > 0 {
 		data.Tags.Foreach(f(true))
 	}
 	if data.SpanContext.HasSpanID() {

experimental/streaming/exporter/reader/reader.go

@@ -311,7 +311,7 @@ func (ro *readerObserver) addMeasurement(e *Event, m stats.Measurement) {
 
 func (ro *readerObserver) readMeasureScope(m stats.Measure) (tag.Map, *readerSpan) {
 	// TODO
-	return nil, nil
+	return tag.NewEmptyMap(), nil
 }
 
 func (ro *readerObserver) readScope(id observer.ScopeID) (tag.Map, *readerSpan) {

sdk/trace/tracer.go

@@ -18,6 +18,7 @@ import (
 	"context"
 
 	"go.opentelemetry.io/api/core"
+	"go.opentelemetry.io/api/tag"
 	apitrace "go.opentelemetry.io/api/trace"
 )
 
@@ -94,5 +95,5 @@ func (tr *tracer) WithComponent(component string) apitrace.Tracer {
 }
 
 func (tr *tracer) Inject(ctx context.Context, span apitrace.Span, injector apitrace.Injector) {
-	injector.Inject(span.SpanContext(), nil)
+	injector.Inject(span.SpanContext(), tag.NewEmptyMap())
 }