vendor/go.opencensus.io/trace/trace.go - third_party/github.com/docker/docker - Git at Google

 // Copyright 2017, OpenCensus 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 trace

 import (
 	"context"
 	crand "crypto/rand"
 	"encoding/binary"
 	"fmt"
 	"math/rand"
 	"sync"
 	"sync/atomic"
 	"time"

 	"go.opencensus.io/internal"
 )

 // Span represents a span of a trace.  It has an associated SpanContext, and
 // stores data accumulated while the span is active.
 //
 // Ideally users should interact with Spans by calling the functions in this
 // package that take a Context parameter.
 type Span struct {
 	// data contains information recorded about the span.
 	//
 	// It will be non-nil if we are exporting the span or recording events for it.
 	// Otherwise, data is nil, and the Span is simply a carrier for the
 	// SpanContext, so that the trace ID is propagated.
 	data        *SpanData
 	mu          sync.Mutex // protects the contents of *data (but not the pointer value.)
 	spanContext SpanContext
 	// spanStore is the spanStore this span belongs to, if any, otherwise it is nil.
 	*spanStore
 	endOnce sync.Once

 	executionTracerTaskEnd func() // ends the execution tracer span
 }

 // IsRecordingEvents returns true if events are being recorded for this span.
 // Use this check to avoid computing expensive annotations when they will never
 // be used.
 func (s *Span) IsRecordingEvents() bool {
 	if s == nil {
 		return false
 	}
 	return s.data != nil
 }

 // TraceOptions contains options associated with a trace span.
 type TraceOptions uint32

 // IsSampled returns true if the span will be exported.
 func (sc SpanContext) IsSampled() bool {
 	return sc.TraceOptions.IsSampled()
 }

 // setIsSampled sets the TraceOptions bit that determines whether the span will be exported.
 func (sc *SpanContext) setIsSampled(sampled bool) {
 	if sampled {
 		sc.TraceOptions |= 1
 	} else {
 		sc.TraceOptions &= ^TraceOptions(1)
 	}
 }

 // IsSampled returns true if the span will be exported.
 func (t TraceOptions) IsSampled() bool {
 	return t&1 == 1
 }

 // SpanContext contains the state that must propagate across process boundaries.
 //
 // SpanContext is not an implementation of context.Context.
 // TODO: add reference to external Census docs for SpanContext.
 type SpanContext struct {
 	TraceID      TraceID
 	SpanID       SpanID
 	TraceOptions TraceOptions
 }

 type contextKey struct{}

 // FromContext returns the Span stored in a context, or nil if there isn't one.
 func FromContext(ctx context.Context) *Span {
 	s, _ := ctx.Value(contextKey{}).(*Span)
 	return s
 }

 // WithSpan returns a new context with the given Span attached.
 //
 // Deprecated: Use NewContext.
 func WithSpan(parent context.Context, s *Span) context.Context {
 	return NewContext(parent, s)
 }

 // NewContext returns a new context with the given Span attached.
 func NewContext(parent context.Context, s *Span) context.Context {
 	return context.WithValue(parent, contextKey{}, s)
 }

 // All available span kinds. Span kind must be either one of these values.
 const (
 	SpanKindUnspecified = iota
 	SpanKindServer
 	SpanKindClient
 )

 // StartOptions contains options concerning how a span is started.
 type StartOptions struct {
 	// Sampler to consult for this Span. If provided, it is always consulted.
 	//
 	// If not provided, then the behavior differs based on whether
 	// the parent of this Span is remote, local, or there is no parent.
 	// In the case of a remote parent or no parent, the
 	// default sampler (see Config) will be consulted. Otherwise,
 	// when there is a non-remote parent, no new sampling decision will be made:
 	// we will preserve the sampling of the parent.
 	Sampler Sampler

 	// SpanKind represents the kind of a span. If none is set,
 	// SpanKindUnspecified is used.
 	SpanKind int
 }

 // StartOption apply changes to StartOptions.
 type StartOption func(*StartOptions)

 // WithSpanKind makes new spans to be created with the given kind.
 func WithSpanKind(spanKind int) StartOption {
 	return func(o *StartOptions) {
 		o.SpanKind = spanKind
 	}
 }

 // WithSampler makes new spans to be be created with a custom sampler.
 // Otherwise, the global sampler is used.
 func WithSampler(sampler Sampler) StartOption {
 	return func(o *StartOptions) {
 		o.Sampler = sampler
 	}
 }

 // StartSpan starts a new child span of the current span in the context. If
 // there is no span in the context, creates a new trace and span.
 func StartSpan(ctx context.Context, name string, o ...StartOption) (context.Context, *Span) {
 	var opts StartOptions
 	var parent SpanContext
 	if p := FromContext(ctx); p != nil {
 		parent = p.spanContext
 	}
 	for _, op := range o {
 		op(&opts)
 	}
 	span := startSpanInternal(name, parent != SpanContext{}, parent, false, opts)

 	ctx, end := startExecutionTracerTask(ctx, name)
 	span.executionTracerTaskEnd = end
 	return NewContext(ctx, span), span
 }

 // StartSpanWithRemoteParent starts a new child span of the span from the given parent.
 //
 // If the incoming context contains a parent, it ignores. StartSpanWithRemoteParent is
 // preferred for cases where the parent is propagated via an incoming request.
 func StartSpanWithRemoteParent(ctx context.Context, name string, parent SpanContext, o ...StartOption) (context.Context, *Span) {
 	var opts StartOptions
 	for _, op := range o {
 		op(&opts)
 	}
 	span := startSpanInternal(name, parent != SpanContext{}, parent, true, opts)
 	ctx, end := startExecutionTracerTask(ctx, name)
 	span.executionTracerTaskEnd = end
 	return NewContext(ctx, span), span
 }

 // NewSpan returns a new span.
 //
 // If parent is not nil, created span will be a child of the parent.
 //
 // Deprecated: Use StartSpan.
 func NewSpan(name string, parent *Span, o StartOptions) *Span {
 	var parentSpanContext SpanContext
 	if parent != nil {
 		parentSpanContext = parent.SpanContext()
 	}
 	return startSpanInternal(name, parent != nil, parentSpanContext, false, o)
 }

 // NewSpanWithRemoteParent returns a new span with the given parent SpanContext.
 //
 // Deprecated: Use StartSpanWithRemoteParent.
 func NewSpanWithRemoteParent(name string, parent SpanContext, o StartOptions) *Span {
 	return startSpanInternal(name, true, parent, true, o)
 }

 func startSpanInternal(name string, hasParent bool, parent SpanContext, remoteParent bool, o StartOptions) *Span {
 	span := &Span{}
 	span.spanContext = parent

 	cfg := config.Load().(*Config)

 	if !hasParent {
 		span.spanContext.TraceID = cfg.IDGenerator.NewTraceID()
 	}
 	span.spanContext.SpanID = cfg.IDGenerator.NewSpanID()
 	sampler := cfg.DefaultSampler

 	if !hasParent || remoteParent || o.Sampler != nil {
 		// If this span is the child of a local span and no Sampler is set in the
 		// options, keep the parent's TraceOptions.
 		//
 		// Otherwise, consult the Sampler in the options if it is non-nil, otherwise
 		// the default sampler.
 		if o.Sampler != nil {
 			sampler = o.Sampler
 		}
 		span.spanContext.setIsSampled(sampler(SamplingParameters{
 			ParentContext:   parent,
 			TraceID:         span.spanContext.TraceID,
 			SpanID:          span.spanContext.SpanID,
 			Name:            name,
 			HasRemoteParent: remoteParent}).Sample)
 	}

 	if !internal.LocalSpanStoreEnabled && !span.spanContext.IsSampled() {
 		return span
 	}

 	span.data = &SpanData{
 		SpanContext:     span.spanContext,
 		StartTime:       time.Now(),
 		SpanKind:        o.SpanKind,
 		Name:            name,
 		HasRemoteParent: remoteParent,
 	}
 	if hasParent {
 		span.data.ParentSpanID = parent.SpanID
 	}
 	if internal.LocalSpanStoreEnabled {
 		var ss *spanStore
 		ss = spanStoreForNameCreateIfNew(name)
 		if ss != nil {
 			span.spanStore = ss
 			ss.add(span)
 		}
 	}

 	return span
 }

 // End ends the span.
 func (s *Span) End() {
 	if !s.IsRecordingEvents() {
 		return
 	}
 	s.endOnce.Do(func() {
 		if s.executionTracerTaskEnd != nil {
 			s.executionTracerTaskEnd()
 		}
 		// TODO: optimize to avoid this call if sd won't be used.
 		sd := s.makeSpanData()
 		sd.EndTime = internal.MonotonicEndTime(sd.StartTime)
 		if s.spanStore != nil {
 			s.spanStore.finished(s, sd)
 		}
 		if s.spanContext.IsSampled() {
 			// TODO: consider holding exportersMu for less time.
 			exportersMu.Lock()
 			for e := range exporters {
 				e.ExportSpan(sd)
 			}
 			exportersMu.Unlock()
 		}
 	})
 }

 // makeSpanData produces a SpanData representing the current state of the Span.
 // It requires that s.data is non-nil.
 func (s *Span) makeSpanData() *SpanData {
 	var sd SpanData
 	s.mu.Lock()
 	sd = *s.data
 	if s.data.Attributes != nil {
 		sd.Attributes = make(map[string]interface{})
 		for k, v := range s.data.Attributes {
 			sd.Attributes[k] = v
 		}
 	}
 	s.mu.Unlock()
 	return &sd
 }

 // SpanContext returns the SpanContext of the span.
 func (s *Span) SpanContext() SpanContext {
 	if s == nil {
 		return SpanContext{}
 	}
 	return s.spanContext
 }

 // SetStatus sets the status of the span, if it is recording events.
 func (s *Span) SetStatus(status Status) {
 	if !s.IsRecordingEvents() {
 		return
 	}
 	s.mu.Lock()
 	s.data.Status = status
 	s.mu.Unlock()
 }

 // AddAttributes sets attributes in the span.
 //
 // Existing attributes whose keys appear in the attributes parameter are overwritten.
 func (s *Span) AddAttributes(attributes ...Attribute) {
 	if !s.IsRecordingEvents() {
 		return
 	}
 	s.mu.Lock()
 	if s.data.Attributes == nil {
 		s.data.Attributes = make(map[string]interface{})
 	}
 	copyAttributes(s.data.Attributes, attributes)
 	s.mu.Unlock()
 }

 // copyAttributes copies a slice of Attributes into a map.
 func copyAttributes(m map[string]interface{}, attributes []Attribute) {
 	for _, a := range attributes {
 		m[a.key] = a.value
 	}
 }

 func (s *Span) lazyPrintfInternal(attributes []Attribute, format string, a ...interface{}) {
 	now := time.Now()
 	msg := fmt.Sprintf(format, a...)
 	var m map[string]interface{}
 	s.mu.Lock()
 	if len(attributes) != 0 {
 		m = make(map[string]interface{})
 		copyAttributes(m, attributes)
 	}
 	s.data.Annotations = append(s.data.Annotations, Annotation{
 		Time:       now,
 		Message:    msg,
 		Attributes: m,
 	})
 	s.mu.Unlock()
 }

 func (s *Span) printStringInternal(attributes []Attribute, str string) {
 	now := time.Now()
 	var a map[string]interface{}
 	s.mu.Lock()
 	if len(attributes) != 0 {
 		a = make(map[string]interface{})
 		copyAttributes(a, attributes)
 	}
 	s.data.Annotations = append(s.data.Annotations, Annotation{
 		Time:       now,
 		Message:    str,
 		Attributes: a,
 	})
 	s.mu.Unlock()
 }

 // Annotate adds an annotation with attributes.
 // Attributes can be nil.
 func (s *Span) Annotate(attributes []Attribute, str string) {
 	if !s.IsRecordingEvents() {
 		return
 	}
 	s.printStringInternal(attributes, str)
 }

 // Annotatef adds an annotation with attributes.
 func (s *Span) Annotatef(attributes []Attribute, format string, a ...interface{}) {
 	if !s.IsRecordingEvents() {
 		return
 	}
 	s.lazyPrintfInternal(attributes, format, a...)
 }

 // AddMessageSendEvent adds a message send event to the span.
 //
 // messageID is an identifier for the message, which is recommended to be
 // unique in this span and the same between the send event and the receive
 // event (this allows to identify a message between the sender and receiver).
 // For example, this could be a sequence id.
 func (s *Span) AddMessageSendEvent(messageID, uncompressedByteSize, compressedByteSize int64) {
 	if !s.IsRecordingEvents() {
 		return
 	}
 	now := time.Now()
 	s.mu.Lock()
 	s.data.MessageEvents = append(s.data.MessageEvents, MessageEvent{
 		Time:                 now,
 		EventType:            MessageEventTypeSent,
 		MessageID:            messageID,
 		UncompressedByteSize: uncompressedByteSize,
 		CompressedByteSize:   compressedByteSize,
 	})
 	s.mu.Unlock()
 }

 // AddMessageReceiveEvent adds a message receive event to the span.
 //
 // messageID is an identifier for the message, which is recommended to be
 // unique in this span and the same between the send event and the receive
 // event (this allows to identify a message between the sender and receiver).
 // For example, this could be a sequence id.
 func (s *Span) AddMessageReceiveEvent(messageID, uncompressedByteSize, compressedByteSize int64) {
 	if !s.IsRecordingEvents() {
 		return
 	}
 	now := time.Now()
 	s.mu.Lock()
 	s.data.MessageEvents = append(s.data.MessageEvents, MessageEvent{
 		Time:                 now,
 		EventType:            MessageEventTypeRecv,
 		MessageID:            messageID,
 		UncompressedByteSize: uncompressedByteSize,
 		CompressedByteSize:   compressedByteSize,
 	})
 	s.mu.Unlock()
 }

 // AddLink adds a link to the span.
 func (s *Span) AddLink(l Link) {
 	if !s.IsRecordingEvents() {
 		return
 	}
 	s.mu.Lock()
 	s.data.Links = append(s.data.Links, l)
 	s.mu.Unlock()
 }

 func (s *Span) String() string {
 	if s == nil {
 		return "<nil>"
 	}
 	if s.data == nil {
 		return fmt.Sprintf("span %s", s.spanContext.SpanID)
 	}
 	s.mu.Lock()
 	str := fmt.Sprintf("span %s %q", s.spanContext.SpanID, s.data.Name)
 	s.mu.Unlock()
 	return str
 }

 var config atomic.Value // access atomically

 func init() {
 	gen := &defaultIDGenerator{}
 	// initialize traceID and spanID generators.
 	var rngSeed int64
 	for _, p := range []interface{}{
 		&rngSeed, &gen.traceIDAdd, &gen.nextSpanID, &gen.spanIDInc,
 	} {
 		binary.Read(crand.Reader, binary.LittleEndian, p)
 	}
 	gen.traceIDRand = rand.New(rand.NewSource(rngSeed))
 	gen.spanIDInc |= 1

 	config.Store(&Config{
 		DefaultSampler: ProbabilitySampler(defaultSamplingProbability),
 		IDGenerator:    gen,
 	})
 }

 type defaultIDGenerator struct {
 	sync.Mutex
 	traceIDRand *rand.Rand
 	traceIDAdd  [2]uint64
 	nextSpanID  uint64
 	spanIDInc   uint64
 }

 // NewSpanID returns a non-zero span ID from a randomly-chosen sequence.
 // mu should be held while this function is called.
 func (gen *defaultIDGenerator) NewSpanID() [8]byte {
 	gen.Lock()
 	id := gen.nextSpanID
 	gen.nextSpanID += gen.spanIDInc
 	if gen.nextSpanID == 0 {
 		gen.nextSpanID += gen.spanIDInc
 	}
 	gen.Unlock()
 	var sid [8]byte
 	binary.LittleEndian.PutUint64(sid[:], id)
 	return sid
 }

 // NewTraceID returns a non-zero trace ID from a randomly-chosen sequence.
 // mu should be held while this function is called.
 func (gen *defaultIDGenerator) NewTraceID() [16]byte {
 	var tid [16]byte
 	// Construct the trace ID from two outputs of traceIDRand, with a constant
 	// added to each half for additional entropy.
 	gen.Lock()
 	binary.LittleEndian.PutUint64(tid[0:8], gen.traceIDRand.Uint64()+gen.traceIDAdd[0])
 	binary.LittleEndian.PutUint64(tid[8:16], gen.traceIDRand.Uint64()+gen.traceIDAdd[1])
 	gen.Unlock()
 	return tid
 }
	// Copyright 2017, OpenCensus 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 trace

	import (
	"context"
	crand "crypto/rand"
	"encoding/binary"
	"fmt"
	"math/rand"
	"sync"
	"sync/atomic"
	"time"

	"go.opencensus.io/internal"
	)

	// Span represents a span of a trace. It has an associated SpanContext, and
	// stores data accumulated while the span is active.
	//
	// Ideally users should interact with Spans by calling the functions in this
	// package that take a Context parameter.
	type Span struct {
	// data contains information recorded about the span.
	//
	// It will be non-nil if we are exporting the span or recording events for it.
	// Otherwise, data is nil, and the Span is simply a carrier for the
	// SpanContext, so that the trace ID is propagated.
	data *SpanData
	mu sync.Mutex // protects the contents of *data (but not the pointer value.)
	spanContext SpanContext
	// spanStore is the spanStore this span belongs to, if any, otherwise it is nil.
	*spanStore
	endOnce sync.Once

	executionTracerTaskEnd func() // ends the execution tracer span
	}

	// IsRecordingEvents returns true if events are being recorded for this span.
	// Use this check to avoid computing expensive annotations when they will never
	// be used.
	func (s *Span) IsRecordingEvents() bool {
	if s == nil {
	return false
	}
	return s.data != nil
	}

	// TraceOptions contains options associated with a trace span.
	type TraceOptions uint32

	// IsSampled returns true if the span will be exported.
	func (sc SpanContext) IsSampled() bool {
	return sc.TraceOptions.IsSampled()
	}

	// setIsSampled sets the TraceOptions bit that determines whether the span will be exported.
	func (sc *SpanContext) setIsSampled(sampled bool) {
	if sampled {
	sc.TraceOptions \|= 1
	} else {
	sc.TraceOptions &= ^TraceOptions(1)
	}
	}

	// IsSampled returns true if the span will be exported.
	func (t TraceOptions) IsSampled() bool {
	return t&1 == 1
	}

	// SpanContext contains the state that must propagate across process boundaries.
	//
	// SpanContext is not an implementation of context.Context.
	// TODO: add reference to external Census docs for SpanContext.
	type SpanContext struct {
	TraceID TraceID
	SpanID SpanID
	TraceOptions TraceOptions
	}

	type contextKey struct{}

	// FromContext returns the Span stored in a context, or nil if there isn't one.
	func FromContext(ctx context.Context) *Span {
	s, _ := ctx.Value(contextKey{}).(*Span)
	return s
	}

	// WithSpan returns a new context with the given Span attached.
	//
	// Deprecated: Use NewContext.
	func WithSpan(parent context.Context, s *Span) context.Context {
	return NewContext(parent, s)
	}

	// NewContext returns a new context with the given Span attached.
	func NewContext(parent context.Context, s *Span) context.Context {
	return context.WithValue(parent, contextKey{}, s)
	}

	// All available span kinds. Span kind must be either one of these values.
	const (
	SpanKindUnspecified = iota
	SpanKindServer
	SpanKindClient
	)

	// StartOptions contains options concerning how a span is started.
	type StartOptions struct {
	// Sampler to consult for this Span. If provided, it is always consulted.
	//
	// If not provided, then the behavior differs based on whether
	// the parent of this Span is remote, local, or there is no parent.
	// In the case of a remote parent or no parent, the
	// default sampler (see Config) will be consulted. Otherwise,
	// when there is a non-remote parent, no new sampling decision will be made:
	// we will preserve the sampling of the parent.
	Sampler Sampler

	// SpanKind represents the kind of a span. If none is set,
	// SpanKindUnspecified is used.
	SpanKind int
	}

	// StartOption apply changes to StartOptions.
	type StartOption func(*StartOptions)

	// WithSpanKind makes new spans to be created with the given kind.
	func WithSpanKind(spanKind int) StartOption {
	return func(o *StartOptions) {
	o.SpanKind = spanKind
	}
	}

	// WithSampler makes new spans to be be created with a custom sampler.
	// Otherwise, the global sampler is used.
	func WithSampler(sampler Sampler) StartOption {
	return func(o *StartOptions) {
	o.Sampler = sampler
	}
	}

	// StartSpan starts a new child span of the current span in the context. If
	// there is no span in the context, creates a new trace and span.
	func StartSpan(ctx context.Context, name string, o ...StartOption) (context.Context, *Span) {
	var opts StartOptions
	var parent SpanContext
	if p := FromContext(ctx); p != nil {
	parent = p.spanContext
	}
	for _, op := range o {
	op(&opts)
	}
	span := startSpanInternal(name, parent != SpanContext{}, parent, false, opts)

	ctx, end := startExecutionTracerTask(ctx, name)
	span.executionTracerTaskEnd = end
	return NewContext(ctx, span), span
	}

	// StartSpanWithRemoteParent starts a new child span of the span from the given parent.
	//
	// If the incoming context contains a parent, it ignores. StartSpanWithRemoteParent is
	// preferred for cases where the parent is propagated via an incoming request.
	func StartSpanWithRemoteParent(ctx context.Context, name string, parent SpanContext, o ...StartOption) (context.Context, *Span) {
	var opts StartOptions
	for _, op := range o {
	op(&opts)
	}
	span := startSpanInternal(name, parent != SpanContext{}, parent, true, opts)
	ctx, end := startExecutionTracerTask(ctx, name)
	span.executionTracerTaskEnd = end
	return NewContext(ctx, span), span
	}

	// NewSpan returns a new span.
	//
	// If parent is not nil, created span will be a child of the parent.
	//
	// Deprecated: Use StartSpan.
	func NewSpan(name string, parent Span, o StartOptions) Span {
	var parentSpanContext SpanContext
	if parent != nil {
	parentSpanContext = parent.SpanContext()
	}
	return startSpanInternal(name, parent != nil, parentSpanContext, false, o)
	}

	// NewSpanWithRemoteParent returns a new span with the given parent SpanContext.
	//
	// Deprecated: Use StartSpanWithRemoteParent.
	func NewSpanWithRemoteParent(name string, parent SpanContext, o StartOptions) *Span {
	return startSpanInternal(name, true, parent, true, o)
	}

	func startSpanInternal(name string, hasParent bool, parent SpanContext, remoteParent bool, o StartOptions) *Span {
	span := &Span{}
	span.spanContext = parent

	cfg := config.Load().(*Config)

	if !hasParent {
	span.spanContext.TraceID = cfg.IDGenerator.NewTraceID()
	}
	span.spanContext.SpanID = cfg.IDGenerator.NewSpanID()
	sampler := cfg.DefaultSampler

	if !hasParent \|\| remoteParent \|\| o.Sampler != nil {
	// If this span is the child of a local span and no Sampler is set in the
	// options, keep the parent's TraceOptions.
	//
	// Otherwise, consult the Sampler in the options if it is non-nil, otherwise
	// the default sampler.
	if o.Sampler != nil {
	sampler = o.Sampler
	}
	span.spanContext.setIsSampled(sampler(SamplingParameters{
	ParentContext: parent,
	TraceID: span.spanContext.TraceID,
	SpanID: span.spanContext.SpanID,
	Name: name,
	HasRemoteParent: remoteParent}).Sample)
	}

	if !internal.LocalSpanStoreEnabled && !span.spanContext.IsSampled() {
	return span
	}

	span.data = &SpanData{
	SpanContext: span.spanContext,
	StartTime: time.Now(),
	SpanKind: o.SpanKind,
	Name: name,
	HasRemoteParent: remoteParent,
	}
	if hasParent {
	span.data.ParentSpanID = parent.SpanID
	}
	if internal.LocalSpanStoreEnabled {
	var ss *spanStore
	ss = spanStoreForNameCreateIfNew(name)
	if ss != nil {
	span.spanStore = ss
	ss.add(span)
	}
	}

	return span
	}

	// End ends the span.
	func (s *Span) End() {
	if !s.IsRecordingEvents() {
	return
	}
	s.endOnce.Do(func() {
	if s.executionTracerTaskEnd != nil {
	s.executionTracerTaskEnd()
	}
	// TODO: optimize to avoid this call if sd won't be used.
	sd := s.makeSpanData()
	sd.EndTime = internal.MonotonicEndTime(sd.StartTime)
	if s.spanStore != nil {
	s.spanStore.finished(s, sd)
	}
	if s.spanContext.IsSampled() {
	// TODO: consider holding exportersMu for less time.
	exportersMu.Lock()
	for e := range exporters {
	e.ExportSpan(sd)
	}
	exportersMu.Unlock()
	}
	})
	}

	// makeSpanData produces a SpanData representing the current state of the Span.
	// It requires that s.data is non-nil.
	func (s Span) makeSpanData() SpanData {
	var sd SpanData
	s.mu.Lock()
	sd = *s.data
	if s.data.Attributes != nil {
	sd.Attributes = make(map[string]interface{})
	for k, v := range s.data.Attributes {
	sd.Attributes[k] = v
	}
	}
	s.mu.Unlock()
	return &sd
	}

	// SpanContext returns the SpanContext of the span.
	func (s *Span) SpanContext() SpanContext {
	if s == nil {
	return SpanContext{}
	}
	return s.spanContext
	}

	// SetStatus sets the status of the span, if it is recording events.
	func (s *Span) SetStatus(status Status) {
	if !s.IsRecordingEvents() {
	return
	}
	s.mu.Lock()
	s.data.Status = status
	s.mu.Unlock()
	}

	// AddAttributes sets attributes in the span.
	//
	// Existing attributes whose keys appear in the attributes parameter are overwritten.
	func (s *Span) AddAttributes(attributes ...Attribute) {
	if !s.IsRecordingEvents() {
	return
	}
	s.mu.Lock()
	if s.data.Attributes == nil {
	s.data.Attributes = make(map[string]interface{})
	}
	copyAttributes(s.data.Attributes, attributes)
	s.mu.Unlock()
	}

	// copyAttributes copies a slice of Attributes into a map.
	func copyAttributes(m map[string]interface{}, attributes []Attribute) {
	for _, a := range attributes {
	m[a.key] = a.value
	}
	}

	func (s *Span) lazyPrintfInternal(attributes []Attribute, format string, a ...interface{}) {
	now := time.Now()
	msg := fmt.Sprintf(format, a...)
	var m map[string]interface{}
	s.mu.Lock()
	if len(attributes) != 0 {
	m = make(map[string]interface{})
	copyAttributes(m, attributes)
	}
	s.data.Annotations = append(s.data.Annotations, Annotation{
	Time: now,
	Message: msg,
	Attributes: m,
	})
	s.mu.Unlock()
	}

	func (s *Span) printStringInternal(attributes []Attribute, str string) {
	now := time.Now()
	var a map[string]interface{}
	s.mu.Lock()
	if len(attributes) != 0 {
	a = make(map[string]interface{})
	copyAttributes(a, attributes)
	}
	s.data.Annotations = append(s.data.Annotations, Annotation{
	Time: now,
	Message: str,
	Attributes: a,
	})
	s.mu.Unlock()
	}

	// Annotate adds an annotation with attributes.
	// Attributes can be nil.
	func (s *Span) Annotate(attributes []Attribute, str string) {
	if !s.IsRecordingEvents() {
	return
	}
	s.printStringInternal(attributes, str)
	}

	// Annotatef adds an annotation with attributes.
	func (s *Span) Annotatef(attributes []Attribute, format string, a ...interface{}) {
	if !s.IsRecordingEvents() {
	return
	}
	s.lazyPrintfInternal(attributes, format, a...)
	}

	// AddMessageSendEvent adds a message send event to the span.
	//
	// messageID is an identifier for the message, which is recommended to be
	// unique in this span and the same between the send event and the receive
	// event (this allows to identify a message between the sender and receiver).
	// For example, this could be a sequence id.
	func (s *Span) AddMessageSendEvent(messageID, uncompressedByteSize, compressedByteSize int64) {
	if !s.IsRecordingEvents() {
	return
	}
	now := time.Now()
	s.mu.Lock()
	s.data.MessageEvents = append(s.data.MessageEvents, MessageEvent{
	Time: now,
	EventType: MessageEventTypeSent,
	MessageID: messageID,
	UncompressedByteSize: uncompressedByteSize,
	CompressedByteSize: compressedByteSize,
	})
	s.mu.Unlock()
	}

	// AddMessageReceiveEvent adds a message receive event to the span.
	//
	// messageID is an identifier for the message, which is recommended to be
	// unique in this span and the same between the send event and the receive
	// event (this allows to identify a message between the sender and receiver).
	// For example, this could be a sequence id.
	func (s *Span) AddMessageReceiveEvent(messageID, uncompressedByteSize, compressedByteSize int64) {
	if !s.IsRecordingEvents() {
	return
	}
	now := time.Now()
	s.mu.Lock()
	s.data.MessageEvents = append(s.data.MessageEvents, MessageEvent{
	Time: now,
	EventType: MessageEventTypeRecv,
	MessageID: messageID,
	UncompressedByteSize: uncompressedByteSize,
	CompressedByteSize: compressedByteSize,
	})
	s.mu.Unlock()
	}

	// AddLink adds a link to the span.
	func (s *Span) AddLink(l Link) {
	if !s.IsRecordingEvents() {
	return
	}
	s.mu.Lock()
	s.data.Links = append(s.data.Links, l)
	s.mu.Unlock()
	}

	func (s *Span) String() string {
	if s == nil {
	return "<nil>"
	}
	if s.data == nil {
	return fmt.Sprintf("span %s", s.spanContext.SpanID)
	}
	s.mu.Lock()
	str := fmt.Sprintf("span %s %q", s.spanContext.SpanID, s.data.Name)
	s.mu.Unlock()
	return str
	}

	var config atomic.Value // access atomically

	func init() {
	gen := &defaultIDGenerator{}
	// initialize traceID and spanID generators.
	var rngSeed int64
	for _, p := range []interface{}{
	&rngSeed, &gen.traceIDAdd, &gen.nextSpanID, &gen.spanIDInc,
	} {
	binary.Read(crand.Reader, binary.LittleEndian, p)
	}
	gen.traceIDRand = rand.New(rand.NewSource(rngSeed))
	gen.spanIDInc \|= 1

	config.Store(&Config{
	DefaultSampler: ProbabilitySampler(defaultSamplingProbability),
	IDGenerator: gen,
	})
	}

	type defaultIDGenerator struct {
	sync.Mutex
	traceIDRand *rand.Rand
	traceIDAdd [2]uint64
	nextSpanID uint64
	spanIDInc uint64
	}

	// NewSpanID returns a non-zero span ID from a randomly-chosen sequence.
	// mu should be held while this function is called.
	func (gen *defaultIDGenerator) NewSpanID() [8]byte {
	gen.Lock()
	id := gen.nextSpanID
	gen.nextSpanID += gen.spanIDInc
	if gen.nextSpanID == 0 {
	gen.nextSpanID += gen.spanIDInc
	}
	gen.Unlock()
	var sid [8]byte
	binary.LittleEndian.PutUint64(sid[:], id)
	return sid
	}

	// NewTraceID returns a non-zero trace ID from a randomly-chosen sequence.
	// mu should be held while this function is called.
	func (gen *defaultIDGenerator) NewTraceID() [16]byte {
	var tid [16]byte
	// Construct the trace ID from two outputs of traceIDRand, with a constant
	// added to each half for additional entropy.
	gen.Lock()
	binary.LittleEndian.PutUint64(tid[0:8], gen.traceIDRand.Uint64()+gen.traceIDAdd[0])
	binary.LittleEndian.PutUint64(tid[8:16], gen.traceIDRand.Uint64()+gen.traceIDAdd[1])
	gen.Unlock()
	return tid
	}