// 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"
"go.opencensus.io/trace/tracestate"
)
// 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
Tracestate *tracestate.Tracestate
}
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
}
// 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.
//
// Returned context contains the newly created span. You can use it to
// propagate the returned span in process.
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.
//
// Returned context contains the newly created span. You can use it to
// propagate the returned span in process.
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
}
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 == nil {
return
}
if s.executionTracerTaskEnd != nil {
s.executionTracerTaskEnd()
}
if !s.IsRecordingEvents() {
return
}
s.endOnce.Do(func() {
exp, _ := exporters.Load().(exportersMap)
mustExport := s.spanContext.IsSampled() && len(exp) > 0
if s.spanStore != nil || mustExport {
sd := s.makeSpanData()
sd.EndTime = internal.MonotonicEndTime(sd.StartTime)
if s.spanStore != nil {
s.spanStore.finished(s, sd)
}
if mustExport {
for e := range exp {
e.ExportSpan(sd)
}
}
}
})
}
// 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
}
// SetName sets the name of the span, if it is recording events.
func (s *Span) SetName(name string) {
if !s.IsRecordingEvents() {
return
}
s.mu.Lock()
s.data.Name = name
s.mu.Unlock()
}
// 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
// Please keep these as the first fields
// so that these 8 byte fields will be aligned on addresses
// divisible by 8, on both 32-bit and 64-bit machines when
// performing atomic increments and accesses.
// See:
// * https://github.com/census-instrumentation/opencensus-go/issues/587
// * https://github.com/census-instrumentation/opencensus-go/issues/865
// * https://golang.org/pkg/sync/atomic/#pkg-note-BUG
nextSpanID uint64
spanIDInc uint64
traceIDAdd [2]uint64
traceIDRand *rand.Rand
}
// NewSpanID returns a non-zero span ID from a randomly-chosen sequence.
func (gen *defaultIDGenerator) NewSpanID() [8]byte {
var id uint64
for id == 0 {
id = atomic.AddUint64(&gen.nextSpanID, gen.spanIDInc)
}
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
}
