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// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package trace
import (
"cmd/internal/traceviewer"
"context"
"encoding/json"
"errors"
"os"
"strings"
"sync/atomic"
"time"
)
// Constants used in event fields.
// See https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU
// for more details.
const (
phaseDurationBegin = "B"
phaseDurationEnd = "E"
phaseFlowStart = "s"
phaseFlowEnd = "f"
bindEnclosingSlice = "e"
)
var traceStarted atomic.Bool
func getTraceContext(ctx context.Context) (traceContext, bool) {
if !traceStarted.Load() {
return traceContext{}, false
}
v := ctx.Value(traceKey{})
if v == nil {
return traceContext{}, false
}
return v.(traceContext), true
}
// StartSpan starts a trace event with the given name. The Span ends when its Done method is called.
func StartSpan(ctx context.Context, name string) (context.Context, *Span) {
tc, ok := getTraceContext(ctx)
if !ok {
return ctx, nil
}
childSpan := &Span{t: tc.t, name: name, tid: tc.tid, start: time.Now()}
tc.t.writeEvent(&traceviewer.Event{
Name: childSpan.name,
Time: float64(childSpan.start.UnixNano()) / float64(time.Microsecond),
TID: childSpan.tid,
Phase: phaseDurationBegin,
})
ctx = context.WithValue(ctx, traceKey{}, traceContext{tc.t, tc.tid})
return ctx, childSpan
}
// StartGoroutine associates the context with a new Thread ID. The Chrome trace viewer associates each
// trace event with a thread, and doesn't expect events with the same thread id to happen at the
// same time.
func StartGoroutine(ctx context.Context) context.Context {
tc, ok := getTraceContext(ctx)
if !ok {
return ctx
}
return context.WithValue(ctx, traceKey{}, traceContext{tc.t, tc.t.getNextTID()})
}
// Flow marks a flow indicating that the 'to' span depends on the 'from' span.
// Flow should be called while the 'to' span is in progress.
func Flow(ctx context.Context, from *Span, to *Span) {
tc, ok := getTraceContext(ctx)
if !ok || from == nil || to == nil {
return
}
id := tc.t.getNextFlowID()
tc.t.writeEvent(&traceviewer.Event{
Name: from.name + " -> " + to.name,
Category: "flow",
ID: id,
Time: float64(from.end.UnixNano()) / float64(time.Microsecond),
Phase: phaseFlowStart,
TID: from.tid,
})
tc.t.writeEvent(&traceviewer.Event{
Name: from.name + " -> " + to.name,
Category: "flow", // TODO(matloob): Add Category to Flow?
ID: id,
Time: float64(to.start.UnixNano()) / float64(time.Microsecond),
Phase: phaseFlowEnd,
TID: to.tid,
BindPoint: bindEnclosingSlice,
})
}
type Span struct {
t *tracer
name string
tid uint64
start time.Time
end time.Time
}
func (s *Span) Done() {
if s == nil {
return
}
s.end = time.Now()
s.t.writeEvent(&traceviewer.Event{
Name: s.name,
Time: float64(s.end.UnixNano()) / float64(time.Microsecond),
TID: s.tid,
Phase: phaseDurationEnd,
})
}
type tracer struct {
file chan traceFile // 1-buffered
nextTID uint64
nextFlowID uint64
}
func (t *tracer) writeEvent(ev *traceviewer.Event) error {
f := <-t.file
defer func() { t.file <- f }()
var err error
if f.entries == 0 {
_, err = f.sb.WriteString("[\n")
} else {
_, err = f.sb.WriteString(",")
}
f.entries++
if err != nil {
return nil
}
if err := f.enc.Encode(ev); err != nil {
return err
}
// Write event string to output file.
_, err = f.f.WriteString(f.sb.String())
f.sb.Reset()
return err
}
func (t *tracer) Close() error {
f := <-t.file
defer func() { t.file <- f }()
_, firstErr := f.f.WriteString("]")
if err := f.f.Close(); firstErr == nil {
firstErr = err
}
return firstErr
}
func (t *tracer) getNextTID() uint64 {
return atomic.AddUint64(&t.nextTID, 1)
}
func (t *tracer) getNextFlowID() uint64 {
return atomic.AddUint64(&t.nextFlowID, 1)
}
// traceKey is the context key for tracing information. It is unexported to prevent collisions with context keys defined in
// other packages.
type traceKey struct{}
type traceContext struct {
t *tracer
tid uint64
}
// Start starts a trace which writes to the given file.
func Start(ctx context.Context, file string) (context.Context, func() error, error) {
traceStarted.Store(true)
if file == "" {
return nil, nil, errors.New("no trace file supplied")
}
f, err := os.Create(file)
if err != nil {
return nil, nil, err
}
t := &tracer{file: make(chan traceFile, 1)}
sb := new(strings.Builder)
t.file <- traceFile{
f: f,
sb: sb,
enc: json.NewEncoder(sb),
}
ctx = context.WithValue(ctx, traceKey{}, traceContext{t: t})
return ctx, t.Close, nil
}
type traceFile struct {
f *os.File
sb *strings.Builder
enc *json.Encoder
entries int64
}
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