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// Copyright 2023 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.
// Trace event writing API for trace2runtime.go.
package runtime
import (
// Event types in the trace, args are given in square brackets.
// Naming scheme:
// - Time range event pairs have suffixes "Begin" and "End".
// - "Start", "Stop", "Create", "Destroy", "Block", "Unblock"
// are suffixes reserved for scheduling resources.
// NOTE: If you add an event type, make sure you also update all
// tables in this file!
type traceEv uint8
const (
traceEvNone traceEv = iota // unused
// Structural events.
traceEvEventBatch // start of per-M batch of events [generation, M ID, timestamp, batch length]
traceEvStacks // start of a section of the stack table [...traceEvStack]
traceEvStack // stack table entry [ID, ...{PC, func string ID, file string ID, line #}]
traceEvStrings // start of a section of the string dictionary [...traceEvString]
traceEvString // string dictionary entry [ID, length, string]
traceEvCPUSamples // start of a section of CPU samples [...traceEvCPUSample]
traceEvCPUSample // CPU profiling sample [timestamp, M ID, P ID, goroutine ID, stack ID]
traceEvFrequency // timestamp units per sec [freq]
// Procs.
traceEvProcsChange // current value of GOMAXPROCS [timestamp, GOMAXPROCS, stack ID]
traceEvProcStart // start of P [timestamp, P ID, P seq]
traceEvProcStop // stop of P [timestamp]
traceEvProcSteal // P was stolen [timestamp, P ID, P seq, M ID]
traceEvProcStatus // P status at the start of a generation [timestamp, P ID, status]
// Goroutines.
traceEvGoCreate // goroutine creation [timestamp, new goroutine ID, new stack ID, stack ID]
traceEvGoCreateSyscall // goroutine appears in syscall (cgo callback) [timestamp, new goroutine ID]
traceEvGoStart // goroutine starts running [timestamp, goroutine ID, goroutine seq]
traceEvGoDestroy // goroutine ends [timestamp]
traceEvGoDestroySyscall // goroutine ends in syscall (cgo callback) [timestamp]
traceEvGoStop // goroutine yields its time, but is runnable [timestamp, reason, stack ID]
traceEvGoBlock // goroutine blocks [timestamp, reason, stack ID]
traceEvGoUnblock // goroutine is unblocked [timestamp, goroutine ID, goroutine seq, stack ID]
traceEvGoSyscallBegin // syscall enter [timestamp, P seq, stack ID]
traceEvGoSyscallEnd // syscall exit [timestamp]
traceEvGoSyscallEndBlocked // syscall exit and it blocked at some point [timestamp]
traceEvGoStatus // goroutine status at the start of a generation [timestamp, goroutine ID, M ID, status]
// STW.
traceEvSTWBegin // STW start [timestamp, kind]
traceEvSTWEnd // STW done [timestamp]
// GC events.
traceEvGCActive // GC active [timestamp, seq]
traceEvGCBegin // GC start [timestamp, seq, stack ID]
traceEvGCEnd // GC done [timestamp, seq]
traceEvGCSweepActive // GC sweep active [timestamp, P ID]
traceEvGCSweepBegin // GC sweep start [timestamp, stack ID]
traceEvGCSweepEnd // GC sweep done [timestamp, swept bytes, reclaimed bytes]
traceEvGCMarkAssistActive // GC mark assist active [timestamp, goroutine ID]
traceEvGCMarkAssistBegin // GC mark assist start [timestamp, stack ID]
traceEvGCMarkAssistEnd // GC mark assist done [timestamp]
traceEvHeapAlloc // gcController.heapLive change [timestamp, heap alloc in bytes]
traceEvHeapGoal // gcController.heapGoal() change [timestamp, heap goal in bytes]
// Annotations.
traceEvGoLabel // apply string label to current running goroutine [timestamp, label string ID]
traceEvUserTaskBegin // trace.NewTask [timestamp, internal task ID, internal parent task ID, name string ID, stack ID]
traceEvUserTaskEnd // end of a task [timestamp, internal task ID, stack ID]
traceEvUserRegionBegin // trace.{Start,With}Region [timestamp, internal task ID, name string ID, stack ID]
traceEvUserRegionEnd // trace.{End,With}Region [timestamp, internal task ID, name string ID, stack ID]
traceEvUserLog // trace.Log [timestamp, internal task ID, key string ID, stack, value string ID]
// Coroutines.
traceEvGoSwitch // goroutine switch (coroswitch) [timestamp, goroutine ID, goroutine seq]
traceEvGoSwitchDestroy // goroutine switch and destroy [timestamp, goroutine ID, goroutine seq]
traceEvGoCreateBlocked // goroutine creation (starts blocked) [timestamp, new goroutine ID, new stack ID, stack ID]
// GoStatus with stack.
traceEvGoStatusStack // goroutine status at the start of a generation, with a stack [timestamp, goroutine ID, M ID, status, stack ID]
// Batch event for an experimental batch with a custom format.
traceEvExperimentalBatch // start of extra data [experiment ID, generation, M ID, timestamp, batch length, batch data...]
// traceArg is a simple wrapper type to help ensure that arguments passed
// to traces are well-formed.
type traceArg uint64
// traceEventWriter is the high-level API for writing trace events.
// See the comment on traceWriter about style for more details as to why
// this type and its methods are structured the way they are.
type traceEventWriter struct {
w traceWriter
// eventWriter creates a new traceEventWriter. It is the main entrypoint for writing trace events.
// Before creating the event writer, this method will emit a status for the current goroutine
// or proc if it exists, and if it hasn't had its status emitted yet. goStatus and procStatus indicate
// what the status of goroutine or P should be immediately *before* the events that are about to
// be written using the eventWriter (if they exist). No status will be written if there's no active
// goroutine or P.
// Callers can elect to pass a constant value here if the status is clear (e.g. a goroutine must have
// been Runnable before a GoStart). Otherwise, callers can query the status of either the goroutine
// or P and pass the appropriate status.
// In this case, the default status should be traceGoBad or traceProcBad to help identify bugs sooner.
func (tl traceLocker) eventWriter(goStatus traceGoStatus, procStatus traceProcStatus) traceEventWriter {
w := tl.writer()
if pp :=; pp != nil && !pp.trace.statusWasTraced(tl.gen) && pp.trace.acquireStatus(tl.gen) {
w = w.writeProcStatus(uint64(, procStatus, pp.trace.inSweep)
if gp :=; gp != nil && !gp.trace.statusWasTraced(tl.gen) && gp.trace.acquireStatus(tl.gen) {
w = w.writeGoStatus(uint64(gp.goid), int64(, goStatus, gp.inMarkAssist, 0 /* no stack */)
return traceEventWriter{w}
// commit writes out a trace event and calls end. It's a helper to make the
// common case of writing out a single event less error-prone.
func (e traceEventWriter) commit(ev traceEv, args ...traceArg) {
e = e.write(ev, args...)
// write writes an event into the trace.
func (e traceEventWriter) write(ev traceEv, args ...traceArg) traceEventWriter {
e.w = e.w.event(ev, args...)
return e
// end finishes writing to the trace. The traceEventWriter must not be used after this call.
func (e traceEventWriter) end() {
// traceEventWrite is the part of traceEvent that actually writes the event.
func (w traceWriter) event(ev traceEv, args ...traceArg) traceWriter {
// Make sure we have room.
w, _ = w.ensure(1 + (len(args)+1)*traceBytesPerNumber)
// Compute the timestamp diff that we'll put in the trace.
ts := traceClockNow()
if ts <= w.traceBuf.lastTime {
ts = w.traceBuf.lastTime + 1
tsDiff := uint64(ts - w.traceBuf.lastTime)
w.traceBuf.lastTime = ts
// Write out event.
for _, arg := range args {
return w
// stack takes a stack trace skipping the provided number of frames.
// It then returns a traceArg representing that stack which may be
// passed to write.
func (tl traceLocker) stack(skip int) traceArg {
return traceArg(traceStack(skip, nil, tl.gen))
// startPC takes a start PC for a goroutine and produces a unique
// stack ID for it.
// It then returns a traceArg representing that stack which may be
// passed to write.
func (tl traceLocker) startPC(pc uintptr) traceArg {
// +PCQuantum because makeTraceFrame expects return PCs and subtracts PCQuantum.
return traceArg(trace.stackTab[tl.gen%2].put([]uintptr{
startPCForTrace(pc) + sys.PCQuantum,
// string returns a traceArg representing s which may be passed to write.
// The string is assumed to be relatively short and popular, so it may be
// stored for a while in the string dictionary.
func (tl traceLocker) string(s string) traceArg {
return traceArg(trace.stringTab[tl.gen%2].put(tl.gen, s))
// uniqueString returns a traceArg representing s which may be passed to write.
// The string is assumed to be unique or long, so it will be written out to
// the trace eagerly.
func (tl traceLocker) uniqueString(s string) traceArg {
return traceArg(trace.stringTab[tl.gen%2].emit(tl.gen, s))
// rtype returns a traceArg representing typ which may be passed to write.
func (tl traceLocker) rtype(typ *abi.Type) traceArg {
return traceArg(trace.typeTab[tl.gen%2].put(typ))