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pprof.go
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912 lines (821 loc) · 27.9 KB
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// Copyright 2010 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 pprof writes runtime profiling data in the format expected
// by the pprof visualization tool.
//
// # Profiling a Go program
//
// The first step to profiling a Go program is to enable profiling.
// Support for profiling benchmarks built with the standard testing
// package is built into go test. For example, the following command
// runs benchmarks in the current directory and writes the CPU and
// memory profiles to cpu.prof and mem.prof:
//
// go test -cpuprofile cpu.prof -memprofile mem.prof -bench .
//
// To add equivalent profiling support to a standalone program, add
// code like the following to your main function:
//
// var cpuprofile = flag.String("cpuprofile", "", "write cpu profile to `file`")
// var memprofile = flag.String("memprofile", "", "write memory profile to `file`")
//
// func main() {
// flag.Parse()
// if *cpuprofile != "" {
// f, err := os.Create(*cpuprofile)
// if err != nil {
// log.Fatal("could not create CPU profile: ", err)
// }
// defer f.Close() // error handling omitted for example
// if err := pprof.StartCPUProfile(f); err != nil {
// log.Fatal("could not start CPU profile: ", err)
// }
// defer pprof.StopCPUProfile()
// }
//
// // ... rest of the program ...
//
// if *memprofile != "" {
// f, err := os.Create(*memprofile)
// if err != nil {
// log.Fatal("could not create memory profile: ", err)
// }
// defer f.Close() // error handling omitted for example
// runtime.GC() // get up-to-date statistics
// if err := pprof.WriteHeapProfile(f); err != nil {
// log.Fatal("could not write memory profile: ", err)
// }
// }
// }
//
// There is also a standard HTTP interface to profiling data. Adding
// the following line will install handlers under the /debug/pprof/
// URL to download live profiles:
//
// import _ "net/http/pprof"
//
// See the net/http/pprof package for more details.
//
// Profiles can then be visualized with the pprof tool:
//
// go tool pprof cpu.prof
//
// There are many commands available from the pprof command line.
// Commonly used commands include "top", which prints a summary of the
// top program hot-spots, and "web", which opens an interactive graph
// of hot-spots and their call graphs. Use "help" for information on
// all pprof commands.
//
// For more information about pprof, see
// https://github.com/google/pprof/blob/master/doc/README.md.
package pprof
import (
"bufio"
"bytes"
"fmt"
"internal/abi"
"io"
"runtime"
"sort"
"strings"
"sync"
"text/tabwriter"
"time"
"unsafe"
)
// BUG(rsc): Profiles are only as good as the kernel support used to generate them.
// See https://golang.org/issue/13841 for details about known problems.
// A Profile is a collection of stack traces showing the call sequences
// that led to instances of a particular event, such as allocation.
// Packages can create and maintain their own profiles; the most common
// use is for tracking resources that must be explicitly closed, such as files
// or network connections.
//
// A Profile's methods can be called from multiple goroutines simultaneously.
//
// Each Profile has a unique name. A few profiles are predefined:
//
// goroutine - stack traces of all current goroutines
// heap - a sampling of memory allocations of live objects
// allocs - a sampling of all past memory allocations
// threadcreate - stack traces that led to the creation of new OS threads
// block - stack traces that led to blocking on synchronization primitives
// mutex - stack traces of holders of contended mutexes
//
// These predefined profiles maintain themselves and panic on an explicit
// Add or Remove method call.
//
// The heap profile reports statistics as of the most recently completed
// garbage collection; it elides more recent allocation to avoid skewing
// the profile away from live data and toward garbage.
// If there has been no garbage collection at all, the heap profile reports
// all known allocations. This exception helps mainly in programs running
// without garbage collection enabled, usually for debugging purposes.
//
// The heap profile tracks both the allocation sites for all live objects in
// the application memory and for all objects allocated since the program start.
// Pprof's -inuse_space, -inuse_objects, -alloc_space, and -alloc_objects
// flags select which to display, defaulting to -inuse_space (live objects,
// scaled by size).
//
// The allocs profile is the same as the heap profile but changes the default
// pprof display to -alloc_space, the total number of bytes allocated since
// the program began (including garbage-collected bytes).
//
// The CPU profile is not available as a Profile. It has a special API,
// the StartCPUProfile and StopCPUProfile functions, because it streams
// output to a writer during profiling.
type Profile struct {
name string
mu sync.Mutex
m map[any][]uintptr
count func() int
write func(io.Writer, int) error
}
// profiles records all registered profiles.
var profiles struct {
mu sync.Mutex
m map[string]*Profile
}
var goroutineProfile = &Profile{
name: "goroutine",
count: countGoroutine,
write: writeGoroutine,
}
var threadcreateProfile = &Profile{
name: "threadcreate",
count: countThreadCreate,
write: writeThreadCreate,
}
var heapProfile = &Profile{
name: "heap",
count: countHeap,
write: writeHeap,
}
var allocsProfile = &Profile{
name: "allocs",
count: countHeap, // identical to heap profile
write: writeAlloc,
}
var blockProfile = &Profile{
name: "block",
count: countBlock,
write: writeBlock,
}
var mutexProfile = &Profile{
name: "mutex",
count: countMutex,
write: writeMutex,
}
func lockProfiles() {
profiles.mu.Lock()
if profiles.m == nil {
// Initial built-in profiles.
profiles.m = map[string]*Profile{
"goroutine": goroutineProfile,
"threadcreate": threadcreateProfile,
"heap": heapProfile,
"allocs": allocsProfile,
"block": blockProfile,
"mutex": mutexProfile,
}
}
}
func unlockProfiles() {
profiles.mu.Unlock()
}
// NewProfile creates a new profile with the given name.
// If a profile with that name already exists, NewProfile panics.
// The convention is to use a 'import/path.' prefix to create
// separate name spaces for each package.
// For compatibility with various tools that read pprof data,
// profile names should not contain spaces.
func NewProfile(name string) *Profile {
lockProfiles()
defer unlockProfiles()
if name == "" {
panic("pprof: NewProfile with empty name")
}
if profiles.m[name] != nil {
panic("pprof: NewProfile name already in use: " + name)
}
p := &Profile{
name: name,
m: map[any][]uintptr{},
}
profiles.m[name] = p
return p
}
// Lookup returns the profile with the given name, or nil if no such profile exists.
func Lookup(name string) *Profile {
lockProfiles()
defer unlockProfiles()
return profiles.m[name]
}
// Profiles returns a slice of all the known profiles, sorted by name.
func Profiles() []*Profile {
lockProfiles()
defer unlockProfiles()
all := make([]*Profile, 0, len(profiles.m))
for _, p := range profiles.m {
all = append(all, p)
}
sort.Slice(all, func(i, j int) bool { return all[i].name < all[j].name })
return all
}
// Name returns this profile's name, which can be passed to Lookup to reobtain the profile.
func (p *Profile) Name() string {
return p.name
}
// Count returns the number of execution stacks currently in the profile.
func (p *Profile) Count() int {
p.mu.Lock()
defer p.mu.Unlock()
if p.count != nil {
return p.count()
}
return len(p.m)
}
// Add adds the current execution stack to the profile, associated with value.
// Add stores value in an internal map, so value must be suitable for use as
// a map key and will not be garbage collected until the corresponding
// call to Remove. Add panics if the profile already contains a stack for value.
//
// The skip parameter has the same meaning as runtime.Caller's skip
// and controls where the stack trace begins. Passing skip=0 begins the
// trace in the function calling Add. For example, given this
// execution stack:
//
// Add
// called from rpc.NewClient
// called from mypkg.Run
// called from main.main
//
// Passing skip=0 begins the stack trace at the call to Add inside rpc.NewClient.
// Passing skip=1 begins the stack trace at the call to NewClient inside mypkg.Run.
func (p *Profile) Add(value any, skip int) {
if p.name == "" {
panic("pprof: use of uninitialized Profile")
}
if p.write != nil {
panic("pprof: Add called on built-in Profile " + p.name)
}
stk := make([]uintptr, 32)
n := runtime.Callers(skip+1, stk[:])
stk = stk[:n]
if len(stk) == 0 {
// The value for skip is too large, and there's no stack trace to record.
stk = []uintptr{abi.FuncPCABIInternal(lostProfileEvent)}
}
p.mu.Lock()
defer p.mu.Unlock()
if p.m[value] != nil {
panic("pprof: Profile.Add of duplicate value")
}
p.m[value] = stk
}
// Remove removes the execution stack associated with value from the profile.
// It is a no-op if the value is not in the profile.
func (p *Profile) Remove(value any) {
p.mu.Lock()
defer p.mu.Unlock()
delete(p.m, value)
}
// WriteTo writes a pprof-formatted snapshot of the profile to w.
// If a write to w returns an error, WriteTo returns that error.
// Otherwise, WriteTo returns nil.
//
// The debug parameter enables additional output.
// Passing debug=0 writes the gzip-compressed protocol buffer described
// in https://github.com/google/pprof/tree/master/proto#overview.
// Passing debug=1 writes the legacy text format with comments
// translating addresses to function names and line numbers, so that a
// programmer can read the profile without tools.
//
// The predefined profiles may assign meaning to other debug values;
// for example, when printing the "goroutine" profile, debug=2 means to
// print the goroutine stacks in the same form that a Go program uses
// when dying due to an unrecovered panic.
func (p *Profile) WriteTo(w io.Writer, debug int) error {
if p.name == "" {
panic("pprof: use of zero Profile")
}
if p.write != nil {
return p.write(w, debug)
}
// Obtain consistent snapshot under lock; then process without lock.
p.mu.Lock()
all := make([][]uintptr, 0, len(p.m))
for _, stk := range p.m {
all = append(all, stk)
}
p.mu.Unlock()
// Map order is non-deterministic; make output deterministic.
sort.Slice(all, func(i, j int) bool {
t, u := all[i], all[j]
for k := 0; k < len(t) && k < len(u); k++ {
if t[k] != u[k] {
return t[k] < u[k]
}
}
return len(t) < len(u)
})
return printCountProfile(w, debug, p.name, stackProfile(all))
}
type stackProfile [][]uintptr
func (x stackProfile) Len() int { return len(x) }
func (x stackProfile) Stack(i int) []uintptr { return x[i] }
func (x stackProfile) Label(i int) *labelMap { return nil }
// A countProfile is a set of stack traces to be printed as counts
// grouped by stack trace. There are multiple implementations:
// all that matters is that we can find out how many traces there are
// and obtain each trace in turn.
type countProfile interface {
Len() int
Stack(i int) []uintptr
Label(i int) *labelMap
}
// printCountCycleProfile outputs block profile records (for block or mutex profiles)
// as the pprof-proto format output. Translations from cycle count to time duration
// are done because The proto expects count and time (nanoseconds) instead of count
// and the number of cycles for block, contention profiles.
// Possible 'scaler' functions are scaleBlockProfile and scaleMutexProfile.
func printCountCycleProfile(w io.Writer, countName, cycleName string, scaler func(int64, float64) (int64, float64), records []runtime.BlockProfileRecord) error {
// Output profile in protobuf form.
b := newProfileBuilder(w)
b.pbValueType(tagProfile_PeriodType, countName, "count")
b.pb.int64Opt(tagProfile_Period, 1)
b.pbValueType(tagProfile_SampleType, countName, "count")
b.pbValueType(tagProfile_SampleType, cycleName, "nanoseconds")
cpuGHz := float64(runtime_cyclesPerSecond()) / 1e9
values := []int64{0, 0}
var locs []uint64
for _, r := range records {
count, nanosec := scaler(r.Count, float64(r.Cycles)/cpuGHz)
values[0] = count
values[1] = int64(nanosec)
// For count profiles, all stack addresses are
// return PCs, which is what appendLocsForStack expects.
locs = b.appendLocsForStack(locs[:0], r.Stack())
b.pbSample(values, locs, nil)
}
b.build()
return nil
}
// printCountProfile prints a countProfile at the specified debug level.
// The profile will be in compressed proto format unless debug is nonzero.
func printCountProfile(w io.Writer, debug int, name string, p countProfile) error {
// Build count of each stack.
var buf bytes.Buffer
key := func(stk []uintptr, lbls *labelMap) string {
buf.Reset()
fmt.Fprintf(&buf, "@")
for _, pc := range stk {
fmt.Fprintf(&buf, " %#x", pc)
}
if lbls != nil {
buf.WriteString("\n# labels: ")
buf.WriteString(lbls.String())
}
return buf.String()
}
count := map[string]int{}
index := map[string]int{}
var keys []string
n := p.Len()
for i := 0; i < n; i++ {
k := key(p.Stack(i), p.Label(i))
if count[k] == 0 {
index[k] = i
keys = append(keys, k)
}
count[k]++
}
sort.Sort(&keysByCount{keys, count})
if debug > 0 {
// Print debug profile in legacy format
tw := tabwriter.NewWriter(w, 1, 8, 1, '\t', 0)
fmt.Fprintf(tw, "%s profile: total %d\n", name, p.Len())
for _, k := range keys {
fmt.Fprintf(tw, "%d %s\n", count[k], k)
printStackRecord(tw, p.Stack(index[k]), false)
}
return tw.Flush()
}
// Output profile in protobuf form.
b := newProfileBuilder(w)
b.pbValueType(tagProfile_PeriodType, name, "count")
b.pb.int64Opt(tagProfile_Period, 1)
b.pbValueType(tagProfile_SampleType, name, "count")
values := []int64{0}
var locs []uint64
for _, k := range keys {
values[0] = int64(count[k])
// For count profiles, all stack addresses are
// return PCs, which is what appendLocsForStack expects.
locs = b.appendLocsForStack(locs[:0], p.Stack(index[k]))
idx := index[k]
var labels func()
if p.Label(idx) != nil {
labels = func() {
for k, v := range *p.Label(idx) {
b.pbLabel(tagSample_Label, k, v, 0)
}
}
}
b.pbSample(values, locs, labels)
}
b.build()
return nil
}
// keysByCount sorts keys with higher counts first, breaking ties by key string order.
type keysByCount struct {
keys []string
count map[string]int
}
func (x *keysByCount) Len() int { return len(x.keys) }
func (x *keysByCount) Swap(i, j int) { x.keys[i], x.keys[j] = x.keys[j], x.keys[i] }
func (x *keysByCount) Less(i, j int) bool {
ki, kj := x.keys[i], x.keys[j]
ci, cj := x.count[ki], x.count[kj]
if ci != cj {
return ci > cj
}
return ki < kj
}
// printStackRecord prints the function + source line information
// for a single stack trace.
func printStackRecord(w io.Writer, stk []uintptr, allFrames bool) {
show := allFrames
frames := runtime.CallersFrames(stk)
for {
frame, more := frames.Next()
name := frame.Function
if name == "" {
show = true
fmt.Fprintf(w, "#\t%#x\n", frame.PC)
} else if name != "runtime.goexit" && (show || !strings.HasPrefix(name, "runtime.")) {
// Hide runtime.goexit and any runtime functions at the beginning.
// This is useful mainly for allocation traces.
show = true
fmt.Fprintf(w, "#\t%#x\t%s+%#x\t%s:%d\n", frame.PC, name, frame.PC-frame.Entry, frame.File, frame.Line)
}
if !more {
break
}
}
if !show {
// We didn't print anything; do it again,
// and this time include runtime functions.
printStackRecord(w, stk, true)
return
}
fmt.Fprintf(w, "\n")
}
// Interface to system profiles.
// WriteHeapProfile is shorthand for Lookup("heap").WriteTo(w, 0).
// It is preserved for backwards compatibility.
func WriteHeapProfile(w io.Writer) error {
return writeHeap(w, 0)
}
// countHeap returns the number of records in the heap profile.
func countHeap() int {
n, _ := runtime.MemProfile(nil, true)
return n
}
// writeHeap writes the current runtime heap profile to w.
func writeHeap(w io.Writer, debug int) error {
return writeHeapInternal(w, debug, "")
}
// writeAlloc writes the current runtime heap profile to w
// with the total allocation space as the default sample type.
func writeAlloc(w io.Writer, debug int) error {
return writeHeapInternal(w, debug, "alloc_space")
}
func writeHeapInternal(w io.Writer, debug int, defaultSampleType string) error {
var memStats *runtime.MemStats
if debug != 0 {
// Read mem stats first, so that our other allocations
// do not appear in the statistics.
memStats = new(runtime.MemStats)
runtime.ReadMemStats(memStats)
}
// Find out how many records there are (MemProfile(nil, true)),
// allocate that many records, and get the data.
// There's a race—more records might be added between
// the two calls—so allocate a few extra records for safety
// and also try again if we're very unlucky.
// The loop should only execute one iteration in the common case.
var p []runtime.MemProfileRecord
n, ok := runtime.MemProfile(nil, true)
for {
// Allocate room for a slightly bigger profile,
// in case a few more entries have been added
// since the call to MemProfile.
p = make([]runtime.MemProfileRecord, n+50)
n, ok = runtime.MemProfile(p, true)
if ok {
p = p[0:n]
break
}
// Profile grew; try again.
}
if debug == 0 {
return writeHeapProto(w, p, int64(runtime.MemProfileRate), defaultSampleType)
}
sort.Slice(p, func(i, j int) bool { return p[i].InUseBytes() > p[j].InUseBytes() })
b := bufio.NewWriter(w)
tw := tabwriter.NewWriter(b, 1, 8, 1, '\t', 0)
w = tw
var total runtime.MemProfileRecord
for i := range p {
r := &p[i]
total.AllocBytes += r.AllocBytes
total.AllocObjects += r.AllocObjects
total.FreeBytes += r.FreeBytes
total.FreeObjects += r.FreeObjects
}
// Technically the rate is MemProfileRate not 2*MemProfileRate,
// but early versions of the C++ heap profiler reported 2*MemProfileRate,
// so that's what pprof has come to expect.
fmt.Fprintf(w, "heap profile: %d: %d [%d: %d] @ heap/%d\n",
total.InUseObjects(), total.InUseBytes(),
total.AllocObjects, total.AllocBytes,
2*runtime.MemProfileRate)
for i := range p {
r := &p[i]
fmt.Fprintf(w, "%d: %d [%d: %d] @",
r.InUseObjects(), r.InUseBytes(),
r.AllocObjects, r.AllocBytes)
for _, pc := range r.Stack() {
fmt.Fprintf(w, " %#x", pc)
}
fmt.Fprintf(w, "\n")
printStackRecord(w, r.Stack(), false)
}
// Print memstats information too.
// Pprof will ignore, but useful for people
s := memStats
fmt.Fprintf(w, "\n# runtime.MemStats\n")
fmt.Fprintf(w, "# Alloc = %d\n", s.Alloc)
fmt.Fprintf(w, "# TotalAlloc = %d\n", s.TotalAlloc)
fmt.Fprintf(w, "# Sys = %d\n", s.Sys)
fmt.Fprintf(w, "# Lookups = %d\n", s.Lookups)
fmt.Fprintf(w, "# Mallocs = %d\n", s.Mallocs)
fmt.Fprintf(w, "# Frees = %d\n", s.Frees)
fmt.Fprintf(w, "# HeapAlloc = %d\n", s.HeapAlloc)
fmt.Fprintf(w, "# HeapSys = %d\n", s.HeapSys)
fmt.Fprintf(w, "# HeapIdle = %d\n", s.HeapIdle)
fmt.Fprintf(w, "# HeapInuse = %d\n", s.HeapInuse)
fmt.Fprintf(w, "# HeapReleased = %d\n", s.HeapReleased)
fmt.Fprintf(w, "# HeapObjects = %d\n", s.HeapObjects)
fmt.Fprintf(w, "# Stack = %d / %d\n", s.StackInuse, s.StackSys)
fmt.Fprintf(w, "# MSpan = %d / %d\n", s.MSpanInuse, s.MSpanSys)
fmt.Fprintf(w, "# MCache = %d / %d\n", s.MCacheInuse, s.MCacheSys)
fmt.Fprintf(w, "# BuckHashSys = %d\n", s.BuckHashSys)
fmt.Fprintf(w, "# GCSys = %d\n", s.GCSys)
fmt.Fprintf(w, "# OtherSys = %d\n", s.OtherSys)
fmt.Fprintf(w, "# NextGC = %d\n", s.NextGC)
fmt.Fprintf(w, "# LastGC = %d\n", s.LastGC)
fmt.Fprintf(w, "# PauseNs = %d\n", s.PauseNs)
fmt.Fprintf(w, "# PauseEnd = %d\n", s.PauseEnd)
fmt.Fprintf(w, "# NumGC = %d\n", s.NumGC)
fmt.Fprintf(w, "# NumForcedGC = %d\n", s.NumForcedGC)
fmt.Fprintf(w, "# GCCPUFraction = %v\n", s.GCCPUFraction)
fmt.Fprintf(w, "# DebugGC = %v\n", s.DebugGC)
// Also flush out MaxRSS on supported platforms.
addMaxRSS(w)
tw.Flush()
return b.Flush()
}
// countThreadCreate returns the size of the current ThreadCreateProfile.
func countThreadCreate() int {
n, _ := runtime.ThreadCreateProfile(nil)
return n
}
// writeThreadCreate writes the current runtime ThreadCreateProfile to w.
func writeThreadCreate(w io.Writer, debug int) error {
// Until https://golang.org/issues/6104 is addressed, wrap
// ThreadCreateProfile because there's no point in tracking labels when we
// don't get any stack-traces.
return writeRuntimeProfile(w, debug, "threadcreate", func(p []runtime.StackRecord, _ []unsafe.Pointer) (n int, ok bool) {
return runtime.ThreadCreateProfile(p)
})
}
// countGoroutine returns the number of goroutines.
func countGoroutine() int {
return runtime.NumGoroutine()
}
// runtime_goroutineProfileWithLabels is defined in runtime/mprof.go
func runtime_goroutineProfileWithLabels(p []runtime.StackRecord, labels []unsafe.Pointer) (n int, ok bool)
// writeGoroutine writes the current runtime GoroutineProfile to w.
func writeGoroutine(w io.Writer, debug int) error {
if debug >= 2 {
return writeGoroutineStacks(w)
}
return writeRuntimeProfile(w, debug, "goroutine", runtime_goroutineProfileWithLabels)
}
func writeGoroutineStacks(w io.Writer) error {
// We don't know how big the buffer needs to be to collect
// all the goroutines. Start with 1 MB and try a few times, doubling each time.
// Give up and use a truncated trace if 64 MB is not enough.
buf := make([]byte, 1<<20)
for i := 0; ; i++ {
n := runtime.Stack(buf, true)
if n < len(buf) {
buf = buf[:n]
break
}
if len(buf) >= 64<<20 {
// Filled 64 MB - stop there.
break
}
buf = make([]byte, 2*len(buf))
}
_, err := w.Write(buf)
return err
}
func writeRuntimeProfile(w io.Writer, debug int, name string, fetch func([]runtime.StackRecord, []unsafe.Pointer) (int, bool)) error {
// Find out how many records there are (fetch(nil)),
// allocate that many records, and get the data.
// There's a race—more records might be added between
// the two calls—so allocate a few extra records for safety
// and also try again if we're very unlucky.
// The loop should only execute one iteration in the common case.
var p []runtime.StackRecord
var labels []unsafe.Pointer
n, ok := fetch(nil, nil)
for {
// Allocate room for a slightly bigger profile,
// in case a few more entries have been added
// since the call to ThreadProfile.
p = make([]runtime.StackRecord, n+10)
labels = make([]unsafe.Pointer, n+10)
n, ok = fetch(p, labels)
if ok {
p = p[0:n]
break
}
// Profile grew; try again.
}
return printCountProfile(w, debug, name, &runtimeProfile{p, labels})
}
type runtimeProfile struct {
stk []runtime.StackRecord
labels []unsafe.Pointer
}
func (p *runtimeProfile) Len() int { return len(p.stk) }
func (p *runtimeProfile) Stack(i int) []uintptr { return p.stk[i].Stack() }
func (p *runtimeProfile) Label(i int) *labelMap { return (*labelMap)(p.labels[i]) }
var cpu struct {
sync.Mutex
profiling bool
done chan bool
}
// StartCPUProfile enables CPU profiling for the current process.
// While profiling, the profile will be buffered and written to w.
// StartCPUProfile returns an error if profiling is already enabled.
//
// On Unix-like systems, StartCPUProfile does not work by default for
// Go code built with -buildmode=c-archive or -buildmode=c-shared.
// StartCPUProfile relies on the SIGPROF signal, but that signal will
// be delivered to the main program's SIGPROF signal handler (if any)
// not to the one used by Go. To make it work, call os/signal.Notify
// for syscall.SIGPROF, but note that doing so may break any profiling
// being done by the main program.
func StartCPUProfile(w io.Writer) error {
// The runtime routines allow a variable profiling rate,
// but in practice operating systems cannot trigger signals
// at more than about 500 Hz, and our processing of the
// signal is not cheap (mostly getting the stack trace).
// 100 Hz is a reasonable choice: it is frequent enough to
// produce useful data, rare enough not to bog down the
// system, and a nice round number to make it easy to
// convert sample counts to seconds. Instead of requiring
// each client to specify the frequency, we hard code it.
const hz = 100
cpu.Lock()
defer cpu.Unlock()
if cpu.done == nil {
cpu.done = make(chan bool)
}
// Double-check.
if cpu.profiling {
return fmt.Errorf("cpu profiling already in use")
}
cpu.profiling = true
runtime.SetCPUProfileRate(hz)
go profileWriter(w)
return nil
}
// readProfile, provided by the runtime, returns the next chunk of
// binary CPU profiling stack trace data, blocking until data is available.
// If profiling is turned off and all the profile data accumulated while it was
// on has been returned, readProfile returns eof=true.
// The caller must save the returned data and tags before calling readProfile again.
func readProfile() (data []uint64, tags []unsafe.Pointer, eof bool)
func profileWriter(w io.Writer) {
b := newProfileBuilder(w)
var err error
for {
time.Sleep(100 * time.Millisecond)
data, tags, eof := readProfile()
if e := b.addCPUData(data, tags); e != nil && err == nil {
err = e
}
if eof {
break
}
}
if err != nil {
// The runtime should never produce an invalid or truncated profile.
// It drops records that can't fit into its log buffers.
panic("runtime/pprof: converting profile: " + err.Error())
}
b.build()
cpu.done <- true
}
// StopCPUProfile stops the current CPU profile, if any.
// StopCPUProfile only returns after all the writes for the
// profile have completed.
func StopCPUProfile() {
cpu.Lock()
defer cpu.Unlock()
if !cpu.profiling {
return
}
cpu.profiling = false
runtime.SetCPUProfileRate(0)
<-cpu.done
}
// countBlock returns the number of records in the blocking profile.
func countBlock() int {
n, _ := runtime.BlockProfile(nil)
return n
}
// countMutex returns the number of records in the mutex profile.
func countMutex() int {
n, _ := runtime.MutexProfile(nil)
return n
}
// writeBlock writes the current blocking profile to w.
func writeBlock(w io.Writer, debug int) error {
return writeProfileInternal(w, debug, "contention", runtime.BlockProfile, scaleBlockProfile)
}
func scaleBlockProfile(cnt int64, ns float64) (int64, float64) {
// Do nothing.
// The current way of block profile sampling makes it
// hard to compute the unsampled number. The legacy block
// profile parse doesn't attempt to scale or unsample.
return cnt, ns
}
// writeMutex writes the current mutex profile to w.
func writeMutex(w io.Writer, debug int) error {
return writeProfileInternal(w, debug, "mutex", runtime.MutexProfile, scaleMutexProfile)
}
// writeProfileInternal writes the current blocking or mutex profile depending on the passed parameters
func writeProfileInternal(w io.Writer, debug int, name string, runtimeProfile func([]runtime.BlockProfileRecord) (int, bool), scaleProfile func(int64, float64) (int64, float64)) error {
var p []runtime.BlockProfileRecord
n, ok := runtimeProfile(nil)
for {
p = make([]runtime.BlockProfileRecord, n+50)
n, ok = runtimeProfile(p)
if ok {
p = p[:n]
break
}
}
sort.Slice(p, func(i, j int) bool { return p[i].Cycles > p[j].Cycles })
if debug <= 0 {
return printCountCycleProfile(w, "contentions", "delay", scaleProfile, p)
}
b := bufio.NewWriter(w)
tw := tabwriter.NewWriter(w, 1, 8, 1, '\t', 0)
w = tw
fmt.Fprintf(w, "--- %v:\n", name)
fmt.Fprintf(w, "cycles/second=%v\n", runtime_cyclesPerSecond())
if name == "mutex" {
fmt.Fprintf(w, "sampling period=%d\n", runtime.SetMutexProfileFraction(-1))
}
for i := range p {
r := &p[i]
fmt.Fprintf(w, "%v %v @", r.Cycles, r.Count)
for _, pc := range r.Stack() {
fmt.Fprintf(w, " %#x", pc)
}
fmt.Fprint(w, "\n")
if debug > 0 {
printStackRecord(w, r.Stack(), true)
}
}
if tw != nil {
tw.Flush()
}
return b.Flush()
}
func scaleMutexProfile(cnt int64, ns float64) (int64, float64) {
period := runtime.SetMutexProfileFraction(-1)
return cnt * int64(period), ns * float64(period)
}
func runtime_cyclesPerSecond() int64