// Copyright 2009 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 testing
import (
"context"
"flag"
"fmt"
"internal/sysinfo"
"io"
"math"
"os"
"runtime"
"slices"
"strconv"
"strings"
"sync"
"sync/atomic"
"time"
"unicode"
)
func initBenchmarkFlags() {
matchBenchmarks = flag.String("test.bench", "", "run only benchmarks matching `regexp`")
benchmarkMemory = flag.Bool("test.benchmem", false, "print memory allocations for benchmarks")
flag.Var(&benchTime, "test.benchtime", "run each benchmark for duration `d` or N times if `d` is of the form Nx")
}
var (
matchBenchmarks *string
benchmarkMemory *bool
benchTime = durationOrCountFlag{d: 1 * time.Second} // changed during test of testing package
)
type durationOrCountFlag struct {
d time.Duration
n int
allowZero bool
}
func (f *durationOrCountFlag) String() string {
if f.n > 0 {
return fmt.Sprintf("%dx", f.n)
}
return f.d.String()
}
func (f *durationOrCountFlag) Set(s string) error {
if strings.HasSuffix(s, "x") {
n, err := strconv.ParseInt(s[:len(s)-1], 10, 0)
if err != nil || n < 0 || (!f.allowZero && n == 0) {
return fmt.Errorf("invalid count")
}
*f = durationOrCountFlag{n: int(n)}
return nil
}
d, err := time.ParseDuration(s)
if err != nil || d < 0 || (!f.allowZero && d == 0) {
return fmt.Errorf("invalid duration")
}
*f = durationOrCountFlag{d: d}
return nil
}
// Global lock to ensure only one benchmark runs at a time.
var benchmarkLock sync.Mutex
// Used for every benchmark for measuring memory.
var memStats runtime.MemStats
// InternalBenchmark is an internal type but exported because it is cross-package;
// it is part of the implementation of the "go test" command.
type InternalBenchmark struct {
Name string
F func(b *B)
}
// B is a type passed to [Benchmark] functions to manage benchmark
// timing and control the number of iterations.
//
// A benchmark ends when its Benchmark function returns or calls any of the methods
// FailNow, Fatal, Fatalf, SkipNow, Skip, or Skipf. Those methods must be called
// only from the goroutine running the Benchmark function.
// The other reporting methods, such as the variations of Log and Error,
// may be called simultaneously from multiple goroutines.
//
// Like in tests, benchmark logs are accumulated during execution
// and dumped to standard output when done. Unlike in tests, benchmark logs
// are always printed, so as not to hide output whose existence may be
// affecting benchmark results.
type B struct {
common
importPath string // import path of the package containing the benchmark
bstate *benchState
N int
previousN int // number of iterations in the previous run
previousDuration time.Duration // total duration of the previous run
benchFunc func(b *B)
benchTime durationOrCountFlag
bytes int64
missingBytes bool // one of the subbenchmarks does not have bytes set.
timerOn bool
showAllocResult bool
result BenchmarkResult
parallelism int // RunParallel creates parallelism*GOMAXPROCS goroutines
// The initial states of memStats.Mallocs and memStats.TotalAlloc.
startAllocs uint64
startBytes uint64
// The net total of this test after being run.
netAllocs uint64
netBytes uint64
// Extra metrics collected by ReportMetric.
extra map[string]float64
// For Loop() to be executed in benchFunc.
// Loop() has its own control logic that skips the loop scaling.
// See issue #61515.
loopN int
}
// StartTimer starts timing a test. This function is called automatically
// before a benchmark starts, but it can also be used to resume timing after
// a call to [B.StopTimer].
func (b *B) StartTimer() {
if !b.timerOn {
runtime.ReadMemStats(&memStats)
b.startAllocs = memStats.Mallocs
b.startBytes = memStats.TotalAlloc
b.start = highPrecisionTimeNow()
b.timerOn = true
}
}
// StopTimer stops timing a test. This can be used to pause the timer
// while performing steps that you don't want to measure.
func (b *B) StopTimer() {
if b.timerOn {
b.duration += highPrecisionTimeSince(b.start)
runtime.ReadMemStats(&memStats)
b.netAllocs += memStats.Mallocs - b.startAllocs
b.netBytes += memStats.TotalAlloc - b.startBytes
b.timerOn = false
}
}
// ResetTimer zeroes the elapsed benchmark time and memory allocation counters
// and deletes user-reported metrics.
// It does not affect whether the timer is running.
func (b *B) ResetTimer() {
if b.extra == nil {
// Allocate the extra map before reading memory stats.
// Pre-size it to make more allocation unlikely.
b.extra = make(map[string]float64, 16)
} else {
clear(b.extra)
}
if b.timerOn {
runtime.ReadMemStats(&memStats)
b.startAllocs = memStats.Mallocs
b.startBytes = memStats.TotalAlloc
b.start = highPrecisionTimeNow()
}
b.duration = 0
b.netAllocs = 0
b.netBytes = 0
}
// SetBytes records the number of bytes processed in a single operation.
// If this is called, the benchmark will report ns/op and MB/s.
func (b *B) SetBytes(n int64) { b.bytes = n }
// ReportAllocs enables malloc statistics for this benchmark.
// It is equivalent to setting -test.benchmem, but it only affects the
// benchmark function that calls ReportAllocs.
func (b *B) ReportAllocs() {
b.showAllocResult = true
}
// runN runs a single benchmark for the specified number of iterations.
func (b *B) runN(n int) {
benchmarkLock.Lock()
defer benchmarkLock.Unlock()
ctx, cancelCtx := context.WithCancel(context.Background())
defer func() {
b.runCleanup(normalPanic)
b.checkRaces()
}()
// Try to get a comparable environment for each run
// by clearing garbage from previous runs.
runtime.GC()
b.resetRaces()
b.N = n
b.loopN = 0
b.ctx = ctx
b.cancelCtx = cancelCtx
b.parallelism = 1
b.ResetTimer()
b.StartTimer()
b.benchFunc(b)
b.StopTimer()
b.previousN = n
b.previousDuration = b.duration
}
// run1 runs the first iteration of benchFunc. It reports whether more
// iterations of this benchmarks should be run.
func (b *B) run1() bool {
if bstate := b.bstate; bstate != nil {
// Extend maxLen, if needed.
if n := len(b.name) + bstate.extLen + 1; n > bstate.maxLen {
bstate.maxLen = n + 8 // Add additional slack to avoid too many jumps in size.
}
}
go func() {
// Signal that we're done whether we return normally
// or by FailNow's runtime.Goexit.
defer func() {
b.signal <- true
}()
b.runN(1)
}()
<-b.signal
if b.failed {
fmt.Fprintf(b.w, "%s--- FAIL: %s\n%s", b.chatty.prefix(), b.name, b.output)
return false
}
// Only print the output if we know we are not going to proceed.
// Otherwise it is printed in processBench.
b.mu.RLock()
finished := b.finished
b.mu.RUnlock()
if b.hasSub.Load() || finished {
tag := "BENCH"
if b.skipped {
tag = "SKIP"
}
if b.chatty != nil && (len(b.output) > 0 || finished) {
b.trimOutput()
fmt.Fprintf(b.w, "%s--- %s: %s\n%s", b.chatty.prefix(), tag, b.name, b.output)
}
return false
}
return true
}
var labelsOnce sync.Once
// run executes the benchmark in a separate goroutine, including all of its
// subbenchmarks. b must not have subbenchmarks.
func (b *B) run() {
labelsOnce.Do(func() {
fmt.Fprintf(b.w, "goos: %s\n", runtime.GOOS)
fmt.Fprintf(b.w, "goarch: %s\n", runtime.GOARCH)
if b.importPath != "" {
fmt.Fprintf(b.w, "pkg: %s\n", b.importPath)
}
if cpu := sysinfo.CPUName(); cpu != "" {
fmt.Fprintf(b.w, "cpu: %s\n", cpu)
}
})
if b.bstate != nil {
// Running go test --test.bench
b.bstate.processBench(b) // Must call doBench.
} else {
// Running func Benchmark.
b.doBench()
}
}
func (b *B) doBench() BenchmarkResult {
go b.launch()
<-b.signal
return b.result
}
func predictN(goalns int64, prevIters int64, prevns int64, last int64) int {
if prevns == 0 {
// Round up to dodge divide by zero. See https://go.dev/issue/70709.
prevns = 1
}
// Order of operations matters.
// For very fast benchmarks, prevIters ~= prevns.
// If you divide first, you get 0 or 1,
// which can hide an order of magnitude in execution time.
// So multiply first, then divide.
n := goalns * prevIters / prevns
// Run more iterations than we think we'll need (1.2x).
n += n / 5
// Don't grow too fast in case we had timing errors previously.
n = min(n, 100*last)
// Be sure to run at least one more than last time.
n = max(n, last+1)
// Don't run more than 1e9 times. (This also keeps n in int range on 32 bit platforms.)
n = min(n, 1e9)
return int(n)
}
// launch launches the benchmark function. It gradually increases the number
// of benchmark iterations until the benchmark runs for the requested benchtime.
// launch is run by the doBench function as a separate goroutine.
// run1 must have been called on b.
func (b *B) launch() {
// Signal that we're done whether we return normally
// or by FailNow's runtime.Goexit.
defer func() {
b.signal <- true
}()
// b.Loop does its own ramp-up logic so we just need to run it once.
// If b.loopN is non zero, it means b.Loop has already run.
if b.loopN == 0 {
// Run the benchmark for at least the specified amount of time.
if b.benchTime.n > 0 {
// We already ran a single iteration in run1.
// If -benchtime=1x was requested, use that result.
// See https://golang.org/issue/32051.
if b.benchTime.n > 1 {
b.runN(b.benchTime.n)
}
} else {
d := b.benchTime.d
for n := int64(1); !b.failed && b.duration < d && n < 1e9; {
last := n
// Predict required iterations.
goalns := d.Nanoseconds()
prevIters := int64(b.N)
n = int64(predictN(goalns, prevIters, b.duration.Nanoseconds(), last))
b.runN(int(n))
}
}
}
b.result = BenchmarkResult{b.N, b.duration, b.bytes, b.netAllocs, b.netBytes, b.extra}
}
// Elapsed returns the measured elapsed time of the benchmark.
// The duration reported by Elapsed matches the one measured by
// [B.StartTimer], [B.StopTimer], and [B.ResetTimer].
func (b *B) Elapsed() time.Duration {
d := b.duration
if b.timerOn {
d += highPrecisionTimeSince(b.start)
}
return d
}
// ReportMetric adds "n unit" to the reported benchmark results.
// If the metric is per-iteration, the caller should divide by b.N,
// and by convention units should end in "/op".
// ReportMetric overrides any previously reported value for the same unit.
// ReportMetric panics if unit is the empty string or if unit contains
// any whitespace.
// If unit is a unit normally reported by the benchmark framework itself
// (such as "allocs/op"), ReportMetric will override that metric.
// Setting "ns/op" to 0 will suppress that built-in metric.
func (b *B) ReportMetric(n float64, unit string) {
if unit == "" {
panic("metric unit must not be empty")
}
if strings.IndexFunc(unit, unicode.IsSpace) >= 0 {
panic("metric unit must not contain whitespace")
}
b.extra[unit] = n
}
func (b *B) stopOrScaleBLoop() bool {
timeElapsed := highPrecisionTimeSince(b.start)
if timeElapsed >= b.benchTime.d {
// Stop the timer so we don't count cleanup time
b.StopTimer()
return false
}
// Loop scaling
goalns := b.benchTime.d.Nanoseconds()
prevIters := int64(b.N)
b.N = predictN(goalns, prevIters, timeElapsed.Nanoseconds(), prevIters)
b.loopN++
return true
}
func (b *B) loopSlowPath() bool {
if b.loopN == 0 {
// If it's the first call to b.Loop() in the benchmark function.
// Allows more precise measurement of benchmark loop cost counts.
// Also initialize b.N to 1 to kick start loop scaling.
b.N = 1
b.loopN = 1
b.ResetTimer()
return true
}
// Handles fixed iterations case
if b.benchTime.n > 0 {
if b.N < b.benchTime.n {
b.N = b.benchTime.n
b.loopN++
return true
}
b.StopTimer()
return false
}
// Handles fixed time case
return b.stopOrScaleBLoop()
}
// Loop returns true as long as the benchmark should continue running.
//
// A typical benchmark is structured like:
//
// func Benchmark(b *testing.B) {
// ... setup ...
// for b.Loop() {
// ... code to measure ...
// }
// ... cleanup ...
// }
//
// Loop resets the benchmark timer the first time it is called in a benchmark,
// so any setup performed prior to starting the benchmark loop does not count
// toward the benchmark measurement. Likewise, when it returns false, it stops
// the timer so cleanup code is not measured.
//
// The compiler never optimizes away calls to functions within the body of a
// "for b.Loop() { ... }" loop. This prevents surprises that can otherwise occur
// if the compiler determines that the result of a benchmarked function is
// unused. The loop must be written in exactly this form, and this only applies
// to calls syntactically between the curly braces of the loop. Optimizations
// are performed as usual in any functions called by the loop.
//
// After Loop returns false, b.N contains the total number of iterations that
// ran, so the benchmark may use b.N to compute other average metrics.
//
// Prior to the introduction of Loop, benchmarks were expected to contain an
// explicit loop from 0 to b.N. Benchmarks should either use Loop or contain a
// loop to b.N, but not both. Loop offers more automatic management of the
// benchmark timer, and runs each benchmark function only once per measurement,
// whereas b.N-based benchmarks must run the benchmark function (and any
// associated setup and cleanup) several times.
func (b *B) Loop() bool {
if b.loopN != 0 && b.loopN < b.N {
b.loopN++
return true
}
return b.loopSlowPath()
}
// BenchmarkResult contains the results of a benchmark run.
type BenchmarkResult struct {
N int // The number of iterations.
T time.Duration // The total time taken.
Bytes int64 // Bytes processed in one iteration.
MemAllocs uint64 // The total number of memory allocations.
MemBytes uint64 // The total number of bytes allocated.
// Extra records additional metrics reported by ReportMetric.
Extra map[string]float64
}
// NsPerOp returns the "ns/op" metric.
func (r BenchmarkResult) NsPerOp() int64 {
if v, ok := r.Extra["ns/op"]; ok {
return int64(v)
}
if r.N <= 0 {
return 0
}
return r.T.Nanoseconds() / int64(r.N)
}
// mbPerSec returns the "MB/s" metric.
func (r BenchmarkResult) mbPerSec() float64 {
if v, ok := r.Extra["MB/s"]; ok {
return v
}
if r.Bytes <= 0 || r.T <= 0 || r.N <= 0 {
return 0
}
return (float64(r.Bytes) * float64(r.N) / 1e6) / r.T.Seconds()
}
// AllocsPerOp returns the "allocs/op" metric,
// which is calculated as r.MemAllocs / r.N.
func (r BenchmarkResult) AllocsPerOp() int64 {
if v, ok := r.Extra["allocs/op"]; ok {
return int64(v)
}
if r.N <= 0 {
return 0
}
return int64(r.MemAllocs) / int64(r.N)
}
// AllocedBytesPerOp returns the "B/op" metric,
// which is calculated as r.MemBytes / r.N.
func (r BenchmarkResult) AllocedBytesPerOp() int64 {
if v, ok := r.Extra["B/op"]; ok {
return int64(v)
}
if r.N <= 0 {
return 0
}
return int64(r.MemBytes) / int64(r.N)
}
// String returns a summary of the benchmark results.
// It follows the benchmark result line format from
// https://golang.org/design/14313-benchmark-format, not including the
// benchmark name.
// Extra metrics override built-in metrics of the same name.
// String does not include allocs/op or B/op, since those are reported
// by [BenchmarkResult.MemString].
func (r BenchmarkResult) String() string {
buf := new(strings.Builder)
fmt.Fprintf(buf, "%8d", r.N)
// Get ns/op as a float.
ns, ok := r.Extra["ns/op"]
if !ok {
ns = float64(r.T.Nanoseconds()) / float64(r.N)
}
if ns != 0 {
buf.WriteByte('\t')
prettyPrint(buf, ns, "ns/op")
}
if mbs := r.mbPerSec(); mbs != 0 {
fmt.Fprintf(buf, "\t%7.2f MB/s", mbs)
}
// Print extra metrics that aren't represented in the standard
// metrics.
var extraKeys []string
for k := range r.Extra {
switch k {
case "ns/op", "MB/s", "B/op", "allocs/op":
// Built-in metrics reported elsewhere.
continue
}
extraKeys = append(extraKeys, k)
}
slices.Sort(extraKeys)
for _, k := range extraKeys {
buf.WriteByte('\t')
prettyPrint(buf, r.Extra[k], k)
}
return buf.String()
}
func prettyPrint(w io.Writer, x float64, unit string) {
// Print all numbers with 10 places before the decimal point
// and small numbers with four sig figs. Field widths are
// chosen to fit the whole part in 10 places while aligning
// the decimal point of all fractional formats.
var format string
switch y := math.Abs(x); {
case y == 0 || y >= 999.95:
format = "%10.0f %s"
case y >= 99.995:
format = "%12.1f %s"
case y >= 9.9995:
format = "%13.2f %s"
case y >= 0.99995:
format = "%14.3f %s"
case y >= 0.099995:
format = "%15.4f %s"
case y >= 0.0099995:
format = "%16.5f %s"
case y >= 0.00099995:
format = "%17.6f %s"
default:
format = "%18.7f %s"
}
fmt.Fprintf(w, format, x, unit)
}
// MemString returns r.AllocedBytesPerOp and r.AllocsPerOp in the same format as 'go test'.
func (r BenchmarkResult) MemString() string {
return fmt.Sprintf("%8d B/op\t%8d allocs/op",
r.AllocedBytesPerOp(), r.AllocsPerOp())
}
// benchmarkName returns full name of benchmark including procs suffix.
func benchmarkName(name string, n int) string {
if n != 1 {
return fmt.Sprintf("%s-%d", name, n)
}
return name
}
type benchState struct {
match *matcher
maxLen int // The largest recorded benchmark name.
extLen int // Maximum extension length.
}
// RunBenchmarks is an internal function but exported because it is cross-package;
// it is part of the implementation of the "go test" command.
func RunBenchmarks(matchString func(pat, str string) (bool, error), benchmarks []InternalBenchmark) {
runBenchmarks("", matchString, benchmarks)
}
func runBenchmarks(importPath string, matchString func(pat, str string) (bool, error), benchmarks []InternalBenchmark) bool {
// If no flag was specified, don't run benchmarks.
if len(*matchBenchmarks) == 0 {
return true
}
// Collect matching benchmarks and determine longest name.
maxprocs := 1
for _, procs := range cpuList {
if procs > maxprocs {
maxprocs = procs
}
}
bstate := &benchState{
match: newMatcher(matchString, *matchBenchmarks, "-test.bench", *skip),
extLen: len(benchmarkName("", maxprocs)),
}
var bs []InternalBenchmark
for _, Benchmark := range benchmarks {
if _, matched, _ := bstate.match.fullName(nil, Benchmark.Name); matched {
bs = append(bs, Benchmark)
benchName := benchmarkName(Benchmark.Name, maxprocs)
if l := len(benchName) + bstate.extLen + 1; l > bstate.maxLen {
bstate.maxLen = l
}
}
}
main := &B{
common: common{
name: "Main",
w: os.Stdout,
bench: true,
},
importPath: importPath,
benchFunc: func(b *B) {
for _, Benchmark := range bs {
b.Run(Benchmark.Name, Benchmark.F)
}
},
benchTime: benchTime,
bstate: bstate,
}
if Verbose() {
main.chatty = newChattyPrinter(main.w)
}
main.runN(1)
return !main.failed
}
// processBench runs bench b for the configured CPU counts and prints the results.
func (s *benchState) processBench(b *B) {
for i, procs := range cpuList {
for j := uint(0); j < *count; j++ {
runtime.GOMAXPROCS(procs)
benchName := benchmarkName(b.name, procs)
// If it's chatty, we've already printed this information.
if b.chatty == nil {
fmt.Fprintf(b.w, "%-*s\t", s.maxLen, benchName)
}
// Recompute the running time for all but the first iteration.
if i > 0 || j > 0 {
b = &B{
common: common{
signal: make(chan bool),
name: b.name,
w: b.w,
chatty: b.chatty,
bench: true,
},
benchFunc: b.benchFunc,
benchTime: b.benchTime,
}
b.run1()
}
r := b.doBench()
if b.failed {
// The output could be very long here, but probably isn't.
// We print it all, regardless, because we don't want to trim the reason
// the benchmark failed.
fmt.Fprintf(b.w, "%s--- FAIL: %s\n%s", b.chatty.prefix(), benchName, b.output)
continue
}
results := r.String()
if b.chatty != nil {
fmt.Fprintf(b.w, "%-*s\t", s.maxLen, benchName)
}
if *benchmarkMemory || b.showAllocResult {
results += "\t" + r.MemString()
}
fmt.Fprintln(b.w, results)
// Unlike with tests, we ignore the -chatty flag and always print output for
// benchmarks since the output generation time will skew the results.
if len(b.output) > 0 {
b.trimOutput()
fmt.Fprintf(b.w, "%s--- BENCH: %s\n%s", b.chatty.prefix(), benchName, b.output)
}
if p := runtime.GOMAXPROCS(-1); p != procs {
fmt.Fprintf(os.Stderr, "testing: %s left GOMAXPROCS set to %d\n", benchName, p)
}
if b.chatty != nil && b.chatty.json {
b.chatty.Updatef("", "=== NAME %s\n", "")
}
}
}
}
// If hideStdoutForTesting is true, Run does not print the benchName.
// This avoids a spurious print during 'go test' on package testing itself,
// which invokes b.Run in its own tests (see sub_test.go).
var hideStdoutForTesting = false
// Run benchmarks f as a subbenchmark with the given name. It reports
// whether there were any failures.
//
// A subbenchmark is like any other benchmark. A benchmark that calls Run at
// least once will not be measured itself and will be called once with N=1.
func (b *B) Run(name string, f func(b *B)) bool {
// Since b has subbenchmarks, we will no longer run it as a benchmark itself.
// Release the lock and acquire it on exit to ensure locks stay paired.
b.hasSub.Store(true)
benchmarkLock.Unlock()
defer benchmarkLock.Lock()
benchName, ok, partial := b.name, true, false
if b.bstate != nil {
benchName, ok, partial = b.bstate.match.fullName(&b.common, name)
}
if !ok {
return true
}
var pc [maxStackLen]uintptr
n := runtime.Callers(2, pc[:])
sub := &B{
common: common{
signal: make(chan bool),
name: benchName,
parent: &b.common,
level: b.level + 1,
creator: pc[:n],
w: b.w,
chatty: b.chatty,
bench: true,
},
importPath: b.importPath,
benchFunc: f,
benchTime: b.benchTime,
bstate: b.bstate,
}
if partial {
// Partial name match, like -bench=X/Y matching BenchmarkX.
// Only process sub-benchmarks, if any.
sub.hasSub.Store(true)
}
if b.chatty != nil {
labelsOnce.Do(func() {
fmt.Printf("goos: %s\n", runtime.GOOS)
fmt.Printf("goarch: %s\n", runtime.GOARCH)
if b.importPath != "" {
fmt.Printf("pkg: %s\n", b.importPath)
}
if cpu := sysinfo.CPUName(); cpu != "" {
fmt.Printf("cpu: %s\n", cpu)
}
})
if !hideStdoutForTesting {
if b.chatty.json {
b.chatty.Updatef(benchName, "=== RUN %s\n", benchName)
}
fmt.Println(benchName)
}
}
if sub.run1() {
sub.run()
}
b.add(sub.result)
return !sub.failed
}
// add simulates running benchmarks in sequence in a single iteration. It is
// used to give some meaningful results in case func Benchmark is used in
// combination with Run.
func (b *B) add(other BenchmarkResult) {
r := &b.result
// The aggregated BenchmarkResults resemble running all subbenchmarks as
// in sequence in a single benchmark.
r.N = 1
r.T += time.Duration(other.NsPerOp())
if other.Bytes == 0 {
// Summing Bytes is meaningless in aggregate if not all subbenchmarks
// set it.
b.missingBytes = true
r.Bytes = 0
}
if !b.missingBytes {
r.Bytes += other.Bytes
}
r.MemAllocs += uint64(other.AllocsPerOp())
r.MemBytes += uint64(other.AllocedBytesPerOp())
}
// trimOutput shortens the output from a benchmark, which can be very long.
func (b *B) trimOutput() {
// The output is likely to appear multiple times because the benchmark
// is run multiple times, but at least it will be seen. This is not a big deal
// because benchmarks rarely print, but just in case, we trim it if it's too long.
const maxNewlines = 10
for nlCount, j := 0, 0; j < len(b.output); j++ {
if b.output[j] == '\n' {
nlCount++
if nlCount >= maxNewlines {
b.output = append(b.output[:j], "\n\t... [output truncated]\n"...)
break
}
}
}
}
// A PB is used by RunParallel for running parallel benchmarks.
type PB struct {
globalN *atomic.Uint64 // shared between all worker goroutines iteration counter
grain uint64 // acquire that many iterations from globalN at once
cache uint64 // local cache of acquired iterations
bN uint64 // total number of iterations to execute (b.N)
}
// Next reports whether there are more iterations to execute.
func (pb *PB) Next() bool {
if pb.cache == 0 {
n := pb.globalN.Add(pb.grain)
if n <= pb.bN {
pb.cache = pb.grain
} else if n < pb.bN+pb.grain {
pb.cache = pb.bN + pb.grain - n
} else {
return false
}
}
pb.cache--
return true
}
// RunParallel runs a benchmark in parallel.
// It creates multiple goroutines and distributes b.N iterations among them.
// The number of goroutines defaults to GOMAXPROCS. To increase parallelism for
// non-CPU-bound benchmarks, call [B.SetParallelism] before RunParallel.
// RunParallel is usually used with the go test -cpu flag.
//
// The body function will be run in each goroutine. It should set up any
// goroutine-local state and then iterate until pb.Next returns false.
// It should not use the [B.StartTimer], [B.StopTimer], or [B.ResetTimer] functions,
// because they have global effect. It should also not call [B.Run].
//
// RunParallel reports ns/op values as wall time for the benchmark as a whole,
// not the sum of wall time or CPU time over each parallel goroutine.
func (b *B) RunParallel(body func(*PB)) {
if b.N == 0 {
return // Nothing to do when probing.
}
// Calculate grain size as number of iterations that take ~100µs.
// 100µs is enough to amortize the overhead and provide sufficient
// dynamic load balancing.
grain := uint64(0)
if b.previousN > 0 && b.previousDuration > 0 {
grain = 1e5 * uint64(b.previousN) / uint64(b.previousDuration)
}
if grain < 1 {
grain = 1
}
// We expect the inner loop and function call to take at least 10ns,
// so do not do more than 100µs/10ns=1e4 iterations.
if grain > 1e4 {
grain = 1e4
}
var n atomic.Uint64
numProcs := b.parallelism * runtime.GOMAXPROCS(0)
var wg sync.WaitGroup
wg.Add(numProcs)
for p := 0; p < numProcs; p++ {
go func() {
defer wg.Done()
pb := &PB{
globalN: &n,
grain: grain,
bN: uint64(b.N),
}
body(pb)
}()
}
wg.Wait()
if n.Load() <= uint64(b.N) && !b.Failed() {
b.Fatal("RunParallel: body exited without pb.Next() == false")
}
}
// SetParallelism sets the number of goroutines used by [B.RunParallel] to p*GOMAXPROCS.
// There is usually no need to call SetParallelism for CPU-bound benchmarks.
// If p is less than 1, this call will have no effect.
func (b *B) SetParallelism(p int) {
if p >= 1 {
b.parallelism = p
}
}
// Benchmark benchmarks a single function. It is useful for creating
// custom benchmarks that do not use the "go test" command.
//
// If f depends on testing flags, then [Init] must be used to register
// those flags before calling Benchmark and before calling [flag.Parse].
//
// If f calls Run, the result will be an estimate of running all its
// subbenchmarks that don't call Run in sequence in a single benchmark.
func Benchmark(f func(b *B)) BenchmarkResult {
b := &B{
common: common{
signal: make(chan bool),
w: discard{},
},
benchFunc: f,
benchTime: benchTime,
}
if b.run1() {
b.run()
}
return b.result
}
type discard struct{}
func (discard) Write(b []byte) (n int, err error) { return len(b), nil }