fmt: make benchmarks parallel

This seems to be the best target to benchmark sync.Pool changes.

This is resend of cl/49910043 which was LGTMed by
TBR=bradfitz

R=golang-codereviews
CC=golang-codereviews
https://golang.org/cl/50140045

diff --git a/src/pkg/fmt/fmt_test.go b/src/pkg/fmt/fmt_test.go
index 444297d9265b02bf69a4455cee175fddea0673f8..971e8a38147c39a86fcbbab904a53543627c405e 100644 (file)
--- a/src/pkg/fmt/fmt_test.go
+++ b/src/pkg/fmt/fmt_test.go
@@ -11,6 +11,7 @@ import (
        "math"
        "runtime"
        "strings"
+       "sync/atomic"
        "testing"
        "time"
        "unicode"
@@ -606,46 +607,66 @@ func TestReorder(t *testing.T) {
 }
 
 func BenchmarkSprintfEmpty(b *testing.B) {
-       for i := 0; i < b.N; i++ {
+       benchmarkSprintf(b, func(buf *bytes.Buffer) {
                Sprintf("")
-       }
+       })
 }
 
 func BenchmarkSprintfString(b *testing.B) {
-       for i := 0; i < b.N; i++ {
+       benchmarkSprintf(b, func(buf *bytes.Buffer) {
                Sprintf("%s", "hello")
-       }
+       })
 }
 
 func BenchmarkSprintfInt(b *testing.B) {
-       for i := 0; i < b.N; i++ {
+       benchmarkSprintf(b, func(buf *bytes.Buffer) {
                Sprintf("%d", 5)
-       }
+       })
 }
 
 func BenchmarkSprintfIntInt(b *testing.B) {
-       for i := 0; i < b.N; i++ {
+       benchmarkSprintf(b, func(buf *bytes.Buffer) {
                Sprintf("%d %d", 5, 6)
-       }
+       })
 }
 
 func BenchmarkSprintfPrefixedInt(b *testing.B) {
-       for i := 0; i < b.N; i++ {
+       benchmarkSprintf(b, func(buf *bytes.Buffer) {
                Sprintf("This is some meaningless prefix text that needs to be scanned %d", 6)
-       }
+       })
 }
 
 func BenchmarkSprintfFloat(b *testing.B) {
-       for i := 0; i < b.N; i++ {
+       benchmarkSprintf(b, func(buf *bytes.Buffer) {
                Sprintf("%g", 5.23184)
-       }
+       })
 }
 
 func BenchmarkManyArgs(b *testing.B) {
-       var buf bytes.Buffer
-       for i := 0; i < b.N; i++ {
+       benchmarkSprintf(b, func(buf *bytes.Buffer) {
                buf.Reset()
-               Fprintf(&buf, "%2d/%2d/%2d %d:%d:%d %s %s\n", 3, 4, 5, 11, 12, 13, "hello", "world")
+               Fprintf(buf, "%2d/%2d/%2d %d:%d:%d %s %s\n", 3, 4, 5, 11, 12, 13, "hello", "world")
+       })
+}
+
+func benchmarkSprintf(b *testing.B, f func(buf *bytes.Buffer)) {
+       const CallsPerSched = 1000
+       procs := runtime.GOMAXPROCS(-1)
+       N := int32(b.N / CallsPerSched)
+       c := make(chan bool, procs)
+       for p := 0; p < procs; p++ {
+               go func() {
+                       var buf bytes.Buffer
+                       for atomic.AddInt32(&N, -1) >= 0 {
+                               for g := 0; g < CallsPerSched; g++ {
+                                       f(&buf)
+                               }
+                       }
+                       c <- true
+               }()
+       }
+       for p := 0; p < procs; p++ {
+               <-c
        }
 }