What steps will reproduce the problem?
1. go run -race the following program:
http://play.golang.org/p/8ju-c1opip
package main
import (
"log"
"math"
"sync"
//"time"
)
type T struct {
Type string
Field string
}
type U struct {
Arg string
}
func main() {
args := []T{
{Type: "constant", Field: "A"},
{Type: "constant", Field: "B"},
{Type: "constant", Field: "C"},
{Type: "constant", Field: "D"},
{Type: "constant", Field: "E"},
{Type: "constant", Field: "F"},
{Type: "constant", Field: "G"},
{Type: "constant", Field: "H"},
}
wg := new(sync.WaitGroup)
wg.Add(len(args))
for _, arg := range args {
log.Printf("doing arg: %+v", arg)
local := U{Arg: arg.Field}
go func() {
defer wg.Done()
_ = busy()
log.Printf("%+v", local)
if arg.Type != "constant" {
log.Printf("argh!")
}
}()
//time.Sleep(100 * time.Millisecond)
}
wg.Wait()
}
func busy() float64 {
x := 0.0
for i := 1; i < 1000000; i++ {
x += math.Log(float64(i))
}
return x
}
What is the expected output? What do you see instead?
Expected:
2014/07/02 23:40:47 doing arg: {Type:constant Field:A}
2014/07/02 23:40:47 doing arg: {Type:constant Field:B}
2014/07/02 23:40:47 doing arg: {Type:constant Field:C}
2014/07/02 23:40:47 doing arg: {Type:constant Field:D}
2014/07/02 23:40:47 doing arg: {Type:constant Field:E}
2014/07/02 23:40:47 doing arg: {Type:constant Field:F}
2014/07/02 23:40:47 doing arg: {Type:constant Field:G}
2014/07/02 23:40:47 doing arg: {Type:constant Field:H}
==================
WARNING: DATA RACE
Write by main goroutine:
main.main()
/tmp/w.go:32 +0x33b
Previous read by goroutine 5:
main.func·001()
/tmp/w.go:39 +0x15f
Goroutine 5 (finished) created at:
main.main()
/tmp/w.go:42 +0x532
==================
2014/07/02 23:40:47 {Arg:A}
2014/07/02 23:40:47 {Arg:B}
2014/07/02 23:40:47 {Arg:C}
2014/07/02 23:40:47 {Arg:D}
2014/07/02 23:40:47 {Arg:E}
2014/07/02 23:40:47 {Arg:F}
2014/07/02 23:40:47 {Arg:G}
2014/07/02 23:40:47 {Arg:H}
Instead:
2014/07/02 23:40:47 doing arg: {Type:constant Field:A}
2014/07/02 23:40:47 doing arg: {Type:constant Field:B}
2014/07/02 23:40:47 doing arg: {Type:constant Field:C}
2014/07/02 23:40:47 doing arg: {Type:constant Field:D}
2014/07/02 23:40:47 doing arg: {Type:constant Field:E}
2014/07/02 23:40:47 doing arg: {Type:constant Field:F}
2014/07/02 23:40:47 doing arg: {Type:constant Field:G}
2014/07/02 23:40:47 doing arg: {Type:constant Field:H}
2014/07/02 23:40:47 {Arg:A}
2014/07/02 23:40:47 {Arg:B}
2014/07/02 23:40:47 {Arg:C}
2014/07/02 23:40:47 {Arg:D}
2014/07/02 23:40:47 {Arg:E}
2014/07/02 23:40:47 {Arg:F}
2014/07/02 23:40:47 {Arg:G}
2014/07/02 23:40:47 {Arg:H}
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