runtime: one strange result for printing different goroutine IDs by runtime.stack method

[TodLiuMeng]

What version of Go are you using (go version)?

go version go1.13 windows/amd64

Does this issue reproduce with the latest release?

What operating system and processor architecture are you using (go env)?

go env Output

$ go env

What did you do?

func GetGoroutineID() uint64 {
	b := make([]byte, 1024)
	runtime.Stack(b, false)
	println(string(b))
	b = bytes.TrimPrefix(b, []byte("goroutine "))
	b = b[:bytes.IndexByte(b, ' ')]
	n, _ := strconv.ParseUint(string(b), 10, 64)
	return n
}

func main() {
	go func() {
		println(1, runTime.GetGoroutineID())
	}()
	time.Sleep(1 * time.Second)
	go println(2, runTime.GetGoroutineID())
	time.Sleep(1 * time.Second)
	println(3, runTime.GetGoroutineID())
	time.Sleep(1 * time.Second)
}

What did you expect to see?

1,goroutineID1
2,goroutineID2
3,1

What did you see instead?

1,goroutineID1
2,1
3,1

More output details:

goroutine 5 [running]:
SimpleGoRepo/src/runTime.GetGoroutineID(0x0)
	D:/GOPATH/src/SimpleGoRepo/src/runTime/routine_id.go:36 +0x85
main.main.func1()
	D:/GOPATH/src/SimpleGoRepo/main.go:186 +0x29
created by main.main
	D:/GOPATH/src/SimpleGoRepo/main.go:185 +0x40
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
1 5

goroutine 1 [running]:
SimpleGoRepo/src/runTime.GetGoroutineID(0x3b9aca00)
	D:/GOPATH/src/SimpleGoRepo/src/runTime/routine_id.go:36 +0x85
main.main()
	D:/GOPATH/src/SimpleGoRepo/main.go:189 +0x52
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
2 1
goroutine 1 [running]:
SimpleGoRepo/src/runTime.GetGoroutineID(0x3b9aca00)
	D:/GOPATH/src/SimpleGoRepo/src/runTime/routine_id.go:36 +0x85
main.main()
	D:/GOPATH/src/SimpleGoRepo/main.go:191 +0x8e
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
3 1

[biter777]

https://play.golang.org/p/iPZaigoakwd its the same:

goroutine 5 [running]:
main.GetGoroutineID(0x0, 0x0)
/tmp/sandbox409247425/prog.go:12 +0x80
main.main.func1()
/tmp/sandbox409247425/prog.go:22 +0x20
created by main.main
/tmp/sandbox409247425/prog.go:21 +0x40

1 5
goroutine 1 [running]:
main.GetGoroutineID(0x3b9aca00, 0x0)
/tmp/sandbox409247425/prog.go:12 +0x80
main.main()
/tmp/sandbox409247425/prog.go:25 +0x80

2 1
goroutine 1 [running]:
main.GetGoroutineID(0x3b9aca00, 0x0)
/tmp/sandbox409247425/prog.go:12 +0x80
main.main()
/tmp/sandbox409247425/prog.go:27 +0x100

3 1

[seankhliao]

the arguments to the goroutine are evaluated before being passed to the function/goroutine,

in this case GetGoroutineID is being called from main, before the result is passed to println which is run in the goroutine

[ianlancetaylor]

Working as expected.