On Sun, May 5, 2019 at 12:45 PM Louki Sumirniy
<louki.sumirniy.stal...@gmail.com> wrote:
>
> https://play.golang.org/p/5KwJQcTsUPg
>
> I fixed it.
Not really. You've introduced a data race.
jnml@4670:~/src/tmp> cat main.go
package main
type WaitGroup struct {
workers int
ops chan int
}
func New() *WaitGroup {
wg := new(WaitGroup)
return wg
}
func startWait(wg *WaitGroup) {
wg.ops = make(chan int)
go func() {
done := false
for !done {
select {
case op := <-wg.ops:
wg.workers += op
if wg.workers < 1 {
done = true
close(wg.ops)
}
}
}
}()
}
// Add adds a non-negative number
func (wg *WaitGroup) Add(delta int) {
if delta < 0 {
return
}
if wg.ops == nil {
startWait(wg)
}
wg.ops <- delta
}
// Done subtracts a non-negative value from the workers count
func (wg *WaitGroup) Done(delta int) {
if delta < 0 {
return
}
wg.ops <- -delta
}
// Wait blocks until the waitgroup decrements to zero
func (wg *WaitGroup) Wait() {
for {
if wg.workers < 1 {
break
}
op, ok := <-wg.ops
if !ok {
break
} else {
wg.ops <- op
}
}
}
var wg = New()
func main() {
for i := 0; i < 2; i++ {
wg.Add(1)
go f()
}
wg.Wait()
}
func f() {
defer wg.Done(1)
for i := 0; i < 2; i++ {
wg.Add(1)
go g()
}
}
func g() { wg.Done(1) }
jnml@4670:~/src/tmp> go run -race main.go
==================
WARNING: DATA RACE
Read at 0x00c00008a000 by main goroutine:
main.(*WaitGroup).Wait()
/home/jnml/src/tmp/main.go:53 +0x6f
main.main()
/home/jnml/src/tmp/main.go:72 +0x104
Previous write at 0x00c00008a000 by goroutine 5:
main.startWait.func1()
/home/jnml/src/tmp/main.go:21 +0xbb
Goroutine 5 (running) created at:
main.startWait()
/home/jnml/src/tmp/main.go:16 +0x9e
main.main()
/home/jnml/src/tmp/main.go:37 +0xdf
==================
Found 1 data race(s)
exit status 66
jnml@4670:~/src/tmp>
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