And how about this one. Also no guarantees to always print 1?
package main
import "fmt"
import "sync/atomic"
import "runtime"
func main() {
runtime.GOMAXPROCS(1)
var a, b int32 = 0, 0
go func() {
atomic.AddInt32(&a, 1)
atomic.AddInt32(&b, 1)
}()
for {
if n := atomic.LoadInt32(&b); n == 1 {
fmt.Println(atomic.LoadInt32(&a)) // always print 1?
break
}
runtime.Gosched()
}
}
On Sunday, October 22, 2017 at 9:59:11 AM UTC-4, T L wrote:
>
> So the Go 1 memory model really make no guarantees that the following
> program will print 1?
>
> package main
>
> import "fmt"
> import "sync/atomic"
> import "runtime"
>
> func main() {
> runtime.GOMAXPROCS(1)
> var a, b int32 = 0, 0
>
> go func() {
> a = 1
> atomic.AddInt32(&b, 1)
> }()
>
> for {
> if n := atomic.LoadInt32(&b); n == 1 {
> fmt.Println(a) // always print 1?
> break
> }
> runtime.Gosched()
> }
>
> On Sunday, October 22, 2017 at 6:33:42 AM UTC-4, T L wrote:
>>
>>
>>
>> On Sunday, October 22, 2017 at 5:55:54 AM UTC-4, Jan Mercl wrote:
>>>
>>> On Sun, Oct 22, 2017 at 9:19 AM T L <tapi...@gmail.com> wrote:
>>>
>>> > why?
>>>
>>> The OP code with line numbes: https://play.golang.org/p/4fmiWqDDc1
>>>
>>> The main goroutine busy loops at lines 15-20. Because of that the
>>> goroutine at line 10 may never run and thus line 17 may never get executed.
>>> If so, line 18 and thus also lines 27 and above may also never get executed.
>>>
>>> --
>>>
>>> -j
>>>
>>
>> Aha, yes, if GOMAXPROCS is 1, then the main goroutine will become greedy.
>>
>>
>
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