2018-03-16 2:16 GMT-07:00 Jérôme Champion <champ...@gmail.com>:
> Any race is a bug. When there is a race, the compiler is free to do whatever
> it wants.
This is a false statement; whether or not a race constitutes a bug
depends on the encapsulating protocol. Consider the following:
package main
import (
"fmt"
"sync"
"sync/atomic"
)
var wg sync.WaitGroup
type Spinlock struct {
state uint32
}
func (s *Spinlock) Lock() {
for atomic.SwapUint32(&s.state, 1) == 1 {
}
}
func (s *Spinlock) Unlock() {
atomic.StoreUint32(&s.state, 0)
}
func locker(s *Spinlock, i int) {
defer wg.Done()
s.Lock()
fmt.Printf("Locker %d acquired lock\n", i)
s.Unlock()
}
func main() {
s := &Spinlock{}
for i := 0; i < 10; i++ {
wg.Add(1)
go locker(s, i)
}
wg.Wait()
}
This program does not have deterministic output because each goroutine
races to acquire the lock, and which gets it first relies on
scheduling, which is effectively stoachastic. (Playground caches
output, so no use illustrating it there.) Despite this, the program
compiles just fine and behaves correctly for any reasonable definition
of correct.
I recognize this is not the issue mentioned in OP, but hopefully it's
clear that this is not just a semantics argument (race doesn't just
mean "only things the race detector can find") and that the statement
"any race is a bug" is false. This race only constitutes a bug when
the requirements of this program require deterministic output.
--dho
> What do you want to do? Do you want to println before or after
> cancelContext? In your example, println could even be executed during
> cancelContext!
> Your example is not enough, such program :
> https://play.golang.org/p/KJsYwu-ivjb would fix your problem, but I don't
> think that's what you asked for :)
>
>
> Le vendredi 16 mars 2018 03:11:49 UTC+1, Anmol Sethi a écrit :
>>
>> https://play.golang.org/p/82Um1jSntBo
>>
>> Please run with the race detector to see the race.
>>
>> This race condition arises because private variables are read via
>> reflection by the fmt package. Is there any elegant way to avoid such a
>> race?
>>
>> --
>> Best,
>> Anmol
>>
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