Hi,
I did a quiz recently, but I'm having problem with the answer.
Quiz: https://github.com/smallnest/go-concurrent-quiz#-quiz-4
package doublecheck
import (
"sync"
)
type Once struct {
m sync.Mutex
done uint32
}
func (o *Once) Do(f func()) {
if o.done == 1 {
return
}
o.m.Lock()
defer o.m.Unlock()
if o.done == 0 {
o.done = 1
f()
}
}
Question
- A: can't compile
- B: can run that implemented the singleton pattern correctly
- C: can run but has not implemented the singleton pattern, function f
may run multi times.
- D: programms will be panic when use this Once concurrently.
Some other people and I think the answer is B, but the author says the
answer is C.
We think this implements happen-before, but the author doesn't think so.
Can anyone help to explain this?
Thanks!
<https://github.com/smallnest/go-concurrent-quiz#-quiz-5>
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