Hi,
I still don't understand this issue completely.
Sure, the call to *wg.Done()* will "happen before" *wg.Wait()* finishes,
but the assignment *"result = &foo{1}"* might still happen concurrently.
I think the problem is the semantics of the *defer* and the discussion is
reduced completely to the question: is the assignment *"result = &foo{1}"*
going
to *happen before" the deferred called to *"wg.Done()"*?
I don't see any occurrence of 'defer' in https://golang.org/ref/mem nor a
proper description in https://golang.org/ref/spec#Defer_statements, so I
feel inclined to conclude this behavior is undefined by the spec.
Daniel.
On Tuesday, August 23, 2016 at 3:23:27 PM UTC+2, Ian Lance Taylor wrote:
>
> On Tue, Aug 23, 2016 at 3:14 AM, Yulrizka <yulr...@gmail.com <javascript:>>
> wrote:
> >
> > But the case here is indeed as Marvin explained, There is race
> condition.
> > But in my example, I make sure that wg done is to protect result pointer
> > before calling it to caller.
> >
> > with this structure some one could easily introduce a race condition if
> he
> > tried to access the result pointer.
> >
> > What I would like to understand if there is case that my snippet causes
> race
> > condition.
> >
> > This is my understanding.
> > 1. Heap memory is shared between go rountine in the same process
> > 2. main routine create a pointer to some struct on the heap (initially
> nil)
> > 3. the go routine allocate memory on the heap for the `foo` struct
> > 4. the go routine assign main's result pointer
> > 5. wg.Done() ensure that step 4 is done before it released
> > 6. process will always returns value generated by the go routine.
> >
> > And I would like to make sure that my understanding of heap is correct.
> That
> > is shared per process and there are no heap copying between go routine.
>
> That is correct.
>
> There is no race in the original program you sent because the wg.Done
> acts as a store-release and the wg.Wait acts as a load-acquire.
>
> Ian
>
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