[vlc-devel] [PATCH 1/6] os2: implement vlc_once()

[KO Myung-Hun]

Romain Vimont wrote:
> On Thu, Apr 05, 2018 at 08:40:57PM +0900, KO Myung-Hun wrote:
>> And if it is 1, it's guaranteed that cb() has been completed. Because
>> function call acts as memory barrier and it will not be reordered
> 
> At least in theory, I think that a function call does not act as a
> memory barrier.
> 

Ok, at least compiler barrier according to your link.

> And even if it did, so that cb() is guaranteed to be completed in the
> first thread, the changes applied by cb() are not guaranteed to be
> visible from the second thread (cache coherence).
> 
> <https://stackoverflow.com/questions/10698253/is-function-call-an-effective-memory-barrier-for-modern-platforms>

For the second thread to use the changes by cb(), it should see done
first. And it can see done with 1, it should be able to see the changes
by cb(). After all, is it possible that changes of cb are not applied
but done is applied to each cache ?


-- 
KO Myung-Hun

Using Mozilla SeaMonkey 2.7.2
Under OS/2 Warp 4 for Korean with FixPak #15
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