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

Rémi Denis-Courmont remi at remlab.net
Sat Apr 7 19:14:49 CEST 2018

Le lauantaina 7. huhtikuuta 2018, 19.06.07 EEST KO Myung-Hun a écrit :
> > At least a compiler barrier *in practice*, but not in theory (so this is
> > not guaranteed). And the CPU might also reorder.
> Reordering of both a compiler and a CPU should guarantee that the result
> of reordering is the same as the one of the sequential in a single thread.

Sure, all the provided patches work fine in the single thread case on any 

But the whole point of vlc_once() is deal with multiple threads and concurrent 

> And compiler cannot see the internal of cb().

With LTO and IPA combined, a compiler can propagate vlc_CPU_init as the cb 
value into vlc_once() from vlc_CPU().

Not that it matters much. The problem is not a lack of release fence. 
Unlocking the mutex provides a release fence. The problem is the lack fo 
acquire fence before reading the flag.


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