What's the use of volatile in Wine code?

[Rob Shearman]

2009/11/11  <Joerg-Cyril.Hoehle at t-systems.com>:
> Hi,
>
> AJ wrote in http://www.winehq.org/pipermail/wine-devel/2009-November/079575.html
>>If there is proper synchronization you don't need
>>volatile, and if there isn't volatile won't magically fix it.
>
> However, mcimidi has in its code since pre 1999:
> :/* it seems that in case of multi-threading, gcc is optimizing just a little bit
> : * too much. Tell gcc not to optimize status value using volatile.
> : */
> :while (((volatile WINE_MCIMIDI*)wmm)->dwStatus == MCI_MODE_PAUSE);
>
> The comment is right. Any C compiler is allowed to optimize this into
> an endless loop without volatile.  But I'd rather see the following:
> :volatile dwStatus = NOT_READY; /* one central declaration */
> :...
> :while (wmm->dwStatus == PAUSE) ; /* what, busy wait!?! */
>
> So what's the use of volatile? When is it appropriate in Wine?

I haven't looked in detail at the context of your patch, but this
looks appropriate to it:
http://lkml.indiana.edu/hypermail/linux/kernel/0607.0/1566.html

Particularly the part about volatile storage vs. access.

-- 
Rob Shearman