Allan ,
>>he might as well go traditional
you mean using the locks ?
Thank you
~Umesh
On Sat, Jul 21, 2018 at 4:20 AM, Allan Sandfeld Jensen
<li...@carewolf.com> wrote:
> On Samstag, 21. Juli 2018 00:21:48 CEST Jonathan Wakely wrote:
>> On Fri, 20 Jul 2018 at 23:06, Allan Sandfeld Jensen wrote:
>> > On Freitag, 20. Juli 2018 14:19:12 CEST Umesh Kalappa wrote:
>> > > Hi All ,
>> > >
>> > > We are looking at the C sample i.e
>> > >
>> > > extern int i,j;
>> > >
>> > > int test()
>> > > {
>> > > while(1)
>> > > { i++;
>> > >
>> > > j=20;
>> > >
>> > > }
>> > > return 0;
>> > > }
>> > >
>> > > command used :(gcc 8.1.0)
>> > > gcc -S test.c -O2
>> > >
>> > > the generated asm for x86
>> > >
>> > > .L2:
>> > > jmp .L2
>> > >
>> > > we understand that,the infinite loop is not deterministic ,compiler
>> > > is free to treat as that as UB and do aggressive optimization ,but we
>> > > need keep the side effects like j=20 untouched by optimization .
>> > >
>> > > Please note that using the volatile qualifier for i and j or empty
>> > > asm("") in the while loop,will stop the optimizer ,but we don't want
>> > > do that.
>> >
>> > But you need to do that! If you want changes to a variable to be
>> > observable in another thread, you need to use either volatile,
>>
>> No, volatile doesn't work for that.
>>
> It does, but you shouldn't use for that due to many other reasons (though the
> linux kernel still does) But if the guy wants to code primitive without using
> system calls or atomics, he might as well go traditional
>
> 'Allan
>
>
