On Tue, 13 Feb 2024 at 12:52, Andres Freund <[email protected]> wrote:
> Hi,
>
> On 2024-02-13 12:49:33 -0500, Dave Cramer wrote:
> > > I think I might have been on to something - if my human emulation of a
> > > preprocessor isn't wrong, we'd end up with
> > >
> > > #define S_UNLOCK(lock) \
> > > do { _ReadWriteBarrier(); (*(lock)) = 0; } while (0)
> > >
> > > on msvc + arm. And that's entirely insufficient - _ReadWriteBarrier()
> just
> > > limits *compiler* level reordering, not CPU level reordering. I think
> it's
> > > even insufficient on x86[-64], but it's definitely insufficient on arm.
> > >
> > In fact ReadWriteBarrier has been deprecated _ReadWriteBarrier |
> Microsoft
> > Learn
> > <
> https://learn.microsoft.com/en-us/cpp/intrinsics/readwritebarrier?view=msvc-170
> >
>
> I'd just ignore that, that's just pushing towards more modern stuff that's
> more applicable to C++ than C.
>
>
> > I did try using atomic_thread_fence as per atomic_thread_fence -
> > cppreference.com
> > <https://en.cppreference.com/w/c/atomic/atomic_thread_fence>
>
> The semantics of atomic_thread_fence are, uh, very odd. I'd just use
> MemoryBarrier().
>
> #define S_UNLOCK(lock) \
do { MemoryBarrier(); (*(lock)) = 0; } while (0)
#endif
Has no effect.
I have no idea if that is what you meant that I should do ?
Dave
