On Tue, 13 Feb 2024 at 16:28, Dave Cramer <davecramer@postgres.rocks> wrote:
>
>
>
> On Tue, 13 Feb 2024 at 12:52, Andres Freund <and...@anarazel.de> 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
>
Revisiting this:
Andrew, can you explain the difference between ninja test (which passes)
and what the build farm does. The buildfarm crashes.
Dave
