Re: Our "fallback" atomics implementation doesn't actually work

Andres Freund <andres@anarazel.de> writes:
> Hm. After a long battle of head vs. wall I think I see what the problem
> is.  For the fallback atomics implementation I somehow had assumed that
> pg_atomic_write_u32() doesn't need to lock, as it's just an unlocked
> write.  But that's not true, because it has to cause
> pg_atomic_compare_exchange_u32 to fail.

Hah ... obvious once you see it.

> For me the problem often takes a lot longer to reproduce (once only
> after 40min), could you run with the attached patch, and see whether
> that fixes things for you?

For me, with the described test case, HEAD fails within a minute,
two times out of three or so.  I've not reproduced it after half an
hour of beating on this patch.  Looks good.
        regards, tom lane