16 Dec
2009
16 Dec
'09
1:57 p.m.
> this was
discussed at some considerable length on jack-devel last
> year, IIRC.
> for single reader/single writer ringbuffers, i believe that we
> concluded that memory barriers are not necessary.
No, to me the conclusion was: we can't programmatically prove that
memory
barriers are needed (even on the most vulnerable architectures),
but the theory
say that they are, and they should be added for correctness.
My understanding
matches Olivier's. Intel processors have strong memory
ordering, and so on them the jack ringbuffer is safe without memory
barriers. However, some PPC processors, and SPARC V9s under linux
(but not
Solaris), use weak memory ordering, and on them, the jack ringbuffer
code
can theoretically fail. See the "ring buffer memory barriers"
discussion on jack-devel back in
October of last year for more information; in particular, this article
by Paul E. McKenney is very helpful:
http://www.linuxjournal.com/article/8211
memory-barriers.txt of the linux kernel documentation is interesting as
well ...