Re: [LAD] a *simple* ring buffer, comments pls?

On Tue, Jul 12, 2011 at 4:20 PM, Olivier Guilyardi <list(a)samalyse.com> wrote: I think the problem is that memory barriers are almost never required when writing "normal" code, and so people (including myself) are not exposed to their implementation or their use very much. and indeed, there are precious few library implementations of memory barriers, nor are they widely documented in a way that suggests that their use is "normal". by contrast, they get used all over the place in the kernel (relatively speaking), so if you tend to have a lot of exposure to kernel code, then calls to mb() or whatever they use these days will be quite familiar. there's the additional problem that this discussion normally ends up confusing two separate topics that many people seem to think are the same (they are not): 1) do you need to actively ensure correct thread-level synchronization between the reader and writer of a single-reader/single-writer FIFO? Put differently, do you need to use synchronization mechanisms semantically equivalent to a mutex to ensure that any arbitrary execution order of the 2 threads does not cause incorrect behaviour? 2) do you need memory barriers to ensure correct synchronization for this kind of data structure in the face of possible hardware level instruction reordering? My feeling is that the answer to (1) is "no" and the answer to (2) is "yes".