On Tue, Jul 12, 2011 at 4:20 PM, Olivier Guilyardi wrote:
> Quite interestingly, I have noticed that discussions about memory barriers are
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
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
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
My feeling is that the answer to (1) is "no" and the answer to (2) is "yes".
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