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Re: mutexes, locks and so on...
On Fri, Nov 12, 2010 at 11:09:20AM +0000, Andrew Doran wrote:
> It was deliberate. rwlocks are only effective in situations where the
> codepath is heavyweight. So I felt while it is worthwhile optimising them
> if possible, an all out jihad is just not warranted (as it might be for
> mutexes). So I made the decision to make them rely on CAS so that the
> implementation is transparent, easier to prove and maintain etc.
To take an example where we grab a rwlock around something that doesn't
need to be heavyweight, see stat() -> VOP_STAT(). With a bit of sneaky
re-engineering that wouldn't need to acquire real locks at all. Something
like Linux's seqlock (poor name) would do great. So to my mind rwlocks
in their current form are a sort of stop-gap and convenience thing.
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