On Apr 12, 2013, at 1:59 PM, Ryosuke Niwa <rn...@webkit.org> wrote: > On Fri, Apr 12, 2013 at 1:50 PM, Filip Pizlo <fpi...@apple.com> wrote: > > On Apr 12, 2013, at 1:39 PM, Jarred Nicholls <jarred.nicho...@gmail.com> > wrote: > >> On Fri, Apr 12, 2013 at 2:54 PM, Filip Pizlo <fpi...@apple.com> wrote: >> >> For as little worth as it is, I agree with you Filip that providing >> low-level primitives would be best in terms of a foundation for many >> parallel programming models. In terms of actually supporting shared mutable >> memory and locks, it would be a challenge for the engines to become >> thread-safe (internally) across contexts that share memory cells. I'd >> envision the sharing of mutable memory being an opt-in semantic, marking a >> piece of memory as being shared/mutable from multiple contexts. > > Fixing the engines is a matter of typing. ;-) > > I don't think we need to add language features for opt-in, though this is an > intriguing idea. > > Without opt-in, the one biggish challenge would be DOM accesses from threads > other than the main thread; I suspect for those the initial implementation > would have to throw an exception from non-main-threads if you try to access a > DOM node. This is akin to what some UI toolkits do: they let you have > threads but prohibit access UI things from anything but the thread on which > the runloop sits. Of course, they don't do the thread-check; we would have > to do it to preserve integrity and security. > > We already have Web workers for this kind of stuff, no? Is your proposal > significantly different from what Web worker offers?
Web workers don't have shared memory. They instead have a really expensive message passing model. Yes, my proposal is significantly different from Web workers. > > This is just a thought but is it possible to infer semantics of what Web > workers and use GPU or SIMD instructions instead of starting a new thread as > appropriate? Probably that would be hard, because the Web Worker semantics are so bizarre: they require copying things all over the place. It's probably an even worse match for SIMD/GPU/multicore than just Array.prototype.forEach(). -Filip > > - R. Niwa
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