On Apr 12, 2013, at 10:43 PM, Ryosuke Niwa <rn...@webkit.org> wrote:
> On Fri, Apr 12, 2013 at 2:13 PM, Filip Pizlo <fpi...@apple.com> wrote: > > 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. > > I never thought Web workers was tied to a message passing model but you've > convinced me of this point in our earlier in-person discussion. >> 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(). > > Yeah, I was thinking that this is possible once we've added a shared memory > model. You've also convinced me in the same in-person discussion and in a > reply to Maciej's response that memory corruption isn't an issue in JS. I'm > totally with you and Zoltan that the current message passing model makes Web > workers pretty much useless. > > Perhaps we can come up with some JS API for shared memory & lock and propose > it in TC39 or WebApps WG? I think that would be wonderful. Anyone else interested? > > - R. Niwa > >
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