[webkit-dev] Proposal: Do not support Windows fibers

[Yusuke SUZUKI]

Thank you for your replies!

On Wed, Dec 6, 2017 at 8:48 AM, Olmstead, Don <Don.Olmstead at sony.com> wrote:

> We’re fine with removing it.
>

That's nice!


>
>
> *From:* webkit-dev [mailto:webkit-dev-bounces at lists.webkit.org] *On
> Behalf Of *Geoffrey Garen
> *Sent:* Tuesday, December 5, 2017 2:35 PM
> *To:* Michael Saboff <msaboff at apple.com>
> *Cc:* John N. Lehner <jlehner at apple.com>; WebKit-Dev <
> webkit-dev at lists.webkit.org>
> *Subject:* Re: [webkit-dev] Proposal: Do not support Windows fibers
>
>
>
> If our Windows clients are cool with it, I think we should remove support
> for fibers.
>
>
>
> I don’t think our current implementation works super well with fibers. It
> is best not to include half-working code in the tree.
>
>
>
> Geoff
>

Yeah, I think we should assume that WebKit is not supporting Windows fibers.


>
>
> On Dec 5, 2017, at 11:19 AM, Michael Saboff <msaboff at apple.com> wrote:
>
>
>
> Here is the reply from iTunes for the WebKit-Dev list
>
>
>
> - Michael
>
>
>
> ——
>
>
>
> From an iTunes perspective, WebKit can eliminate any remaining Windows
> Fiber API support.
>
>
>
> iTunes still uses some cooperative threading, but implements its own
> mechanism on top of regular preemptive Windows threads. And we believe
> we've fixed all occurrences of calling WebKit/JSC from our non-main
> cooperative threads.
>
>
>
> - John
>
>
Nice. So Windows fiber is not used :)



>
>
> On Dec 5, 2017, at 10:26 AM, Michael Saboff <msaboff at apple.com> wrote:
>
>
>
> [Bringing John Lehner from the iTunes team into the discussion]
>
>
>
> Last I knew, the iTunes team uses fibers.  IIRC, the thread they use to
> call into WebKit/JSC only has one fiber, other parts of the app use
> multiple fibers on one thread but don’t have JS objects active in those
> threads / fibers.
>
>
>
> John, have things changed for iTunes on Windows such that we can eliminate
> support for fibers?
>
>
>
> - Michael
>
>
>
> On Dec 5, 2017, at 10:16 AM, Ryosuke Niwa <rniwa at webkit.org> wrote:
>
>
>
> Yeah, I don't think there is much need to support fibers. With features
> like web workers, supporting fibers doesn't make much sense.
>
>
Yeah. At least, I think the platform provided fibers are not encouraged in
WebKit.


>
> - R. Niwa
>
>
>
> On Tue, Dec 5, 2017 at 9:44 AM, Yusuke SUZUKI <utatane.tea at gmail.com>
> wrote:
>
> Hi, Webkittens,
>
>
>
> I would like to make sure OR declare that WebKit does not support Windows
> fibers.
>
> While fiber related functions are used in WTF, I believe that it is
> because fiber local storage (FLS) can have destructors. And it is not
> intended to support fibers explicitly.
>
>
>
> Actually, I believe the current WebKit does not work well with Windows
> fibers right now.
>
> For example, our JSC GC is conservative for stack and registers. It means
> that GC needs to scan stack and registers to gather conservative roots. But
> if your fiber is not executed at that time, JSC GC will miss to scan the
> stack and registers of those inactive fibers. As a result, managed objects
> will be collected if it is only referenced from the roots in the inactive
> fibers.
>
>
>
> And I think we can potentially improve performance of our TLS by using
> thread_local implementation in VC++ instead of using FLS. FLS is slow and
> it causes some problems[1]. I'm not sure the performance characteristics
> and implementation details of thread_local in VC++, but it's worth checking.
>
>
>
> So, I think we should not support Windows fibers. I would like to hear
> opinions about it.
>
>
>
> [1]: https://bugs.webkit.org/show_bug.cgi?id=146448
>
>
>
> Best regards,
>
> Yusuke Suzuki
>
>
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