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

Ryosuke Niwa rniwa at webkit.org
Tue Dec 5 10:16:18 PST 2017

Yeah, I don't think there is much need to support fibers. With features
like web workers, supporting fibers doesn't make much sense.

- 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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