[webkit-qt] webkit2, v8, diplomacy

Balazs Kelemen kbalazs at webkit.org
Tue Jun 5 06:22:02 PDT 2012

On 06/05/2012 03:12 PM, Coda Highland wrote:
> On Tue, Jun 5, 2012 at 7:53 AM, Balazs Kelemen<kbalazs at webkit.org>  wrote:
>>      Hi all!
>> I think it's time to decide how important is the v8 integration for us. I'm
>> not saying it's hyper-super important, I'm just curious about your opinion.
>> In fact we have a qt5 release blocker bug for that:
>> https://bugs.webkit.org/show_bug.cgi?id=76778 (although at the time when it
>> has been filed we did not expect that much community resistance) and it's
>> also quite clear that this could save a lot of memory (1 js engine instead
>> of 2). It's evident that we don't want to go against the community, but
>> still I think they should be more open to this. It's really just some lines
>> of boilerplate glue code to webkit2, and we choose a solution that provides
>> source compatibility with WebKitTestRunner. Btw, there are the bugs:
>>      - https://bugs.webkit.org/show_bug.cgi?id=76778 (meta)
>>      - https://bugs.webkit.org/show_bug.cgi?id=87872 shim for wtr
>>      - https://bugs.webkit.org/show_bug.cgi?id=84457 wk2+v8
>> If the case is that we want to go for this, I would definitely need your
>> help to get community acceptance since I'm not a reviewer and honestly I am
>> not very good in diplomacy :)
>> Anyway, I would not like to make the false illusion that pushing these
>> patches will solve every problem and just save memory. In fact, in order to
>> get the desired benefit we have to solve other issues:
>>      - using the same copy of v8 (fork) in declarative and webkit. this is
>> tricky because webkit needs the most up-to-date v8 version
>>      - using v8 in qtscript, or detaching qtscrpit from qtdeclarative (I
>> heard qtscript is a dependency)
>> Cheers,
>> -kbalazs
> I don't understand why the push for V8 in the first place. JSC and V8
> are in an arms race for performance, so you can't categorically say V8
> is faster because that's not always true.

I did not say it's faster or superior but using two js engines in a 
stack is insane.

> JSC also has broader support
> (see Konstantin's post). Furthermore, my understanding is that V8
> doesn't expose the necessary APIs to be able to provide the full scope
> of the QtScript API. (Has this changed since the original plans to
> move to V8 were announced?)

I don't think v8 lack's any API that JSC has. If we only consider public 
API, I think v8 is much more rich - maybe I'm wrong. Anyway, declarative 
- which is really a fundamental of Qt5 - is using v8 and I guess there 
is a reason for that and it's not desirable to move it to JSC.

> Is there some specific feature that makes V8 qualitatively superior to
> JSC for Qt's use cases? So far I've not seen anything that really
> sells me on the idea.
> /s/ Adam

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