[Webkit-unassigned] [Bug 49739] WebIDL attributes should be implemented as getters and setters on the prototype object.

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Sun Jun 19 17:08:39 PDT 2011


--- Comment #8 from Dominic Cooney <dominicc at chromium.org>  2011-06-19 17:08:39 PST ---
(In reply to comment #7)

Thanks for the insight.

> Correction: I know that setters aren't cached.  Assigning to dom properties would be hammered, but they are theoretically already slow.  If we added caching to setters we would probably end up with a net win.
> > Getters will be hit by additional branches to validate the proto chain which is unfortunate.
> This will suck, but given that they're getter/setter pairs that we provide we might be able to remove at least _a_ branch from the current cached path.  We should also be able to avoid constructing an actual function wrapper until we absolutely have to (getOwnPropertyDescriptor requires us to provide the function object)

Could you point me to where this cache is in JSC?

> > The big change will be the property accessors in the dom will need to do type checks and that's an additional virtual call.  Could be fixed if class info was hung off of structure but then Structure becomes much larger. :-/
> A virtual call is no longer necessary but there's still going to be an additional (unavoidable) cost here, but also we'll nee to go through _every_ custom getter or setter and ensure correct behaviour.  
> > Additionally JSC API probably won't be able to do this for custom getters, etc
> This has been dealt with already by geoff -- API objects kill optimisation :(
> > I believe classes with index property accessors are going to magically become proxies, but i don't believe the semantics for that is sufficiently described yet.
> This is really an issue that needs to be resolves -- do index properties move to the prototype or do they stay own properties?

According to the Web IDL spec, indexed properties are on the host object, not the prototype <http://www.w3.org/TR/WebIDL/#indexed-properties>

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