499201 - Need support for classes with virtual properties in jsapi

Status: RESOLVED INCOMPLETE

(Core :: JavaScript Engine, defect, P2)

Description

[Boris Zbarsky [:bzbarsky]]

This is actually somewhat described in bug 497795, but to be more precise what we need is:

1)  A way to flag objects as having IndexGetter/IndexSetter
2)  A way to quickly ask the object what range of indices it supports, and a way
    for it to indicate "all integers".
3)  For indices in the supported range, a way to quickly call the relevant
    getter/setter function.
4)  Filing followup bugs to make our DOM classes use this.
5)  Filing followup bugs to make the JS engine use this as needed.

A key goal here is avoiding all the overhead of resolving the indices, then calling getters, etc.  The premise is that all the index stuff will live on the object, not the proto, so we don't need all that overhead.

I ran into a case where this seems like it would help when profiling the domJQueryAttributeFilters benchmark in the dom section of the peacekeeper benchmark.  That code is doing Array.slice() on the return value of querySelectorAll, which ends up spending about 2/3 as much time as the querySelectorAll call did...  Some of this might be xpconnect wrapping of the nodes, but some is just pure overhead.

Comment 1

[Boris Zbarsky [:bzbarsky]]

Attachment: Microbenchmark

Comment 2

[Boris Zbarsky [:bzbarsky]]

https://wiki.mozilla.org/Platform/Performance:IndexGetterSetter

Comment 3

[Florian Bender]

A lot has changed in the recent years. Is this bug still relevant, or are there different solutions?

Comment 4

[Jeff Walden [:Waldo]]

At this point we're well along on doing what this bug wants with proxies.  I don't think this bug's particularly useful any more -- proxy work would go in other bugs.

Comment 5

[Boris Zbarsky [:bzbarsky]]

We're well along to doing with proxies everything except the "fast" parts of comment 0.  ;)