[Harmony Proxies] Proposal: Property fixing

Brendan Eich brendan at mozilla.com
Thu Jun 16 16:54:50 PDT 2011


On Jun 16, 2011, at 4:32 PM, Mark S. Miller wrote:

> My "Bonus" remark was *only* about Array length. For a great number of non-configurable properties (e.g. global vars in ES5 implementations, not created by eval), we JIT authors need a general attribute to consult. We aren't hardcoding, as we do for Array length (all the fast VMs optimize a.length expressions in the dense array, or any array, case).
> 
> Can we gather a list of all magical host properties that WebIDL says are currently non-configurable but that proxies can't emulate unless they are made configurable?

See the recent public-script-coord threads -- but I'm not sure enumerating cases will help.  We do not want to hardcode a list, even if short. Array length, we hardcode for competitive reasons; that cost is mostly sunk (and there's no sunk cost fallacy that I can see, just details about how one optimizes arrays).

For any more general set of non-configurable properties, we want one bit to condition judgment about how sealed or frozen the property is. We want this from JIT code, and also for deciding whether it is safe to share deeply frozen objects across threads via workers.

/be
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