On May 16, 2011, at 12:47 AM, Erik Corry wrote: > I think the objects used as keys in weak maps need to be somehow > annotated with this information so that the GC can clean up the weak > maps when the keys die. This means that if you take an object that is > frozen and use it as a key in a weak map then it will need to be > mutated in some way and can't be on a read-only page.
That's already false in Firefox nightlies. We support Object.freeze. We have a WeakMap implementation. We do not mutate the frozen object. Its GC metadata does not reside in a header for it, or even in the same OS page. > Perhaps you have a different, efficient, implementation. I can't see > us gaining much from putting frozen objects on read-only pages, thus I > can't accept it as a very strong argument about the way that frozen > objects should work together with a new feature. This is a bit too subjective an argument, sorry. My point about 50+ years of OS and MMU firewalling is important. Chrome (recently hacked by French spook-types, but also hacked over a year ago with a two-step attack) is a convincing example. Sure, we have user-code isolation tools in our belts, including fancy compiler/runtime pairs. But it's hard to beat processes if you want to be sure. No silver bullet, simply "stronger isolation". >> Weak maps are in Firefox nightlies. We're playing with page protection too >> (not for freezing, yet). This seems like a dare, but it also seems to be >> dodging my point in replying again: that private names cannot be used to >> extend frozen objects in the "[[Extensible]] = true" sense of the spec. > > Is there a description anywhere about how you have implemented GC of weak > maps? http://hg.mozilla.org/tracemonkey/rev/7dcd0d16cc08 Look for WeakMap::mark... names. There's no need to mutate a key object. There should not be, either. Yes, this GC can iterate. A lot, but a "fix" doesn't obviously require mutating (possibly frozen) key objects. Also, since POITROAE we are going to measure twice, Optimize once. /be _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
