The "initialization" steps for Web browsers
ian at hixie.ch
Mon Jul 21 16:59:17 PDT 2014
On Mon, 21 Jul 2014, Allen Wirfs-Brock wrote:
> Yes, this is pretty much what I had in mind.
> I mentioned in other message, I can refractor things a bit to make it a
> bit easier to express.
Cool, ok. Let me know when I should start speccing things on my end.
> However, Realms don't provide the isolation that is required for
> different origin documents. See the discussion at
I think this is confusing two things: the same-origin policy, and event
loops. Multiple documents with different effective script origins can (and
frequently do) share one event loop, with script from one origin on the
stack below script from another origin. In single-process browsers,
there's only one event loop, even though they support cross-origin
iframes, tabs, etc. In fact, to make it worse, scripts can on-the-fly
change their origin using document.domain. Exactly how this works isn't
exactly defined yet, but the work to define this is described here:
It's defined at a level slightly above ES itself. It doesn't re-use the
"realm" machinery per se. What prevents two realms from different origins
from ever sharing anything isn't anything in ES, it's just that we never
actually provide a way for references to make it across (except in edge
cases involving document.domain manipulation, though those only allow it
for what we call "similar origins").
Event loops, though, are true isolation. If a browser has two documents in
two different event loops, they can never share anything. They have
different heaps, stacks, etc.
Structured cloning was invented to allow data to be passed between event
loops. However, even with one event loop, you still need structured
cloning to tranfser data between realms sometimes, because the Web
platform logically isolates them, as discussed above.
Ian Hickson U+1047E )\._.,--....,'``. fL
http://ln.hixie.ch/ U+263A /, _.. \ _\ ;`._ ,.
Things that are impossible just take longer. `._.-(,_..'--(,_..'`-.;.'
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