It might be better to ask this on v8-dev.
Erik
On Tue, Sep 29, 2009 at 10:07 AM, Jens Alfke <s...@google.com> wrote:
> A big V8/DOM memory leak I was chasing down turns out to be not a real leak,
> it's just that it takes five full GCs after closing a document for its
> resources to be freed. I'd been getting bored after two GCs, so it wasn't
> till Ivan mentioned the stickiness of the generated-function caches that I
> thought to turn it up to 5.
> This still seems like an opportunity for optimization — the
> WebCore::Document and WebCore::DOMWindow can have a lot of stuff hanging off
> of them, so we should try to clean them up more quickly after a same-process
> child tab closes.
> The sticky reference is actually to the v8::Context. The DOM objects hang on
> because they're pointed to by that context's globals. So if the context's
> globals could be cleared when Chrome's V8Proxy disposes the context, the DOM
> objects should go away at the next GC.
> Good news: There is a v8::Context::DetachGlobal method that appears to
> separate the globals from the context. Bad news: it doesn't appear to do
> what I expected it to. After it's called the context still seems to have a
> reference to the globals, because they still don't go away until later when
> the context is collected.
> I looked at the implementation, Bootstrapper::DetachGlobal
> (bootstrapper.cc:361) but I don't really understand what it's doing. The
> context internally has both a global() and a global_proxy() object, and this
> method seems to detach the latter but not the former. From the way they're
> created it looks like the global() points to the global_proxy(), explaining
> why there's still a connection after detaching.
> Is there a way I can sever the relationship from the context to the globals?
> Would it require adding a new V8 API method similar to DetachGlobal?
> (I did find one approach that sort of works: iterating over the global
> object's properties and removing them all. Unfortunately I can't use this
> because in some cases the V8Proxy requires the global object to stay intact
> after disposing the context, so it can be used with a new context, and at
> the point where the context is disposed I don't know whether that's going to
> happen or not.)
> Thanks,
> —Jens
> >
>
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