[webkit-dev] Breaking cycles in mutation observers in JSC

Adam Barth abarth at webkit.org
Thu Aug 23 13:04:23 PDT 2012

Another approach might be to implement hidden properties in
JavaScriptCore, but I don't know what would be involved in doing that.


On Thu, Aug 23, 2012 at 12:39 PM, Elliott Sprehn <esprehn at chromium.org> wrote:
> I'm trying to fix the memory leaks in MutationObservers
> (http://www.w3.org/TR/dom/#mutation-observers),
> https://bugs.webkit.org/show_bug.cgi?id=93661
> This is easy in V8 where I've put a hidden property on the MutationObserver
> wrapper, and the V8MutationCallback object accesses this hidden property.
> The MutationObserver is then an ActiveDOMObject which keeps the wrapper
> alive as long as the observer has DOM nodes it's listening on, even if it's
> unreachable from JS.
> In the JSC side I'm not sure how to handle the cycle problem. Do I need to
> use a JSC::Weak in JSMutationCallback and then use visitChildren on the
> JSMutationObserver to call
> addOpaqueRoot(thisObject->impl()->callback->jsValue) ?
> In general if someone could explain visitChildren and
> isReachableFromOpaqueRoots and when I want slotVistor.append or
> addOpaqueRoot etc. it would be very helpful.
> - E
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