Thanks ggaren! I filed a bug here: https://bugs.webkit.org/show_bug.cgi?id=88834
> I believe you could achieve (a) (i.e., preserve all reachable nodes without > help from the JavaScript garbage collector) with these semantics in the C++ > DOM: > > ===== Design ===== > > ref(): > > ++this->refCount > ++root()->refCount > > deref(): > > --this->refCount > --root()->refCount Actually I've tried the approach yesterday but confirmed 25.9% performance regression, even if I have TreeShared hold a pointer to the root. Please look at the WIP patch and the performance test in https://bugs.webkit.org/show_bug.cgi?id=88834. What I've learned is that we must not insert any line to ref() and deref(), which are performance sensitive:) I am now trying another approach that hacks Node destruction. Let's discuss the implementation details in the bug. Thanks! On Tue, Jun 12, 2012 at 12:18 PM, Geoffrey Garen <gga...@apple.com> wrote: > > IMHO, (a) would be the best semantics. > > > I agree, and I think that the specification actually does require this. > > The real issue here is how to fix this bug efficiently. I believe that Geoff > Garen has been contemplating this and also has a proposal for how to do it. > > > I believe you could achieve (a) (i.e., preserve all reachable nodes without > help from the JavaScript garbage collector) with these semantics in the C++ > DOM: > > ===== Design ===== > > ref(): > > ++this->refCount > ++root()->refCount > > deref(): > > --this->refCount > --root()->refCount > > if !root()->refCount: > assert(!this->refCount) > for each descendent of root(): > delete descendent > delete root() > > Remove 'this' from tree: > > assert(this->refCount) // clients must put a node into a RefPtr to remove it > from a tree > > root()->refCount -= this->refCount > > for each descendent of this: > this->refCount += descendent->refCount > > Insert 'this' into tree: > > root()->refCount += this->refCount > > for each descendent of this: > this->refCount -= descendent->refCount > > What is "root()"?: > > If this is in a document: > root() == document() > > else: > root() == the highest link in the parentNode chain > > > ===== FAQ ===== > > Cycles? > > No cycles are possible because the DOM API does not allow cycles in a DOM > tree. > > Is O(n) subtree insertion and removal OK? > > I believe these operations are already O(n). > > Is average case O(log n) access to disconnected root() OK? > > If n is small and/or ref/deref of disconnected subnodes are rare, then yes. > > Otherwise, we can optimize this case by putting a direct pointer to root() in > rare data. > > Geoff > -- Kentaro Hara, Tokyo, Japan (http://haraken.info) _______________________________________________ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
