- From: Jonas Sicking <jonas@sicking.cc>
- Date: Wed, 7 Mar 2012 12:35:40 -0800
- To: Adam Klein <adamk@chromium.org>
- Cc: www-dom@w3.org, Anne van Kesteren <annevk@opera.com>, Olli@pettay.fi
On Wed, Mar 7, 2012 at 8:52 AM, Adam Klein <adamk@chromium.org> wrote: > http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#concept-mo-invoke > describes an algorithm for delivering MutationRecords to MutationObservers. > In particular, it describes an order of delivery, and I wonder if tweaking > it a little bit would make it simpler to implement. Note that I don't think > the particular order is of much importance: it's just important that there > is a well-defined order. In particular, there are two cases I'm worried > about: > > 1. Assume observers A, B, and C (created in the order A, B, C). Say that at > the beginning of the algorithm, only A and C have non-empty queues. But > during A's callback, it mutates DOM that causes a record to be added to B's > queue. > > 2. Assume an observer A with a non-empty queue. During its callback, it > creates a new observer B, starts B observing, and mutates DOM that adds a > record to both A's and B's queue. > > By the spec, case (1) would result in the delivery order A-B-C. And (2) > would be A-B-A. > > In the WebKit implementation, though, only the "active" observers (those > with records in their queues) are kept in a list (this makes it fast in the > common case that there's no delivery necessary). This makes our algorithm > more like this: > > I. Make a copy of the existing "active" list, clear the list, and then > iterate over the copy. > II. When that iteration is complete, the active list is checked again; if > it's non-empty, go back to step I. > > When applied to the cases above, (1) results in the order A-C-B (B doesn't > get notified until the next time around the loop), and (2) results in A-A-B > (again, the newly-added observer doesn't get notified until the second time > through the loop). > > Thoughts? Also, if the above is too hard to follow, I have test-cases that > demonstrate these cases, and could point at those instead. This sounds good to me, though I'm happy to defer to Olli. / Jonas
Received on Wednesday, 7 March 2012 20:36:44 UTC