Changes between Version 10 and Version 11 of DOMInJavaScript

Timestamp:

Sep 28, 2012 7:05:49 AM (12 years ago)

Author:

haraken@chromium.org

Comment:

--

DOMInJavaScript

@@ -28 +28 @@
 
 My understanding is that getPropertyAtKnownOffset is similar to JSC::JSObject::getDirectOffset. The key is to create JavaScript wrappers for DOM nodes in such a way that initial offsets are know to correspond to particular properties (e.g., the four basic DOM pointers.)
+
+== The relationship between wrappers and DOM objects ==
+
+=== Option 1: Wrappers are mandatory
+
+This approach creates wrappers for all DOM objects.
+
+Pros:
+* GC is simplified. Since all DOM tree edges are represented in the JS side, GC does not need to transfer information between a JS engine and WebKit.
+
+Cons:
+* We need to create wrappers for DOM objects that are not touched by JS. This would not be a problem for JS-heavy workloads but might become a problem for JS-light workloads. For JS-light workloads, the mandatory-wrapper approach might end up increasing the number of wrappers in a JS heap and regresses performance of GC.
+
+=== Option 2: Wrappers are optional
+
+This approach creates wrappers for only DOM objects that are touched by JS as is done in the current JSC/V8 + WebKit. As a fast path, in a case where a wrapper object exists, .nextSibling is realized by normal JavaScript property access. As a slow path, in a case where a wrapper object does not exist, .nextSibling is realized by Node::nextSibling() as is done in the current WebKit.
+
+Pros:
+* For JS-light workloads, the optional-wrapper approach would be faster than the mandatory-wrapper approach. The optional-wrapper approach does not need to create wrappers just for representing tree edges.
+
+Cons:
+* GC is not simplified. Since some tree edges are represented in the JS side and other tree edges are represented in the WebKit side, GC still needs to transfer information between a JS engine and WebKit.
+* We need to reserve space for .firstChild, .nextSibling, etc on both WebKit and JavaScript.