Added versioning to DOM nodes.

There is now an inclusive_descendants_version field of each node, which
increases each time the node, or any of its descendants, is dirtied.
This can be used for cache invalidation, by caching a version number
and comparting the current version number against the cached version number.

components/script/dom/node.rs

@@ -57,6 +57,7 @@ use selectors::parser::Selector;
 use selectors::parser::parse_author_origin_selector_list_from_str;
 use std::borrow::ToOwned;
 use std::cell::{Cell, Ref, RefCell, RefMut};
+use std::cmp::max;
 use std::default::Default;
 use std::iter::{self, FilterMap, Peekable};
 use std::mem;
@@ -105,6 +106,9 @@ pub struct Node {
     /// A bitfield of flags for node items.
     flags: Cell<NodeFlags>,
 
+    /// The maximum version of any inclusive descendant of this node.
+    inclusive_descendants_version: Cell<u64>,
+
     /// Layout information. Only the layout task may touch this data.
     ///
     /// Must be sent back to the layout task to be destroyed when this
@@ -489,6 +493,19 @@ impl Node {
     }
 
     pub fn dirty_impl(&self, damage: NodeDamage, force_ancestors: bool) {
+
+        // 0. Set version counter
+        // The new version counter is 1 plus the max of the node's current version counter,
+        // its descendants version, and the document's version. Normally, this will just be
+        // the document's version, but we do have to deal with the case where the node has moved
+        // document, so may have a higher version count than its owning document.
+        let doc: Root<Node> = Root::upcast(self.owner_doc());
+        let version = max(self.get_inclusive_descendants_version(), doc.get_inclusive_descendants_version()) + 1;
+        for ancestor in self.inclusive_ancestors() {
+            ancestor.inclusive_descendants_version.set(version);
+        }
+        doc.inclusive_descendants_version.set(version);
+
         // 1. Dirty self.
         match damage {
             NodeDamage::NodeStyleDamaged => {}
@@ -520,6 +537,11 @@ impl Node {
         }
     }
 
+    /// The maximum version number of this node's descendants, including itself
+    pub fn get_inclusive_descendants_version(&self) -> u64 {
+        self.inclusive_descendants_version.get()
+    }
+
     /// Iterates over this node and all its descendants, in preorder.
     pub fn traverse_preorder(&self) -> TreeIterator {
         TreeIterator::new(self)
@@ -1284,6 +1306,7 @@ impl Node {
             child_list: Default::default(),
             children_count: Cell::new(0u32),
             flags: Cell::new(flags),
+            inclusive_descendants_version: Cell::new(0),
 
             layout_data: LayoutDataRef::new(),
 

tests/unit/script/size_of.rs

@@ -38,10 +38,10 @@ macro_rules! sizeof_checker (
 
 // Update the sizes here
 sizeof_checker!(size_event_target, EventTarget, 40);
-sizeof_checker!(size_node, Node, 168);
-sizeof_checker!(size_element, Element, 312);
-sizeof_checker!(size_htmlelement, HTMLElement, 328);
-sizeof_checker!(size_div, HTMLDivElement, 328);
-sizeof_checker!(size_span, HTMLSpanElement, 328);
-sizeof_checker!(size_text, Text, 200);
-sizeof_checker!(size_characterdata, CharacterData, 200);
+sizeof_checker!(size_node, Node, 176);
+sizeof_checker!(size_element, Element, 320);
+sizeof_checker!(size_htmlelement, HTMLElement, 336);
+sizeof_checker!(size_div, HTMLDivElement, 336);
+sizeof_checker!(size_span, HTMLSpanElement, 336);
+sizeof_checker!(size_text, Text, 208);
+sizeof_checker!(size_characterdata, CharacterData, 208);