layout: Switch parallel selector matching over to using work stealing.

10% speedup over what we had before.

src/components/main/css/matching.rs

@@ -8,19 +8,14 @@ use css::node_style::StyledNode;
 use layout::incremental;
 use layout::util::LayoutDataAccess;
 use layout::wrapper::LayoutNode;
-use servo_util::task::spawn_named;
 
-use extra::arc::{Arc, RWArc};
+use extra::arc::Arc;
-use std::cast;
-use std::libc::uintptr_t;
-use std::rt;
-use std::vec;
 use style::{TNode, Stylist, cascade};
 use style::{Before, After};
 
 pub trait MatchMethods {
     fn match_node(&self, stylist: &Stylist);
-    fn match_subtree(&self, stylist: RWArc<Stylist>);
+    fn match_subtree(&self, stylist: &Stylist);
 
     fn cascade_subtree(&self, parent: Option<LayoutNode>);
 }
@@ -47,53 +42,12 @@ impl<'ln> MatchMethods for LayoutNode<'ln> {
             None => fail!("no layout data")
         }
     }
-    fn match_subtree(&self, stylist: RWArc<Stylist>) {
-        let num_tasks = rt::default_sched_threads() * 2;
-        let mut node_count = 0;
-        let mut nodes_per_task = vec::from_elem(num_tasks, ~[]);
 
+    fn match_subtree(&self, stylist: &Stylist) {
         for node in self.traverse_preorder() {
             if node.is_element() {
-                nodes_per_task[node_count % num_tasks].push(node);
-                node_count += 1;
-            }
-        }
-
-        let (port, chan) = SharedChan::new();
-        let mut num_spawned = 0;
-
-        for nodes in nodes_per_task.move_iter() {
-            if nodes.len() > 0 {
-                let chan = chan.clone();
-                let stylist = stylist.clone();
-
-                // FIXME(pcwalton): This transmute is to work around the fact that we have no
-                // mechanism for safe fork/join parallelism. If we had such a thing, then we could
-                // close over the lifetime-bounded `LayoutNode`. But we can't, so we force it with
-                // a transmute.
-                let evil: uintptr_t = unsafe {
-                    cast::transmute(nodes)
-                };
-
-                let evil = Some(evil);
-                spawn_named("MatchMethods for LayoutNode", proc() {
-                    let mut evil = evil;
-                    let nodes: ~[LayoutNode] = unsafe {
-                        cast::transmute(evil.take_unwrap())
-                    };
-
-                    stylist.read(|stylist| {
-                        for node in nodes.iter() {
                 node.match_node(stylist);
             }
-                    });
-                    chan.send(());
-                });
-                num_spawned += 1;
-            }
-        }
-        for _ in range(0, num_spawned) {
-            port.recv();
         }
     }
 

src/components/main/layout/context.rs

@@ -18,6 +18,7 @@ use gfx::font_context::{FontContext, FontContextInfo};
 use servo_msg::constellation_msg::ConstellationChan;
 use servo_net::local_image_cache::LocalImageCache;
 use servo_util::geometry::Au;
+use style::Stylist;
 
 #[thread_local]
 static mut FONT_CONTEXT: *mut FontContext = 0 as *mut FontContext;
@@ -39,6 +40,11 @@ pub struct LayoutContext {
 
     /// Information needed to construct a font context.
     font_context_info: FontContextInfo,
+
+    /// The CSS selector stylist.
+    ///
+    /// FIXME(pcwalton): Make this no longer an unsafe pointer once we have fast `RWArc`s.
+    stylist: *Stylist,
 }
 
 impl LayoutContext {

src/components/main/layout/layout_task.rs

@@ -22,7 +22,7 @@ use layout::parallel;
 use layout::util::{LayoutDataAccess, OpaqueNode, LayoutDataWrapper};
 use layout::wrapper::LayoutNode;
 
-use extra::arc::{Arc, MutexArc, RWArc};
+use extra::arc::{Arc, MutexArc};
 use geom::rect::Rect;
 use geom::size::Size2D;
 use gfx::display_list::{ClipDisplayItemClass, DisplayItem, DisplayItemIterator, DisplayList};
@@ -91,7 +91,7 @@ pub struct LayoutTask {
     /// A cached display list.
     display_list: Option<Arc<DisplayList<OpaqueNode>>>,
 
-    stylist: RWArc<Stylist>,
+    stylist: ~Stylist,
 
     /// The workers that we use for parallel operation.
     parallel_traversal: Option<WorkQueue<*mut LayoutContext,UnsafeFlow>>,
@@ -274,7 +274,7 @@ impl LayoutTask {
             leaf_set: MutexArc::new(LeafSet::new()),
 
             display_list: None,
-            stylist: RWArc::new(new_stylist()),
+            stylist: ~new_stylist(),
             parallel_traversal: parallel_traversal,
             profiler_chan: profiler_chan,
             opts: opts.clone()
@@ -302,6 +302,7 @@ impl LayoutTask {
             constellation_chan: self.constellation_chan.clone(),
             leaf_set: self.leaf_set.clone(),
             font_context_info: font_context_info,
+            stylist: &*self.stylist,
         }
     }
 
@@ -379,10 +380,7 @@ impl LayoutTask {
     }
 
     fn handle_add_stylesheet(&mut self, sheet: Stylesheet) {
-        let mut sheet = Some(sheet);
+        self.stylist.add_stylesheet(sheet, AuthorOrigin)
-        self.stylist.write(|stylist| {
-            stylist.add_stylesheet(sheet.take_unwrap(), AuthorOrigin);
-        });
     }
 
     /// Builds the flow tree.
@@ -521,7 +519,12 @@ impl LayoutTask {
             ReflowDocumentDamage => {}
             _ => {
                 profile(time::LayoutSelectorMatchCategory, self.profiler_chan.clone(), || {
-                    node.match_subtree(self.stylist.clone());
+                    match self.parallel_traversal {
+                        None => node.match_subtree(self.stylist),
+                        Some(ref mut traversal) => {
+                            parallel::match_subtree(node, &mut layout_ctx, traversal)
+                        }
+                    }
                 });
                 profile(time::LayoutSelectorCascadeCategory, self.profiler_chan.clone(), || {
                     node.cascade_subtree(None);

src/components/main/layout/parallel.rs

@@ -2,19 +2,25 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-//! Implements parallel traversals over the flow tree.
+//! Implements parallel traversals over the DOM and flow trees.
+//!
+//! This code is highly unsafe. Keep this file small and easy to audit.
 
+use css::matching::MatchMethods;
 use layout::context::LayoutContext;
 use layout::flow::{Flow, LeafSet, PostorderFlowTraversal};
 use layout::flow;
 use layout::layout_task::{AssignHeightsAndStoreOverflowTraversal, BubbleWidthsTraversal};
+use layout::wrapper::LayoutNode;
 
 use extra::arc::MutexArc;
 use servo_util::time::{ProfilerChan, profile};
 use servo_util::time;
 use servo_util::workqueue::{WorkQueue, WorkUnit, WorkerProxy};
 use std::cast;
+use std::ptr;
 use std::sync::atomics::{AtomicInt, Relaxed, SeqCst};
+use style::{Stylist, TNode};
 
 pub enum TraversalKind {
     BubbleWidthsTraversalKind,
@@ -39,6 +45,14 @@ pub fn mut_owned_flow_to_unsafe_flow(flow: *mut ~Flow) -> UnsafeFlow {
     }
 }
 
+pub type UnsafeLayoutNode = (uint, uint);
+
+fn layout_node_to_unsafe_layout_node(node: &LayoutNode) -> UnsafeLayoutNode {
+    unsafe {
+        cast::transmute_copy(node)
+    }
+}
+
 /// Information that we need stored in each flow.
 pub struct FlowParallelInfo {
     /// The number of children that still need work done.
@@ -101,6 +115,30 @@ impl<'a> ParallelPostorderFlowTraversal for BubbleWidthsTraversal<'a> {}
 
 impl<'a> ParallelPostorderFlowTraversal for AssignHeightsAndStoreOverflowTraversal<'a> {}
 
+fn match_node(unsafe_layout_node: UnsafeLayoutNode,
+              proxy: &mut WorkerProxy<*mut LayoutContext,UnsafeLayoutNode>) {
+    unsafe {
+        let layout_context: &mut LayoutContext = cast::transmute(*proxy.user_data());
+
+        // Get a real layout node.
+        let node: LayoutNode = cast::transmute(unsafe_layout_node);
+
+        // Enqueue kids.
+        for kid in node.children() {
+            if kid.is_element() {
+                proxy.push(WorkUnit {
+                    fun: match_node,
+                    data: layout_node_to_unsafe_layout_node(&kid),
+                });
+            }
+        }
+
+        // Perform the CSS selector matching.
+        let stylist: &Stylist = cast::transmute(layout_context.stylist);
+        node.match_node(stylist);
+    }
+}
+
 fn bubble_widths(unsafe_flow: UnsafeFlow, proxy: &mut WorkerProxy<*mut LayoutContext,UnsafeFlow>) {
     let layout_context: &mut LayoutContext = unsafe {
         cast::transmute(*proxy.user_data())
@@ -122,6 +160,24 @@ fn assign_heights_and_store_overflow(unsafe_flow: UnsafeFlow,
     assign_heights_traversal.run_parallel(unsafe_flow)
 }
 
+pub fn match_subtree(root_node: &LayoutNode,
+                     layout_context: &mut LayoutContext,
+                     queue: &mut WorkQueue<*mut LayoutContext,UnsafeLayoutNode>) {
+    unsafe {
+        queue.data = cast::transmute(layout_context)
+    }
+
+    // Enqueue the root node.
+    queue.push(WorkUnit {
+        fun: match_node,
+        data: layout_node_to_unsafe_layout_node(root_node),
+    });
+
+    queue.run();
+
+    queue.data = ptr::mut_null()
+}
+
 pub fn traverse_flow_tree(kind: TraversalKind,
                           leaf_set: &MutexArc<LeafSet>,
                           profiler_chan: ProfilerChan,
@@ -147,6 +203,8 @@ pub fn traverse_flow_tree(kind: TraversalKind,
         })
     });
 
-    queue.run()
+    queue.run();
+
+    queue.data = ptr::mut_null()
 }