add pipeline.rs, modularized pipelines communicating with constellation

19 files changed, 525 insertions, 314 deletions

diff --git a/src/components/gfx/render_task.rs b/src/components/gfx/render_task.rs
index 62d2094c1e3..68a6b3874ec 100644
--- a/src/components/gfx/render_task.rs
+++ b/src/components/gfx/render_task.rs
@@ -8,7 +8,8 @@ use azure::{AzFloat, AzGLContext};
 use azure::azure_hl::{B8G8R8A8, DrawTarget};
 use display_list::DisplayList;
 use servo_msg::compositor::{RenderListener, IdleRenderState, RenderingRenderState, LayerBuffer};
-use servo_msg::compositor::LayerBufferSet;
+use servo_msg::compositor::{CompositorToken, LayerBufferSet};
+use servo_msg::engine::{EngineChan, TokenSurrenderMsg};
 use font_context::FontContext;
 use geom::matrix2d::Matrix2D;
 use geom::point::Point2D;
@@ -20,6 +21,7 @@ use render_context::RenderContext;
 use std::cell::Cell;
 use std::comm::{Chan, Port, SharedChan};
 use std::uint;
+use std::util::replace;
 
 use servo_util::time::{ProfilerChan, profile};
 use servo_util::time;
@@ -29,70 +31,32 @@ pub struct RenderLayer {
     size: Size2D<uint>
 }
 
-pub enum Msg<C> {
-    AttachCompositorMsg(C),
+pub enum Msg {
     RenderMsg(RenderLayer),
     ReRenderMsg(f32),
+    TokenBestowMsg(~CompositorToken),
+    TokenProcureMsg,
     ExitMsg(Chan<()>),
 }
 
-pub struct RenderChan<C> {
-    chan: SharedChan<Msg<C>>,
+#[deriving(Clone)]
+pub struct RenderChan {
+    chan: SharedChan<Msg>,
 }
 
-impl<C: RenderListener + Owned> Clone for RenderChan<C> {
-    pub fn clone(&self) -> RenderChan<C> {
-        RenderChan {
-            chan: self.chan.clone(),
-        }
-    }
-}
-
-impl<C: RenderListener + Owned> RenderChan<C> {
-    pub fn new(chan: Chan<Msg<C>>) -> RenderChan<C> {
+impl RenderChan {
+    pub fn new(chan: Chan<Msg>) -> RenderChan {
         RenderChan {
             chan: SharedChan::new(chan),
         }
     }
-    pub fn send(&self, msg: Msg<C>) {
+    pub fn send(&self, msg: Msg) {
         self.chan.send(msg);
     }
 }
 
-pub fn create_render_task<C: RenderListener + Owned>(port: Port<Msg<C>>,
-                                                     compositor: C,
-                                                     opts: Opts,
-                                                     profiler_chan: ProfilerChan) {
-    let compositor_cell = Cell::new(compositor);
-    let opts_cell = Cell::new(opts);
-    let port = Cell::new(port);
-
-    do spawn {
-        let compositor = compositor_cell.take();
-        let share_gl_context = compositor.get_gl_context();
-        let opts = opts_cell.with_ref(|o| copy *o);
-        let profiler_chan = profiler_chan.clone();
-        let profiler_chan_copy = profiler_chan.clone();
-
-        // FIXME: rust/#5967
-        let mut renderer = Renderer {
-            port: port.take(),
-            compositor: compositor,
-            font_ctx: @mut FontContext::new(opts.render_backend,
-                                            false,
-                                            profiler_chan),
-            opts: opts_cell.take(),
-            profiler_chan: profiler_chan_copy,
-            share_gl_context: share_gl_context,
-            render_layer: None,
-        };
-
-        renderer.start();
-    }
-}
-
-priv struct Renderer<C> {
-    port: Port<Msg<C>>,
+priv struct RenderTask<C> {
+    port: Port<Msg>,
     compositor: C,
     font_ctx: @mut FontContext,
     opts: Opts,
@@ -104,15 +68,58 @@ priv struct Renderer<C> {
 
     /// The layer to be rendered
     render_layer: Option<RenderLayer>,
+    /// A channel to the engine task for surrendering token
+    engine_chan: EngineChan,
+    /// A token that grants permission to send paint messages to compositor
+    compositor_token: Option<~CompositorToken>,
+    /// Cached copy of last layers rendered
+    next_paint_msg: Option<(LayerBufferSet, Size2D<uint>)>,
 }
 
-impl<C: RenderListener + Owned> Renderer<C> {
+impl<C: RenderListener + Owned> RenderTask<C> {
+    pub fn create(port: Port<Msg>,
+                  compositor: C,
+                  opts: Opts,
+                  engine_chan: EngineChan,
+                  profiler_chan: ProfilerChan) {
+        let compositor_cell = Cell::new(compositor);
+        let opts_cell = Cell::new(opts);
+        let port = Cell::new(port);
+        let engine_chan = Cell::new(engine_chan);
+
+        do spawn {
+            let compositor = compositor_cell.take();
+            let share_gl_context = compositor.get_gl_context();
+            let opts = opts_cell.with_ref(|o| copy *o);
+            let profiler_chan = profiler_chan.clone();
+            let profiler_chan_clone = profiler_chan.clone();
+
+            // FIXME: rust/#5967
+            let mut render_task = RenderTask {
+                port: port.take(),
+                compositor: compositor,
+                font_ctx: @mut FontContext::new(opts.render_backend,
+                                                false,
+                                                profiler_chan),
+                opts: opts_cell.take(),
+                profiler_chan: profiler_chan_clone,
+                share_gl_context: share_gl_context,
+                render_layer: None,
+
+                engine_chan: engine_chan.take(),
+                compositor_token: None,
+                next_paint_msg: None,
+            };
+
+            render_task.start();
+        }
+    }
+
     fn start(&mut self) {
-        debug!("renderer: beginning rendering loop");
+        debug!("render_task: beginning rendering loop");
 
         loop {
             match self.port.recv() {
-                AttachCompositorMsg(compositor) => self.compositor = compositor,
                 RenderMsg(render_layer) => {
                     self.render_layer = Some(render_layer);
                     self.render(1.0);
@@ -120,6 +127,21 @@ impl<C: RenderListener + Owned> Renderer<C> {
                 ReRenderMsg(scale) => {
                     self.render(scale);
                 }
+                TokenBestowMsg(token) => {
+                    self.compositor_token = Some(token);
+                    let next_paint_msg = replace(&mut self.next_paint_msg, None);
+                    match next_paint_msg {
+                        Some((layer_buffer_set, layer_size)) => {
+                            println("retrieving cached paint msg");
+                            self.compositor.paint(layer_buffer_set, layer_size);
+                            self.compositor.set_render_state(IdleRenderState);
+                        }
+                        None => {}
+                    }
+                }
+                TokenProcureMsg => {
+                    self.engine_chan.send(TokenSurrenderMsg(self.compositor_token.swap_unwrap()));
+                }
                 ExitMsg(response_ch) => {
                     response_ch.send(());
                     break;
@@ -129,7 +151,7 @@ impl<C: RenderListener + Owned> Renderer<C> {
     }
 
     fn render(&mut self, scale: f32) {
-        debug!("renderer: rendering");
+        debug!("render_task: rendering");
         
         let render_layer;
         match (self.render_layer) {
@@ -164,7 +186,8 @@ impl<C: RenderListener + Owned> Renderer<C> {
                         let buffer = LayerBuffer {
                             draw_target: DrawTarget::new_with_fbo(self.opts.render_backend,
                                                                   self.share_gl_context,
-                                                                  Size2D(width as i32, height as i32),
+                                                                  Size2D(width as i32,
+                                                                         height as i32),
                                                                   B8G8R8A8),
                             rect: tile_rect,
                             screen_pos: screen_rect,
@@ -210,8 +233,14 @@ impl<C: RenderListener + Owned> Renderer<C> {
                 buffers: new_buffers,
             };
 
-            debug!("renderer: returning surface");
-            self.compositor.paint(layer_buffer_set, render_layer.size);
+            debug!("render_task: returning surface");
+            if self.compositor_token.is_some() {
+                self.compositor.paint(layer_buffer_set, render_layer.size);
+            }
+            else {
+                println("caching paint msg");
+                self.next_paint_msg = Some((layer_buffer_set, render_layer.size));
+            }
             self.compositor.set_render_state(IdleRenderState);
         }
     }
diff --git a/src/components/main/compositing/mod.rs b/src/components/main/compositing/mod.rs
index 9e3a2a1067e..873c46a645a 100644
--- a/src/components/main/compositing/mod.rs
+++ b/src/components/main/compositing/mod.rs
@@ -89,7 +89,7 @@ pub enum Msg {
     /// Sets the channel to the current layout task
     SetLayoutChan(LayoutChan),
     /// Sets the channel to the current renderer
-    SetRenderChan(RenderChan<CompositorChan>),
+    SetRenderChan(RenderChan),
 }
 
 /// Azure surface wrapping to work with the layers infrastructure.
@@ -176,7 +176,7 @@ impl CompositorTask {
         let local_zoom = @mut 1f32;
         // Channel to the current renderer.
         // FIXME: This probably shouldn't be stored like this.
-        let render_chan: @mut Option<RenderChan<CompositorChan>> = @mut None;
+        let render_chan: @mut Option<RenderChan> = @mut None;
 
         let update_layout_callbacks: @fn(LayoutChan) = |layout_chan: LayoutChan| {
             let layout_chan_clone = layout_chan.clone();
@@ -432,3 +432,4 @@ fn on_osmain(f: ~fn()) {
         f();
     }
 }
+
diff --git a/src/components/main/engine.rs b/src/components/main/engine.rs
index cdabbba1ae2..41e6fafe783 100644
--- a/src/components/main/engine.rs
+++ b/src/components/main/engine.rs
@@ -10,28 +10,69 @@ use std::comm;
 use std::comm::Port;
 use std::task;
 use gfx::opts::Opts;
-use gfx::render_task::RenderChan;
-use gfx::render_task;
-use servo_msg::compositor::{ScriptListener, ReadyState};
-use servo_msg::engine::{EngineChan, ExitMsg, LoadUrlMsg, Msg};
-use script::layout_interface::LayoutChan;
-use script::layout_interface;
-use script::script_task::{ExecuteMsg, LoadMsg, ScriptMsg, ScriptContext, ScriptChan};
-use script::script_task;
+use gfx::render_task::{TokenBestowMsg, TokenProcureMsg};
+use pipeline::Pipeline;
+use servo_msg::compositor::{CompositorToken};
+use servo_msg::engine::{EngineChan, ExitMsg, LoadUrlMsg, Msg, RendererReadyMsg, TokenSurrenderMsg};
+use script::script_task::{ExecuteMsg, LoadMsg};
 use servo_net::image_cache_task::{ImageCacheTask, ImageCacheTaskClient};
 use servo_net::resource_task::ResourceTask;
 use servo_net::resource_task;
-use servo_util::time::{ProfilerChan};
+use servo_util::time::ProfilerChan;
+use std::hashmap::HashMap;
 
 pub struct Engine {
+    chan: EngineChan,
     request_port: Port<Msg>,
     compositor_chan: CompositorChan,
-    render_chan: RenderChan<CompositorChan>,
     resource_task: ResourceTask,
     image_cache_task: ImageCacheTask,
-    layout_chan: LayoutChan,
-    script_chan: ScriptChan,
+    pipelines: HashMap<uint, Pipeline>,
+    navigation_context: NavigationContext,
+    next_id: uint,
+    current_token_holder: Option<uint>,
+    loading: Option<uint>,
     profiler_chan: ProfilerChan,
+    opts: Opts,
+}
+
+pub struct NavigationContext {
+    previous: ~[uint],
+    next: ~[uint],
+    current: Option<uint>,
+}
+
+impl NavigationContext {
+    pub fn new() -> NavigationContext {
+        NavigationContext {
+            previous: ~[],
+            next: ~[],
+            current: None,
+        }
+    }
+
+    pub fn back(&mut self) -> uint {
+        do self.current.mutate |id| {
+            self.next.push(id);
+            self.previous.pop()
+        }
+        self.current.get()
+    }
+
+    pub fn forward(&mut self) -> uint {
+        do self.current.mutate |id| {
+            self.previous.push(id);
+            self.next.pop()
+        }
+        self.current.get()
+    }
+
+    pub fn navigate(&mut self, id: uint) {
+        do self.current.mutate_default(id) |cur_id| {
+            self.previous.push(cur_id);
+            id
+        }
+    }
 }
 
 impl Engine {
@@ -41,105 +82,99 @@ impl Engine {
                  image_cache_task: ImageCacheTask,
                  profiler_chan: ProfilerChan)
                  -> EngineChan {
-        macro_rules! closure_stream(
-            ($Msg:ty, $Chan:ident) => (
-                {
-                    let (port, chan) = comm::stream::<$Msg>();
-                    (Cell::new(port), $Chan::new(chan))
-                }
-            );
-        )
             
-        // Create the script port and channel.
-        let (script_port, script_chan) = closure_stream!(ScriptMsg, ScriptChan);
-
-        // Create the engine port and channel.
-        let (engine_port, engine_chan) = closure_stream!(Msg, EngineChan);
-        
-        // Create the layout port and channel.
-        let (layout_port, layout_chan) = closure_stream!(layout_interface::Msg, LayoutChan);
-
-        let (render_port, render_chan) = comm::stream::<render_task::Msg<CompositorChan>>();
-        let (render_port, render_chan) = (Cell::new(render_port), RenderChan::new(render_chan));
-
+        let opts = Cell::new(copy *opts);
 
-        compositor_chan.send(SetLayoutChan(layout_chan.clone()));
-        compositor_chan.send(SetRenderChan(render_chan.clone()));
+        let (engine_port, engine_chan) = comm::stream();
+        let (engine_port, engine_chan) = (Cell::new(engine_port), EngineChan::new(engine_chan));
 
         let compositor_chan = Cell::new(compositor_chan);
-
-        let opts = Cell::new(copy *opts);
-
+        let engine_chan_clone = Cell::new(engine_chan.clone());
         {
-            let engine_chan = engine_chan.clone();
             do task::spawn {
-                let compositor_chan = compositor_chan.take();
-                render_task::create_render_task(render_port.take(),
-                                                compositor_chan.clone(),
-                                                opts.with_ref(|o| copy *o),
-                                                profiler_chan.clone());
-
-                let opts = opts.take();
-
-                layout_task::create_layout_task(layout_port.take(),
-                                                script_chan.clone(),
-                                                render_chan.clone(),
-                                                image_cache_task.clone(),
-                                                opts,
-                                                profiler_chan.clone());
-
-                let compositor_chan_clone = compositor_chan.clone();
-                ScriptContext::create_script_context(layout_chan.clone(),
-                                                     script_port.take(),
-                                                     script_chan.clone(),
-                                                     engine_chan.clone(),
-                                                     |msg: ReadyState| {
-                                                         compositor_chan_clone.set_ready_state(msg)
-                                                     },
-                                                     resource_task.clone(),
-                                                     image_cache_task.clone());
-
-                Engine {
+                let mut engine = Engine {
+                    chan: engine_chan_clone.take(),
                     request_port: engine_port.take(),
-                    compositor_chan: compositor_chan.clone(),
-                    render_chan: render_chan.clone(),
+                    compositor_chan: compositor_chan.take(),
                     resource_task: resource_task.clone(),
                     image_cache_task: image_cache_task.clone(),
-                    layout_chan: layout_chan.clone(),
-                    script_chan: script_chan.clone(),
+                    pipelines: HashMap::new(),
+                    navigation_context: NavigationContext::new(),
+                    next_id: 0,
+                    current_token_holder: None,
+                    loading: None,
                     profiler_chan: profiler_chan.clone(),
-                }.run();
+                    opts: opts.take(),
+                };
+                engine.run();
             }
         }
         engine_chan
     }
 
-    fn run(&self) {
-        while self.handle_request(self.request_port.recv()) {
-            // Go on...
+    fn run(&mut self) {
+        loop {
+            let request = self.request_port.recv();
+            if !self.handle_request(request) {
+                break;
+            }
         }
     }
 
-    fn handle_request(&self, request: Msg) -> bool {
+    fn get_next_id(&mut self) -> uint {
+        let id = self.next_id;
+        self.next_id = id + 1;
+        id
+    }
+
+    fn handle_request(&mut self, request: Msg) -> bool {
         match request {
             LoadUrlMsg(url) => {
+                let pipeline_id = self.get_next_id();
+                let pipeline = Pipeline::create(pipeline_id,
+                                                self.chan.clone(),
+                                                self.compositor_chan.clone(),
+                                                self.image_cache_task.clone(),
+                                                self.resource_task.clone(),
+                                                self.profiler_chan.clone(),
+                                                copy self.opts);
                 if url.path.ends_with(".js") {
-                    self.script_chan.send(ExecuteMsg(url))
+                    pipeline.script_chan.send(ExecuteMsg(url));
                 } else {
-                    self.script_chan.send(LoadMsg(url))
+                    pipeline.script_chan.send(LoadMsg(url));
+                    self.loading = Some(pipeline_id);
                 }
-                return true
+                self.pipelines.insert(pipeline_id, pipeline);
             }
 
-            ExitMsg(sender) => {
-                self.script_chan.send(script_task::ExitMsg);
-                self.layout_chan.send(layout_interface::ExitMsg);
-
-                let (response_port, response_chan) = comm::stream();
+            RendererReadyMsg(pipeline_id) => {
+                let loading = self.loading.clone();
+                do loading.map() |&id| {
+                    if pipeline_id == id {
+                        match self.current_token_holder {
+                            Some(ref id) => {
+                                let current_holder = self.pipelines.find(id).get();
+                                current_holder.render_chan.send(TokenProcureMsg);
+                            }
+                            None => self.bestow_compositor_token(id, ~CompositorToken::new())
+                        }
+                    }
+                };
+            }
 
-                self.render_chan.send(render_task::ExitMsg(response_chan));
-                response_port.recv();
+            TokenSurrenderMsg(token) => {
+                self.remove_active_pipeline();
+                let loading = self.loading.clone();
+                let token = Cell::new(token);
+                do loading.map |&id| {
+                    self.bestow_compositor_token(id, token.take());
+                };
+            }
 
+            ExitMsg(sender) => {
+                for self.pipelines.each |_, pipeline| {
+                    pipeline.exit();
+                }
                 self.image_cache_task.exit();
                 self.resource_task.send(resource_task::Exit);
 
@@ -147,6 +182,31 @@ impl Engine {
                 return false
             }
         }
+        true
+    }
+    
+    fn remove_active_pipeline(&mut self) {
+// FIXME(tkuehn): currently, pipelines are not removed at all
+//        do self.current_token_holder.map |id| {
+//            self.pipelines.pop(id).unwrap().exit();
+//        };
+
+        self.current_token_holder = None;
+    }
+
+    fn bestow_compositor_token(&mut self, id: uint, compositor_token: ~CompositorToken) {
+        let pipeline = self.pipelines.find(&id);
+        match pipeline {
+            None => fail!("Id of pipeline that made token request does not have a \
+                          corresponding struct in Engine's pipelines. This is a bug. :-("),
+            Some(pipeline) => {
+                pipeline.render_chan.send(TokenBestowMsg(compositor_token));
+                self.compositor_chan.send(SetLayoutChan(pipeline.layout_chan.clone()));
+                self.current_token_holder = Some(id);
+                self.loading = None;
+                self.navigation_context.navigate(id);
+            }
+        }
     }
 }
 
diff --git a/src/components/main/layout/layout_task.rs b/src/components/main/layout/layout_task.rs
index 7f91d3dce29..29c3d800902 100644
--- a/src/components/main/layout/layout_task.rs
+++ b/src/components/main/layout/layout_task.rs
@@ -5,7 +5,6 @@
 //! The layout task. Performs layout on the DOM, builds display lists and sends them to be
 /// rendered.
 
-use compositing::CompositorChan;
 use css::matching::MatchMethods;
 use css::select::new_css_select_ctx;
 use layout::aux::{LayoutData, LayoutAuxMethods};
@@ -34,7 +33,7 @@ use script::dom::node::{AbstractNode, LayoutView};
 use script::layout_interface::{AddStylesheetMsg, ContentBoxQuery};
 use script::layout_interface::{HitTestQuery, ContentBoxResponse, HitTestResponse};
 use script::layout_interface::{ContentBoxesQuery, ContentBoxesResponse, ExitMsg, LayoutQuery};
-use script::layout_interface::{LayoutResponse, MatchSelectorsDocumentDamage, Msg};
+use script::layout_interface::{MatchSelectorsDocumentDamage, Msg};
 use script::layout_interface::{QueryMsg, RouteScriptMsg, Reflow, ReflowDocumentDamage};
 use script::layout_interface::{ReflowForDisplay, ReflowMsg};
 use script::script_task::{ReflowCompleteMsg, ScriptChan, ScriptMsg, SendEventMsg};
@@ -45,28 +44,10 @@ use servo_util::time::{ProfilerChan, profile, time};
 use servo_util::time;
 use extra::net::url::Url;
 
-pub fn create_layout_task(port: Port<Msg>,
-                          script_chan: ScriptChan,
-                          render_chan: RenderChan<CompositorChan>,
-                          img_cache_task: ImageCacheTask,
-                          opts: Opts,
-                          profiler_chan: ProfilerChan) {
-    let port = Cell::new(port);
-    do spawn {
-        let mut layout = Layout::new(port.take(),
-                                     script_chan.clone(),
-                                     render_chan.clone(),
-                                     img_cache_task.clone(),
-                                     &opts,
-                                     profiler_chan.clone());
-        layout.start();
-    };
-}
-
-struct Layout {
+struct LayoutTask {
     port: Port<Msg>,
     script_chan: ScriptChan,
-    render_chan: RenderChan<CompositorChan>,
+    render_chan: RenderChan,
     image_cache_task: ImageCacheTask,
     local_image_cache: @mut LocalImageCache,
     font_ctx: @mut FontContext,
@@ -80,17 +61,35 @@ struct Layout {
     profiler_chan: ProfilerChan,
 }
 
-impl Layout {
+impl LayoutTask {
+    pub fn create(port: Port<Msg>,
+                              script_chan: ScriptChan,
+                              render_chan: RenderChan,
+                              img_cache_task: ImageCacheTask,
+                              opts: Opts,
+                              profiler_chan: ProfilerChan) {
+        let port = Cell::new(port);
+        do spawn {
+            let mut layout = LayoutTask::new(port.take(),
+                                         script_chan.clone(),
+                                         render_chan.clone(),
+                                         img_cache_task.clone(),
+                                         &opts,
+                                         profiler_chan.clone());
+            layout.start();
+        };
+    }
+
     fn new(port: Port<Msg>,
            script_chan: ScriptChan,
-           render_chan: RenderChan<CompositorChan>, 
+           render_chan: RenderChan, 
            image_cache_task: ImageCacheTask,
            opts: &Opts,
            profiler_chan: ProfilerChan)
-           -> Layout {
+           -> LayoutTask {
         let fctx = @mut FontContext::new(opts.render_backend, true, profiler_chan.clone());
 
-        Layout {
+        LayoutTask {
             port: port,
             script_chan: script_chan,
             render_chan: render_chan,
@@ -135,10 +134,10 @@ impl Layout {
                     self.handle_reflow(data.take());
                 }
             }
-            QueryMsg(query, chan) => {
-                let chan = Cell::new(chan);
+            QueryMsg(query) => {
+                let query = Cell::new(query);
                 do profile(time::LayoutQueryCategory, self.profiler_chan.clone()) {
-                    self.handle_query(query, chan.take());
+                    self.handle_query(query.take());
                 }
             }
             RouteScriptMsg(script_msg) => {
@@ -268,9 +267,9 @@ impl Layout {
 
     /// Handles a query from the script task. This is the main routine that DOM functions like
     /// `getClientRects()` or `getBoundingClientRect()` ultimately invoke.
-    fn handle_query(&self, query: LayoutQuery, reply_chan: Chan<Result<LayoutResponse,()>>) {
+    fn handle_query(&self, query: LayoutQuery) {
         match query {
-            ContentBoxQuery(node) => {
+            ContentBoxQuery(node, reply_chan) => {
                 // FIXME: Isolate this transmutation into a single "bridge" module.
                 let node: AbstractNode<LayoutView> = unsafe {
                     transmute(node)
@@ -302,7 +301,7 @@ impl Layout {
 
                 reply_chan.send(response)
             }
-            ContentBoxesQuery(node) => {
+            ContentBoxesQuery(node, reply_chan) => {
                 // FIXME: Isolate this transmutation into a single "bridge" module.
                 let node: AbstractNode<LayoutView> = unsafe {
                     transmute(node)
@@ -322,7 +321,7 @@ impl Layout {
 
                 reply_chan.send(response)
             }
-            HitTestQuery(node, point) => {
+            HitTestQuery(node, point, reply_chan) => {
                 // FIXME: Isolate this transmutation into a single "bridge" module.
                 let node: AbstractNode<LayoutView> = unsafe {
                     transmute(node)
diff --git a/src/components/main/macros.rs b/src/components/main/macros.rs
index 8fe65bccfb6..169e0a0a201 100644
--- a/src/components/main/macros.rs
+++ b/src/components/main/macros.rs
@@ -1,7 +1,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * 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/. */
-
+#[macro_escape];
 {
     macro_rules! move_ref(
         { $x:expr } => { unsafe { let y <- *ptr::to_unsafe_ptr(*$x); y } }
@@ -68,4 +68,13 @@
             ])+)
         }
     )
+
+    macro_rules! closure_stream(
+        ($Msg:ty, $Chan:ident) => (
+            {
+                let (port, chan) = comm::stream::<$Msg>();
+                (Cell(port), $Chan::new(chan))
+            }
+        );
+    )
 }
diff --git a/src/components/main/pipeline.rs b/src/components/main/pipeline.rs
new file mode 100644
index 00000000000..95a247cca3b
--- /dev/null
+++ b/src/components/main/pipeline.rs
@@ -0,0 +1,105 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use compositing::CompositorChan;
+use gfx::render_task::{RenderChan, RenderTask};
+use gfx::render_task;
+use gfx::opts::Opts;
+use layout::layout_task::LayoutTask;
+use script::layout_interface::LayoutChan;
+use script::layout_interface;
+use servo_msg::engine::{EngineChan};
+use script::script_task::{ScriptTask, ScriptChan, ScriptMsg};
+use script::script_task;
+use servo_net::image_cache_task::ImageCacheTask;
+use servo_net::resource_task::ResourceTask;
+use servo_util::time::ProfilerChan;
+use std::comm;
+
+/// A uniquely-identifiable pipeline of stript task, layout task, and render task. 
+pub struct Pipeline {
+    id: uint,
+    script_chan: ScriptChan,
+    layout_chan: LayoutChan,
+    render_chan: RenderChan,
+}
+
+impl Pipeline {
+    /// Starts a render task, layout task, and script task. Returns the channels wrapped in a struct.
+    pub fn create(id: uint,
+                  engine_chan: EngineChan,
+                  compositor_chan: CompositorChan,
+                  image_cache_task: ImageCacheTask,
+                  resource_task: ResourceTask,
+                  profiler_chan: ProfilerChan,
+                  opts: Opts) -> Pipeline {
+        
+        macro_rules! closure_stream(
+            ($Msg:ty, $Chan:ident) => (
+                {
+                    let (port, chan) = comm::stream::<$Msg>();
+                    (port, $Chan::new(chan))
+                }
+            );
+        )
+        // Create the script port and channel.
+        let (script_port, script_chan) = closure_stream!(ScriptMsg, ScriptChan);
+
+        // Create the layout port and channel.
+        let (layout_port, layout_chan) = closure_stream!(layout_interface::Msg, LayoutChan);
+
+        let (render_port, render_chan) = comm::stream::<render_task::Msg>();
+        let render_chan = RenderChan::new(render_chan);
+
+        RenderTask::create(render_port,
+                           compositor_chan.clone(),
+                           copy opts,
+                           engine_chan.clone(),
+                           profiler_chan.clone());
+
+        LayoutTask::create(layout_port,
+                           script_chan.clone(),
+                           render_chan.clone(),
+                           image_cache_task.clone(),
+                           copy opts,
+                           profiler_chan.clone());
+
+        ScriptTask::create(id,
+                           compositor_chan.clone(),
+                           layout_chan.clone(),
+                           script_port,
+                           script_chan.clone(),
+                           engine_chan,
+                           resource_task.clone(),
+                           image_cache_task.clone());
+
+        Pipeline::new(id,
+                      script_chan,
+                      layout_chan,
+                      render_chan)
+    }
+
+    pub fn new(id: uint,
+               script_chan: ScriptChan,
+               layout_chan: LayoutChan,
+               render_chan: RenderChan)
+               -> Pipeline {
+        Pipeline {
+            id: id,
+            script_chan: script_chan,
+            layout_chan: layout_chan,
+            render_chan: render_chan,
+        }
+    }
+
+    pub fn exit(&self) {
+        self.script_chan.send(script_task::ExitMsg);
+        self.layout_chan.send(layout_interface::ExitMsg);
+
+        let (response_port, response_chan) = comm::stream();
+        self.render_chan.send(render_task::ExitMsg(response_chan));
+        response_port.recv();
+    }
+}
+
diff --git a/src/components/main/servo.rc b/src/components/main/servo.rc
index d2b3ae08c41..73ac4fa0a1d 100755
--- a/src/components/main/servo.rc
+++ b/src/components/main/servo.rc
@@ -63,6 +63,7 @@ pub mod css {
 }
 
 pub mod engine;
+pub mod pipeline;
 
 pub mod layout {
     pub mod block;
diff --git a/src/components/msg/compositor.rs b/src/components/msg/compositor.rs
index 6b6311fd1ba..6d8fe2ecc50 100644
--- a/src/components/msg/compositor.rs
+++ b/src/components/msg/compositor.rs
@@ -6,6 +6,7 @@ use azure::azure_hl::DrawTarget;
 use azure::azure::AzGLContext;
 use geom::rect::Rect;
 use geom::size::Size2D;
+use std::util::NonCopyable;
 
 pub struct LayerBuffer {
     draw_target: DrawTarget,
@@ -33,14 +34,6 @@ pub enum RenderState {
     RenderingRenderState,
 }
 
-/// The interface used by the renderer to acquire draw targets for each rendered frame and
-/// submit them to be drawn to the display.
-pub trait RenderListener {
-    fn get_gl_context(&self) -> AzGLContext;
-    fn paint(&self, layer_buffer_set: LayerBufferSet, new_size: Size2D<uint>);
-    fn set_render_state(&self, render_state: RenderState);
-}
-
 pub enum ReadyState {
     /// Informs the compositor that a page is loading. Used for setting status
     Loading,
@@ -50,8 +43,30 @@ pub enum ReadyState {
     FinishedLoading,
 }
 
+/// The interface used by the renderer to acquire draw targets for each render frame and
+/// submit them to be drawn to the display.
+pub trait RenderListener {
+    fn get_gl_context(&self) -> AzGLContext;
+    fn paint(&self, layer_buffer_set: LayerBufferSet, new_size: Size2D<uint>);
+    fn set_render_state(&self, render_state: RenderState);
+}
+
 /// The interface used by the script task to tell the compositor to update its ready state,
 /// which is used in displaying the appropriate message in the window's title.
 pub trait ScriptListener : Clone {
     fn set_ready_state(&self, ReadyState);
 }
+
+/// Signifies control of the compositor. Only the render task controlling
+/// the compositor token may send paint messages to the compositor
+pub struct CompositorToken {
+    construction_restrictor: NonCopyable,
+}
+
+impl CompositorToken {
+    pub fn new() -> CompositorToken {
+        CompositorToken {
+            construction_restrictor: NonCopyable::new(),
+        }
+    }
+}
diff --git a/src/components/msg/engine.rs b/src/components/msg/engine.rs
index 83e0f085ee0..b03893d14ca 100644
--- a/src/components/msg/engine.rs
+++ b/src/components/msg/engine.rs
@@ -7,6 +7,9 @@
 
 use std::comm::{Chan, SharedChan};
 use extra::net::url::Url;
+use compositor::CompositorToken;
+
+pub use compositor;
 
 #[deriving(Clone)]
 pub struct EngineChan {
@@ -27,5 +30,7 @@ impl EngineChan {
 pub enum Msg {
     LoadUrlMsg(Url),
     ExitMsg(Chan<()>),
+    RendererReadyMsg(uint),
+    TokenSurrenderMsg(~CompositorToken),
 }
 
diff --git a/src/components/script/dom/bindings/element.rs b/src/components/script/dom/bindings/element.rs
index 9a34f7c5dc6..b79daf75db7 100644
--- a/src/components/script/dom/bindings/element.rs
+++ b/src/components/script/dom/bindings/element.rs
@@ -16,6 +16,7 @@ use std::cast;
 use std::i32;
 use std::libc;
 use std::libc::c_uint;
+use std::comm;
 use std::ptr;
 use std::ptr::null;
 use std::result;
@@ -229,13 +230,9 @@ extern fn HTMLImageElement_getWidth(cx: *JSContext, _argc: c_uint, vp: *mut JSVa
         let width = match node.type_id() {
             ElementNodeTypeId(HTMLImageElementTypeId) => {
                 let script_context = task_from_context(cx);
-                match (*script_context).query_layout(ContentBoxQuery(node)) {
-                    Ok(rect) => {
-                        match rect {
-                            ContentBoxResponse(rect) => rect.size.width.to_px(),
-                            _ => fail!(~"unexpected layout reply")
-                        }
-                    }
+                let (port, chan) = comm::stream();
+                match (*script_context).query_layout(ContentBoxQuery(node, chan), port) {
+                    Ok(ContentBoxResponse(rect)) => rect.size.width.to_px(),
                     Err(()) => 0
                 }
                 // TODO: if nothing is being rendered(?), return zero dimensions
diff --git a/src/components/script/dom/bindings/proxyhandler.rs b/src/components/script/dom/bindings/proxyhandler.rs
index 2780a969eb2..cbbc4f1525d 100644
--- a/src/components/script/dom/bindings/proxyhandler.rs
+++ b/src/components/script/dom/bindings/proxyhandler.rs
@@ -71,7 +71,7 @@ pub fn _obj_toString(cx: *JSContext, className: *libc::c_char) -> *JSString {
         return ptr::null();
     }
 
-    let result = ~"[object " + name + ~"]";
+    let result = ~"[object " + name + "]";
     for result.iter().enumerate().advance |(i, c)| {
       *chars.offset(i) = c as jschar;
     }
@@ -86,4 +86,4 @@ pub fn _obj_toString(cx: *JSContext, className: *libc::c_char) -> *JSString {
 
 pub fn GetExpandoObject(_proxy: *JSObject) -> *JSObject {
     ptr::null()
-}
\ No newline at end of file
+}
diff --git a/src/components/script/dom/bindings/utils.rs b/src/components/script/dom/bindings/utils.rs
index 9d3105fefca..5a42e109268 100644
--- a/src/components/script/dom/bindings/utils.rs
+++ b/src/components/script/dom/bindings/utils.rs
@@ -21,12 +21,12 @@ use js::glue::{PROPERTY_STUB, STRICT_PROPERTY_STUB, ENUMERATE_STUB, CONVERT_STUB
 use js::jsapi::{JS_AlreadyHasOwnProperty, JS_NewObject, JS_NewFunction};
 use js::jsapi::{JS_DefineProperties, JS_WrapValue, JS_ForwardGetPropertyTo};
 use js::jsapi::{JS_EncodeString, JS_free, JS_GetStringCharsAndLength};
-use js::jsapi::{JS_GetClass, JS_GetPrototype, JS_LinkConstructorAndPrototype};
+use js::jsapi::{JS_GetClass, JS_LinkConstructorAndPrototype};
 use js::jsapi::{JS_GetFunctionPrototype, JS_InternString, JS_GetFunctionObject};
 use js::jsapi::{JS_HasPropertyById, JS_GetPrototype, JS_GetGlobalForObject};
 use js::jsapi::{JS_NewStringCopyN, JS_DefineFunctions, JS_DefineProperty};
 use js::jsapi::{JS_ValueToString, JS_GetReservedSlot, JS_SetReservedSlot};
-use js::jsapi::{JSContext, JSVal, JSObject, JSBool, jsid, JSClass, JSNative};
+use js::jsapi::{JSContext, JSObject, JSBool, jsid, JSClass, JSNative};
 use js::jsapi::{JSFunctionSpec, JSPropertySpec, JSVal, JSPropertyDescriptor};
 use js::jsfriendapi::bindgen::JS_NewObjectWithUniqueType;
 use js::rust::Compartment;
@@ -83,7 +83,7 @@ extern fn InterfaceObjectToString(cx: *JSContext, _argc: uint, vp: *mut JSVal) -
     }
 
     let name = jsval_to_str(cx, *v).get();
-    let retval = str(~"function " + name + ~"() {\n    [native code]\n}");
+    let retval = str(~"function " + name + "() {\n    [native code]\n}");
     *vp = domstring_to_jsval(cx, &retval);
     return 1;
   }
diff --git a/src/components/script/dom/element.rs b/src/components/script/dom/element.rs
index e707a95ebb9..2595a68657d 100644
--- a/src/components/script/dom/element.rs
+++ b/src/components/script/dom/element.rs
@@ -12,6 +12,7 @@ use layout_interface::{ContentBoxQuery, ContentBoxResponse, ContentBoxesQuery};
 use layout_interface::{ContentBoxesResponse};
 
 use std::cell::Cell;
+use std::comm;
 use std::uint;
 use std::str::eq_slice;
 use extra::net::url::Url;
@@ -165,20 +166,19 @@ impl<'self> Element {
                     Some(win) => {
                         let node = self.parent.abstract.get();
                         assert!(node.is_element());
-                        let script_context = unsafe {
-                            &mut *win.script_context
+                        let script_task = unsafe {
+                            &mut *win.script_task
                         };
-                        match script_context.query_layout(ContentBoxesQuery(node)) {
-                            Ok(rects) => match rects {
-                                ContentBoxesResponse(rects) =>
-                                    do rects.map |r| {
-                                        ClientRect::new(
-                                             r.origin.y.to_f32(),
-                                             (r.origin.y + r.size.height).to_f32(),
-                                             r.origin.x.to_f32(),
-                                             (r.origin.x + r.size.width).to_f32())
-                                    },
-                                _ => fail!(~"unexpected layout reply")
+                        let (port, chan) = comm::stream();
+                        match script_task.query_layout(ContentBoxesQuery(node, chan), port) {
+                            Ok(ContentBoxesResponse(rects)) => {
+                                do rects.map |r| {
+                                    ClientRect::new(
+                                         r.origin.y.to_f32(),
+                                         (r.origin.y + r.size.height).to_f32(),
+                                         r.origin.x.to_f32(),
+                                         (r.origin.x + r.size.width).to_f32())
+                                }
                             },
                             Err(()) => {
                                 debug!("layout query error");
@@ -207,16 +207,15 @@ impl<'self> Element {
                     Some(win) => {
                         let node = self.parent.abstract.get();
                         assert!(node.is_element());
-                        let script_context = unsafe { &mut *win.script_context };
-                        match script_context.query_layout(ContentBoxQuery(node)) {
-                            Ok(rect) => match rect {
-                                ContentBoxResponse(rect) =>
-                                    Some(ClientRect::new(
-                                             rect.origin.y.to_f32(),
-                                             (rect.origin.y + rect.size.height).to_f32(),
-                                             rect.origin.x.to_f32(),
-                                             (rect.origin.x + rect.size.width).to_f32())),
-                                _ => fail!(~"unexpected layout result")
+                        let script_task = unsafe { &mut *win.script_task };
+                        let (port, chan) = comm::stream();
+                        match script_task.query_layout(ContentBoxQuery(node, chan), port) {
+                            Ok(ContentBoxResponse(rect)) => {
+                                Some(ClientRect::new(
+                                         rect.origin.y.to_f32(),
+                                         (rect.origin.y + rect.size.height).to_f32(),
+                                         rect.origin.x.to_f32(),
+                                         (rect.origin.x + rect.size.width).to_f32()))
                             },
                             Err(()) => {
                                 debug!("error querying layout");
diff --git a/src/components/script/dom/event.rs b/src/components/script/dom/event.rs
index 047b734e6b4..6b4be15b701 100644
--- a/src/components/script/dom/event.rs
+++ b/src/components/script/dom/event.rs
@@ -9,8 +9,6 @@ use dom::bindings::utils::{DOMString, ErrorResult, WrapperCache};
 
 use geom::point::Point2D;
 
-use std::comm;
-
 pub enum Event {
     ResizeEvent(uint, uint), 
     ReflowEvent,
diff --git a/src/components/script/dom/window.rs b/src/components/script/dom/window.rs
index 5fb07c66f07..41f99eaa9e9 100644
--- a/src/components/script/dom/window.rs
+++ b/src/components/script/dom/window.rs
@@ -6,7 +6,7 @@ use dom::bindings::utils::WrapperCache;
 use dom::bindings::window;
 
 use layout_interface::ReflowForScriptQuery;
-use script_task::{ExitMsg, FireTimerMsg, ScriptChan, ScriptContext};
+use script_task::{ExitMsg, FireTimerMsg, ScriptChan, ScriptTask};
 
 use std::comm;
 use std::comm::Chan;
@@ -29,7 +29,7 @@ pub enum TimerControlMsg {
 pub struct Window {
     timer_chan: Chan<TimerControlMsg>,
     script_chan: ScriptChan,
-    script_context: *mut ScriptContext,
+    script_task: *mut ScriptTask,
     wrapper: WrapperCache
 }
 
@@ -89,11 +89,11 @@ impl Window {
 
     pub fn content_changed(&self) {
         unsafe {
-            (*self.script_context).reflow_all(ReflowForScriptQuery)
+            (*self.script_task).reflow_all(ReflowForScriptQuery)
         }
     }
 
-    pub fn new(script_chan: ScriptChan, script_context: *mut ScriptContext)
+    pub fn new(script_chan: ScriptChan, script_task: *mut ScriptTask)
                -> @mut Window {
         let script_chan_clone = script_chan.clone();
         let win = @mut Window {
@@ -112,11 +112,11 @@ impl Window {
                 }
                 timer_chan
             },
-            script_context: script_context,
+            script_task: script_task,
         };
 
         unsafe {
-            let compartment = (*script_context).js_compartment;
+            let compartment = (*script_task).js_compartment;
             window::create(compartment, win);
         }
         win
diff --git a/src/components/script/html/hubbub_html_parser.rs b/src/components/script/html/hubbub_html_parser.rs
index 6309e488d7e..9540fcc87d4 100644
--- a/src/components/script/html/hubbub_html_parser.rs
+++ b/src/components/script/html/hubbub_html_parser.rs
@@ -303,9 +303,9 @@ pub fn parse_html(url: Url,
                 // Handle CSS style sheets from <link> elements
                 ElementNodeTypeId(HTMLLinkElementTypeId) => {
                     do node.with_imm_element |element| {
-                        match (element.get_attr(~"rel"), element.get_attr(~"href")) {
+                        match (element.get_attr("rel"), element.get_attr("href")) {
                             (Some(rel), Some(href)) => {
-                                if rel == ~"stylesheet" {
+                                if rel == "stylesheet" {
                                     debug!("found CSS stylesheet: %s", href);
                                     let url = make_url(href.to_str(), Some(url2.clone()));
                                     css_chan2.send(CSSTaskNewFile(UrlProvenance(url)));
@@ -317,7 +317,7 @@ pub fn parse_html(url: Url,
                 },
                 ElementNodeTypeId(HTMLImageElementTypeId) => {
                     do node.with_mut_image_element |image_element| {
-                        let src_opt = image_element.parent.get_attr(~"src").map(|x| x.to_str());
+                        let src_opt = image_element.parent.get_attr("src").map(|x| x.to_str());
                         match src_opt {
                             None => {}
                             Some(src) => {
@@ -401,7 +401,7 @@ pub fn parse_html(url: Url,
                 unsafe {
                     let script: AbstractNode<ScriptView> = NodeWrapping::from_hubbub_node(script);
                     do script.with_imm_element |script| {
-                        match script.get_attr(~"src") {
+                        match script.get_attr("src") {
                             Some(src) => {
                                 debug!("found script: %s", src);
                                 let new_url = make_url(src.to_str(), Some(url.clone()));
diff --git a/src/components/script/layout_interface.rs b/src/components/script/layout_interface.rs
index 3a1531b83e6..766c728067b 100644
--- a/src/components/script/layout_interface.rs
+++ b/src/components/script/layout_interface.rs
@@ -30,7 +30,7 @@ pub enum Msg {
     /// Performs a synchronous layout request.
     ///
     /// FIXME(pcwalton): As noted below, this isn't very type safe.
-    QueryMsg(LayoutQuery, Chan<Result<LayoutResponse,()>>),
+    QueryMsg(LayoutQuery),
 
     /// Routes a message (usually from the compositor) to the appropriate script task
     RouteScriptMsg(ScriptMsg),
@@ -42,25 +42,16 @@ pub enum Msg {
 /// Synchronous messages that script can send to layout.
 pub enum LayoutQuery {
     /// Requests the dimensions of the content box, as in the `getBoundingClientRect()` call.
-    ContentBoxQuery(AbstractNode<ScriptView>),
+    ContentBoxQuery(AbstractNode<ScriptView>, Chan<Result<ContentBoxResponse, ()>>),
     /// Requests the dimensions of all the content boxes, as in the `getClientRects()` call.
-    ContentBoxesQuery(AbstractNode<ScriptView>),
+    ContentBoxesQuery(AbstractNode<ScriptView>, Chan<Result<ContentBoxesResponse, ()>>),
     /// Requests the node containing the point of interest
-    HitTestQuery(AbstractNode<ScriptView>, Point2D<f32>),
+    HitTestQuery(AbstractNode<ScriptView>, Point2D<f32>, Chan<Result<HitTestResponse, ()>>),
 }
 
-/// The reply of a synchronous message from script to layout.
-///
-/// FIXME(pcwalton): This isn't very type safe. Maybe `LayoutQuery` objects should include
-/// response channels?
-pub enum LayoutResponse {
-    /// A response to the `ContentBoxQuery` message.
-    ContentBoxResponse(Rect<Au>),
-    /// A response to the `ContentBoxesQuery` message.
-    ContentBoxesResponse(~[Rect<Au>]),
-    /// A response to the `HitTestQuery` message.
-    HitTestResponse(AbstractNode<LayoutView>),
-}
+pub struct ContentBoxResponse(Rect<Au>);
+pub struct ContentBoxesResponse(~[Rect<Au>]);
+pub struct HitTestResponse(AbstractNode<LayoutView>);
 
 /// Determines which part of the 
 pub enum DocumentDamageLevel {
diff --git a/src/components/script/script_task.rs b/src/components/script/script_task.rs
index 7ef0b0035e1..ce89ef5efd7 100644
--- a/src/components/script/script_task.rs
+++ b/src/components/script/script_task.rs
@@ -5,19 +5,21 @@
 /// The script task is the task that owns the DOM in memory, runs JavaScript, and spawns parsing
 /// and layout tasks.
 
-use servo_msg::compositor::{ReadyState, Loading, PerformingLayout, FinishedLoading};
+use servo_msg::compositor::{ScriptListener, Loading, PerformingLayout};
+use servo_msg::compositor::FinishedLoading;
 use dom::bindings::utils::GlobalStaticData;
 use dom::document::Document;
 use dom::element::Element;
 use dom::event::{Event, ResizeEvent, ReflowEvent, ClickEvent, MouseDownEvent, MouseUpEvent};
 use dom::node::{AbstractNode, ScriptView, define_bindings};
 use dom::window::Window;
-use layout_interface::{AddStylesheetMsg, DocumentDamage, DocumentDamageLevel, HitTestQuery};
-use layout_interface::{HitTestResponse, LayoutQuery, LayoutResponse, LayoutChan};
-use layout_interface::{MatchSelectorsDocumentDamage, QueryMsg, Reflow, ReflowDocumentDamage};
-use layout_interface::{ReflowForDisplay, ReflowForScriptQuery, ReflowGoal, ReflowMsg};
+use layout_interface::{AddStylesheetMsg, DocumentDamage};
+use layout_interface::{DocumentDamageLevel, HitTestQuery, HitTestResponse, LayoutQuery};
+use layout_interface::{LayoutChan, MatchSelectorsDocumentDamage, QueryMsg, Reflow};
+use layout_interface::{ReflowDocumentDamage, ReflowForDisplay, ReflowForScriptQuery, ReflowGoal};
+use layout_interface::ReflowMsg;
 use layout_interface;
-use servo_msg::engine::{EngineChan, LoadUrlMsg};
+use servo_msg::engine::{EngineChan, LoadUrlMsg, RendererReadyMsg};
 
 use std::cast::transmute;
 use std::cell::Cell;
@@ -91,7 +93,9 @@ pub struct Frame {
 /// frames.
 ///
 /// FIXME: Rename to `Page`, following WebKit?
-pub struct ScriptContext {
+pub struct ScriptTask {
+    /// A unique identifier to the script's pipeline
+    id: uint,
     /// A handle to the layout task.
     layout_chan: LayoutChan,
     /// A handle to the image cache task.
@@ -110,8 +114,8 @@ pub struct ScriptContext {
 
     /// For communicating load url messages to the engine
     engine_chan: EngineChan,
-    /// For communicating loading messages to the compositor
-    compositor_task: ~fn(ReadyState),
+    /// For permission to communicate ready state messages to the compositor
+    compositor: @ScriptListener,
 
     /// The JavaScript runtime.
     js_runtime: js::rust::rt,
@@ -134,26 +138,26 @@ pub struct ScriptContext {
     damage: Option<DocumentDamage>,
 }
 
-fn global_script_context_key(_: @ScriptContext) {}
+fn global_script_context_key(_: @ScriptTask) {}
 
 /// Returns this task's script context singleton.
-pub fn global_script_context() -> @ScriptContext {
+pub fn global_script_context() -> @ScriptTask {
     unsafe {
         local_data::local_data_get(global_script_context_key).get()
     }
 }
 
-/// Returns the script context from the JS Context.
+/// Returns the script task from the JS Context.
 ///
 /// FIXME: Rename to `script_context_from_js_context`.
-pub fn task_from_context(js_context: *JSContext) -> *mut ScriptContext {
+pub fn task_from_context(js_context: *JSContext) -> *mut ScriptTask {
     unsafe {
-        JS_GetContextPrivate(js_context) as *mut ScriptContext
+        JS_GetContextPrivate(js_context) as *mut ScriptTask
     }
 }
 
 #[unsafe_destructor]
-impl Drop for ScriptContext {
+impl Drop for ScriptTask {
     fn finalize(&self) {
         unsafe {
             let _ = local_data::local_data_pop(global_script_context_key);
@@ -161,16 +165,17 @@ impl Drop for ScriptContext {
     }
 }
 
-impl ScriptContext {
-    /// Creates a new script context.
-    pub fn new(layout_chan: LayoutChan,
+impl ScriptTask {
+    /// Creates a new script task.
+    pub fn new(id: uint,
+               compositor: @ScriptListener,
+               layout_chan: LayoutChan,
                script_port: Port<ScriptMsg>,
                script_chan: ScriptChan,
                engine_chan: EngineChan,
-               compositor_task: ~fn(ReadyState),
                resource_task: ResourceTask,
                img_cache_task: ImageCacheTask)
-               -> @mut ScriptContext {
+               -> @mut ScriptTask {
         let js_runtime = js::rust::rt();
         let js_context = js_runtime.cx();
 
@@ -182,7 +187,10 @@ impl ScriptContext {
               Err(()) => fail!("Failed to create a compartment"),
         };
 
-        let script_context = @mut ScriptContext {
+        let script_task = @mut ScriptTask {
+            id: id,
+            compositor: compositor,
+
             layout_chan: layout_chan,
             image_cache_task: img_cache_task,
             resource_task: resource_task,
@@ -192,7 +200,6 @@ impl ScriptContext {
             script_chan: script_chan,
 
             engine_chan: engine_chan,
-            compositor_task: compositor_task,
 
             js_runtime: js_runtime,
             js_context: js_context,
@@ -207,17 +214,17 @@ impl ScriptContext {
             damage: None,
         };
         // Indirection for Rust Issue #6248, dynamic freeze scope artifically extended
-        let script_context_ptr = {
-            let borrowed_ctx= &mut *script_context;
-            borrowed_ctx as *mut ScriptContext
+        let script_task_ptr = {
+            let borrowed_ctx= &mut *script_task;
+            borrowed_ctx as *mut ScriptTask
         };
 
         unsafe {
-            js_context.set_cx_private(script_context_ptr as *());
-            local_data::local_data_set(global_script_context_key, transmute(script_context))
+            js_context.set_cx_private(script_task_ptr as *());
+            local_data::local_data_set(global_script_context_key, transmute(script_task))
         }
 
-        script_context
+        script_task
     }
 
     /// Starts the script task. After calling this method, the script task will loop receiving
@@ -228,27 +235,29 @@ impl ScriptContext {
         }
     }
 
-    pub fn create_script_context(layout_chan: LayoutChan,
-                                 script_port: Port<ScriptMsg>,
-                                 script_chan: ScriptChan,
-                                 engine_chan: EngineChan,
-                                 compositor_task: ~fn(ReadyState),
-                                 resource_task: ResourceTask,
-                                 image_cache_task: ImageCacheTask) {
+    pub fn create<C: ScriptListener + Owned>(id: uint,
+                  compositor: C,
+                  layout_chan: LayoutChan,
+                  script_port: Port<ScriptMsg>,
+                  script_chan: ScriptChan,
+                  engine_chan: EngineChan,
+                  resource_task: ResourceTask,
+                  image_cache_task: ImageCacheTask) {
+        let compositor = Cell::new(compositor);
         let script_port = Cell::new(script_port);
-        let compositor_task = Cell::new(compositor_task);
         // FIXME: rust#6399
         let mut the_task = task();
         the_task.sched_mode(SingleThreaded);
-        do the_task.spawn {
-            let script_context = ScriptContext::new(layout_chan.clone(),
-                                                    script_port.take(),
-                                                    script_chan.clone(),
-                                                    engine_chan.clone(),
-                                                    compositor_task.take(),
-                                                    resource_task.clone(),
-                                                    image_cache_task.clone());
-            script_context.start();
+        do spawn {
+            let script_task = ScriptTask::new(id,
+                                              @compositor.take() as @ScriptListener,
+                                              layout_chan.clone(),
+                                              script_port.take(),
+                                              script_chan.clone(),
+                                              engine_chan.clone(),
+                                              resource_task.clone(),
+                                              image_cache_task.clone());
+            script_task.start();
         }
     }
 
@@ -324,7 +333,8 @@ impl ScriptContext {
     /// Handles a notification that reflow completed.
     fn handle_reflow_complete_msg(&mut self) {
         self.layout_join_port = None;
-        self.set_ready_state(FinishedLoading)
+        self.engine_chan.send(RendererReadyMsg(self.id));
+        self.compositor.set_ready_state(FinishedLoading);
     }
 
     /// Handles a request to exit the script task and shut down layout.
@@ -337,12 +347,6 @@ impl ScriptContext {
         self.layout_chan.send(layout_interface::ExitMsg)
     }
 
-    // tells the compositor when loading starts and finishes
-    // FIXME ~compositor_interface doesn't work right now, which is why this is necessary
-    fn set_ready_state(&self, msg: ReadyState) {
-        (self.compositor_task)(msg);
-    }
-
     /// The entry point to document loading. Defines bindings, sets up the window and document
     /// objects, parses HTML and CSS, and kicks off initial layout.
     fn load(&mut self, url: Url) {
@@ -354,7 +358,7 @@ impl ScriptContext {
             self.bindings_initialized = true
         }
 
-        self.set_ready_state(Loading);
+        self.compositor.set_ready_state(Loading);
         // Parse HTML.
         //
         // Note: We can parse the next document in parallel with any previous documents.
@@ -446,7 +450,7 @@ impl ScriptContext {
         self.join_layout();
 
         // Tell the user that we're performing layout.
-        self.set_ready_state(PerformingLayout);
+        self.compositor.set_ready_state(PerformingLayout);
 
         // Layout will let us know when it's done.
         let (join_port, join_chan) = comm::stream();
@@ -478,7 +482,7 @@ impl ScriptContext {
     /// FIXME: This should basically never be used.
     pub fn reflow_all(&mut self, goal: ReflowGoal) {
         for self.root_frame.iter().advance |root_frame| {
-            ScriptContext::damage(&mut self.damage,
+            ScriptTask::damage(&mut self.damage,
                                   root_frame.document.root,
                                   MatchSelectorsDocumentDamage)
         }
@@ -487,12 +491,10 @@ impl ScriptContext {
     }
 
     /// Sends the given query to layout.
-    pub fn query_layout(&mut self, query: LayoutQuery) -> Result<LayoutResponse,()> {
-         self.join_layout();
-
-         let (response_port, response_chan) = comm::stream();
-         self.layout_chan.send(QueryMsg(query, response_chan));
-         response_port.recv()
+    pub fn query_layout<T: Owned>(&mut self, query: LayoutQuery, response_port: Port<Result<T, ()>>) -> Result<T,()> {
+        self.join_layout();
+        self.layout_chan.send(QueryMsg(query));
+        response_port.recv()
     }
 
     /// Adds the given damage.
@@ -526,7 +528,7 @@ impl ScriptContext {
                 self.window_size = Size2D(new_width, new_height);
 
                 for self.root_frame.iter().advance |root_frame| {
-                    ScriptContext::damage(&mut self.damage,
+                    ScriptTask::damage(&mut self.damage,
                                           root_frame.document.root,
                                           ReflowDocumentDamage);
                 }
@@ -541,7 +543,7 @@ impl ScriptContext {
                 debug!("script got reflow event");
 
                 for self.root_frame.iter().advance |root_frame| {
-                    ScriptContext::damage(&mut self.damage,
+                    ScriptTask::damage(&mut self.damage,
                                           root_frame.document.root,
                                           MatchSelectorsDocumentDamage);
                 }
@@ -557,7 +559,8 @@ impl ScriptContext {
                     Some(ref frame) => frame.document.root,
                     None => fail!("root frame is None")
                 };
-                match self.query_layout(HitTestQuery(root, point)) {
+                let (port, chan) = comm::stream();
+                match self.query_layout(HitTestQuery(root, point, chan), port) {
                     Ok(node) => match node {
                         HitTestResponse(node) => {
                             debug!("clicked on %?", node.debug_str());
@@ -580,7 +583,6 @@ impl ScriptContext {
                                 }
                             }
                         }
-                        _ => fail!(~"unexpected layout reply")
                     },
                     Err(()) => {
                         debug!(fmt!("layout query error"));
@@ -594,7 +596,7 @@ impl ScriptContext {
 
     priv fn load_url_from_element(&self, element: &Element) {
         // if the node's element is "a," load url from href attr
-        for element.attrs.each |attr| {
+        for element.attrs.iter().advance |attr| {
             if attr.name == ~"href" {
                 debug!("clicked on link to %?", attr.value); 
                 let current_url = match self.root_frame {
diff --git a/src/support/alert/rust-alert b/src/support/alert/rust-alert
-Subproject 68875af396cb583e670dd5caad99431dac62f8d
+Subproject 502ec156da38860a4dff911cf8f33f388a0a188