Auto merge of #6795 - pcwalton:display-list-e10s-fixes, r=glennw

Send display lists over IPC in multiprocess mode.

This patch set introduces the `--multiprocess` (`-M`) switch. Right now, all it does it cause display lists to be serialized, but eventually it will cause actual processes to be spawned.

r? @metajack

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16 files changed, 258 insertions, 189 deletions

diff --git a/components/compositing/compositor.rs b/components/compositing/compositor.rs
index 0061a4baa40..b3830a11140 100644
--- a/components/compositing/compositor.rs
+++ b/components/compositing/compositor.rs
@@ -4,8 +4,7 @@
 
 use surface_map::SurfaceMap;
 use compositor_layer::{CompositorData, CompositorLayer, WantsScrollEventsFlag};
-use compositor_task::{CompositorEventListener, CompositorProxy, CompositorReceiver};
-use compositor_task::Msg;
+use compositor_task::{CompositorEventListener, CompositorProxy, CompositorReceiver, Msg};
 use constellation::SendableFrameTree;
 use pipeline::CompositionPipeline;
 use scrolling::ScrollingTimerProxy;
@@ -18,8 +17,7 @@ use euclid::rect::{Rect, TypedRect};
 use euclid::scale_factor::ScaleFactor;
 use euclid::size::{Size2D, TypedSize2D};
 use gfx_traits::color;
-use gfx::paint_task::Msg as PaintMsg;
-use gfx::paint_task::PaintRequest;
+use gfx::paint_task::{ChromeToPaintMsg, PaintRequest};
 use gleam::gl::types::{GLint, GLsizei};
 use gleam::gl;
 use ipc_channel::ipc;
@@ -1306,8 +1304,8 @@ impl<Window: WindowMethods> IOCompositor<Window> {
             self.convert_buffer_requests_to_pipeline_requests_map(layers_and_requests);
 
         for (pipeline_id, requests) in pipeline_requests.into_iter() {
-            let msg = PaintMsg::Paint(requests, self.frame_tree_id);
-            let _ = self.get_pipeline(pipeline_id).paint_chan.send(msg);
+            let msg = ChromeToPaintMsg::Paint(requests, self.frame_tree_id);
+            let _ = self.get_pipeline(pipeline_id).chrome_to_paint_chan.send(msg);
         }
 
         true
diff --git a/components/compositing/pipeline.rs b/components/compositing/pipeline.rs
index d1acc51b641..83e5c0c2bc1 100644
--- a/components/compositing/pipeline.rs
+++ b/components/compositing/pipeline.rs
@@ -11,8 +11,7 @@ use compositor_task;
 use devtools_traits::{DevtoolsControlChan, DevtoolsControlMsg, ScriptToDevtoolsControlMsg};
 use euclid::rect::{TypedRect};
 use euclid::scale_factor::ScaleFactor;
-use gfx::paint_task::Msg as PaintMsg;
-use gfx::paint_task::{PaintChan, PaintTask};
+use gfx::paint_task::{ChromeToPaintMsg, LayoutToPaintMsg, PaintTask};
 use gfx::font_cache_task::FontCacheTask;
 use ipc_channel::ipc::{self, IpcReceiver, IpcSender};
 use ipc_channel::router::ROUTER;
@@ -30,7 +29,9 @@ use std::mem;
 use std::sync::mpsc::{Receiver, Sender, channel};
 use std::thread;
 use url::Url;
+use util;
 use util::geometry::{PagePx, ViewportPx};
+use util::ipc::OptionalIpcSender;
 use util::opts;
 
 /// A uniquely-identifiable pipeline of script task, layout task, and paint task.
@@ -40,7 +41,7 @@ pub struct Pipeline {
     pub script_chan: ScriptControlChan,
     /// A channel to layout, for performing reflows and shutdown.
     pub layout_chan: LayoutControlChan,
-    pub paint_chan: PaintChan,
+    pub chrome_to_paint_chan: Sender<ChromeToPaintMsg>,
     pub layout_shutdown_port: Receiver<()>,
     pub paint_shutdown_port: Receiver<()>,
     /// URL corresponding to the most recently-loaded page.
@@ -60,7 +61,7 @@ pub struct CompositionPipeline {
     pub id: PipelineId,
     pub script_chan: ScriptControlChan,
     pub layout_chan: LayoutControlChan,
-    pub paint_chan: PaintChan,
+    pub chrome_to_paint_chan: Sender<ChromeToPaintMsg>,
 }
 
 impl Pipeline {
@@ -84,7 +85,8 @@ impl Pipeline {
                            device_pixel_ratio: ScaleFactor<ViewportPx, DevicePixel, f32>)
                            -> (Pipeline, PipelineContent)
                            where LTF: LayoutTaskFactory, STF:ScriptTaskFactory {
-        let (paint_port, paint_chan) = PaintChan::new();
+        let (layout_to_paint_chan, layout_to_paint_port) = util::ipc::optional_ipc_channel();
+        let (chrome_to_paint_chan, chrome_to_paint_port) = channel();
         let (paint_shutdown_chan, paint_shutdown_port) = channel();
         let (layout_shutdown_chan, layout_shutdown_port) = channel();
         let (pipeline_chan, pipeline_port) = ipc::channel().unwrap();
@@ -123,7 +125,7 @@ impl Pipeline {
                     new_pipeline_id: id,
                     subpage_id: subpage_id,
                     load_data: load_data.clone(),
-                    paint_chan: box paint_chan.clone() as Box<Any + Send>,
+                    paint_chan: box layout_to_paint_chan.clone() as Box<Any + Send>,
                     failure: failure,
                     pipeline_port: mem::replace(&mut pipeline_port, None).unwrap(),
                     layout_shutdown_chan: layout_shutdown_chan.clone(),
@@ -144,7 +146,7 @@ impl Pipeline {
                                      parent_info,
                                      script_chan.clone(),
                                      LayoutControlChan(pipeline_chan),
-                                     paint_chan.clone(),
+                                     chrome_to_paint_chan.clone(),
                                      layout_shutdown_port,
                                      paint_shutdown_port,
                                      load_data.url.clone(),
@@ -167,8 +169,10 @@ impl Pipeline {
             load_data: load_data,
             failure: failure,
             script_port: script_port,
-            paint_chan: paint_chan,
-            paint_port: Some(paint_port),
+            layout_to_paint_chan: layout_to_paint_chan,
+            chrome_to_paint_chan: chrome_to_paint_chan,
+            layout_to_paint_port: Some(layout_to_paint_port),
+            chrome_to_paint_port: Some(chrome_to_paint_port),
             pipeline_port: pipeline_port,
             paint_shutdown_chan: paint_shutdown_chan,
             layout_shutdown_chan: layout_shutdown_chan,
@@ -181,7 +185,7 @@ impl Pipeline {
                parent_info: Option<(PipelineId, SubpageId)>,
                script_chan: ScriptControlChan,
                layout_chan: LayoutControlChan,
-               paint_chan: PaintChan,
+               chrome_to_paint_chan: Sender<ChromeToPaintMsg>,
                layout_shutdown_port: Receiver<()>,
                paint_shutdown_port: Receiver<()>,
                url: Url,
@@ -192,7 +196,7 @@ impl Pipeline {
             parent_info: parent_info,
             script_chan: script_chan,
             layout_chan: layout_chan,
-            paint_chan: paint_chan,
+            chrome_to_paint_chan: chrome_to_paint_chan,
             layout_shutdown_port: layout_shutdown_port,
             paint_shutdown_port: paint_shutdown_port,
             url: url,
@@ -204,12 +208,12 @@ impl Pipeline {
     }
 
     pub fn grant_paint_permission(&self) {
-        let _ = self.paint_chan.send(PaintMsg::PaintPermissionGranted);
+        let _ = self.chrome_to_paint_chan.send(ChromeToPaintMsg::PaintPermissionGranted);
     }
 
     pub fn revoke_paint_permission(&self) {
         debug!("pipeline revoking paint channel paint permission");
-        let _ = self.paint_chan.send(PaintMsg::PaintPermissionRevoked);
+        let _ = self.chrome_to_paint_chan.send(ChromeToPaintMsg::PaintPermissionRevoked);
     }
 
     pub fn exit(&self, exit_type: PipelineExitType) {
@@ -242,7 +246,9 @@ impl Pipeline {
         let _ = script_channel.send(
             ConstellationControlMsg::ExitPipeline(self.id,
                                                   PipelineExitType::PipelineOnly)).unwrap();
-        let _ = self.paint_chan.send(PaintMsg::Exit(None, PipelineExitType::PipelineOnly));
+        let _ = self.chrome_to_paint_chan.send(ChromeToPaintMsg::Exit(
+                    None,
+                    PipelineExitType::PipelineOnly));
         let LayoutControlChan(ref layout_channel) = self.layout_chan;
         let _ = layout_channel.send(
             LayoutControlMsg::ExitNow(PipelineExitType::PipelineOnly)).unwrap();
@@ -253,7 +259,7 @@ impl Pipeline {
             id: self.id.clone(),
             script_chan: self.script_chan.clone(),
             layout_chan: self.layout_chan.clone(),
-            paint_chan: self.paint_chan.clone(),
+            chrome_to_paint_chan: self.chrome_to_paint_chan.clone(),
         }
     }
 
@@ -296,8 +302,10 @@ pub struct PipelineContent {
     load_data: LoadData,
     failure: Failure,
     script_port: Option<Receiver<ConstellationControlMsg>>,
-    paint_chan: PaintChan,
-    paint_port: Option<Receiver<PaintMsg>>,
+    layout_to_paint_chan: OptionalIpcSender<LayoutToPaintMsg>,
+    chrome_to_paint_chan: Sender<ChromeToPaintMsg>,
+    layout_to_paint_port: Option<Receiver<LayoutToPaintMsg>>,
+    chrome_to_paint_port: Option<Receiver<ChromeToPaintMsg>>,
     paint_shutdown_chan: Sender<()>,
     pipeline_port: Option<IpcReceiver<LayoutControlMsg>>,
     layout_shutdown_chan: Sender<()>,
@@ -344,7 +352,7 @@ impl PipelineContent {
                                   self.constellation_chan,
                                   self.failure,
                                   self.script_chan.clone(),
-                                  self.paint_chan.clone(),
+                                  self.layout_to_paint_chan.clone(),
                                   self.image_cache_task,
                                   self.font_cache_task,
                                   self.time_profiler_chan,
@@ -355,8 +363,9 @@ impl PipelineContent {
     pub fn start_paint_task(&mut self) {
         PaintTask::create(self.id,
                           self.load_data.url.clone(),
-                          self.paint_chan.clone(),
-                          mem::replace(&mut self.paint_port, None).unwrap(),
+                          self.chrome_to_paint_chan.clone(),
+                          mem::replace(&mut self.layout_to_paint_port, None).unwrap(),
+                          mem::replace(&mut self.chrome_to_paint_port, None).unwrap(),
                           self.compositor_proxy.clone_compositor_proxy(),
                           self.constellation_chan.clone(),
                           self.font_cache_task.clone(),
diff --git a/components/gfx/display_list/mod.rs b/components/gfx/display_list/mod.rs
index 9610c78b80f..e87a5888ea9 100644
--- a/components/gfx/display_list/mod.rs
+++ b/components/gfx/display_list/mod.rs
@@ -42,7 +42,7 @@ use style::computed_values::{pointer_events};
 use style::properties::ComputedValues;
 use util::cursor::Cursor;
 use util::geometry::{self, Au, MAX_RECT, ZERO_RECT};
-use util::linked_list::{SerializableLinkedList, prepend_from};
+use util::linked_list::prepend_from;
 use util::mem::HeapSizeOf;
 use util::opts;
 use util::range::Range;
@@ -84,19 +84,19 @@ impl OpaqueNode {
 #[derive(HeapSizeOf, Deserialize, Serialize)]
 pub struct DisplayList {
     /// The border and backgrounds for the root of this stacking context: steps 1 and 2.
-    pub background_and_borders: SerializableLinkedList<DisplayItem>,
+    pub background_and_borders: LinkedList<DisplayItem>,
     /// Borders and backgrounds for block-level descendants: step 4.
-    pub block_backgrounds_and_borders: SerializableLinkedList<DisplayItem>,
+    pub block_backgrounds_and_borders: LinkedList<DisplayItem>,
     /// Floats: step 5. These are treated as pseudo-stacking contexts.
-    pub floats: SerializableLinkedList<DisplayItem>,
+    pub floats: LinkedList<DisplayItem>,
     /// All non-positioned content.
-    pub content: SerializableLinkedList<DisplayItem>,
+    pub content: LinkedList<DisplayItem>,
     /// All positioned content that does not get a stacking context.
-    pub positioned_content: SerializableLinkedList<DisplayItem>,
+    pub positioned_content: LinkedList<DisplayItem>,
     /// Outlines: step 10.
-    pub outlines: SerializableLinkedList<DisplayItem>,
+    pub outlines: LinkedList<DisplayItem>,
     /// Child stacking contexts.
-    pub children: SerializableLinkedList<Arc<StackingContext>>,
+    pub children: LinkedList<Arc<StackingContext>>,
 }
 
 impl DisplayList {
@@ -104,13 +104,13 @@ impl DisplayList {
     #[inline]
     pub fn new() -> DisplayList {
         DisplayList {
-            background_and_borders: SerializableLinkedList::new(LinkedList::new()),
-            block_backgrounds_and_borders: SerializableLinkedList::new(LinkedList::new()),
-            floats: SerializableLinkedList::new(LinkedList::new()),
-            content: SerializableLinkedList::new(LinkedList::new()),
-            positioned_content: SerializableLinkedList::new(LinkedList::new()),
-            outlines: SerializableLinkedList::new(LinkedList::new()),
-            children: SerializableLinkedList::new(LinkedList::new()),
+            background_and_borders: LinkedList::new(),
+            block_backgrounds_and_borders: LinkedList::new(),
+            floats: LinkedList::new(),
+            content: LinkedList::new(),
+            positioned_content: LinkedList::new(),
+            outlines: LinkedList::new(),
+            children: LinkedList::new(),
         }
     }
 
@@ -118,34 +118,34 @@ impl DisplayList {
     /// `other` in the process.
     #[inline]
     pub fn append_from(&mut self, other: &mut DisplayList) {
-        self.background_and_borders.append(&mut *other.background_and_borders);
-        self.block_backgrounds_and_borders.append(&mut *other.block_backgrounds_and_borders);
-        self.floats.append(&mut *other.floats);
-        self.content.append(&mut *other.content);
-        self.positioned_content.append(&mut *other.positioned_content);
-        self.outlines.append(&mut *other.outlines);
-        self.children.append(&mut *other.children);
+        self.background_and_borders.append(&mut other.background_and_borders);
+        self.block_backgrounds_and_borders.append(&mut other.block_backgrounds_and_borders);
+        self.floats.append(&mut other.floats);
+        self.content.append(&mut other.content);
+        self.positioned_content.append(&mut other.positioned_content);
+        self.outlines.append(&mut other.outlines);
+        self.children.append(&mut other.children);
     }
 
     /// Merges all display items from all non-float stacking levels to the `float` stacking level.
     #[inline]
     pub fn form_float_pseudo_stacking_context(&mut self) {
-        prepend_from(&mut *self.floats, &mut *self.outlines);
-        prepend_from(&mut *self.floats, &mut *self.positioned_content);
-        prepend_from(&mut *self.floats, &mut *self.content);
-        prepend_from(&mut *self.floats, &mut *self.block_backgrounds_and_borders);
-        prepend_from(&mut *self.floats, &mut *self.background_and_borders);
+        prepend_from(&mut self.floats, &mut self.outlines);
+        prepend_from(&mut self.floats, &mut self.positioned_content);
+        prepend_from(&mut self.floats, &mut self.content);
+        prepend_from(&mut self.floats, &mut self.block_backgrounds_and_borders);
+        prepend_from(&mut self.floats, &mut self.background_and_borders);
     }
 
     /// Merges all display items from all non-positioned-content stacking levels to the
     /// positioned-content stacking level.
     #[inline]
     pub fn form_pseudo_stacking_context_for_positioned_content(&mut self) {
-        prepend_from(&mut *self.positioned_content, &mut *self.outlines);
-        prepend_from(&mut *self.positioned_content, &mut *self.content);
-        prepend_from(&mut *self.positioned_content, &mut *self.floats);
-        prepend_from(&mut *self.positioned_content, &mut *self.block_backgrounds_and_borders);
-        prepend_from(&mut *self.positioned_content, &mut *self.background_and_borders);
+        prepend_from(&mut self.positioned_content, &mut self.outlines);
+        prepend_from(&mut self.positioned_content, &mut self.content);
+        prepend_from(&mut self.positioned_content, &mut self.floats);
+        prepend_from(&mut self.positioned_content, &mut self.block_backgrounds_and_borders);
+        prepend_from(&mut self.positioned_content, &mut self.background_and_borders);
     }
 
     /// Returns a list of all items in this display list concatenated together. This is extremely
diff --git a/components/gfx/font_context.rs b/components/gfx/font_context.rs
index 5621807827f..718e64c7e91 100644
--- a/components/gfx/font_context.rs
+++ b/components/gfx/font_context.rs
@@ -42,7 +42,7 @@ fn create_scaled_font(template: &Arc<FontTemplateData>, pt_size: Au) -> ScaledFo
 
 #[cfg(target_os="macos")]
 fn create_scaled_font(template: &Arc<FontTemplateData>, pt_size: Au) -> ScaledFont {
-    let cgfont = template.ctfont.as_ref().unwrap().copy_to_CGFont();
+    let cgfont = template.ctfont().as_ref().unwrap().copy_to_CGFont();
     ScaledFont::new(BackendType::Skia, &cgfont, pt_size.to_f32_px())
 }
 
diff --git a/components/gfx/lib.rs b/components/gfx/lib.rs
index abeaea80b0e..d13251123ca 100644
--- a/components/gfx/lib.rs
+++ b/components/gfx/lib.rs
@@ -9,6 +9,7 @@
 #![feature(custom_derive)]
 #![feature(hashmap_hasher)]
 #![cfg_attr(any(target_os="linux", target_os = "android"), feature(heap_api))]
+#![feature(mpsc_select)]
 #![feature(plugin)]
 #![feature(str_char)]
 #![feature(vec_push_all)]
diff --git a/components/gfx/paint_task.rs b/components/gfx/paint_task.rs
index ba9f73a154d..39f0ace7155 100644
--- a/components/gfx/paint_task.rs
+++ b/components/gfx/paint_task.rs
@@ -32,7 +32,7 @@ use skia::gl_context::GLContext;
 use std::borrow::ToOwned;
 use std::mem as std_mem;
 use std::sync::Arc;
-use std::sync::mpsc::{Receiver, Sender, channel};
+use std::sync::mpsc::{Receiver, Select, Sender, channel};
 use std::collections::HashMap;
 use url::Url;
 use util::geometry::{Au, ZERO_POINT};
@@ -72,38 +72,30 @@ pub struct PaintRequest {
 }
 
 pub enum Msg {
+    FromLayout(LayoutToPaintMsg),
+    FromChrome(ChromeToPaintMsg),
+}
+
+#[derive(Deserialize, Serialize)]
+pub enum LayoutToPaintMsg {
     PaintInit(Epoch, Arc<StackingContext>),
     CanvasLayer(LayerId, IpcSender<CanvasMsg>),
+    Exit(Option<IpcSender<()>>, PipelineExitType),
+}
+
+pub enum ChromeToPaintMsg {
     Paint(Vec<PaintRequest>, FrameTreeId),
     PaintPermissionGranted,
     PaintPermissionRevoked,
     CollectReports(ReportsChan),
-    Exit(Option<Sender<()>>, PipelineExitType),
-}
-
-#[derive(Clone)]
-pub struct PaintChan(Sender<Msg>);
-
-impl PaintChan {
-    pub fn new() -> (Receiver<Msg>, PaintChan) {
-        let (chan, port) = channel();
-        (port, PaintChan(chan))
-    }
-
-    pub fn send(&self, msg: Msg) {
-        assert!(self.send_opt(msg).is_ok(), "PaintChan.send: paint port closed")
-    }
-
-    pub fn send_opt(&self, msg: Msg) -> Result<(), Msg> {
-        let &PaintChan(ref chan) = self;
-        chan.send(msg).map_err(|e| e.0)
-    }
+    Exit(Option<IpcSender<()>>, PipelineExitType),
 }
 
 pub struct PaintTask<C> {
     id: PipelineId,
     _url: Url,
-    port: Receiver<Msg>,
+    layout_to_paint_port: Receiver<LayoutToPaintMsg>,
+    chrome_to_paint_port: Receiver<ChromeToPaintMsg>,
     compositor: C,
     constellation_chan: ConstellationChan,
 
@@ -137,8 +129,9 @@ macro_rules! native_display(
 impl<C> PaintTask<C> where C: PaintListener + Send + 'static {
     pub fn create(id: PipelineId,
                   url: Url,
-                  chan: PaintChan,
-                  port: Receiver<Msg>,
+                  chrome_to_paint_chan: Sender<ChromeToPaintMsg>,
+                  layout_to_paint_port: Receiver<LayoutToPaintMsg>,
+                  chrome_to_paint_port: Receiver<ChromeToPaintMsg>,
                   compositor: C,
                   constellation_chan: ConstellationChan,
                   font_cache_task: FontCacheTask,
@@ -162,7 +155,8 @@ impl<C> PaintTask<C> where C: PaintListener + Send + 'static {
                 let mut paint_task = PaintTask {
                     id: id,
                     _url: url,
-                    port: port,
+                    layout_to_paint_port: layout_to_paint_port,
+                    chrome_to_paint_port: chrome_to_paint_port,
                     compositor: compositor,
                     constellation_chan: constellation_chan,
                     time_profiler_chan: time_profiler_chan,
@@ -177,12 +171,12 @@ impl<C> PaintTask<C> where C: PaintListener + Send + 'static {
                 let reporter_name = format!("paint-reporter-{}", id.0);
                 let (reporter_sender, reporter_receiver) =
                     ipc::channel::<ReporterRequest>().unwrap();
-                let paint_chan_for_reporter = chan.clone();
+                let paint_chan_for_reporter = chrome_to_paint_chan.clone();
                 ROUTER.add_route(reporter_receiver.to_opaque(), box move |message| {
                     // Just injects an appropriate event into the paint task's queue.
                     let request: ReporterRequest = message.to().unwrap();
-                    paint_chan_for_reporter.0.send(Msg::CollectReports(request.reports_channel))
-                                             .unwrap();
+                    paint_chan_for_reporter.send(ChromeToPaintMsg::CollectReports(
+                            request.reports_channel)).unwrap();
                 });
                 mem_profiler_chan.send(mem::ProfilerMsg::RegisterReporter(
                         reporter_name.clone(),
@@ -208,8 +202,26 @@ impl<C> PaintTask<C> where C: PaintListener + Send + 'static {
         debug!("PaintTask: beginning painting loop");
 
         loop {
-            match self.port.recv().unwrap() {
-                Msg::PaintInit(epoch, stacking_context) => {
+            let message = {
+                let select = Select::new();
+                let mut layout_to_paint_handle = select.handle(&self.layout_to_paint_port);
+                let mut chrome_to_paint_handle = select.handle(&self.chrome_to_paint_port);
+                unsafe {
+                    layout_to_paint_handle.add();
+                    chrome_to_paint_handle.add();
+                }
+                let result = select.wait();
+                if result == layout_to_paint_handle.id() {
+                    Msg::FromLayout(self.layout_to_paint_port.recv().unwrap())
+                } else if result == chrome_to_paint_handle.id() {
+                    Msg::FromChrome(self.chrome_to_paint_port.recv().unwrap())
+                } else {
+                    panic!("unexpected select result")
+                }
+            };
+
+            match message {
+                Msg::FromLayout(LayoutToPaintMsg::PaintInit(epoch, stacking_context)) => {
                     self.current_epoch = Some(epoch);
                     self.root_stacking_context = Some(stacking_context.clone());
 
@@ -223,11 +235,11 @@ impl<C> PaintTask<C> where C: PaintListener + Send + 'static {
                     self.initialize_layers();
                 }
                 // Inserts a new canvas renderer to the layer map
-                Msg::CanvasLayer(layer_id, canvas_renderer) => {
+                Msg::FromLayout(LayoutToPaintMsg::CanvasLayer(layer_id, canvas_renderer)) => {
                     debug!("Renderer received for canvas with layer {:?}", layer_id);
                     self.canvas_map.insert(layer_id, canvas_renderer);
                 }
-                Msg::Paint(requests, frame_tree_id) => {
+                Msg::FromChrome(ChromeToPaintMsg::Paint(requests, frame_tree_id)) => {
                     if !self.paint_permission {
                         debug!("PaintTask: paint ready msg");
                         let ConstellationChan(ref mut c) = self.constellation_chan;
@@ -254,27 +266,28 @@ impl<C> PaintTask<C> where C: PaintListener + Send + 'static {
                                                            replies,
                                                            frame_tree_id);
                 }
-                Msg::PaintPermissionGranted => {
+                Msg::FromChrome(ChromeToPaintMsg::PaintPermissionGranted) => {
                     self.paint_permission = true;
 
                     if self.root_stacking_context.is_some() {
                         self.initialize_layers();
                     }
                 }
-                Msg::PaintPermissionRevoked => {
+                Msg::FromChrome(ChromeToPaintMsg::PaintPermissionRevoked) => {
                     self.paint_permission = false;
                 }
-                Msg::CollectReports(ref channel) => {
+                Msg::FromChrome(ChromeToPaintMsg::CollectReports(ref channel)) => {
                     // FIXME(njn): should eventually measure the paint task.
                     channel.send(Vec::new())
                 }
-                Msg::Exit(response_channel, _) => {
+                Msg::FromLayout(LayoutToPaintMsg::Exit(ref response_channel, _)) |
+                Msg::FromChrome(ChromeToPaintMsg::Exit(ref response_channel, _)) => {
                     // Ask the compositor to remove any layers it is holding for this paint task.
                     // FIXME(mrobinson): This can probably move back to the constellation now.
                     self.compositor.notify_paint_task_exiting(self.id);
 
                     debug!("PaintTask: Exiting.");
-                    response_channel.map(|channel| channel.send(()));
+                    response_channel.as_ref().map(|channel| channel.send(()));
                     break;
                 }
             }
diff --git a/components/gfx/platform/macos/font.rs b/components/gfx/platform/macos/font.rs
index a6e431407e1..b8474aa6da9 100644
--- a/components/gfx/platform/macos/font.rs
+++ b/components/gfx/platform/macos/font.rs
@@ -64,7 +64,7 @@ impl FontHandleMethods for FontHandle {
             Some(s) => s.to_f64_px(),
             None => 0.0
         };
-        match *template.ctfont {
+        match template.ctfont() {
             Some(ref ctfont) => {
                 Ok(FontHandle {
                     font_data: template.clone(),
diff --git a/components/gfx/platform/macos/font_template.rs b/components/gfx/platform/macos/font_template.rs
index e5c0c9c194b..e84691971ac 100644
--- a/components/gfx/platform/macos/font_template.rs
+++ b/components/gfx/platform/macos/font_template.rs
@@ -11,6 +11,7 @@ use serde::de::{Error, Visitor};
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
 use std::borrow::ToOwned;
 use std::ops::Deref;
+use std::sync::Mutex;
 use string_cache::Atom;
 
 /// Platform specific font representation for mac.
@@ -26,7 +27,7 @@ pub struct FontTemplateData {
     /// When sending a `FontTemplateData` instance across processes, this will be set to `None` on
     /// the other side, because `CTFont` instances cannot be sent across processes. This is
     /// harmless, however, because it can always be recreated.
-    pub ctfont: CachedCTFont,
+    ctfont: CachedCTFont,
 
     pub identifier: Atom,
     pub font_data: Option<Vec<u8>>
@@ -52,18 +53,27 @@ impl FontTemplateData {
         };
 
         FontTemplateData {
-            ctfont: CachedCTFont(ctfont),
+            ctfont: CachedCTFont(Mutex::new(ctfont)),
             identifier: identifier.to_owned(),
             font_data: font_data
         }
     }
+
+    /// Retrieves the Core Text font instance, instantiating it if necessary.
+    pub fn ctfont(&self) -> Option<CTFont> {
+        let mut ctfont = self.ctfont.lock().unwrap();
+        if ctfont.is_none() {
+            *ctfont = core_text::font::new_from_name(self.identifier.as_slice(), 0.0).ok()
+        }
+        ctfont.as_ref().map(|ctfont| (*ctfont).clone())
+    }
 }
 
-pub struct CachedCTFont(Option<CTFont>);
+pub struct CachedCTFont(Mutex<Option<CTFont>>);
 
 impl Deref for CachedCTFont {
-    type Target = Option<CTFont>;
-    fn deref(&self) -> &Option<CTFont> {
+    type Target = Mutex<Option<CTFont>>;
+    fn deref(&self) -> &Mutex<Option<CTFont>> {
         &self.0
     }
 }
@@ -84,7 +94,7 @@ impl Deserialize for CachedCTFont {
 
             #[inline]
             fn visit_none<E>(&mut self) -> Result<CachedCTFont,E> where E: Error {
-                Ok(CachedCTFont(None))
+                Ok(CachedCTFont(Mutex::new(None)))
             }
         }
 
diff --git a/components/layout/layout_task.rs b/components/layout/layout_task.rs
index 803b8fb1a0a..001f8f42d2a 100644
--- a/components/layout/layout_task.rs
+++ b/components/layout/layout_task.rs
@@ -37,8 +37,7 @@ use gfx_traits::color;
 use gfx::display_list::{ClippingRegion, DisplayItemMetadata, DisplayList, OpaqueNode};
 use gfx::display_list::StackingContext;
 use gfx::font_cache_task::FontCacheTask;
-use gfx::paint_task::Msg as PaintMsg;
-use gfx::paint_task::{PaintChan, PaintLayer};
+use gfx::paint_task::{LayoutToPaintMsg, PaintLayer};
 use ipc_channel::ipc::{self, IpcReceiver, IpcSender};
 use ipc_channel::router::ROUTER;
 use layout_traits::LayoutTaskFactory;
@@ -79,6 +78,7 @@ use style::stylesheets::{Origin, Stylesheet, CSSRuleIteratorExt};
 use url::Url;
 use util::cursor::Cursor;
 use util::geometry::{Au, MAX_RECT, ZERO_POINT};
+use util::ipc::OptionalIpcSender;
 use util::logical_geometry::{LogicalPoint, WritingMode};
 use util::mem::HeapSizeOf;
 use util::opts;
@@ -188,7 +188,7 @@ pub struct LayoutTask {
     pub script_chan: ScriptControlChan,
 
     /// The channel on which messages can be sent to the painting task.
-    pub paint_chan: PaintChan,
+    pub paint_chan: OptionalIpcSender<LayoutToPaintMsg>,
 
     /// The channel on which messages can be sent to the time profiler.
     pub time_profiler_chan: time::ProfilerChan,
@@ -228,7 +228,7 @@ impl LayoutTaskFactory for LayoutTask {
               constellation_chan: ConstellationChan,
               failure_msg: Failure,
               script_chan: ScriptControlChan,
-              paint_chan: PaintChan,
+              paint_chan: OptionalIpcSender<LayoutToPaintMsg>,
               image_cache_task: ImageCacheTask,
               font_cache_task: FontCacheTask,
               time_profiler_chan: time::ProfilerChan,
@@ -318,7 +318,7 @@ impl LayoutTask {
            pipeline_port: IpcReceiver<LayoutControlMsg>,
            constellation_chan: ConstellationChan,
            script_chan: ScriptControlChan,
-           paint_chan: PaintChan,
+           paint_chan: OptionalIpcSender<LayoutToPaintMsg>,
            image_cache_task: ImageCacheTask,
            font_cache_task: FontCacheTask,
            time_profiler_chan: time::ProfilerChan,
@@ -647,7 +647,9 @@ impl LayoutTask {
                                   info.constellation_chan,
                                   info.failure,
                                   ScriptControlChan(info.script_chan.clone()),
-                                  *info.paint_chan.downcast::<PaintChan>().unwrap(),
+                                  *info.paint_chan
+                                       .downcast::<OptionalIpcSender<LayoutToPaintMsg>>()
+                                       .unwrap(),
                                   self.image_cache_task.clone(),
                                   self.font_cache_task.clone(),
                                   self.time_profiler_chan.clone(),
@@ -689,7 +691,7 @@ impl LayoutTask {
     fn exit_now<'a>(&'a self,
                     possibly_locked_rw_data: &mut Option<MutexGuard<'a, LayoutTaskData>>,
                     exit_type: PipelineExitType) {
-        let (response_chan, response_port) = channel();
+        let (response_chan, response_port) = ipc::channel().unwrap();
 
         {
             let mut rw_data = self.lock_rw_data(possibly_locked_rw_data);
@@ -699,7 +701,7 @@ impl LayoutTask {
             LayoutTask::return_rw_data(possibly_locked_rw_data, rw_data);
         }
 
-        self.paint_chan.send(PaintMsg::Exit(Some(response_chan), exit_type));
+        self.paint_chan.send(LayoutToPaintMsg::Exit(Some(response_chan), exit_type)).unwrap();
         response_port.recv().unwrap()
     }
 
@@ -1071,7 +1073,9 @@ impl LayoutTask {
                 debug!("Layout done!");
 
                 rw_data.epoch.next();
-                self.paint_chan.send(PaintMsg::PaintInit(rw_data.epoch, stacking_context));
+                self.paint_chan
+                    .send(LayoutToPaintMsg::PaintInit(rw_data.epoch, stacking_context))
+                    .unwrap();
             }
         });
     }
@@ -1175,7 +1179,7 @@ impl LayoutTask {
         // Send new canvas renderers to the paint task
         while let Ok((layer_id, renderer)) = self.canvas_layers_receiver.try_recv() {
             // Just send if there's an actual renderer
-            self.paint_chan.send(PaintMsg::CanvasLayer(layer_id, renderer));
+            self.paint_chan.send(LayoutToPaintMsg::CanvasLayer(layer_id, renderer)).unwrap();
         }
 
         // Perform post-style recalculation layout passes.
diff --git a/components/layout_traits/lib.rs b/components/layout_traits/lib.rs
index 361ba3c2654..d75817911a7 100644
--- a/components/layout_traits/lib.rs
+++ b/components/layout_traits/lib.rs
@@ -22,7 +22,7 @@ extern crate util;
 //   that these modules won't have to depend on layout.
 
 use gfx::font_cache_task::FontCacheTask;
-use gfx::paint_task::PaintChan;
+use gfx::paint_task::LayoutToPaintMsg;
 use ipc_channel::ipc::{IpcReceiver, IpcSender};
 use msg::constellation_msg::{ConstellationChan, Failure, PipelineId};
 use profile_traits::mem;
@@ -31,6 +31,7 @@ use net_traits::image_cache_task::ImageCacheTask;
 use script_traits::{LayoutControlMsg, ScriptControlChan, OpaqueScriptLayoutChannel};
 use std::sync::mpsc::Sender;
 use url::Url;
+use util::ipc::OptionalIpcSender;
 
 /// A channel wrapper for constellation messages
 #[derive(Clone, Deserialize, Serialize)]
@@ -49,7 +50,7 @@ pub trait LayoutTaskFactory {
               constellation_chan: ConstellationChan,
               failure_msg: Failure,
               script_chan: ScriptControlChan,
-              paint_chan: PaintChan,
+              layout_to_paint_chan: OptionalIpcSender<LayoutToPaintMsg>,
               image_cache_task: ImageCacheTask,
               font_cache_task: FontCacheTask,
               time_profiler_chan: time::ProfilerChan,
diff --git a/components/servo/Cargo.lock b/components/servo/Cargo.lock
index 26bd154f535..c1c4a62cd58 100644
--- a/components/servo/Cargo.lock
+++ b/components/servo/Cargo.lock
@@ -225,7 +225,7 @@ dependencies = [
 [[package]]
 name = "core-text"
 version = "0.1.0"
-source = "git+https://github.com/servo/core-text-rs#c12e41b35141e094bf784017ca4a6f71d90c9877"
+source = "git+https://github.com/servo/core-text-rs#d97cd4ae33509857f956e64c71f43cc71c98430f"
 dependencies = [
  "core-foundation 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "core-graphics 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1497,6 +1497,7 @@ dependencies = [
  "bitflags 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "cssparser 0.3.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "ipc-channel 0.1.0 (git+https://github.com/pcwalton/ipc-channel)",
  "lazy_static 0.1.12 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.1.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/components/util/Cargo.toml b/components/util/Cargo.toml
index a61600c8d5a..6558792b21b 100644
--- a/components/util/Cargo.toml
+++ b/components/util/Cargo.toml
@@ -25,6 +25,9 @@ git = "https://github.com/servo/rust-azure"
 version = "0.3"
 features = [ "serde-serialization" ]
 
+[dependencies.ipc-channel]
+git = "https://github.com/pcwalton/ipc-channel"
+
 [dependencies]
 log = "0.3"
 bitflags = "0.3"
diff --git a/components/util/ipc.rs b/components/util/ipc.rs
new file mode 100644
index 00000000000..7e47ff696f7
--- /dev/null
+++ b/components/util/ipc.rs
@@ -0,0 +1,94 @@
+/* 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 opts;
+
+use ipc_channel::ipc::{self, IpcSender};
+use ipc_channel::router::ROUTER;
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
+use std::any::Any;
+use std::collections::HashMap;
+use std::sync::Mutex;
+use std::sync::atomic::{ATOMIC_USIZE_INIT, AtomicUsize, Ordering};
+use std::sync::mpsc::{self, Receiver, Sender};
+
+lazy_static! {
+    static ref IN_PROCESS_SENDERS: Mutex<HashMap<usize,Box<Any + Send>>> =
+        Mutex::new(HashMap::new());
+}
+
+static NEXT_SENDER_ID: AtomicUsize = ATOMIC_USIZE_INIT;
+
+pub enum OptionalIpcSender<T> where T: Deserialize + Serialize + Send + Any {
+    OutOfProcess(IpcSender<T>),
+    InProcess(Sender<T>),
+}
+
+impl<T> OptionalIpcSender<T> where T: Deserialize + Serialize + Send + Any {
+    pub fn send(&self, value: T) -> Result<(),()> {
+        match *self {
+            OptionalIpcSender::OutOfProcess(ref ipc_sender) => ipc_sender.send(value),
+            OptionalIpcSender::InProcess(ref sender) => sender.send(value).map_err(|_| ()),
+        }
+    }
+}
+
+impl<T> Clone for OptionalIpcSender<T> where T: Deserialize + Serialize + Send + Any {
+    fn clone(&self) -> OptionalIpcSender<T> {
+        match *self {
+            OptionalIpcSender::OutOfProcess(ref ipc_sender) => {
+                OptionalIpcSender::OutOfProcess((*ipc_sender).clone())
+            }
+            OptionalIpcSender::InProcess(ref sender) => {
+                OptionalIpcSender::InProcess((*sender).clone())
+            }
+        }
+    }
+}
+
+impl<T> Deserialize for OptionalIpcSender<T> where T: Deserialize + Serialize + Send + Any {
+    fn deserialize<D>(deserializer: &mut D)
+                      -> Result<OptionalIpcSender<T>,D::Error> where D: Deserializer {
+        if opts::get().multiprocess {
+            return Ok(OptionalIpcSender::OutOfProcess(try!(Deserialize::deserialize(
+                            deserializer))))
+        }
+        let id: usize = try!(Deserialize::deserialize(deserializer));
+        let sender = (*IN_PROCESS_SENDERS.lock()
+                                         .unwrap()
+                                         .remove(&id)
+                                         .unwrap()
+                                         .downcast_ref::<Sender<T>>()
+                                         .unwrap()).clone();
+        Ok(OptionalIpcSender::InProcess(sender))
+     }
+}
+
+impl<T> Serialize for OptionalIpcSender<T> where T: Deserialize + Serialize + Send + Any {
+    fn serialize<S>(&self, serializer: &mut S) -> Result<(),S::Error> where S: Serializer {
+        match *self {
+            OptionalIpcSender::OutOfProcess(ref ipc_sender) => ipc_sender.serialize(serializer),
+            OptionalIpcSender::InProcess(ref sender) => {
+                let id = NEXT_SENDER_ID.fetch_add(1, Ordering::SeqCst);
+                IN_PROCESS_SENDERS.lock()
+                                  .unwrap()
+                                  .insert(id, Box::new((*sender).clone()) as Box<Any + Send>);
+                id.serialize(serializer)
+            }
+        }
+    }
+}
+
+pub fn optional_ipc_channel<T>() -> (OptionalIpcSender<T>, Receiver<T>)
+                                 where T: Deserialize + Serialize + Send + Any {
+    if opts::get().multiprocess {
+        let (ipc_sender, ipc_receiver) = ipc::channel().unwrap();
+        let receiver = ROUTER.route_ipc_receiver_to_new_mpsc_receiver(ipc_receiver);
+        (OptionalIpcSender::OutOfProcess(ipc_sender), receiver)
+    } else {
+        let (sender, receiver) = mpsc::channel();
+        (OptionalIpcSender::InProcess(sender), receiver)
+    }
+}
+
diff --git a/components/util/lib.rs b/components/util/lib.rs
index b108c516acc..8db4b17f5ec 100644
--- a/components/util/lib.rs
+++ b/components/util/lib.rs
@@ -31,6 +31,7 @@ extern crate alloc;
 #[macro_use] extern crate cssparser;
 extern crate euclid;
 extern crate getopts;
+extern crate ipc_channel;
 extern crate libc;
 extern crate num as num_lib;
 extern crate num_cpus;
@@ -49,6 +50,7 @@ pub mod debug_utils;
 pub mod deque;
 pub mod linked_list;
 pub mod geometry;
+pub mod ipc;
 pub mod logical_geometry;
 pub mod mem;
 pub mod opts;
diff --git a/components/util/linked_list.rs b/components/util/linked_list.rs
index bf20f434d54..5114f02c0e4 100644
--- a/components/util/linked_list.rs
+++ b/components/util/linked_list.rs
@@ -4,81 +4,8 @@
 
 //! Utility functions for doubly-linked lists.
 
-use mem::HeapSizeOf;
-
-use serde::de::{Error, SeqVisitor, Visitor};
-use serde::ser::impls::SeqIteratorVisitor;
-use serde::{Deserialize, Deserializer, Serialize, Serializer};
 use std::collections::LinkedList;
-use std::marker::PhantomData;
 use std::mem;
-use std::ops::{Deref, DerefMut};
-
-pub struct SerializableLinkedList<T>(LinkedList<T>);
-
-impl<T> SerializableLinkedList<T> {
-    pub fn new(linked_list: LinkedList<T>) -> SerializableLinkedList<T> {
-        SerializableLinkedList(linked_list)
-    }
-}
-
-impl<T> Deref for SerializableLinkedList<T> {
-    type Target = LinkedList<T>;
-
-    fn deref(&self) -> &LinkedList<T> {
-        &self.0
-    }
-}
-
-impl<T> DerefMut for SerializableLinkedList<T> {
-    fn deref_mut(&mut self) -> &mut LinkedList<T> {
-        &mut self.0
-    }
-}
-
-impl<T: HeapSizeOf> HeapSizeOf for SerializableLinkedList<T> {
-    fn heap_size_of_children(&self) -> usize {
-        self.0.heap_size_of_children()
-    }
-}
-
-impl<T> Serialize for SerializableLinkedList<T> where T: Serialize {
-    fn serialize<S>(&self, serializer: &mut S) -> Result<(), S::Error> where S: Serializer {
-        serializer.visit_seq(SeqIteratorVisitor::new(self.0.iter(), Some(self.0.len())))
-    }
-}
-
-impl<T> Deserialize for SerializableLinkedList<T> where T: Deserialize {
-    fn deserialize<D>(deserializer: &mut D) -> Result<SerializableLinkedList<T>, D::Error>
-                      where D: Deserializer {
-        struct SerializableLinkedListVisitor<T> {
-            marker: PhantomData<T>,
-        }
-
-        impl<T> Visitor for SerializableLinkedListVisitor<T> where T: Deserialize {
-            type Value = SerializableLinkedList<T>;
-
-            #[inline]
-            fn visit_seq<V>(&mut self, mut visitor: V)
-                            -> Result<SerializableLinkedList<T>, V::Error>
-                            where V: SeqVisitor {
-                let mut list = LinkedList::new();
-                for _ in 0..visitor.size_hint().0 {
-                    match try!(visitor.visit()) {
-                        Some(element) => list.push_back(element),
-                        None => return Err(Error::end_of_stream_error()),
-                    }
-                }
-                try!(visitor.end());
-                Ok(SerializableLinkedList(list))
-            }
-        }
-
-        deserializer.visit_seq(SerializableLinkedListVisitor {
-            marker: PhantomData,
-        })
-    }
-}
 
 /// Splits the head off a list in O(1) time, and returns the head.
 pub fn split_off_head<T>(list: &mut LinkedList<T>) -> LinkedList<T> {
diff --git a/components/util/opts.rs b/components/util/opts.rs
index c8f65c97e54..efc580bd5e6 100644
--- a/components/util/opts.rs
+++ b/components/util/opts.rs
@@ -132,6 +132,9 @@ pub struct Opts {
     /// An optional string allowing the user agent to be set for testing.
     pub user_agent: Option<String>,
 
+    /// Whether to run in multiprocess mode.
+    pub multiprocess: bool,
+
     /// Dumps the flow tree after a layout.
     pub dump_flow_tree: bool,
 
@@ -251,6 +254,7 @@ pub fn default_opts() -> Opts {
         webdriver_port: None,
         initial_window_size: Size2D::typed(800, 600),
         user_agent: None,
+        multiprocess: false,
         dump_flow_tree: false,
         dump_display_list: false,
         dump_display_list_json: false,
@@ -291,6 +295,7 @@ pub fn from_cmdline_args(args: &[String]) {
         getopts::optflagopt("", "webdriver", "Start remote WebDriver server on port", "7000"),
         getopts::optopt("", "resolution", "Set window resolution.", "800x600"),
         getopts::optopt("u", "user-agent", "Set custom user agent string", "NCSA Mosaic/1.0 (X11;SunOS 4.1.4 sun4m)"),
+        getopts::optflag("M", "multiprocess", "Run in multiprocess mode"),
         getopts::optopt("Z", "debug",
                         "A comma-separated string of debug options. Pass help to show available options.", ""),
         getopts::optflag("h", "help", "Print this message"),
@@ -421,6 +426,7 @@ pub fn from_cmdline_args(args: &[String]) {
         webdriver_port: webdriver_port,
         initial_window_size: initial_window_size,
         user_agent: opt_match.opt_str("u"),
+        multiprocess: opt_match.opt_present("M"),
         show_debug_borders: debug_options.contains(&"show-compositor-borders"),
         show_debug_fragment_borders: debug_options.contains(&"show-fragment-borders"),
         show_debug_parallel_paint: debug_options.contains(&"show-parallel-paint"),