Revert "auto merge of #1356 : ksh8281/servo/remove_@_in_LayoutTask.FontContext, r=pcwalton"

This reverts commit e8ffac13d7e0ebc0701b87b774491b2b1b895607, reversing
changes made to db923feffe4ef1f15c34c2a50acdf74a4321e2d4.

Reverting this change because FreeType is *not* thread safe. See the
documentation here:

http://www.freetype.org/freetype2/docs/reference/ft2-base_interface.html

"In multi-threaded applications, make sure that the same FT_Library
object or any of its children doesn't get accessed in parallel."

We will need to use a `MutexArc` instead.

13 files changed, 120 insertions, 122 deletions

diff --git a/src/components/gfx/display_list.rs b/src/components/gfx/display_list.rs
index a477bc71a5d..440659c84d8 100644
--- a/src/components/gfx/display_list.rs
+++ b/src/components/gfx/display_list.rs
@@ -93,7 +93,7 @@ pub struct SolidColorDisplayItem<E> {
 /// Renders text.
 pub struct TextDisplayItem<E> {
     base: BaseDisplayItem<E>,
-    text_run: Arc<~TextRun>,
+    text_run: ~TextRun,
     range: Range,
     color: Color,
 }
@@ -163,8 +163,7 @@ impl<E> DisplayItem<E> {
                 debug!("Drawing text at {:?}.", text.base.bounds);
 
                 // FIXME(pcwalton): Allocating? Why?
-                let text_run = text.text_run.get();
-                let font = render_context.font_ctx.get_font_by_descriptor(&text_run.font_descriptor).unwrap();
+                let font = render_context.font_ctx.get_font_by_descriptor(&text.text_run.font_descriptor).unwrap();
 
                 let font_metrics = font.with_borrow( |font| {
                     font.metrics.clone()
@@ -173,7 +172,7 @@ impl<E> DisplayItem<E> {
                 let baseline_origin = Point2D(origin.x, origin.y + font_metrics.ascent);
                 font.with_mut_borrow( |font| {
                     font.draw_text_into_context(render_context,
-                                                text.text_run.get(),
+                                                &text.text_run,
                                                 &text.range,
                                                 baseline_origin,
                                                 text.color);
@@ -184,18 +183,18 @@ impl<E> DisplayItem<E> {
                 let strikeout_size = font_metrics.strikeout_size;
                 let strikeout_offset = font_metrics.strikeout_offset;
 
-                if text_run.decoration.underline {
+                if text.text_run.decoration.underline {
                     let underline_y = baseline_origin.y - underline_offset;
                     let underline_bounds = Rect(Point2D(baseline_origin.x, underline_y),
                                                 Size2D(width, underline_size));
                     render_context.draw_solid_color(&underline_bounds, text.color);
                 }
-                if text_run.decoration.overline {
+                if text.text_run.decoration.overline {
                     let overline_bounds = Rect(Point2D(baseline_origin.x, origin.y),
                                                Size2D(width, underline_size));
                     render_context.draw_solid_color(&overline_bounds, text.color);
                 }
-                if text_run.decoration.line_through {
+                if text.text_run.decoration.line_through {
                     let strikeout_y = baseline_origin.y - strikeout_offset;
                     let strikeout_bounds = Rect(Point2D(baseline_origin.x, strikeout_y),
                                                 Size2D(width, strikeout_size));
diff --git a/src/components/gfx/font_context.rs b/src/components/gfx/font_context.rs
index 256e31329cc..72b37de0d25 100644
--- a/src/components/gfx/font_context.rs
+++ b/src/components/gfx/font_context.rs
@@ -31,6 +31,7 @@ pub fn dummy_style() -> FontStyle {
 }
 
 pub trait FontContextHandleMethods {
+    fn clone(&self) -> FontContextHandle;
     fn create_font_from_identifier(&self, ~str, UsedFontStyle) -> Result<FontHandle, ()>;
 }
 
diff --git a/src/components/gfx/platform/linux/font.rs b/src/components/gfx/platform/linux/font.rs
index 0f4e2b3b331..cb2573a9a13 100644
--- a/src/components/gfx/platform/linux/font.rs
+++ b/src/components/gfx/platform/linux/font.rs
@@ -8,6 +8,7 @@ use font::{CSSFontWeight, FontHandleMethods, FontMetrics, FontTableMethods};
 use font::{FontTableTag, FractionalPixel, SpecifiedFontStyle, UsedFontStyle, FontWeight100};
 use font::{FontWeight200, FontWeight300, FontWeight400, FontWeight500, FontWeight600};
 use font::{FontWeight700, FontWeight800, FontWeight900};
+use font_context::FontContextHandleMethods;
 use servo_util::geometry::Au;
 use servo_util::geometry;
 use platform::font_context::FontContextHandle;
@@ -78,7 +79,7 @@ impl FontHandleMethods for FontHandle {
                            buf: ~[u8],
                            style: &SpecifiedFontStyle)
                         -> Result<FontHandle, ()> {
-        let ft_ctx: FT_Library = fctx.ctx.get().ctx;
+        let ft_ctx: FT_Library = fctx.ctx.ctx;
         if ft_ctx.is_null() { return Err(()); }
 
         let face_result = do buf.as_imm_buf |bytes: *u8, len: uint| {
@@ -291,7 +292,7 @@ impl<'self> FontHandle {
     pub fn new_from_file(fctx: &FontContextHandle, file: &str,
                          style: &SpecifiedFontStyle) -> Result<FontHandle, ()> {
         unsafe {
-            let ft_ctx: FT_Library = fctx.ctx.get().ctx;
+            let ft_ctx: FT_Library = fctx.ctx.ctx;
             if ft_ctx.is_null() { return Err(()); }
 
             let mut face: FT_Face = ptr::null();
@@ -319,7 +320,7 @@ impl<'self> FontHandle {
     pub fn new_from_file_unstyled(fctx: &FontContextHandle, file: ~str)
                                -> Result<FontHandle, ()> {
         unsafe {
-            let ft_ctx: FT_Library = fctx.ctx.get().ctx;
+            let ft_ctx: FT_Library = fctx.ctx.ctx;
             if ft_ctx.is_null() { return Err(()); }
 
             let mut face: FT_Face = ptr::null();
diff --git a/src/components/gfx/platform/linux/font_context.rs b/src/components/gfx/platform/linux/font_context.rs
index 8fd427ec411..4619454d10d 100644
--- a/src/components/gfx/platform/linux/font_context.rs
+++ b/src/components/gfx/platform/linux/font_context.rs
@@ -11,23 +11,30 @@ use freetype::freetype::{FTErrorMethods, FT_Library};
 use freetype::freetype::{FT_Done_FreeType, FT_Init_FreeType};
 
 use std::ptr;
-use extra::arc::Arc;
 
 #[deriving(Clone)]
 struct FreeTypeLibraryHandle {
     ctx: FT_Library,
 }
 
-#[deriving(Clone)]
+// FIXME(ksh8281) this value have to use atomic operation for counting ref
+static mut font_context_ref_count: uint = 0;
+static mut ft_pointer: Option<FT_Library> = None;
 pub struct FontContextHandle {
-    ctx: Arc<FreeTypeLibraryHandle>,
+    ctx: FreeTypeLibraryHandle,
 }
 
-impl Drop for FreeTypeLibraryHandle {
+impl Drop for FontContextHandle {
     #[fixed_stack_segment]
     fn drop(&mut self) {
-        assert!(self.ctx.is_not_null());
-        unsafe { FT_Done_FreeType(self.ctx) };
+        assert!(self.ctx.ctx.is_not_null());
+        unsafe {
+            assert!(font_context_ref_count >= 1);
+            font_context_ref_count = font_context_ref_count - 1;
+            if font_context_ref_count == 0 {
+                FT_Done_FreeType(self.ctx.ctx);
+            }
+        }
     }
 }
 
@@ -35,17 +42,38 @@ impl FontContextHandle {
     #[fixed_stack_segment]
     pub fn new() -> FontContextHandle {
         unsafe {
-            let ctx: FT_Library = ptr::null();
-            let result = FT_Init_FreeType(&ctx);
-            if !result.succeeded() { fail!("Unable to initialize FreeType library"); }
-            FontContextHandle {
-                ctx: Arc::new(FreeTypeLibraryHandle { ctx: ctx }),
+            match ft_pointer {
+                Some(ref ctx) => {
+                    font_context_ref_count = font_context_ref_count + 1;
+                    FontContextHandle {
+                        ctx: FreeTypeLibraryHandle { ctx: ctx.clone() },
+                    }
+                },
+                None => {
+                    let ctx: FT_Library = ptr::null();
+                    let result = FT_Init_FreeType(ptr::to_unsafe_ptr(&ctx));
+                    if !result.succeeded() { fail!("Unable to initialize FreeType library"); }
+                    ft_pointer = Some(ctx);
+                    font_context_ref_count = font_context_ref_count + 1;
+                    FontContextHandle {
+                        ctx: FreeTypeLibraryHandle { ctx: ctx },
+                    }
+                }
             }
         }
     }
 }
 
 impl FontContextHandleMethods for FontContextHandle {
+    fn clone(&self) -> FontContextHandle {
+        unsafe {
+            font_context_ref_count = font_context_ref_count + 1;
+            FontContextHandle {
+                ctx: self.ctx.clone()
+            }
+        }
+    }
+
     fn create_font_from_identifier(&self, name: ~str, style: UsedFontStyle)
                                 -> Result<FontHandle, ()> {
         debug!("Creating font handle for {:s}", name);
diff --git a/src/components/gfx/platform/linux/font_list.rs b/src/components/gfx/platform/linux/font_list.rs
index deadb966245..74fe4449445 100644
--- a/src/components/gfx/platform/linux/font_list.rs
+++ b/src/components/gfx/platform/linux/font_list.rs
@@ -19,6 +19,7 @@ use fontconfig::fontconfig::{
 
 
 use font::{FontHandleMethods, UsedFontStyle};
+use font_context::FontContextHandleMethods;
 use font_list::{FontEntry, FontFamily, FontFamilyMap};
 use platform::font::FontHandle;
 use platform::font_context::FontContextHandle;
diff --git a/src/components/gfx/platform/macos/font_context.rs b/src/components/gfx/platform/macos/font_context.rs
index 4a4afe6cefb..0c824073573 100644
--- a/src/components/gfx/platform/macos/font_context.rs
+++ b/src/components/gfx/platform/macos/font_context.rs
@@ -8,12 +8,10 @@ use platform::macos::font::FontHandle;
 
 use core_text;
 
-#[deriving(Clone)]
 pub struct FontContextHandle {
     ctx: ()
 }
 
-#[deriving(Clone)]
 impl FontContextHandle {
     // this is a placeholder until NSFontManager or whatever is bound in here.
     pub fn new() -> FontContextHandle {
@@ -22,6 +20,12 @@ impl FontContextHandle {
 }
 
 impl FontContextHandleMethods for FontContextHandle {
+    fn clone(&self) -> FontContextHandle {
+        FontContextHandle {
+            ctx: self.ctx
+        }
+    }
+
     fn create_font_from_identifier(&self,
                                    name: ~str,
                                    style: UsedFontStyle)
diff --git a/src/components/main/layout/box.rs b/src/components/main/layout/box.rs
index 3159c0863b0..6328328459e 100644
--- a/src/components/main/layout/box.rs
+++ b/src/components/main/layout/box.rs
@@ -5,7 +5,7 @@
 //! The `Box` type, which represents the leaves of the layout tree.
 
 use extra::url::Url;
-use extra::arc::{MutexArc,Arc};
+use extra::arc::MutexArc;
 use geom::{Point2D, Rect, Size2D, SideOffsets2D};
 use gfx::color::rgb;
 use gfx::display_list::{BaseDisplayItem, BorderDisplayItem, BorderDisplayItemClass};
@@ -160,7 +160,7 @@ impl ImageBoxInfo {
 /// object.
 pub struct ScannedTextBoxInfo {
     /// The text run that this represents.
-    run: Arc<~TextRun>,
+    run: @TextRun,
 
     /// The range within the above text run that this represents.
     range: Range,
@@ -168,7 +168,7 @@ pub struct ScannedTextBoxInfo {
 
 impl ScannedTextBoxInfo {
     /// Creates the information specific to a scanned text box from a range and a text run.
-    pub fn new(run: Arc<~TextRun>, range: Range) -> ScannedTextBoxInfo {
+    pub fn new(run: @TextRun, range: Range) -> ScannedTextBoxInfo {
         ScannedTextBoxInfo {
             run: run,
             range: range,
@@ -630,12 +630,21 @@ impl Box {
 
                 // Create the text box.
                 do list.with_mut_ref |list| {
+                    // FIXME(pcwalton): Allocation? Why?!
+                    let run = ~TextRun {
+                        text: text_box.run.text.clone(),
+                        font_descriptor: text_box.run.font_descriptor.clone(),
+                        font_metrics: text_box.run.font_metrics.clone(),
+                        font_style: text_box.run.font_style.clone(),
+                        decoration: text_box.run.decoration.clone(),
+                        glyphs: text_box.run.glyphs.clone()
+                    };
                     let text_display_item = ~TextDisplayItem {
                         base: BaseDisplayItem {
                             bounds: absolute_box_bounds,
                             extra: ExtraDisplayListData::new(&self),
                         },
-                        text_run: text_box.run.clone(),
+                        text_run: run,
                         range: text_box.range,
                         color: color,
                     };
@@ -668,7 +677,7 @@ impl Box {
                     // Draw a rectangle representing the baselines.
                     //
                     // TODO(Issue #221): Create and use a Line display item for the baseline.
-                    let ascent = text_box.run.get().metrics_for_range(
+                    let ascent = text_box.run.metrics_for_range(
                         &text_box.range).ascent;
                     let baseline = Rect(absolute_box_bounds.origin + Point2D(Au(0), ascent),
                                         Size2D(absolute_box_bounds.size.width, Au(0)));
@@ -781,12 +790,11 @@ impl Box {
             }
             ScannedTextBox(ref text_box_info) => {
                 let range = &text_box_info.range;
-                let text_run = text_box_info.run.get();
-                let min_line_width = text_run.min_width_for_range(range);
+                let min_line_width = text_box_info.run.min_width_for_range(range);
 
                 let mut max_line_width = Au::new(0);
-                for line_range in text_run.iter_natural_lines_for_range(range) {
-                    let line_metrics = text_run.metrics_for_range(&line_range);
+                for line_range in text_box_info.run.iter_natural_lines_for_range(range) {
+                    let line_metrics = text_box_info.run.metrics_for_range(&line_range);
                     max_line_width = Au::max(max_line_width, line_metrics.advance_width);
                 }
 
@@ -816,7 +824,7 @@ impl Box {
             }
             ScannedTextBox(ref text_box_info) => {
                 // Compute the height based on the line-height and font size.
-                let (range, run) = (&text_box_info.range, &text_box_info.run.get());
+                let (range, run) = (&text_box_info.range, &text_box_info.run);
                 let text_bounds = run.metrics_for_range(range).bounding_box;
                 let em_size = text_bounds.size.height;
                 self.calculate_line_height(em_size)
@@ -838,12 +846,11 @@ impl Box {
 
                 debug!("split_to_width: splitting text box (strlen={:u}, range={}, \
                                                             avail_width={})",
-                       text_box_info.run.get().text.get().len(),
+                       text_box_info.run.text.get().len(),
                        text_box_info.range,
                        max_width);
 
-                let text_run = text_box_info.run.get();
-                for (glyphs, offset, slice_range) in text_run.iter_slices_for_range(
+                for (glyphs, offset, slice_range) in text_box_info.run.iter_slices_for_range(
                         &text_box_info.range) {
                     debug!("split_to_width: considering slice (offset={}, range={}, \
                                                                remain_width={})",
@@ -851,7 +858,7 @@ impl Box {
                            slice_range,
                            remaining_width);
 
-                    let metrics = text_run.metrics_for_slice(glyphs, &slice_range);
+                    let metrics = text_box_info.run.metrics_for_slice(glyphs, &slice_range);
                     let advance = metrics.advance_width;
 
                     let should_continue;
@@ -902,23 +909,20 @@ impl Box {
                 }
 
                 let left_box = if left_range.length() > 0 {
-
-                    let new_text_box_info = ScannedTextBoxInfo::new(text_box_info.run.clone(), left_range);
-                    let new_size = text_box_info.run.get().
-                        metrics_for_range(&left_range).bounding_box.size;
+                    let new_text_box_info = ScannedTextBoxInfo::new(text_box_info.run, left_range);
                     let new_text_box = @Box::new(self.node, ScannedTextBox(new_text_box_info));
-                    new_text_box.set_size(new_size);
+                    let new_metrics = new_text_box_info.run.metrics_for_range(&left_range);
+                    new_text_box.set_size(new_metrics.bounding_box.size);
                     Some(new_text_box)
                 } else {
                     None
                 };
 
                 let right_box = right_range.map_default(None, |range: Range| {
-                    let new_text_box_info = ScannedTextBoxInfo::new(text_box_info.run.clone(), range);
-                    let new_size = text_box_info.run.get().
-                        metrics_for_range(&range).bounding_box.size;
+                    let new_text_box_info = ScannedTextBoxInfo::new(text_box_info.run, range);
                     let new_text_box = @Box::new(self.node, ScannedTextBox(new_text_box_info));
-                    new_text_box.set_size(new_size);
+                    let new_metrics = new_text_box_info.run.metrics_for_range(&range);
+                    new_text_box.set_size(new_metrics.bounding_box.size);
                     Some(new_text_box)
                 });
 
@@ -971,7 +975,7 @@ impl Box {
     /// Cleans up all the memory associated with this box.
     pub fn teardown(&self) {
         match self.specific {
-            ScannedTextBox(ref text_box_info) => text_box_info.run.get().teardown(),
+            ScannedTextBox(ref text_box_info) => text_box_info.run.teardown(),
             _ => {}
         }
     }
diff --git a/src/components/main/layout/construct.rs b/src/components/main/layout/construct.rs
index e758409c31c..18ff1654888 100644
--- a/src/components/main/layout/construct.rs
+++ b/src/components/main/layout/construct.rs
@@ -33,7 +33,7 @@ use layout::util::LayoutDataAccess;
 use script::dom::element::HTMLImageElementTypeId;
 use script::dom::node::{AbstractNode, CommentNodeTypeId, DoctypeNodeTypeId};
 use script::dom::node::{DocumentFragmentNodeTypeId, DocumentNodeTypeId, ElementNodeTypeId};
-use script::dom::node::{LayoutView, PostorderNodeMutTraversal, TextNodeTypeId};
+use script::dom::node::{LayoutView, PostorderNodeTraversal, TextNodeTypeId};
 use servo_util::slot::Slot;
 use servo_util::tree::TreeNodeRef;
 use std::util;
@@ -173,7 +173,7 @@ pub struct FlowConstructor<'self> {
     /// The layout context.
     ///
     /// FIXME(pcwalton): Why does this contain `@`??? That destroys parallelism!!!
-    layout_context: &'self mut LayoutContext,
+    layout_context: &'self LayoutContext,
 
     /// The next flow ID to assign.
     ///
@@ -183,7 +183,7 @@ pub struct FlowConstructor<'self> {
 
 impl<'self> FlowConstructor<'self> {
     /// Creates a new flow constructor.
-    pub fn init<'a>(layout_context: &'a mut LayoutContext) -> FlowConstructor<'a> {
+    pub fn init<'a>(layout_context: &'a LayoutContext) -> FlowConstructor<'a> {
         FlowConstructor {
             layout_context: layout_context,
             next_flow_id: Slot::init(0),
@@ -198,7 +198,7 @@ impl<'self> FlowConstructor<'self> {
     }
 
     /// Builds the `ImageBoxInfo` for the given image. This is out of line to guide inlining.
-    fn build_box_info_for_image(&mut self, node: AbstractNode<LayoutView>) -> Option<ImageBoxInfo> {
+    fn build_box_info_for_image(&self, node: AbstractNode<LayoutView>) -> Option<ImageBoxInfo> {
         // FIXME(pcwalton): Don't copy URLs.
         let url = node.with_imm_image_element(|image_element| {
             image_element.image.as_ref().map(|url| (*url).clone())
@@ -215,7 +215,7 @@ impl<'self> FlowConstructor<'self> {
     }
 
     /// Builds a `Box` for the given node.
-    fn build_box_for_node(&mut self, node: AbstractNode<LayoutView>) -> @Box {
+    fn build_box_for_node(&self, node: AbstractNode<LayoutView>) -> @Box {
         let specific = match node.type_id() {
             ElementNodeTypeId(HTMLImageElementTypeId) => {
                 match self.build_box_info_for_image(node) {
@@ -234,7 +234,7 @@ impl<'self> FlowConstructor<'self> {
     /// `#[inline(always)]` because this is performance critical and LLVM will not inline it
     /// otherwise.
     #[inline(always)]
-    fn flush_inline_boxes_to_flow(&mut self,
+    fn flush_inline_boxes_to_flow(&self,
                                   boxes: ~[@Box],
                                   flow: &mut ~Flow:,
                                   node: AbstractNode<LayoutView>) {
@@ -248,7 +248,7 @@ impl<'self> FlowConstructor<'self> {
 
     /// Creates an inline flow from a set of inline boxes, if present, and adds it as a child of
     /// the given flow.
-    fn flush_inline_boxes_to_flow_if_necessary(&mut self,
+    fn flush_inline_boxes_to_flow_if_necessary(&self,
                                                opt_boxes: &mut Option<~[@Box]>,
                                                flow: &mut ~Flow:,
                                                node: AbstractNode<LayoutView>) {
@@ -261,7 +261,7 @@ impl<'self> FlowConstructor<'self> {
     /// Builds the children flows underneath a node with `display: block`. After this call,
     /// other `BlockFlow`s or `InlineFlow`s will be populated underneath this node, depending on
     /// whether {ib} splits needed to happen.
-    fn build_children_of_block_flow(&mut self,
+    fn build_children_of_block_flow(&self,
                                     flow: &mut ~Flow:,
                                     node: AbstractNode<LayoutView>) {
         // Gather up boxes for the inline flows we might need to create.
@@ -341,7 +341,7 @@ impl<'self> FlowConstructor<'self> {
     /// Builds a flow for a node with `display: block`. This yields a `BlockFlow` with possibly
     /// other `BlockFlow`s or `InlineFlow`s underneath it, depending on whether {ib} splits needed
     /// to happen.
-    fn build_flow_for_block(&mut self, node: AbstractNode<LayoutView>) -> ~Flow: {
+    fn build_flow_for_block(&self, node: AbstractNode<LayoutView>) -> ~Flow: {
         let base = FlowData::new(self.next_flow_id(), node);
         let box = self.build_box_for_node(node);
         let mut flow = ~BlockFlow::from_box(base, box) as ~Flow:;
@@ -351,7 +351,7 @@ impl<'self> FlowConstructor<'self> {
 
     /// Builds the flow for a node with `float: {left|right}`. This yields a float `BlockFlow` with
     /// a `BlockFlow` underneath it.
-    fn build_flow_for_floated_block(&mut self, node: AbstractNode<LayoutView>, float_type: FloatType)
+    fn build_flow_for_floated_block(&self, node: AbstractNode<LayoutView>, float_type: FloatType)
                                     -> ~Flow: {
         let base = FlowData::new(self.next_flow_id(), node);
         let box = self.build_box_for_node(node);
@@ -363,7 +363,7 @@ impl<'self> FlowConstructor<'self> {
     /// Concatenates the boxes of kids, adding in our own borders/padding/margins if necessary.
     /// Returns the `InlineBoxesConstructionResult`, if any. There will be no
     /// `InlineBoxesConstructionResult` if this node consisted entirely of ignorable whitespace.
-    fn build_boxes_for_nonreplaced_inline_content(&mut self, node: AbstractNode<LayoutView>)
+    fn build_boxes_for_nonreplaced_inline_content(&self, node: AbstractNode<LayoutView>)
                                                   -> ConstructionResult {
         let mut opt_inline_block_splits = None;
         let mut opt_box_accumulator = None;
@@ -429,7 +429,7 @@ impl<'self> FlowConstructor<'self> {
 
     /// Creates an `InlineBoxesConstructionResult` for replaced content. Replaced content doesn't
     /// render its children, so this just nukes a child's boxes and creates a `Box`.
-    fn build_boxes_for_replaced_inline_content(&mut self, node: AbstractNode<LayoutView>)
+    fn build_boxes_for_replaced_inline_content(&self, node: AbstractNode<LayoutView>)
                                                -> ConstructionResult {
         for kid in node.children() {
             kid.set_flow_construction_result(NoConstructionResult)
@@ -446,7 +446,7 @@ impl<'self> FlowConstructor<'self> {
 
     /// Builds one or more boxes for a node with `display: inline`. This yields an
     /// `InlineBoxesConstructionResult`.
-    fn build_boxes_for_inline(&mut self, node: AbstractNode<LayoutView>) -> ConstructionResult {
+    fn build_boxes_for_inline(&self, node: AbstractNode<LayoutView>) -> ConstructionResult {
         // Is this node replaced content?
         if !node.is_replaced_content() {
             // Go to a path that concatenates our kids' boxes.
@@ -458,11 +458,11 @@ impl<'self> FlowConstructor<'self> {
     }
 }
 
-impl<'self> PostorderNodeMutTraversal for FlowConstructor<'self> {
+impl<'self> PostorderNodeTraversal for FlowConstructor<'self> {
     // `#[inline(always)]` because this is always called from the traversal function and for some
     // reason LLVM's inlining heuristics go awry here.
     #[inline(always)]
-    fn process(&mut self, node: AbstractNode<LayoutView>) -> bool {
+    fn process(&self, node: AbstractNode<LayoutView>) -> bool {
         // Get the `display` property for this node, and determine whether this node is floated.
         let (display, float) = match node.type_id() {
             ElementNodeTypeId(_) => (node.style().Box.display, node.style().Box.float),
diff --git a/src/components/main/layout/context.rs b/src/components/main/layout/context.rs
index 2eaa7eafc8c..748ed66d4ad 100644
--- a/src/components/main/layout/context.rs
+++ b/src/components/main/layout/context.rs
@@ -13,7 +13,7 @@ use extra::arc::MutexArc;
 
 /// Data needed by the layout task.
 pub struct LayoutContext {
-    font_ctx: ~FontContext,
+    font_ctx: @mut FontContext,
     image_cache: MutexArc<LocalImageCache>,
     screen_size: Rect<Au>
 }
diff --git a/src/components/main/layout/inline.rs b/src/components/main/layout/inline.rs
index b63b6066d70..11852060d6f 100644
--- a/src/components/main/layout/inline.rs
+++ b/src/components/main/layout/inline.rs
@@ -702,7 +702,7 @@ impl Flow for InlineFlow {
                     },
                     ScannedTextBox(ref text_box) => {
                         let range = &text_box.range;
-                        let run = text_box.run.get();
+                        let run = &text_box.run;
                         
                         // Compute the height based on the line-height and font size
                         let text_bounds = run.metrics_for_range(range).bounding_box;
@@ -711,7 +711,7 @@ impl Flow for InlineFlow {
 
                         // Find the top and bottom of the content area.
                         // Those are used in text-top and text-bottom value of 'vertical-align'
-                        let text_ascent = run.font_metrics.ascent;
+                        let text_ascent = text_box.run.font_metrics.ascent;
                        
                         // Offset from the top of the box is 1/2 of the leading + ascent
                         let text_offset = text_ascent + (line_height - em_size).scale_by(0.5);
diff --git a/src/components/main/layout/layout_task.rs b/src/components/main/layout/layout_task.rs
index fdface606fd..d1e8cb63671 100644
--- a/src/components/main/layout/layout_task.rs
+++ b/src/components/main/layout/layout_task.rs
@@ -77,6 +77,9 @@ struct LayoutTask {
     /// The local image cache.
     local_image_cache: MutexArc<LocalImageCache>,
 
+    /// The local font context.
+    font_ctx: @mut FontContext,
+
     /// The size of the viewport.
     screen_size: Option<Size2D<Au>>,
 
@@ -87,8 +90,6 @@ struct LayoutTask {
 
     /// The channel on which messages can be sent to the profiler.
     profiler_chan: ProfilerChan,
-
-    opts: Opts
 }
 
 /// The damage computation traversal.
@@ -228,6 +229,7 @@ impl LayoutTask {
            opts: &Opts,
            profiler_chan: ProfilerChan)
            -> LayoutTask {
+        let fctx = @mut FontContext::new(opts.render_backend, true, profiler_chan.clone());
 
         LayoutTask {
             id: id,
@@ -237,13 +239,13 @@ impl LayoutTask {
             render_chan: render_chan,
             image_cache_task: image_cache_task.clone(),
             local_image_cache: MutexArc::new(LocalImageCache(image_cache_task)),
+            font_ctx: fctx,
             screen_size: None,
 
             display_list: None,
 
             stylist: RWArc::new(new_stylist()),
             profiler_chan: profiler_chan,
-            opts: opts.clone()
         }
     }
 
@@ -257,8 +259,7 @@ impl LayoutTask {
     // Create a layout context for use in building display lists, hit testing, &c.
     fn build_layout_context(&self) -> LayoutContext {
         let image_cache = self.local_image_cache.clone();
-        let font_ctx = ~FontContext::new(self.opts.render_backend, true,
-                                            self.profiler_chan.clone());
+        let font_ctx = self.font_ctx;
         let screen_size = self.screen_size.unwrap();
 
         LayoutContext {
@@ -343,9 +344,9 @@ impl LayoutTask {
     /// is intertwined with selector matching, making it difficult to compare directly. It is
     /// marked `#[inline(never)]` to aid benchmarking in sampling profilers.
     #[inline(never)]
-    fn construct_flow_tree(&self, layout_context: &mut LayoutContext, node: AbstractNode<LayoutView>)
+    fn construct_flow_tree(&self, layout_context: &LayoutContext, node: AbstractNode<LayoutView>)
                            -> ~Flow: {
-        node.traverse_postorder_mut(&mut FlowConstructor::init(layout_context));
+        node.traverse_postorder(&FlowConstructor::init(layout_context));
 
         let result = match *node.mutate_layout_data().ptr {
             Some(ref mut layout_data) => {
@@ -440,7 +441,7 @@ impl LayoutTask {
         // Construct the flow tree.
         let mut layout_root = profile(time::LayoutTreeBuilderCategory,
                                       self.profiler_chan.clone(),
-                                      || self.construct_flow_tree(&mut layout_ctx, *node));
+                                      || self.construct_flow_tree(&layout_ctx, *node));
 
         // Propagate damage.
         layout_root.traverse_preorder(&mut PropagateDamageTraversal {
diff --git a/src/components/main/layout/text.rs b/src/components/main/layout/text.rs
index fe49dd7c8c2..e42ede37b56 100644
--- a/src/components/main/layout/text.rs
+++ b/src/components/main/layout/text.rs
@@ -11,7 +11,6 @@ use layout::flow::Flow;
 use gfx::text::text_run::TextRun;
 use gfx::text::util::{CompressWhitespaceNewline, transform_text};
 use std::vec;
-use extra::arc::Arc;
 use servo_util::range::Range;
 
 /// A stack-allocated object for scanning an inline flow into `TextRun`-containing `TextBox`es.
@@ -26,7 +25,7 @@ impl TextRunScanner {
         }
     }
 
-    pub fn scan_for_runs(&mut self, ctx: &mut LayoutContext, flow: &mut Flow) {
+    pub fn scan_for_runs(&mut self, ctx: &LayoutContext, flow: &mut Flow) {
         {
             let inline = flow.as_immutable_inline();
             // FIXME: this assertion fails on wikipedia, but doesn't seem
@@ -76,7 +75,7 @@ impl TextRunScanner {
     /// responsible for swapping out the list. It is not clear to me (pcwalton) that this is still
     /// necessary.
     pub fn flush_clump_to_list(&mut self,
-                               ctx: &mut LayoutContext,
+                               ctx: &LayoutContext,
                                flow: &mut Flow,
                                last_whitespace: bool,
                                out_boxes: &mut ~[@Box])
@@ -126,15 +125,14 @@ impl TextRunScanner {
                     // font group fonts. This is probably achieved by creating the font group above
                     // and then letting `FontGroup` decide which `Font` to stick into the text run.
                     let fontgroup = ctx.font_ctx.get_resolved_font_for_style(&font_style);
-                    let run = Arc::new(~fontgroup.with_borrow(|fg| fg.create_textrun(transformed_text.clone(), decoration)));
+                    let run = @fontgroup.with_borrow(|fg| fg.create_textrun(transformed_text.clone(), decoration));
 
                     debug!("TextRunScanner: pushing single text box in range: {} ({})",
                            self.clump,
                            *text);
-                    let range = Range::new(0, run.get().char_len());
-                    let new_metrics = run.get().metrics_for_range(&range);
+                    let range = Range::new(0, run.char_len());
                     let new_text_box_info = ScannedTextBoxInfo::new(run, range);
-
+                    let new_metrics = run.metrics_for_range(&range);
                     let new_box = @old_box.transform(new_metrics.bounding_box.size,
                                                      ScannedTextBox(new_text_box_info));
                     out_boxes.push(new_box)
@@ -192,7 +190,7 @@ impl TextRunScanner {
                 let run = if clump.length() != 0 && run_str.len() > 0 {
                     fontgroup.with_borrow( |fg| {
                         fg.fonts[0].with_mut_borrow( |font| {
-                            Some(Arc::new(~TextRun::new(font, run_str.clone(), decoration)))
+                            Some(@TextRun::new(font, run_str.clone(), decoration))
                         })
                     })
                 } else {
@@ -210,8 +208,8 @@ impl TextRunScanner {
                         continue
                     }
 
-                    let new_text_box_info = ScannedTextBoxInfo::new(run.get_ref().clone(), range);
-                    let new_metrics = new_text_box_info.run.get().metrics_for_range(&range);
+                    let new_text_box_info = ScannedTextBoxInfo::new(run.unwrap(), range);
+                    let new_metrics = new_text_box_info.run.metrics_for_range(&range);
                     let new_box = @in_boxes[i].transform(new_metrics.bounding_box.size,
                                                          ScannedTextBox(new_text_box_info));
                     out_boxes.push(new_box)
diff --git a/src/components/script/dom/node.rs b/src/components/script/dom/node.rs
index a3edd1eb054..b0394528d95 100644
--- a/src/components/script/dom/node.rs
+++ b/src/components/script/dom/node.rs
@@ -1217,20 +1217,6 @@ pub trait PostorderNodeTraversal {
     }
 }
 
-/// A bottom-up, parallelizable traversal.
-pub trait PostorderNodeMutTraversal {
-    /// The operation to perform. Return true to continue or false to stop.
-    fn process(&mut self, node: AbstractNode<LayoutView>) -> bool;
-
-    /// Returns true if this node should be pruned. If this returns true, we skip the operation
-    /// entirely and do not process any descendant nodes. This is called *before* child nodes are
-    /// visited. The default implementation never prunes any nodes.
-    fn should_prune(&self, _node: AbstractNode<LayoutView>) -> bool {
-        false
-    }
-}
-
-
 impl AbstractNode<LayoutView> {
     /// Traverses the tree in postorder.
     ///
@@ -1255,29 +1241,4 @@ impl AbstractNode<LayoutView> {
 
         traversal.process(self)
     }
-
-    /// Traverses the tree in postorder.
-    ///
-    /// TODO(pcwalton): Offer a parallel version with a compatible API.
-    pub fn traverse_postorder_mut<T:PostorderNodeMutTraversal>(mut self, traversal: &mut T) -> bool {
-        if traversal.should_prune(self) {
-            return true
-        }
-
-        let mut opt_kid = self.first_child();
-        loop {
-            match opt_kid {
-                None => break,
-                Some(kid) => {
-                    if !kid.traverse_postorder_mut(traversal) {
-                        return false
-                    }
-                    opt_kid = kid.next_sibling()
-                }
-            }
-        }
-
-        traversal.process(self)
-    }
-
 }