layout: Port parallel layout over to a generic "work queue"

infrastructure.

The work queue accepts abstract generic "work units", which in this case
are layout operations. The same speedups have been observed.

12 files changed, 516 insertions, 349 deletions

diff --git a/src/components/main/compositing/compositor.rs b/src/components/main/compositing/compositor.rs
index 5d309f1b913..d6abea53368 100644
--- a/src/components/main/compositing/compositor.rs
+++ b/src/components/main/compositing/compositor.rs
@@ -198,6 +198,9 @@ impl IOCompositor {
         // Drain compositor port, sometimes messages contain channels that are blocking
         // another task from finishing (i.e. SetIds)
         while self.port.try_recv().is_some() {}
+
+        // Tell the profiler to shut down.
+        self.profiler_chan.send(time::ExitMsg);
     }
 
     fn handle_message(&mut self) {
diff --git a/src/components/main/layout/block.rs b/src/components/main/layout/block.rs
index b7c945c0d93..5219fe9cd75 100644
--- a/src/components/main/layout/block.rs
+++ b/src/components/main/layout/block.rs
@@ -329,7 +329,7 @@ impl BlockFlow {
         // top or bottom borders nor top or bottom padding, and it has a 'height' of either 0 or 'auto',
         // and it does not contain a line box, and all of its in-flow children's margins (if any) collapse.
 
-        let screen_height = ctx.shared.screen_size.height;
+        let screen_height = ctx.screen_size.height;
 
         let mut height = if self.is_root {
             // FIXME(pcwalton): The max is taken here so that you can scroll the page, but this is
@@ -627,7 +627,7 @@ impl Flow for BlockFlow {
         if self.is_root {
             debug!("Setting root position");
             self.base.position.origin = Au::zero_point();
-            self.base.position.size.width = ctx.shared.screen_size.width;
+            self.base.position.size.width = ctx.screen_size.width;
             self.base.floats_in = FloatContext::new(self.base.num_floats);
             self.base.flags_info.flags.set_inorder(false);
         }
@@ -672,7 +672,7 @@ impl Flow for BlockFlow {
                                                margin_bottom,
                                                margin_left));
 
-            let screen_size = ctx.shared.screen_size;
+            let screen_size = ctx.screen_size;
             let (x, w) = box_.get_x_coord_and_new_width_if_fixed(screen_size.width, 
                                                                  screen_size.height,
                                                                  width,
diff --git a/src/components/main/layout/box_.rs b/src/components/main/layout/box_.rs
index 297f70e5adf..66125587be9 100644
--- a/src/components/main/layout/box_.rs
+++ b/src/components/main/layout/box_.rs
@@ -1338,7 +1338,7 @@ impl Box {
                iframe_box.pipeline_id,
                iframe_box.subpage_id);
         let msg = FrameRectMsg(iframe_box.pipeline_id, iframe_box.subpage_id, rect);
-        layout_context.shared.constellation_chan.send(msg)
+        layout_context.constellation_chan.send(msg)
     }
 }
 
diff --git a/src/components/main/layout/construct.rs b/src/components/main/layout/construct.rs
index 80809899a89..bfc151fb012 100644
--- a/src/components/main/layout/construct.rs
+++ b/src/components/main/layout/construct.rs
@@ -32,6 +32,7 @@ use layout::text::TextRunScanner;
 use layout::util::LayoutDataAccess;
 use layout::wrapper::{LayoutNode, PostorderNodeMutTraversal};
 
+use gfx::font_context::FontContext;
 use script::dom::element::{HTMLIframeElementTypeId, HTMLImageElementTypeId};
 use script::dom::node::{CommentNodeTypeId, DoctypeNodeTypeId, DocumentFragmentNodeTypeId};
 use script::dom::node::{DocumentNodeTypeId, ElementNodeTypeId, TextNodeTypeId};
@@ -209,14 +210,19 @@ pub struct FlowConstructor<'a> {
     ///
     /// FIXME(pcwalton): This is going to have to be atomic; can't we do something better?
     next_flow_id: RefCell<int>,
+
+    /// The font context.
+    font_context: ~FontContext,
 }
 
 impl<'fc> FlowConstructor<'fc> {
     /// Creates a new flow constructor.
     pub fn init<'a>(layout_context: &'a mut LayoutContext) -> FlowConstructor<'a> {
+        let font_context = ~FontContext::new(layout_context.font_context_info.clone());
         FlowConstructor {
             layout_context: layout_context,
             next_flow_id: RefCell::new(0),
+            font_context: font_context,
         }
     }
 
@@ -235,7 +241,7 @@ impl<'fc> FlowConstructor<'fc> {
             Some(url) => {
                 // FIXME(pcwalton): The fact that image boxes store the cache within them makes
                 // little sense to me.
-                Some(ImageBoxInfo::new(&node, url, self.layout_context.shared.image_cache.clone()))
+                Some(ImageBoxInfo::new(&node, url, self.layout_context.image_cache.clone()))
             }
         }
     }
@@ -262,20 +268,19 @@ impl<'fc> FlowConstructor<'fc> {
     /// otherwise.
     #[inline(always)]
     fn flush_inline_boxes_to_flow(&mut self, boxes: ~[Box], flow: &mut ~Flow, node: LayoutNode) {
-        if boxes.len() > 0 {
-            let inline_base = BaseFlow::new(self.next_flow_id(), node);
-
-            let mut inline_flow = ~InlineFlow::from_boxes(inline_base, boxes) as ~Flow;
-
-            self.layout_context.shared.leaf_set.access(|leaf_set| leaf_set.insert(&inline_flow));
+        if boxes.len() == 0 {
+            return
+        }
 
-            TextRunScanner::new().scan_for_runs(self.layout_context, inline_flow);
-            let mut inline_flow = Some(inline_flow);
+        let inline_base = BaseFlow::new(self.next_flow_id(), node);
+        let mut inline_flow = ~InlineFlow::from_boxes(inline_base, boxes) as ~Flow;
+        self.layout_context.leaf_set.access(|leaf_set| leaf_set.insert(&inline_flow));
+        TextRunScanner::new().scan_for_runs(self.font_context, inline_flow);
 
-            self.layout_context.shared.leaf_set.access(|leaf_set| {
-                flow.add_new_child(inline_flow.take_unwrap(), leaf_set)
-            })
-        }
+        let mut inline_flow = Some(inline_flow);
+        self.layout_context.leaf_set.access(|leaf_set| {
+            flow.add_new_child(inline_flow.take_unwrap(), leaf_set)
+        })
     }
 
     /// Creates an inline flow from a set of inline boxes, if present, and adds it as a child of
@@ -319,7 +324,7 @@ impl<'fc> FlowConstructor<'fc> {
                                                                  flow,
                                                                  node);
                     let mut kid_flow = Some(kid_flow);
-                    self.layout_context.shared.leaf_set.access(|leaf_set| {
+                    self.layout_context.leaf_set.access(|leaf_set| {
                         flow.add_new_child(kid_flow.take_unwrap(), leaf_set)
                     })
                 }
@@ -362,7 +367,7 @@ impl<'fc> FlowConstructor<'fc> {
                                 // Push the flow generated by the {ib} split onto our list of
                                 // flows.
                                 let mut kid_flow = Some(kid_flow);
-                                self.layout_context.shared.leaf_set.access(|leaf_set| {
+                                self.layout_context.leaf_set.access(|leaf_set| {
                                     flow.add_new_child(kid_flow.take_unwrap(), leaf_set)
                                 })
                             }
@@ -391,7 +396,7 @@ impl<'fc> FlowConstructor<'fc> {
         let box_ = self.build_box_for_node(node);
         let mut flow = ~BlockFlow::from_box(base, box_, is_fixed) as ~Flow;
 
-        self.layout_context.shared.leaf_set.access(|leaf_set| leaf_set.insert(&flow));
+        self.layout_context.leaf_set.access(|leaf_set| leaf_set.insert(&flow));
 
         self.build_children_of_block_flow(&mut flow, node);
         flow
@@ -406,7 +411,7 @@ impl<'fc> FlowConstructor<'fc> {
 
         let mut flow = ~BlockFlow::float_from_box(base, float_type, box_) as ~Flow;
 
-        self.layout_context.shared.leaf_set.access(|leaf_set| leaf_set.insert(&flow));
+        self.layout_context.leaf_set.access(|leaf_set| leaf_set.insert(&flow));
 
         self.build_children_of_block_flow(&mut flow, node);
         flow
@@ -484,7 +489,7 @@ impl<'fc> FlowConstructor<'fc> {
     fn set_inline_info_for_inline_child(&mut self, boxes: &mut ~[Box], parent_node: LayoutNode) {
         let parent_box = self.build_box_for_node(parent_node);
         let font_style = parent_box.font_style();
-        let font_group = self.layout_context.font_ctx.get_resolved_font_for_style(&font_style);
+        let font_group = self.font_context.get_resolved_font_for_style(&font_style);
         let (font_ascent,font_descent) = font_group.borrow().with_mut( |fg| {
             fg.fonts[0].borrow().with_mut( |font| {
                 (font.metrics.ascent,font.metrics.descent)
@@ -569,7 +574,7 @@ impl<'a> PostorderNodeMutTraversal for FlowConstructor<'a> {
             // `display: none` contributes no flow construction result. Nuke the flow construction
             // results of children.
             (display::none, _, _) => {
-                self.layout_context.shared.leaf_set.access(|leaf_set| {
+                self.layout_context.leaf_set.access(|leaf_set| {
                     for child in node.children() {
                         let mut old_result = child.swap_out_construction_result();
                         old_result.destroy(leaf_set)
diff --git a/src/components/main/layout/context.rs b/src/components/main/layout/context.rs
index 4b62d4236d1..fb797196e71 100644
--- a/src/components/main/layout/context.rs
+++ b/src/components/main/layout/context.rs
@@ -5,17 +5,26 @@
 //! Data needed by the layout task.
 
 use extra::arc::MutexArc;
+use green::task::GreenTask;
 use layout::flow::LeafSet;
+use std::cast;
+use std::ptr;
+use std::rt::Runtime;
+use std::rt::local::Local;
+use std::rt::task::Task;
 
 use geom::size::Size2D;
-use gfx::font_context::FontContext;
+use gfx::font_context::{FontContext, FontContextInfo};
 use servo_msg::constellation_msg::ConstellationChan;
 use servo_net::local_image_cache::LocalImageCache;
 use servo_util::geometry::Au;
 
+#[thread_local]
+static mut FONT_CONTEXT: *mut FontContext = 0 as *mut FontContext;
+
 /// Data shared by all layout workers.
 #[deriving(Clone)]
-pub struct SharedLayoutInfo {
+pub struct LayoutContext {
     /// The local image cache.
     image_cache: MutexArc<LocalImageCache>,
 
@@ -27,14 +36,30 @@ pub struct SharedLayoutInfo {
 
     /// The set of leaf flows.
     leaf_set: MutexArc<LeafSet>,
+
+    /// Information needed to construct a font context.
+    font_context_info: FontContextInfo,
 }
 
-/// Data specific to a layout worker.
-pub struct LayoutContext {
-    /// Shared layout info.
-    shared: SharedLayoutInfo,
+impl LayoutContext {
+    pub fn font_context<'a>(&'a mut self) -> &'a mut FontContext {
+        // Sanity check.
+        let mut task = Local::borrow(None::<Task>);
+        match task.get().maybe_take_runtime::<GreenTask>() {
+            Some(green) => {
+                task.get().put_runtime(green as ~Runtime);
+                fail!("can't call this on a green task!")
+            }
+            None => {}
+        }
 
-    /// The current font context.
-    font_ctx: ~FontContext,
+        unsafe {
+            if FONT_CONTEXT == ptr::mut_null() {
+                let context = ~FontContext::new(self.font_context_info.clone());
+                FONT_CONTEXT = cast::transmute(context)
+            }
+            cast::transmute(FONT_CONTEXT)
+        }
+    }
 }
 
diff --git a/src/components/main/layout/layout_task.rs b/src/components/main/layout/layout_task.rs
index 4a10dac03c3..6ad34addd76 100644
--- a/src/components/main/layout/layout_task.rs
+++ b/src/components/main/layout/layout_task.rs
@@ -9,7 +9,7 @@ use css::matching::MatchMethods;
 use css::select::new_stylist;
 use css::node_style::StyledNode;
 use layout::construct::{FlowConstructionResult, FlowConstructor, NoConstructionResult};
-use layout::context::{LayoutContext, SharedLayoutInfo};
+use layout::context::LayoutContext;
 use layout::display_list_builder::{DisplayListBuilder, ToGfxColor};
 use layout::extra::LayoutAuxMethods;
 use layout::flow::{Flow, ImmutableFlowUtils, LeafSet, MutableFlowUtils, MutableOwnedFlowUtils};
@@ -17,7 +17,8 @@ use layout::flow::{PreorderFlowTraversal, PostorderFlowTraversal};
 use layout::flow;
 use layout::incremental::RestyleDamage;
 use layout::parallel::{AssignHeightsAndStoreOverflowTraversalKind, BubbleWidthsTraversalKind};
-use layout::parallel::{ParallelPostorderFlowTraversal};
+use layout::parallel::{UnsafeFlow};
+use layout::parallel;
 use layout::util::{LayoutDataAccess, OpaqueNode, LayoutDataWrapper};
 use layout::wrapper::LayoutNode;
 
@@ -25,7 +26,7 @@ use extra::arc::{Arc, MutexArc, RWArc};
 use geom::rect::Rect;
 use geom::size::Size2D;
 use gfx::display_list::{ClipDisplayItemClass, DisplayItem, DisplayItemIterator, DisplayList};
-use gfx::font_context::{FontContext, FontContextInfo};
+use gfx::font_context::FontContextInfo;
 use gfx::opts::Opts;
 use gfx::render_task::{RenderMsg, RenderChan, RenderLayer};
 use gfx::{render_task, color};
@@ -46,10 +47,12 @@ use servo_util::geometry::Au;
 use servo_util::time::{ProfilerChan, profile};
 use servo_util::time;
 use servo_util::task::spawn_named;
+use servo_util::workqueue::WorkQueue;
 use std::cast::transmute;
 use std::cast;
 use std::cell::RefCell;
 use std::comm::Port;
+use std::ptr;
 use std::util;
 use style::{AuthorOrigin, Stylesheet, Stylist};
 
@@ -91,7 +94,7 @@ pub struct LayoutTask {
     stylist: RWArc<Stylist>,
 
     /// The workers that we use for parallel operation.
-    parallel_traversal: Option<ParallelPostorderFlowTraversal>,
+    parallel_traversal: Option<WorkQueue<*mut LayoutContext,UnsafeFlow>>,
 
     /// The channel on which messages can be sent to the profiler.
     profiler_chan: ProfilerChan,
@@ -142,12 +145,14 @@ impl PreorderFlowTraversal for PropagateDamageTraversal {
 
 /// The bubble-widths traversal, the first part of layout computation. This computes preferred
 /// and intrinsic widths and bubbles them up the tree.
-pub struct BubbleWidthsTraversal<'a>(&'a mut LayoutContext);
+pub struct BubbleWidthsTraversal<'a> {
+    layout_context: &'a mut LayoutContext,
+}
 
 impl<'a> PostorderFlowTraversal for BubbleWidthsTraversal<'a> {
     #[inline]
     fn process(&mut self, flow: &mut Flow) -> bool {
-        flow.bubble_widths(**self);
+        flow.bubble_widths(self.layout_context);
         true
     }
 
@@ -174,13 +179,15 @@ impl<'a> PreorderFlowTraversal for AssignWidthsTraversal<'a> {
 /// The assign-heights-and-store-overflow traversal, the last (and most expensive) part of layout
 /// computation. Determines the final heights for all layout objects, computes positions, and
 /// computes overflow regions. In Gecko this corresponds to `FinishAndStoreOverflow`.
-pub struct AssignHeightsAndStoreOverflowTraversal<'a>(&'a mut LayoutContext);
+pub struct AssignHeightsAndStoreOverflowTraversal<'a> {
+    layout_context: &'a mut LayoutContext,
+}
 
 impl<'a> PostorderFlowTraversal for AssignHeightsAndStoreOverflowTraversal<'a> {
     #[inline]
     fn process(&mut self, flow: &mut Flow) -> bool {
-        flow.assign_height(**self);
-        flow.store_overflow(**self);
+        flow.assign_height(self.layout_context);
+        flow.store_overflow(self.layout_context);
         true
     }
 
@@ -248,13 +255,8 @@ impl LayoutTask {
            -> LayoutTask {
         let local_image_cache = MutexArc::new(LocalImageCache(image_cache_task.clone()));
         let screen_size = Size2D(Au(0), Au(0));
-        let font_context_info = FontContextInfo {
-            backend: opts.render_backend,
-            needs_font_list: true,
-            profiler_chan: profiler_chan.clone(),
-        };
         let parallel_traversal = if opts.layout_threads != 1 {
-            Some(ParallelPostorderFlowTraversal::new(font_context_info, opts.layout_threads))
+            Some(WorkQueue::new(opts.layout_threads, ptr::mut_null()))
         } else {
             None
         };
@@ -288,20 +290,18 @@ impl LayoutTask {
 
     // Create a layout context for use in building display lists, hit testing, &c.
     fn build_layout_context(&self) -> LayoutContext {
-        let font_ctx = ~FontContext::new(FontContextInfo {
+        let font_context_info = FontContextInfo {
             backend: self.opts.render_backend,
             needs_font_list: true,
             profiler_chan: self.profiler_chan.clone(),
-        });
+        };
 
         LayoutContext {
-            shared: SharedLayoutInfo {
-                image_cache: self.local_image_cache.clone(),
-                screen_size: self.screen_size.clone(),
-                constellation_chan: self.constellation_chan.clone(),
-                leaf_set: self.leaf_set.clone(),
-            },
-            font_ctx: font_ctx,
+            image_cache: self.local_image_cache.clone(),
+            screen_size: self.screen_size.clone(),
+            constellation_chan: self.constellation_chan.clone(),
+            leaf_set: self.leaf_set.clone(),
+            font_context_info: font_context_info,
         }
     }
 
@@ -418,7 +418,12 @@ impl LayoutTask {
     fn solve_constraints(&mut self,
                          layout_root: &mut Flow,
                          layout_context: &mut LayoutContext) {
-        layout_root.traverse_postorder(&mut BubbleWidthsTraversal(layout_context));
+        {
+            let mut traversal = BubbleWidthsTraversal {
+                layout_context: layout_context,
+            };
+            layout_root.traverse_postorder(&mut traversal);
+        }
 
         // FIXME(kmc): We want to prune nodes without the Reflow restyle damage
         // bit, but FloatContext values can't be reused, so we need to
@@ -428,8 +433,12 @@ impl LayoutTask {
         layout_root.traverse_preorder(&mut AssignWidthsTraversal(layout_context));
 
         // FIXME(pcwalton): Prune this pass as well.
-        layout_root.traverse_postorder(&mut AssignHeightsAndStoreOverflowTraversal(
-                layout_context));
+        {
+            let mut traversal = AssignHeightsAndStoreOverflowTraversal {
+                layout_context: layout_context,
+            };
+            layout_root.traverse_postorder(&mut traversal);
+        }
     }
 
     /// Performs layout constraint solving in parallel.
@@ -443,9 +452,11 @@ impl LayoutTask {
         match self.parallel_traversal {
             None => fail!("solve_contraints_parallel() called with no parallel traversal ready"),
             Some(ref mut traversal) => {
-                traversal.start(BubbleWidthsTraversalKind,
-                                layout_context,
-                                self.profiler_chan.clone());
+                parallel::traverse_flow_tree(BubbleWidthsTraversalKind,
+                                             &self.leaf_set,
+                                             self.profiler_chan.clone(),
+                                             layout_context,
+                                             traversal);
 
                 // NOTE: this currently computes borders, so any pruning should separate that
                 // operation out.
@@ -453,9 +464,11 @@ impl LayoutTask {
                 // because this is a top-down traversal, unlike the others.
                 layout_root.traverse_preorder(&mut AssignWidthsTraversal(layout_context));
 
-                traversal.start(AssignHeightsAndStoreOverflowTraversalKind,
-                                layout_context,
-                                self.profiler_chan.clone());
+                parallel::traverse_flow_tree(AssignHeightsAndStoreOverflowTraversalKind,
+                                             &self.leaf_set,
+                                             self.profiler_chan.clone(),
+                                             layout_context,
+                                             traversal);
             }
         }
     }
diff --git a/src/components/main/layout/parallel.rs b/src/components/main/layout/parallel.rs
index 480ec886d8f..b38e6abc9b5 100644
--- a/src/components/main/layout/parallel.rs
+++ b/src/components/main/layout/parallel.rs
@@ -4,44 +4,29 @@
 
 //! Implements parallel traversals over the flow tree.
 
-use layout::context::{LayoutContext, SharedLayoutInfo};
-use layout::flow::{Flow, PostorderFlowTraversal};
+use layout::context::LayoutContext;
+use layout::flow::{Flow, LeafSet, PostorderFlowTraversal};
 use layout::flow;
 use layout::layout_task::{AssignHeightsAndStoreOverflowTraversal, BubbleWidthsTraversal};
 
-use gfx::font_context::{FontContext, FontContextInfo};
-use native;
+use extra::arc::MutexArc;
 use servo_util::time::{ProfilerChan, profile};
 use servo_util::time;
+use servo_util::workqueue::{WorkQueue, WorkUnit, WorkerProxy};
 use std::cast;
-use std::comm::SharedChan;
-use std::libc::c_void;
-use std::ptr;
 use std::sync::atomics::{AtomicInt, Relaxed, SeqCst};
-use std::sync::deque::{Abort, BufferPool, Data, Empty, Stealer, Worker};
-use std::util;
 
-enum WorkerMsg {
-    /// Tells the worker to start a traversal.
-    StartMsg(Worker<UnsafeFlow>, TraversalKind, SharedLayoutInfo),
-
-    /// Tells the worker to stop. It can be restarted again with a `StartMsg`.
-    StopMsg,
-
-    /// Tells the worker thread to terminate.
-    ExitMsg,
+pub enum TraversalKind {
+    BubbleWidthsTraversalKind,
+    AssignHeightsAndStoreOverflowTraversalKind,
 }
 
-enum SupervisorMsg {
-    /// Sent once the last flow is processed.
-    FinishedMsg,
+pub type UnsafeFlow = (uint, uint);
 
-    /// Returns the deque to the supervisor.
-    ReturnDequeMsg(uint, Worker<UnsafeFlow>),
+fn null_unsafe_flow() -> UnsafeFlow {
+    (0, 0)
 }
 
-pub type UnsafeFlow = (*c_void, *c_void);
-
 pub fn owned_flow_to_unsafe_flow(flow: *~Flow) -> UnsafeFlow {
     unsafe {
         cast::transmute_copy(&*flow)
@@ -54,10 +39,6 @@ pub fn mut_owned_flow_to_unsafe_flow(flow: *mut ~Flow) -> UnsafeFlow {
     }
 }
 
-fn null_unsafe_flow() -> UnsafeFlow {
-    (ptr::null(), ptr::null())
-}
-
 /// Information that we need stored in each flow.
 pub struct FlowParallelInfo {
     /// The number of children that still need work done.
@@ -75,270 +56,97 @@ impl FlowParallelInfo {
     }
 }
 
-/// Information that the supervisor thread keeps about the worker threads.
-struct WorkerInfo {
-    /// The communication channel to the workers.
-    chan: Chan<WorkerMsg>,
-    /// The buffer pool for this deque.
-    pool: BufferPool<UnsafeFlow>,
-    /// The worker end of the deque, if we have it.
-    deque: Option<Worker<UnsafeFlow>>,
-    /// The thief end of the work-stealing deque.
-    thief: Stealer<UnsafeFlow>,
-}
-
-/// Information that each worker needs to do its job.
-struct PostorderWorker {
-    /// The font context.
-    font_context: Option<~FontContext>,
-    /// Communications for the worker.
-    comm: PostorderWorkerComm,
-}
-
-/// Communication channels for postorder workers.
-struct PostorderWorkerComm {
-    /// The index of this worker.
-    index: uint,
-    /// The communication port from the supervisor.
-    port: Port<WorkerMsg>,
-    /// The communication channel to the supervisor.
-    chan: SharedChan<SupervisorMsg>,
-    /// The thief end of the work-stealing deque for all other workers.
-    other_deques: ~[Stealer<UnsafeFlow>],
-}
-
-/// The type of traversal we're performing.
-pub enum TraversalKind {
-    BubbleWidthsTraversalKind,
-    AssignHeightsAndStoreOverflowTraversalKind,
-}
-
-impl PostorderWorker {
-    /// Starts up the worker and listens for messages.
-    pub fn start(&mut self) {
+/// A parallel bottom-up flow traversal.
+trait ParallelPostorderFlowTraversal : PostorderFlowTraversal {
+    fn run_parallel(&mut self, mut unsafe_flow: UnsafeFlow) {
         loop {
-            // Wait for a start message.
-            let (mut deque, kind, shared_layout_info) = match self.comm.port.recv() {
-                StopMsg => fail!("unexpected stop message"),
-                StartMsg(deque, kind, shared_layout_info) => (deque, kind, shared_layout_info),
-                ExitMsg => return,
-            };
+            unsafe {
+                // Get a real flow.
+                let flow: &mut ~Flow = cast::transmute(&unsafe_flow);
 
-            // Set up our traversal context.
-            let mut traversal = LayoutContext {
-                shared: shared_layout_info,
-                font_ctx: self.font_context.take_unwrap(),
-            };
-
-            // And we're off!
-            'outer: loop {
-                let unsafe_flow;
-                match deque.pop() {
-                    Some(the_flow) => unsafe_flow = the_flow,
-                    None => {
-                        // Become a thief.
-                        let mut i = 0;
-                        loop {
-                            if self.comm.other_deques.len() != 0 {
-                                match self.comm.other_deques[i].steal() {
-                                    Empty => {
-                                        // Try the next one.
-                                        i += 1;
-                                        if i >= self.comm.other_deques.len() {
-                                            i = 0
-                                        }
-                                    }
-                                    Abort => {
-                                        // Continue.
-                                    }
-                                    Data(the_flow) => {
-                                        unsafe_flow = the_flow;
-                                        break
-                                    }
-                                }
-                            }
-
-                            if i == 0 {
-                                match self.comm.port.try_recv() {
-                                    Some(StopMsg) => break 'outer,
-                                    Some(ExitMsg) => return,
-                                    Some(_) => fail!("unexpected message!"),
-                                    None => {}
-                                }
-                            }
-                        }
-                    }
+                // Perform the appropriate traversal.
+                if self.should_process(*flow) {
+                    self.process(*flow);
                 }
 
-                // OK, we've got some data. The rest of this is unsafe code.
-                unsafe {
-                    // Get a real flow.
-                    let flow: &mut ~Flow = cast::transmute(&unsafe_flow);
-
-                    // Perform the appropriate traversal.
-                    match kind {
-                        BubbleWidthsTraversalKind => {
-                            let mut traversal = BubbleWidthsTraversal(&mut traversal);
-                            if traversal.should_process(*flow) {
-                                traversal.process(*flow);
-                            }
-                        }
-                        AssignHeightsAndStoreOverflowTraversalKind => {
-                            let mut traversal =
-                                AssignHeightsAndStoreOverflowTraversal(&mut traversal);
-                            if traversal.should_process(*flow) {
-                                traversal.process(*flow);
-                            }
-                        }
-                    }
+                let base = flow::mut_base(*flow);
 
-                    let base = flow::mut_base(*flow);
+                // Reset the count of children for the next layout traversal.
+                base.parallel.children_count.store(base.children.len() as int, Relaxed);
 
-                    // Reset the count of children for the next layout traversal.
-                    base.parallel.children_count.store(base.children.len() as int, Relaxed);
+                // Possibly enqueue the parent.
+                let unsafe_parent = base.parallel.parent;
+                if unsafe_parent == null_unsafe_flow() {
+                    // We're done!
+                    break
+                }
 
-                    // Possibly enqueue the parent.
-                    let unsafe_parent = base.parallel.parent;
-                    if unsafe_parent == null_unsafe_flow() {
-                        // We're done!
-                        self.comm.chan.send(FinishedMsg);
-                    } else {
-                        // No, we're not at the root yet. Then are we the last sibling of our
-                        // parent? If so, we can enqueue our parent; otherwise, we've gotta wait.
-                        let parent: &mut ~Flow = cast::transmute(&unsafe_parent);
-                        let parent_base = flow::mut_base(*parent);
-                        if parent_base.parallel.children_count.fetch_sub(1, SeqCst) == 1 {
-                            // We were the last child of our parent. Enqueue the parent.
-                            deque.push(unsafe_parent)
-                        }
-                    }
+                // No, we're not at the root yet. Then are we the last sibling of our parent? If
+                // so, we can continue on with our parent; otherwise, we've gotta wait.
+                let parent: &mut ~Flow = cast::transmute(&unsafe_parent);
+                let parent_base = flow::mut_base(*parent);
+                if parent_base.parallel.children_count.fetch_sub(1, SeqCst) == 1 {
+                    // We were the last child of our parent. Reflow our parent.
+                    unsafe_flow = unsafe_parent
+                } else {
+                    // Stop.
+                    break
                 }
             }
-
-            // Destroy the traversal and save the font context.
-            let LayoutContext {
-                font_ctx: font_context,
-                ..
-            } = traversal;
-            self.font_context = Some(font_context);
-
-            // Give the deque back to the supervisor.
-            self.comm.chan.send(ReturnDequeMsg(self.comm.index, deque))
         }
     }
 }
 
-/// A parallel bottom-up traversal.
-pub struct ParallelPostorderFlowTraversal {
-    /// Information about each of the workers.
-    workers: ~[WorkerInfo],
-    /// A port on which information can be received from the workers.
-    port: Port<SupervisorMsg>,
-}
+impl<'a> ParallelPostorderFlowTraversal for BubbleWidthsTraversal<'a> {}
 
-impl ParallelPostorderFlowTraversal {
-    pub fn new(font_context_info: FontContextInfo, thread_count: uint)
-               -> ParallelPostorderFlowTraversal {
-        let (supervisor_port, supervisor_chan) = SharedChan::new();
-        let (mut infos, mut comms) = (~[], ~[]);
-        for i in range(0, thread_count) {
-            let (worker_port, worker_chan) = Chan::new();
-            let mut pool = BufferPool::new();
-            let (worker, thief) = pool.deque();
-            infos.push(WorkerInfo {
-                chan: worker_chan,
-                pool: pool,
-                deque: Some(worker),
-                thief: thief,
-            });
-            comms.push(PostorderWorkerComm {
-                index: i,
-                port: worker_port,
-                chan: supervisor_chan.clone(),
-                other_deques: ~[],
-            });
-        }
+impl<'a> ParallelPostorderFlowTraversal for AssignHeightsAndStoreOverflowTraversal<'a> {}
 
-        for i in range(0, thread_count) {
-            for j in range(0, thread_count) {
-                if i != j {
-                    comms[i].other_deques.push(infos[j].thief.clone())
-                }
-            }
-            assert!(comms[i].other_deques.len() == thread_count - 1)
-        }
-
-        for comm in comms.move_iter() {
-            let font_context_info = font_context_info.clone();
-            native::task::spawn(proc() {
-                let mut worker = PostorderWorker {
-                    font_context: Some(~FontContext::new(font_context_info)),
-                    comm: comm,
-                };
-                worker.start()
-            })
-        }
+fn bubble_widths(unsafe_flow: UnsafeFlow, proxy: &mut WorkerProxy<*mut LayoutContext,UnsafeFlow>) {
+    let layout_context: &mut LayoutContext = unsafe {
+        cast::transmute(*proxy.user_data())
+    };
+    let mut bubble_widths_traversal = BubbleWidthsTraversal {
+        layout_context: layout_context,
+    };
+    bubble_widths_traversal.run_parallel(unsafe_flow)
+}
 
-        ParallelPostorderFlowTraversal {
-            workers: infos,
-            port: supervisor_port,
-        }
-    }
+fn assign_heights_and_store_overflow(unsafe_flow: UnsafeFlow,
+                                     proxy: &mut WorkerProxy<*mut LayoutContext,UnsafeFlow>) {
+    let layout_context: &mut LayoutContext = unsafe {
+        cast::transmute(*proxy.user_data())
+    };
+    let mut assign_heights_traversal = AssignHeightsAndStoreOverflowTraversal {
+        layout_context: layout_context,
+    };
+    assign_heights_traversal.run_parallel(unsafe_flow)
+}
 
-    /// TODO(pcwalton): This could be parallelized.
-    fn warmup(&mut self, layout_context: &mut LayoutContext) {
-        layout_context.shared.leaf_set.access(|leaf_set| {
-            for &flow in leaf_set.iter() {
-                match self.workers[0].deque {
-                    None => fail!("no deque!"),
-                    Some(ref mut deque) => {
-                        deque.push(flow);
-                    }
-                }
-            }
-        });
+pub fn traverse_flow_tree(kind: TraversalKind,
+                          leaf_set: &MutexArc<LeafSet>,
+                          profiler_chan: ProfilerChan,
+                          layout_context: &mut LayoutContext,
+                          queue: &mut WorkQueue<*mut LayoutContext,UnsafeFlow>) {
+    unsafe {
+        queue.data = cast::transmute(layout_context)
     }
 
-    /// Traverses the given flow tree in parallel.
-    pub fn start(&mut self,
-                 kind: TraversalKind,
-                 layout_context: &mut LayoutContext,
-                 profiler_chan: ProfilerChan) {
-        profile(time::LayoutParallelWarmupCategory, profiler_chan, || self.warmup(layout_context));
-
-        for worker in self.workers.mut_iter() {
-            worker.chan.send(StartMsg(util::replace(&mut worker.deque, None).unwrap(),
-                                      kind,
-                                      layout_context.shared.clone()))
-        }
-
-        // Wait for them to finish.
-        let _ = self.port.recv();
-
-        // Tell everyone to stop.
-        for worker in self.workers.iter() {
-            worker.chan.send(StopMsg);
-        }
+    let fun = match kind {
+        BubbleWidthsTraversalKind => bubble_widths,
+        AssignHeightsAndStoreOverflowTraversalKind => assign_heights_and_store_overflow,
+    };
 
-        // Get our deques back.
-        //
-        // TODO(pcwalton): Might be able to get a little parallelism over multiple traversals by
-        // doing this lazily.
-        for _ in range(0, self.workers.len()) {
-            match self.port.recv() {
-                ReturnDequeMsg(returned_deque_index, returned_deque) => {
-                    self.workers[returned_deque_index].deque = Some(returned_deque)
-                }
-                _ => fail!("unexpected message received during return queue phase"),
+    profile(time::LayoutParallelWarmupCategory, profiler_chan, || {
+        leaf_set.access(|leaf_set| {
+            for &flow in leaf_set.iter() {
+                queue.push(WorkUnit {
+                    fun: fun,
+                    data: flow,
+                })
             }
-        }
-    }
+        })
+    });
 
-    /// Shuts down all the worker threads.
-    pub fn shutdown(&mut self) {
-        for worker in self.workers.iter() {
-            worker.chan.send(ExitMsg)
-        }
-    }
+    queue.run()
 }
 
diff --git a/src/components/main/layout/text.rs b/src/components/main/layout/text.rs
index e4ad1f8bc57..b8913c6499e 100644
--- a/src/components/main/layout/text.rs
+++ b/src/components/main/layout/text.rs
@@ -5,10 +5,10 @@
 //! Text layout.
 
 use layout::box_::{Box, ScannedTextBox, ScannedTextBoxInfo, UnscannedTextBox};
-use layout::context::LayoutContext;
 use layout::flow::Flow;
 
 use extra::arc::Arc;
+use gfx::font_context::FontContext;
 use gfx::text::text_run::TextRun;
 use gfx::text::util::{CompressWhitespaceNewline, transform_text, CompressNone};
 use servo_util::range::Range;
@@ -27,7 +27,7 @@ impl TextRunScanner {
         }
     }
 
-    pub fn scan_for_runs(&mut self, ctx: &mut LayoutContext, flow: &mut Flow) {
+    pub fn scan_for_runs(&mut self, font_context: &mut FontContext, flow: &mut Flow) {
         {
             let inline = flow.as_immutable_inline();
             debug!("TextRunScanner: scanning {:u} boxes for text runs...", inline.boxes.len());
@@ -40,13 +40,16 @@ impl TextRunScanner {
             if box_i > 0 && !can_coalesce_text_nodes(flow.as_immutable_inline().boxes,
                                                      box_i - 1,
                                                      box_i) {
-                last_whitespace = self.flush_clump_to_list(ctx, flow, last_whitespace, &mut out_boxes);
+                last_whitespace = self.flush_clump_to_list(font_context,
+                                                           flow,
+                                                           last_whitespace,
+                                                           &mut out_boxes);
             }
             self.clump.extend_by(1);
         }
         // handle remaining clumps
         if self.clump.length() > 0 {
-            self.flush_clump_to_list(ctx, flow, last_whitespace, &mut out_boxes);
+            self.flush_clump_to_list(font_context, flow, last_whitespace, &mut out_boxes);
         }
 
         debug!("TextRunScanner: swapping out boxes.");
@@ -73,7 +76,7 @@ impl TextRunScanner {
     /// FIXME(pcwalton): Stop cloning boxes. Instead we will need to consume the `in_box`es as we
     /// iterate over them.
     pub fn flush_clump_to_list(&mut self,
-                               ctx: &mut LayoutContext,
+                               font_context: &mut FontContext,
                                flow: &mut Flow,
                                last_whitespace: bool,
                                out_boxes: &mut ~[Box])
@@ -130,7 +133,7 @@ impl TextRunScanner {
                     // TODO(#177): Text run creation must account for the renderability of text by
                     // 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 fontgroup = font_context.get_resolved_font_for_style(&font_style);
                     let run = ~fontgroup.borrow().with(|fg| fg.create_textrun(transformed_text.clone(), decoration));
 
                     debug!("TextRunScanner: pushing single text box in range: {} ({})",
@@ -151,7 +154,7 @@ impl TextRunScanner {
                 // and then letting `FontGroup` decide which `Font` to stick into the text run.
                 let in_box = &in_boxes[self.clump.begin()];
                 let font_style = in_box.font_style();
-                let fontgroup = ctx.font_ctx.get_resolved_font_for_style(&font_style);
+                let fontgroup = font_context.get_resolved_font_for_style(&font_style);
                 let decoration = in_box.text_decoration();
 
                 // TODO(#115): Use the actual CSS `white-space` property of the relevant style.
diff --git a/src/components/main/servo.rc b/src/components/main/servo.rc
index 60f6902a591..342aacae57f 100755
--- a/src/components/main/servo.rc
+++ b/src/components/main/servo.rc
@@ -6,7 +6,7 @@
 #[comment = "The Servo Parallel Browser Project"];
 #[license = "MPL"];
 
-#[feature(globs, macro_rules, managed_boxes)];
+#[feature(globs, macro_rules, managed_boxes, thread_local)];
 
 extern mod alert;
 extern mod azure;
diff --git a/src/components/util/time.rs b/src/components/util/time.rs
index b4ac13ef095..426cfad705a 100644
--- a/src/components/util/time.rs
+++ b/src/components/util/time.rs
@@ -37,10 +37,12 @@ impl ProfilerChan {
 }
 
 pub enum ProfilerMsg {
-    // Normal message used for reporting time
+    /// Normal message used for reporting time
     TimeMsg(ProfilerCategory, f64),
-    // Message used to force print the profiling metrics
+    /// Message used to force print the profiling metrics
     PrintMsg,
+    /// Tells the profiler to shut down.
+    ExitMsg,
 }
 
 #[deriving(Eq, Clone, TotalEq, TotalOrd)]
@@ -136,7 +138,12 @@ impl Profiler {
             None => {
                 // no-op to handle profiler messages when the profiler is inactive
                 spawn_named("Profiler", proc() {
-                    while port.recv_opt().is_some() {}
+                    loop {
+                        match port.recv_opt() {
+                            None | Some(ExitMsg) => break,
+                            _ => {}
+                        }
+                    }
                 });
             }
         }
@@ -156,13 +163,17 @@ impl Profiler {
         loop {
             let msg = self.port.recv_opt();
             match msg {
-               Some (msg) => self.handle_msg(msg),
+               Some(msg) => {
+                   if !self.handle_msg(msg) {
+                       break
+                   }
+               }
                None => break
             }
         }
     }
 
-    fn handle_msg(&mut self, msg: ProfilerMsg) {
+    fn handle_msg(&mut self, msg: ProfilerMsg) -> bool {
         match msg {
             TimeMsg(category, t) => self.buckets.find_mut(&category).unwrap().push(t),
             PrintMsg => match self.last_msg {
@@ -170,8 +181,10 @@ impl Profiler {
                 Some(TimeMsg(..)) => self.print_buckets(),
                 _ => ()
             },
+            ExitMsg => return false,
         };
         self.last_msg = Some(msg);
+        true
     }
 
     fn print_buckets(&mut self) {
diff --git a/src/components/util/util.rc b/src/components/util/util.rc
index 50af03c67a7..1fb520c0c7b 100644
--- a/src/components/util/util.rc
+++ b/src/components/util/util.rc
@@ -9,6 +9,7 @@
 
 extern mod extra;
 extern mod geom;
+extern mod native;
 
 pub mod cache;
 pub mod geometry;
@@ -19,4 +20,5 @@ pub mod vec;
 pub mod debug;
 pub mod io;
 pub mod task;
+pub mod workqueue;
 
diff --git a/src/components/util/workqueue.rs b/src/components/util/workqueue.rs
new file mode 100644
index 00000000000..0254b0c573f
--- /dev/null
+++ b/src/components/util/workqueue.rs
@@ -0,0 +1,295 @@
+/* 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/. */
+
+//! A work queue for scheduling units of work across threads in a fork-join fashion.
+//!
+//! Data associated with queues is simply a pair of unsigned integers. It is expected that a
+//! higher-level API on top of this could allow safe fork-join parallelism.
+
+use native;
+use std::cast;
+use std::rand::{Rng, XorShiftRng};
+use std::rand;
+use std::sync::atomics::{AtomicUint, SeqCst};
+use std::sync::deque::{Abort, BufferPool, Data, Empty, Stealer, Worker};
+use std::unstable::intrinsics;
+
+/// A unit of work.
+///
+/// The type parameter `QUD` stands for "queue user data" and represents global custom data for the
+/// entire work queue, and the type parameter `WUD` stands for "work user data" and represents
+/// custom data specific to each unit of work.
+pub struct WorkUnit<QUD,WUD> {
+    /// The function to execute.
+    fun: extern "Rust" fn(WUD, &mut WorkerProxy<QUD,WUD>),
+    /// Arbitrary data.
+    data: WUD,
+}
+
+/// Messages from the supervisor to the worker.
+enum WorkerMsg<QUD,WUD> {
+    /// Tells the worker to start work.
+    StartMsg(Worker<WorkUnit<QUD,WUD>>, *mut AtomicUint, *QUD),
+
+    /// Tells the worker to stop. It can be restarted again with a `StartMsg`.
+    StopMsg,
+
+    /// Tells the worker thread to terminate.
+    ExitMsg,
+}
+
+/// Messages to the supervisor.
+enum SupervisorMsg<QUD,WUD> {
+    FinishedMsg,
+    ReturnDequeMsg(uint, Worker<WorkUnit<QUD,WUD>>),
+}
+
+/// Information that the supervisor thread keeps about the worker threads.
+struct WorkerInfo<QUD,WUD> {
+    /// The communication channel to the workers.
+    chan: Chan<WorkerMsg<QUD,WUD>>,
+    /// The buffer pool for this deque.
+    pool: BufferPool<WorkUnit<QUD,WUD>>,
+    /// The worker end of the deque, if we have it.
+    deque: Option<Worker<WorkUnit<QUD,WUD>>>,
+    /// The thief end of the work-stealing deque.
+    thief: Stealer<WorkUnit<QUD,WUD>>,
+}
+
+/// Information specific to each worker thread that the thread keeps.
+struct WorkerThread<QUD,WUD> {
+    /// The index of this worker.
+    index: uint,
+    /// The communication port from the supervisor.
+    port: Port<WorkerMsg<QUD,WUD>>,
+    /// The communication channel on which messages are sent to the supervisor.
+    chan: SharedChan<SupervisorMsg<QUD,WUD>>,
+    /// The thief end of the work-stealing deque for all other workers.
+    other_deques: ~[Stealer<WorkUnit<QUD,WUD>>],
+    /// The random number generator for this worker.
+    rng: XorShiftRng,
+}
+
+static SPIN_COUNT: uint = 1000;
+
+impl<QUD:Send,WUD:Send> WorkerThread<QUD,WUD> {
+    /// The main logic. This function starts up the worker and listens for
+    /// messages.
+    pub fn start(&mut self) {
+        loop {
+            // Wait for a start message.
+            let (mut deque, ref_count, queue_data) = match self.port.recv() {
+                StartMsg(deque, ref_count, queue_data) => (deque, ref_count, queue_data),
+                StopMsg => fail!("unexpected stop message"),
+                ExitMsg => return,
+            };
+
+            // We're off!
+            //
+            // FIXME(pcwalton): Can't use labeled break or continue cross-crate due to a Rust bug.
+            loop {
+                // FIXME(pcwalton): Nasty workaround for the lack of labeled break/continue
+                // cross-crate.
+                let mut work_unit = unsafe {
+                    intrinsics::uninit()
+                };
+                match deque.pop() {
+                    Some(work) => work_unit = work,
+                    None => {
+                        // Become a thief.
+                        let mut i = 0;
+                        let mut should_continue = true;
+                        loop {
+                            let victim = (self.rng.next_u32() as uint) % self.other_deques.len();
+                            match self.other_deques[victim].steal() {
+                                Empty | Abort => {
+                                    // Continue.
+                                }
+                                Data(work) => {
+                                    work_unit = work;
+                                    break
+                                }
+                            }
+
+                            if i == SPIN_COUNT {
+                                match self.port.try_recv() {
+                                    Some(StopMsg) => {
+                                        should_continue = false;
+                                        break
+                                    }
+                                    Some(ExitMsg) => return,
+                                    Some(_) => fail!("unexpected message"),
+                                    None => {}
+                                }
+
+                                i = 0
+                            } else {
+                                i += 1
+                            }
+                        }
+
+                        if !should_continue {
+                            break
+                        }
+                    }
+                }
+
+                // At this point, we have some work. Perform it.
+                let mut proxy = WorkerProxy {
+                    worker: &mut deque,
+                    ref_count: ref_count,
+                    queue_data: queue_data,
+                };
+                (work_unit.fun)(work_unit.data, &mut proxy);
+
+                // The work is done. Now decrement the count of outstanding work items. If this was
+                // the last work unit in the queue, then send a message on the channel.
+                unsafe {
+                    if (*ref_count).fetch_sub(1, SeqCst) == 1 {
+                        self.chan.send(FinishedMsg)
+                    }
+                }
+            }
+
+            // Give the deque back to the supervisor.
+            self.chan.send(ReturnDequeMsg(self.index, deque))
+        }
+    }
+}
+
+/// A handle to the work queue that individual work units have.
+pub struct WorkerProxy<'a,QUD,WUD> {
+    priv worker: &'a mut Worker<WorkUnit<QUD,WUD>>,
+    priv ref_count: *mut AtomicUint,
+    priv queue_data: *QUD,
+}
+
+impl<'a,QUD,WUD:Send> WorkerProxy<'a,QUD,WUD> {
+    /// Enqueues a block into the work queue.
+    #[inline]
+    pub fn push(&mut self, work_unit: WorkUnit<QUD,WUD>) {
+        unsafe {
+            drop((*self.ref_count).fetch_add(1, SeqCst));
+        }
+        self.worker.push(work_unit);
+    }
+
+    /// Retrieves the queue user data.
+    #[inline]
+    pub fn user_data<'a>(&'a self) -> &'a QUD {
+        unsafe {
+            cast::transmute(self.queue_data)
+        }
+    }
+}
+
+/// A work queue on which units of work can be submitted.
+pub struct WorkQueue<QUD,WUD> {
+    /// Information about each of the workers.
+    priv workers: ~[WorkerInfo<QUD,WUD>],
+    /// A port on which deques can be received from the workers.
+    priv port: Port<SupervisorMsg<QUD,WUD>>,
+    /// The amount of work that has been enqueued.
+    priv work_count: uint,
+    /// Arbitrary user data.
+    data: QUD,
+}
+
+impl<QUD:Send,WUD:Send> WorkQueue<QUD,WUD> {
+    /// Creates a new work queue and spawns all the threads associated with
+    /// it.
+    pub fn new(thread_count: uint, user_data: QUD) -> WorkQueue<QUD,WUD> {
+        // Set up data structures.
+        let (supervisor_port, supervisor_chan) = SharedChan::new();
+        let (mut infos, mut threads) = (~[], ~[]);
+        for i in range(0, thread_count) {
+            let (worker_port, worker_chan) = Chan::new();
+            let mut pool = BufferPool::new();
+            let (worker, thief) = pool.deque();
+            infos.push(WorkerInfo {
+                chan: worker_chan,
+                pool: pool,
+                deque: Some(worker),
+                thief: thief,
+            });
+            threads.push(WorkerThread {
+                index: i,
+                port: worker_port,
+                chan: supervisor_chan.clone(),
+                other_deques: ~[],
+                rng: rand::weak_rng(),
+            });
+        }
+
+        // Connect workers to one another.
+        for i in range(0, thread_count) {
+            for j in range(0, thread_count) {
+                if i != j {
+                    threads[i].other_deques.push(infos[j].thief.clone())
+                }
+            }
+            assert!(threads[i].other_deques.len() == thread_count - 1)
+        }
+
+        // Spawn threads.
+        for thread in threads.move_iter() {
+            native::task::spawn(proc() {
+                let mut thread = thread;
+                thread.start()
+            })
+        }
+
+        WorkQueue {
+            workers: infos,
+            port: supervisor_port,
+            work_count: 0,
+            data: user_data,
+        }
+    }
+
+    /// Enqueues a block into the work queue.
+    #[inline]
+    pub fn push(&mut self, work_unit: WorkUnit<QUD,WUD>) {
+        match self.workers[0].deque {
+            None => {
+                fail!("tried to push a block but we don't have the deque?!")
+            }
+            Some(ref mut deque) => deque.push(work_unit),
+        }
+        self.work_count += 1
+    }
+
+    /// Synchronously runs all the enqueued tasks and waits for them to complete.
+    pub fn run(&mut self) {
+        // Tell the workers to start.
+        let mut work_count = AtomicUint::new(self.work_count);
+        for worker in self.workers.mut_iter() {
+            worker.chan.send(StartMsg(worker.deque.take_unwrap(), &mut work_count, &self.data))
+        }
+
+        // Wait for the work to finish.
+        drop(self.port.recv());
+        self.work_count = 0;
+
+        // Tell everyone to stop.
+        for worker in self.workers.iter() {
+            worker.chan.send(StopMsg)
+        }
+
+        // Get our deques back.
+        for _ in range(0, self.workers.len()) {
+            match self.port.recv() {
+                ReturnDequeMsg(index, deque) => self.workers[index].deque = Some(deque),
+                FinishedMsg => fail!("unexpected finished message!"),
+            }
+        }
+    }
+
+    pub fn shutdown(&mut self) {
+        for worker in self.workers.iter() {
+            worker.chan.send(ExitMsg)
+        }
+    }
+}
+