Add transparent Traceable and Untraceable types to aid proper rooting practices, and replace ad-hoc Untraceable structs with empty Encodable implementations.

14 files changed, 217 insertions, 195 deletions

diff --git a/src/components/script/dom/bindings/codegen/CodegenRust.py b/src/components/script/dom/bindings/codegen/CodegenRust.py
index 9470b61fab2..8d89fe1b879 100644
--- a/src/components/script/dom/bindings/codegen/CodegenRust.py
+++ b/src/components/script/dom/bindings/codegen/CodegenRust.py
@@ -1864,7 +1864,7 @@ def CreateBindingJSObject(descriptor, parent=None):
         assert not descriptor.createGlobal
         handler = """
   let js_info = aScope.get().page().js_info();
-  let handler = js_info.get_ref().dom_static.proxy_handlers.get(&(PrototypeList::id::%s as uint));
+  let handler = js_info.get_ref().dom_static.proxy_handlers.deref().get(&(PrototypeList::id::%s as uint));
 """ % descriptor.name
         create += handler + """  let obj = NewProxyObject(aCx, *handler,
                            &PrivateValue(squirrel_away_unique(aObject) as *libc::c_void),
@@ -2204,7 +2204,7 @@ class CGDefineDOMInterfaceMethod(CGAbstractMethod):
        ('Some(%s)' % TRACE_HOOK_NAME),
        self.descriptor.name)
 
-        return (body + """  let cx = js_info.js_context.deref().ptr;
+        return (body + """  let cx = (*js_info.js_context).deref().ptr;
   let receiver = js_info.js_compartment.global_obj;
   let global: *JSObject = JS_GetGlobalForObject(cx, receiver);
   assert!(%s(cx, global, receiver).is_not_null());""" % (getter))
@@ -4517,7 +4517,7 @@ class CGBindingRoot(CGThing):
             'dom::bindings::utils::{ThrowingConstructor,  unwrap, unwrap_jsmanaged}',
             'dom::bindings::utils::{VoidVal, with_gc_disabled}',
             'dom::bindings::utils::{with_gc_enabled}',
-            'dom::bindings::trace::Traceable',
+            'dom::bindings::trace::JSTraceable',
             'dom::bindings::callback::{CallbackContainer,CallbackInterface}',
             'dom::bindings::callback::{CallSetup,ExceptionHandling}',
             'dom::bindings::callback::{WrapCallThisObject}',
@@ -5472,7 +5472,7 @@ class GlobalGenRoots():
         allprotos = [CGGeneric("#[allow(unused_imports)];\n"),
                      CGGeneric("use dom::types::*;\n"),
                      CGGeneric("use dom::bindings::js::JS;\n"),
-                     CGGeneric("use dom::bindings::trace::Traceable;\n"),
+                     CGGeneric("use dom::bindings::trace::JSTraceable;\n"),
                      CGGeneric("use serialize::{Encodable, Encoder};\n"),
                      CGGeneric("use js::jsapi::JSTracer;\n\n")]
         for descriptor in descriptors:
@@ -5523,7 +5523,7 @@ class GlobalGenRoots():
                  'toBound': name + 'Derived'})),
                     CGGeneric("impl %s for %s {}\n\n" % (name + 'Cast', name))]
 
-            trace = [CGGeneric(string.Template('''impl Traceable for ${name} {
+            trace = [CGGeneric(string.Template('''impl JSTraceable for ${name} {
     fn trace(&self, tracer: *mut JSTracer) {
         unsafe {
             self.encode(&mut *tracer);
diff --git a/src/components/script/dom/bindings/js.rs b/src/components/script/dom/bindings/js.rs
index 71ca2d7ac86..5d2640a2bdf 100644
--- a/src/components/script/dom/bindings/js.rs
+++ b/src/components/script/dom/bindings/js.rs
@@ -44,8 +44,9 @@ impl<T: Reflectable> JS<T> {
 
 
     pub unsafe fn from_trusted_node_address(inner: TrustedNodeAddress) -> JS<T> {
+        let TrustedNodeAddress(addr) = inner;
         JS {
-            ptr: RefCell::new(inner as *mut T)
+            ptr: RefCell::new(addr as *mut T)
         }
     }
 }
diff --git a/src/components/script/dom/bindings/trace.rs b/src/components/script/dom/bindings/trace.rs
index 1cedf246728..4e32bacec68 100644
--- a/src/components/script/dom/bindings/trace.rs
+++ b/src/components/script/dom/bindings/trace.rs
@@ -8,6 +8,7 @@ use dom::bindings::utils::{Reflectable, Reflector};
 use js::jsapi::{JSTracer, JS_CallTracer, JSTRACE_OBJECT};
 
 use std::cast;
+use std::cell::RefCell;
 use std::libc;
 use std::ptr;
 use std::ptr::null;
@@ -30,7 +31,7 @@ impl<S: Encoder> Encodable<S> for Reflector {
     }
 }
 
-pub trait Traceable {
+pub trait JSTraceable {
     fn trace(&self, trc: *mut JSTracer);
 }
 
@@ -46,3 +47,69 @@ pub fn trace_reflector(tracer: *mut JSTracer, description: &str, reflector: &Ref
         });
     }
 }
+
+/// Encapsulates a type that cannot easily have Encodable derived automagically,
+/// but also does not need to be made known to the SpiderMonkey garbage collector.
+/// Use only with types that are not associated with a JS reflector and do not contain
+/// fields of types associated with JS reflectors.
+pub struct Untraceable<T> {
+    priv inner: T,
+}
+
+impl<T> Untraceable<T> {
+    pub fn new(val: T) -> Untraceable<T> {
+        Untraceable {
+            inner: val
+        }
+    }
+}
+
+impl<S: Encoder, T> Encodable<S> for Untraceable<T> {
+    fn encode(&self, _s: &mut S) {
+    }
+}
+
+impl<T> Deref<T> for Untraceable<T> {
+    fn deref<'a>(&'a self) -> &'a T {
+        &self.inner
+    }
+}
+
+impl<T> DerefMut<T> for Untraceable<T> {
+    fn deref_mut<'a>(&'a mut self) -> &'a mut T {
+        &mut self.inner
+    }
+}
+
+/// Encapsulates a type that can be traced but is boxed in a type we don't control
+/// (such as RefCell). Wrap a field in Traceable and implement the Encodable trait
+/// for that new concrete type to achieve magic compiler-derived trace hooks.
+pub struct Traceable<T> {
+    priv inner: T
+}
+
+impl<T> Traceable<T> {
+    pub fn new(val: T) -> Traceable<T> {
+        Traceable {
+            inner: val
+        }
+    }
+}
+
+impl<T> Deref<T> for Traceable<T> {
+    fn deref<'a>(&'a self) -> &'a T {
+        &self.inner
+    }
+}
+
+impl<T> DerefMut<T> for Traceable<T> {
+    fn deref_mut<'a>(&'a mut self) -> &'a mut T {
+        &mut self.inner
+    }
+}
+
+impl<S: Encoder, T: Encodable<S>> Encodable<S> for Traceable<RefCell<T>> {
+    fn encode(&self, s: &mut S) {
+        self.borrow().encode(s)
+    }
+}
\ No newline at end of file
diff --git a/src/components/script/dom/bindings/utils.rs b/src/components/script/dom/bindings/utils.rs
index ec1472bac28..71c82ae86dc 100644
--- a/src/components/script/dom/bindings/utils.rs
+++ b/src/components/script/dom/bindings/utils.rs
@@ -6,6 +6,7 @@ use dom::bindings::codegen::PrototypeList;
 use dom::bindings::codegen::PrototypeList::MAX_PROTO_CHAIN_LENGTH;
 use dom::bindings::conversions::FromJSValConvertible;
 use dom::bindings::js::JS;
+use dom::bindings::trace::Untraceable;
 use dom::window;
 use servo_util::str::DOMString;
 
@@ -42,13 +43,14 @@ use js::JSPROP_PERMANENT;
 use js::{JSFUN_CONSTRUCTOR, JSPROP_READONLY};
 use js;
 
+#[deriving(Encodable)]
 pub struct GlobalStaticData {
-    proxy_handlers: HashMap<uint, *libc::c_void>
+    proxy_handlers: Untraceable<HashMap<uint, *libc::c_void>>
 }
 
 pub fn GlobalStaticData() -> GlobalStaticData {
     GlobalStaticData {
-        proxy_handlers: HashMap::new()
+        proxy_handlers: Untraceable::new(HashMap::new())
     }
 }
 
@@ -533,7 +535,7 @@ fn cx_for_dom_reflector(obj: *JSObject) -> *JSContext {
     let win = global_object_for_js_object(obj);
     let js_info = win.get().page().js_info();
     match *js_info {
-        Some(ref info) => info.js_context.deref().ptr,
+        Some(ref info) => info.js_context.deref().deref().ptr,
         None => fail!("no JS context for DOM global")
     }
 }
diff --git a/src/components/script/dom/document.rs b/src/components/script/dom/document.rs
index f4391e4e541..637785a6bbc 100644
--- a/src/components/script/dom/document.rs
+++ b/src/components/script/dom/document.rs
@@ -8,6 +8,7 @@ use dom::bindings::codegen::InheritTypes::{HTMLHeadElementCast, TextCast, Elemen
 use dom::bindings::codegen::InheritTypes::{DocumentTypeCast, HTMLHtmlElementCast};
 use dom::bindings::codegen::DocumentBinding;
 use dom::bindings::js::JS;
+use dom::bindings::trace::Untraceable;
 use dom::bindings::utils::{Reflectable, Reflector, reflect_dom_object};
 use dom::bindings::error::{ErrorResult, Fallible, NotSupported, InvalidCharacter, HierarchyRequest, NamespaceError};
 use dom::bindings::utils::{xml_name_type, InvalidXMLName, Name, QName};
@@ -46,8 +47,6 @@ use js::jsapi::JSContext;
 use std::ascii::StrAsciiExt;
 use url::{Url, from_str};
 
-use serialize::{Encoder, Encodable};
-
 #[deriving(Eq,Encodable)]
 pub enum IsHTMLDocument {
     HTMLDocument,
@@ -64,17 +63,8 @@ pub struct Document {
     content_type: DOMString,
     encoding_name: DOMString,
     is_html_document: bool,
-    priv extra: Untraceable,
-}
-
-struct Untraceable {
-    url: Url,
-    quirks_mode: QuirksMode,
-}
-
-impl<S: Encoder> Encodable<S> for Untraceable {
-    fn encode(&self, _: &mut S) {
-    }
+    url: Untraceable<Url>,
+    quirks_mode: Untraceable<QuirksMode>,
 }
 
 impl DocumentDerived for EventTarget {
@@ -106,6 +96,8 @@ impl Document {
                          url: Option<Url>,
                          is_html_document: IsHTMLDocument,
                          content_type: Option<DOMString>) -> Document {
+        let url = url.unwrap_or_else(|| from_str("about:blank").unwrap());
+
         Document {
             node: Node::new_without_doc(DocumentNodeTypeId),
             reflector_: Reflector::new(),
@@ -121,14 +113,9 @@ impl Document {
                     NonHTMLDocument => ~"application/xml"
                 }
             },
-            extra: Untraceable {
-                url: match url {
-                    None => from_str("about:blank").unwrap(),
-                    Some(_url) => _url
-                },
-                // http://dom.spec.whatwg.org/#concept-document-quirks
-                quirks_mode: NoQuirks,
-            },
+            url: Untraceable::new(url),
+            // http://dom.spec.whatwg.org/#concept-document-quirks
+            quirks_mode: Untraceable::new(NoQuirks),
             // http://dom.spec.whatwg.org/#concept-document-encoding
             encoding_name: ~"utf-8",
             is_html_document: is_html_document == HTMLDocument,
@@ -143,7 +130,7 @@ impl Document {
 
 impl Document {
     pub fn url<'a>(&'a self) -> &'a Url {
-        &self.extra.url
+        &*self.url
     }
 }
 
@@ -185,18 +172,18 @@ impl Document {
 
     // http://dom.spec.whatwg.org/#dom-document-compatmode
     pub fn CompatMode(&self) -> DOMString {
-        match self.extra.quirks_mode {
+        match *self.quirks_mode {
             NoQuirks => ~"CSS1Compat",
             LimitedQuirks | FullQuirks => ~"BackCompat"
         }
     }
 
     pub fn quirks_mode(&self) -> QuirksMode {
-        self.extra.quirks_mode
+        *self.quirks_mode
     }
 
     pub fn set_quirks_mode(&mut self, mode: QuirksMode) {
-        self.extra.quirks_mode = mode;
+        *self.quirks_mode = mode;
     }
 
     // http://dom.spec.whatwg.org/#dom-document-characterset
diff --git a/src/components/script/dom/htmliframeelement.rs b/src/components/script/dom/htmliframeelement.rs
index c98634682a6..d0f127fbc94 100644
--- a/src/components/script/dom/htmliframeelement.rs
+++ b/src/components/script/dom/htmliframeelement.rs
@@ -4,8 +4,9 @@
 
 use dom::bindings::codegen::HTMLIFrameElementBinding;
 use dom::bindings::codegen::InheritTypes::{ElementCast, HTMLIFrameElementDerived, HTMLElementCast};
-use dom::bindings::js::JS;
 use dom::bindings::error::ErrorResult;
+use dom::bindings::js::JS;
+use dom::bindings::trace::Untraceable;
 use dom::document::Document;
 use dom::element::{HTMLIFrameElementTypeId, Element};
 use dom::element::AttributeHandlers;
@@ -16,7 +17,6 @@ use dom::virtualmethods::VirtualMethods;
 use dom::windowproxy::WindowProxy;
 use servo_util::str::DOMString;
 
-use serialize::{Encoder, Encodable};
 use servo_msg::constellation_msg::{PipelineId, SubpageId};
 use std::ascii::StrAsciiExt;
 use url::Url;
@@ -34,20 +34,11 @@ enum SandboxAllowance {
 #[deriving(Encodable)]
 pub struct HTMLIFrameElement {
     htmlelement: HTMLElement,
-    priv extra: Untraceable,
+    frame: Untraceable<Option<Url>>,
     size: Option<IFrameSize>,
     sandbox: Option<u8>
 }
 
-struct Untraceable {
-    frame: Option<Url>,
-}
-
-impl<S: Encoder> Encodable<S> for Untraceable {
-    fn encode(&self, _s: &mut S) {
-    }
-}
-
 impl HTMLIFrameElementDerived for EventTarget {
     fn is_htmliframeelement(&self) -> bool {
         match self.type_id {
@@ -69,7 +60,7 @@ impl HTMLIFrameElement {
     }
 
     pub fn set_frame(&mut self, frame: Url) {
-        self.extra.frame = Some(frame);
+        *self.frame = Some(frame);
     }
 }
 
@@ -77,9 +68,7 @@ impl HTMLIFrameElement {
     pub fn new_inherited(localName: DOMString, document: JS<Document>) -> HTMLIFrameElement {
         HTMLIFrameElement {
             htmlelement: HTMLElement::new_inherited(HTMLIFrameElementTypeId, localName, document),
-            extra: Untraceable {
-                frame: None
-            },
+            frame: Untraceable::new(None),
             size: None,
             sandbox: None,
         }
diff --git a/src/components/script/dom/htmlimageelement.rs b/src/components/script/dom/htmlimageelement.rs
index 3b966bbfe24..a62aea8b991 100644
--- a/src/components/script/dom/htmlimageelement.rs
+++ b/src/components/script/dom/htmlimageelement.rs
@@ -5,8 +5,9 @@
 use dom::bindings::codegen::HTMLImageElementBinding;
 use dom::bindings::codegen::InheritTypes::{NodeCast, HTMLImageElementDerived};
 use dom::bindings::codegen::InheritTypes::{ElementCast, HTMLElementCast};
-use dom::bindings::js::JS;
 use dom::bindings::error::ErrorResult;
+use dom::bindings::js::JS;
+use dom::bindings::trace::Untraceable;
 use dom::document::Document;
 use dom::element::{Element, HTMLImageElementTypeId};
 use dom::element::AttributeHandlers;
@@ -21,21 +22,10 @@ use servo_util::url::parse_url;
 use servo_util::str::DOMString;
 use url::Url;
 
-use serialize::{Encoder, Encodable};
-
 #[deriving(Encodable)]
 pub struct HTMLImageElement {
     htmlelement: HTMLElement,
-    priv extra: Untraceable,
-}
-
-struct Untraceable {
-    image: Option<Url>,
-}
-
-impl<S: Encoder> Encodable<S> for Untraceable {
-    fn encode(&self, _s: &mut S) {
-    }
+    image: Untraceable<Option<Url>>,
 }
 
 impl HTMLImageElementDerived for EventTarget {
@@ -51,9 +41,7 @@ impl HTMLImageElement {
     pub fn new_inherited(localName: DOMString, document: JS<Document>) -> HTMLImageElement {
         HTMLImageElement {
             htmlelement: HTMLElement::new_inherited(HTMLImageElementTypeId, localName, document),
-            extra: Untraceable {
-                image: None,
-            }
+            image: Untraceable::new(None),
         }
     }
 
@@ -65,7 +53,7 @@ impl HTMLImageElement {
 
 impl HTMLImageElement {
     pub fn image<'a>(&'a self) -> &'a Option<Url> {
-        &self.extra.image
+        &*self.image
     }
 
     /// Makes the local `image` member match the status of the `src` attribute and starts
@@ -77,11 +65,11 @@ impl HTMLImageElement {
         let image_cache = &window.image_cache_task;
         match value {
             None => {
-                self.extra.image = None;
+                *self.image = None;
             }
             Some(src) => {
                 let img_url = parse_url(src, url);
-                self.extra.image = Some(img_url.clone());
+                *self.image = Some(img_url.clone());
 
                 // inform the image cache to load this, but don't store a
                 // handle.
diff --git a/src/components/script/dom/htmlstyleelement.rs b/src/components/script/dom/htmlstyleelement.rs
index ed335dd70eb..32e4276a2a1 100644
--- a/src/components/script/dom/htmlstyleelement.rs
+++ b/src/components/script/dom/htmlstyleelement.rs
@@ -88,7 +88,7 @@ impl StyleElementHelpers for JS<HTMLStyleElement> {
 
         let data = node.get().GetTextContent(&node).expect("Element.textContent must be a string");
         let sheet = parse_inline_css(url, data);
-        let LayoutChan(ref layout_chan) = win.get().page().layout_chan;
+        let LayoutChan(ref layout_chan) = *win.get().page().layout_chan;
         layout_chan.send(AddStylesheetMsg(sheet));
     }
 }
diff --git a/src/components/script/dom/location.rs b/src/components/script/dom/location.rs
index 168ded0a4c7..f813b375eca 100644
--- a/src/components/script/dom/location.rs
+++ b/src/components/script/dom/location.rs
@@ -18,26 +18,14 @@ use serialize::{Encoder, Encodable};
 #[deriving(Encodable)]
 pub struct Location {
     reflector_: Reflector, //XXXjdm cycle: window->Location->window
-    priv extra: Untraceable,
-}
-
-struct Untraceable {
     page: Rc<Page>,
 }
 
-impl<S: Encoder> Encodable<S> for Untraceable {
-    fn encode(&self, s: &mut S) {
-        self.page.encode(s);
-    }
-}
-
 impl Location {
     pub fn new_inherited(page: Rc<Page>) -> Location {
         Location {
             reflector_: Reflector::new(),
-            extra: Untraceable {
-                page: page
-            }
+            page: page
         }
     }
 
@@ -60,7 +48,7 @@ impl Location {
     }
 
     pub fn Href(&self) -> DOMString {
-        self.extra.page.get_url().to_str()
+        self.page.get_url().to_str()
     }
 
     pub fn SetHref(&self, _href: DOMString) -> Fallible<()> {
diff --git a/src/components/script/dom/node.rs b/src/components/script/dom/node.rs
index bf2669512ff..fd55732da82 100644
--- a/src/components/script/dom/node.rs
+++ b/src/components/script/dom/node.rs
@@ -37,6 +37,7 @@ use std::cast::transmute;
 use std::cast;
 use std::cell::{RefCell, Ref, RefMut};
 use std::iter::{Map, Filter};
+use std::libc;
 use std::libc::uintptr_t;
 use std::mem;
 
@@ -562,7 +563,7 @@ impl NodeHelpers for JS<Node> {
     }
 
     fn to_trusted_node_address(&self) -> TrustedNodeAddress {
-        self.get() as *Node as TrustedNodeAddress
+        TrustedNodeAddress(self.get() as *Node as *libc::c_void)
     }
 }
 
diff --git a/src/components/script/dom/window.rs b/src/components/script/dom/window.rs
index a0b7ef3740b..87d94eaff62 100644
--- a/src/components/script/dom/window.rs
+++ b/src/components/script/dom/window.rs
@@ -4,6 +4,7 @@
 
 use dom::bindings::codegen::WindowBinding;
 use dom::bindings::js::JS;
+use dom::bindings::trace::Untraceable;
 use dom::bindings::utils::{Reflectable, Reflector};
 use dom::document::Document;
 use dom::element::Element;
@@ -84,29 +85,19 @@ pub struct Window {
     image_cache_task: ImageCacheTask,
     active_timers: ~HashMap<i32, TimerHandle>,
     next_timer_handle: i32,
-    priv extra: Untraceable
-}
-
-struct Untraceable {
+    compositor: Untraceable<~ScriptListener>,
+    timer_chan: Untraceable<Sender<TimerControlMsg>>,
     page: Rc<Page>,
-    compositor: ~ScriptListener,
-    timer_chan: Sender<TimerControlMsg>,
-}
-
-impl<S: Encoder> Encodable<S> for Untraceable {
-    fn encode(&self, s: &mut S) {
-        self.page.encode(s);
-    }
 }
 
 impl Window {
     pub fn get_cx(&self) -> *JSObject {
         let js_info = self.page().js_info();
-        js_info.get_ref().js_compartment.cx.deref().ptr
+        js_info.get_ref().js_compartment.deref().cx.deref().ptr
     }
 
     pub fn page<'a>(&'a self) -> &'a Page {
-        &*self.extra.page
+        &*self.page
     }
     pub fn get_url(&self) -> Url {
         self.page().get_url()
@@ -116,7 +107,7 @@ impl Window {
 #[unsafe_destructor]
 impl Drop for Window {
     fn drop(&mut self) {
-        self.extra.timer_chan.send(TimerMessageClose);
+        self.timer_chan.send(TimerMessageClose);
         for timer_handle in self.active_timers.values() {
             timer_handle.cancel();
         }
@@ -140,7 +131,7 @@ impl Window {
     }
 
     pub fn Close(&self) {
-        self.extra.timer_chan.send(TimerMessageTriggerExit);
+        self.timer_chan.deref().send(TimerMessageTriggerExit);
     }
 
     pub fn Document(&self) -> JS<Document> {
@@ -181,7 +172,7 @@ impl Window {
 
     pub fn Location(&mut self, abstract_self: &JS<Window>) -> JS<Location> {
         if self.location.is_none() {
-            self.location = Some(Location::new(abstract_self, self.extra.page.clone()));
+            self.location = Some(Location::new(abstract_self, self.page.clone()));
         }
         self.location.get_ref().clone()
     }
@@ -236,7 +227,7 @@ impl Window {
         // to the relevant script handler that will deal with it.
         let tm = Timer::new().unwrap();
         let (cancel_chan, cancel_port) = channel();
-        let chan = self.extra.timer_chan.clone();
+        let chan = self.timer_chan.clone();
         let spawn_name = if is_interval {
             "Window:SetInterval"
         } else {
@@ -304,7 +295,7 @@ impl Window {
         // currently rely on the display list, which means we can't destroy it by
         // doing a query reflow.
         self.page().damage(damage);
-        self.page().reflow(ReflowForDisplay, self.script_chan.clone(), self.extra.compositor);
+        self.page().reflow(ReflowForDisplay, self.script_chan.clone(), *self.compositor);
     }
 
     pub fn wait_until_safe_to_modify_dom(&self) {
@@ -319,29 +310,27 @@ impl Window {
                compositor: ~ScriptListener,
                image_cache_task: ImageCacheTask)
                -> JS<Window> {
+        let script_chan_clone = script_chan.clone();
+        let (timer_chan, timer_port): (Sender<TimerControlMsg>, Receiver<TimerControlMsg>) = channel();
+        let id = page.id.clone();
+        spawn_named("timer controller", proc() {
+            let ScriptChan(script_chan) = script_chan;
+            loop {
+                match timer_port.recv() {
+                    TimerMessageClose => break,
+                    TimerMessageFire(td) => script_chan.send(FireTimerMsg(id, td)),
+                    TimerMessageTriggerExit => script_chan.send(ExitWindowMsg(id)),
+                }
+            }
+        });
+
         let win = ~Window {
             eventtarget: EventTarget::new_inherited(WindowTypeId),
-            script_chan: script_chan.clone(),
+            script_chan: script_chan_clone,
             console: None,
-            extra: Untraceable {
-                compositor: compositor,
-                page: page.clone(),
-                timer_chan: {
-                    let (timer_chan, timer_port): (Sender<TimerControlMsg>, Receiver<TimerControlMsg>) = channel();
-                    let id = page.id.clone();
-                    spawn_named("timer controller", proc() {
-                        let ScriptChan(script_chan) = script_chan;
-                        loop {
-                            match timer_port.recv() {
-                                TimerMessageClose => break,
-                                TimerMessageFire(td) => script_chan.send(FireTimerMsg(id, td)),
-                                TimerMessageTriggerExit => script_chan.send(ExitWindowMsg(id)),
-                            }
-                        }
-                    });
-                    timer_chan
-                }
-            },
+            compositor: Untraceable::new(compositor),
+            timer_chan: Untraceable::new(timer_chan),
+            page: page.clone(),
             location: None,
             navigator: None,
             image_cache_task: image_cache_task,
diff --git a/src/components/script/html/hubbub_html_parser.rs b/src/components/script/html/hubbub_html_parser.rs
index c7c4e79b165..b9dd26311ff 100644
--- a/src/components/script/html/hubbub_html_parser.rs
+++ b/src/components/script/html/hubbub_html_parser.rs
@@ -252,7 +252,7 @@ pub fn parse_html(page: &Page,
                   resource_task: ResourceTask)
                   -> HtmlParserResult {
     debug!("Hubbub: parsing {:?}", url);
-    let next_subpage_id: SubpageId = *page.next_subpage_id.borrow();
+    let next_subpage_id: SubpageId = *page.next_subpage_id.deref().borrow();
     // Spawn a CSS parser to receive links to CSS style sheets.
     let resource_task2 = resource_task.clone();
 
diff --git a/src/components/script/layout_interface.rs b/src/components/script/layout_interface.rs
index 197bd123e3f..a29aa2fa08e 100644
--- a/src/components/script/layout_interface.rs
+++ b/src/components/script/layout_interface.rs
@@ -6,7 +6,8 @@
 /// coupling between these two components, and enables the DOM to be placed in a separate crate
 /// from layout.
 
-use dom::node::LayoutDataRef;
+use dom::bindings::js::JS;
+use dom::node::{Node, LayoutDataRef};
 
 use geom::point::Point2D;
 use geom::rect::Rect;
@@ -19,6 +20,8 @@ use std::libc::c_void;
 use style::Stylesheet;
 use url::Url;
 
+use serialize::{Encodable, Encoder};
+
 /// Asynchronous messages that script can send to layout.
 ///
 /// FIXME(pcwalton): I think this should probably be merged with `LayoutQuery` below.
@@ -62,7 +65,17 @@ pub enum LayoutQuery {
 
 /// The address of a node known to be valid. These must only be sent from content -> layout,
 /// because we do not trust layout.
-pub type TrustedNodeAddress = *c_void;
+pub struct TrustedNodeAddress(*c_void);
+
+impl<S: Encoder> Encodable<S> for TrustedNodeAddress {
+    fn encode(&self, s: &mut S) {
+        let TrustedNodeAddress(addr) = *self;
+        let node = addr as *Node as *mut Node;
+        unsafe {
+            JS::from_raw(node).encode(s)
+        }
+    }
+}
 
 /// The address of a node. Layout sends these back. They must be validated via
 /// `from_untrusted_node_address` before they can be used, because we do not trust layout.
@@ -74,7 +87,7 @@ pub struct HitTestResponse(UntrustedNodeAddress);
 pub struct MouseOverResponse(~[UntrustedNodeAddress]);
 
 /// Determines which part of the
-#[deriving(Eq, Ord, TotalEq, TotalOrd)]
+#[deriving(Eq, Ord, TotalEq, TotalOrd, Encodable)]
 pub enum DocumentDamageLevel {
     /// Reflow, but do not perform CSS selector matching.
     ReflowDocumentDamage,
@@ -94,6 +107,7 @@ impl DocumentDamageLevel {
 /// What parts of the document have changed, as far as the script task can tell.
 ///
 /// Note that this is fairly coarse-grained and is separate from layout's notion of the document
+#[deriving(Encodable)]
 pub struct DocumentDamage {
     /// The topmost node in the tree that has changed.
     root: TrustedNodeAddress,
diff --git a/src/components/script/script_task.rs b/src/components/script/script_task.rs
index 096a0d40b6a..854b060513d 100644
--- a/src/components/script/script_task.rs
+++ b/src/components/script/script_task.rs
@@ -8,6 +8,7 @@
 use dom::bindings::codegen::RegisterBindings;
 use dom::bindings::codegen::InheritTypes::{EventTargetCast, NodeCast, ElementCast, EventCast};
 use dom::bindings::js::JS;
+use dom::bindings::trace::{Traceable, Untraceable};
 use dom::bindings::utils::{Reflectable, GlobalStaticData, with_gc_enabled};
 use dom::document::{Document, HTMLDocument};
 use dom::element::{Element, AttributeHandlers};
@@ -107,50 +108,44 @@ impl ScriptChan {
 }
 
 /// Encapsulates a handle to a frame and its associated layout information.
+#[deriving(Encodable)]
 pub struct Page {
     /// Pipeline id associated with this page.
     id: PipelineId,
 
     /// Unique id for last reflow request; used for confirming completion reply.
-    last_reflow_id: RefCell<uint>,
+    last_reflow_id: Traceable<RefCell<uint>>,
 
     /// The outermost frame containing the document, window, and page URL.
-    frame: RefCell<Option<Frame>>,
+    frame: Traceable<RefCell<Option<Frame>>>,
 
     /// A handle for communicating messages to the layout task.
-    layout_chan: LayoutChan,
+    layout_chan: Untraceable<LayoutChan>,
 
     /// The port that we will use to join layout. If this is `None`, then layout is not running.
-    layout_join_port: RefCell<Option<Receiver<()>>>,
+    layout_join_port: Untraceable<RefCell<Option<Receiver<()>>>>,
 
     /// What parts of the document are dirty, if any.
-    damage: RefCell<Option<DocumentDamage>>,
+    damage: Traceable<RefCell<Option<DocumentDamage>>>,
 
     /// The current size of the window, in pixels.
-    window_size: RefCell<Size2D<uint>>,
+    window_size: Untraceable<RefCell<Size2D<uint>>>,
 
-    js_info: RefCell<Option<JSPageInfo>>,
+    js_info: Traceable<RefCell<Option<JSPageInfo>>>,
 
     /// Cached copy of the most recent url loaded by the script
     /// TODO(tkuehn): this currently does not follow any particular caching policy
     /// and simply caches pages forever (!). The bool indicates if reflow is required
     /// when reloading.
-    url: RefCell<Option<(Url, bool)>>,
+    url: Untraceable<RefCell<Option<(Url, bool)>>>,
 
-    next_subpage_id: RefCell<SubpageId>,
+    next_subpage_id: Untraceable<RefCell<SubpageId>>,
 
     /// Pending resize event, if any.
-    resize_event: RefCell<Option<Size2D<uint>>>,
+    resize_event: Untraceable<RefCell<Option<Size2D<uint>>>>,
 
     /// Pending scroll to fragment event, if any
-    fragment_node: RefCell<Option<JS<Element>>>
-}
-
-impl<S: Encoder> Encodable<S> for Page {
-    fn encode(&self, s: &mut S) {
-        let fragment_node = self.fragment_node.borrow();
-        fragment_node.encode(s);
-   }
+    fragment_node: Traceable<RefCell<Option<JS<Element>>>>
 }
 
 pub struct PageTree {
@@ -167,17 +162,17 @@ impl PageTree {
         PageTree {
             page: Rc::new(Page {
                 id: id,
-                frame: RefCell::new(None),
-                layout_chan: layout_chan,
-                layout_join_port: RefCell::new(None),
-                damage: RefCell::new(None),
-                window_size: RefCell::new(window_size),
-                js_info: RefCell::new(None),
-                url: RefCell::new(None),
-                next_subpage_id: RefCell::new(SubpageId(0)),
-                resize_event: RefCell::new(None),
-                fragment_node: RefCell::new(None),
-                last_reflow_id: RefCell::new(0)
+                frame: Traceable::new(RefCell::new(None)),
+                layout_chan: Untraceable::new(layout_chan),
+                layout_join_port: Untraceable::new(RefCell::new(None)),
+                damage: Traceable::new(RefCell::new(None)),
+                window_size: Untraceable::new(RefCell::new(window_size)),
+                js_info: Traceable::new(RefCell::new(None)),
+                url: Untraceable::new(RefCell::new(None)),
+                next_subpage_id: Untraceable::new(RefCell::new(SubpageId(0))),
+                resize_event: Untraceable::new(RefCell::new(None)),
+                fragment_node: Traceable::new(RefCell::new(None)),
+                last_reflow_id: Traceable::new(RefCell::new(0))
             }),
             inner: ~[],
         }
@@ -251,27 +246,27 @@ impl<'a> Iterator<Rc<Page>> for PageTreeIterator<'a> {
 
 impl Page {
     pub fn mut_js_info<'a>(&'a self) -> RefMut<'a, Option<JSPageInfo>> {
-        self.js_info.borrow_mut()
+        self.js_info.deref().borrow_mut()
     }
 
     pub fn js_info<'a>(&'a self) -> Ref<'a, Option<JSPageInfo>> {
-        self.js_info.borrow()
+        self.js_info.deref().borrow()
     }
 
     pub fn url<'a>(&'a self) -> Ref<'a, Option<(Url, bool)>> {
-        self.url.borrow()
+        self.url.deref().borrow()
     }
 
     pub fn mut_url<'a>(&'a self) -> RefMut<'a, Option<(Url, bool)>> {
-        self.url.borrow_mut()
+        self.url.deref().borrow_mut()
     }
 
     pub fn frame<'a>(&'a self) -> Ref<'a, Option<Frame>> {
-        self.frame.borrow()
+        self.frame.deref().borrow()
     }
 
     pub fn mut_frame<'a>(&'a self) -> RefMut<'a, Option<Frame>> {
-        self.frame.borrow_mut()
+        self.frame.deref().borrow_mut()
     }
 
     /// Adds the given damage.
@@ -284,7 +279,7 @@ impl Page {
             None => {},
             Some(root) => {
                 let root: JS<Node> = NodeCast::from(&root);
-                let mut damage = *self.damage.borrow_mut();
+                let mut damage = *self.damage.deref().borrow_mut();
                 match damage {
                     None => {}
                     Some(ref mut damage) => {
@@ -295,7 +290,7 @@ impl Page {
                     }
                 }
 
-                *self.damage.borrow_mut() = Some(DocumentDamage {
+                *self.damage.deref().borrow_mut() = Some(DocumentDamage {
                     root: root.to_trusted_node_address(),
                     level: level,
                 })
@@ -310,7 +305,7 @@ impl Page {
     /// Sends a ping to layout and waits for the response. The response will arrive when the
     /// layout task has finished any pending request messages.
     pub fn join_layout(&self) {
-        let mut layout_join_port = self.layout_join_port.borrow_mut();
+        let mut layout_join_port = self.layout_join_port.deref().borrow_mut();
         if layout_join_port.is_some() {
             let join_port = replace(&mut *layout_join_port, None);
             match join_port {
@@ -339,7 +334,7 @@ impl Page {
                                  response_port: Receiver<T>)
                                  -> T {
         self.join_layout();
-        let LayoutChan(ref chan) = self.layout_chan;
+        let LayoutChan(ref chan) = *self.layout_chan;
         chan.send(QueryMsg(query));
         response_port.recv()
     }
@@ -375,15 +370,15 @@ impl Page {
 
                 // Layout will let us know when it's done.
                 let (join_chan, join_port) = channel();
-                let mut layout_join_port = self.layout_join_port.borrow_mut();
+                let mut layout_join_port = self.layout_join_port.deref().borrow_mut();
                 *layout_join_port = Some(join_port);
 
-                let mut last_reflow_id = self.last_reflow_id.borrow_mut();
+                let mut last_reflow_id = self.last_reflow_id.deref().borrow_mut();
                 *last_reflow_id += 1;
 
                 let root: JS<Node> = NodeCast::from(&root);
-                let mut damage = self.damage.borrow_mut();
-                let window_size = self.window_size.borrow();
+                let mut damage = self.damage.deref().borrow_mut();
+                let window_size = self.window_size.deref().borrow();
 
                 // Send new document and relevant styles to layout.
                 let reflow = ~Reflow {
@@ -397,7 +392,7 @@ impl Page {
                     id: *last_reflow_id,
                 };
 
-                let LayoutChan(ref chan) = self.layout_chan;
+                let LayoutChan(ref chan) = *self.layout_chan;
                 chan.send(ReflowMsg(reflow));
 
                 debug!("script: layout forked")
@@ -443,8 +438,8 @@ impl Page {
         let mut js_info = self.mut_js_info();
         *js_info = Some(JSPageInfo {
             dom_static: GlobalStaticData(),
-            js_compartment: compartment,
-            js_context: js_context,
+            js_compartment: Untraceable::new(compartment),
+            js_context: Untraceable::new(js_context),
         });
     }
 }
@@ -459,13 +454,14 @@ pub struct Frame {
 }
 
 /// Encapsulation of the javascript information associated with each frame.
+#[deriving(Encodable)]
 pub struct JSPageInfo {
     /// Global static data related to the DOM.
     dom_static: GlobalStaticData,
     /// The JavaScript compartment for the origin associated with the script task.
-    js_compartment: Rc<Compartment>,
+    js_compartment: Untraceable<Rc<Compartment>>,
     /// The JavaScript context.
-    js_context: Rc<Cx>,
+    js_context: Untraceable<Rc<Cx>>,
 }
 
 /// Information for an entire page. Pages are top-level browsing contexts and can contain multiple
@@ -573,9 +569,9 @@ impl ScriptTask {
             let mut page_tree = self.page_tree.borrow_mut();
             for page in page_tree.iter() {
                 // Only process a resize if layout is idle.
-                let layout_join_port = page.layout_join_port.borrow();
+                let layout_join_port = page.layout_join_port.deref().borrow();
                 if layout_join_port.is_none() {
-                    let mut resize_event = page.resize_event.borrow_mut();
+                    let mut resize_event = page.resize_event.deref().borrow_mut();
                     match resize_event.take() {
                         Some(size) => resizes.push((page.id, size)),
                         None => ()
@@ -599,7 +595,7 @@ impl ScriptTask {
                 ResizeMsg(id, size) => {
                     let mut page_tree = self.page_tree.borrow_mut();
                     let page = page_tree.find(id).expect("resize sent to nonexistent pipeline").page();
-                    let mut resize_event = page.resize_event.borrow_mut();
+                    let mut resize_event = page.resize_event.deref().borrow_mut();
                     *resize_event = Some(size);
                 }
                 _ => {
@@ -646,7 +642,7 @@ impl ScriptTask {
             whose parent has a PipelineId which does not correspond to a pipeline in the script
             task's page tree. This is a bug.");
         let new_page_tree = {
-            let window_size = parent_page_tree.page().window_size.borrow();
+            let window_size = parent_page_tree.page().window_size.deref().borrow();
             PageTree::new(new_id, layout_chan, *window_size)
         };
         parent_page_tree.inner.push(new_page_tree);
@@ -680,7 +676,7 @@ impl ScriptTask {
 
         // TODO: Support extra arguments. This requires passing a `*JSVal` array as `argv`.
         let rval = NullValue();
-        let cx = js_info.get_ref().js_context.deref().ptr;
+        let cx = js_info.get_ref().js_context.deref().deref().ptr;
         with_gc_enabled(cx, || {
             unsafe {
                 JS_CallFunctionValue(cx, this_value, timer_data.funval, 0, ptr::null(), &rval);
@@ -695,9 +691,9 @@ impl ScriptTask {
         let page = page_tree.find(pipeline_id).expect(
             "ScriptTask: received a load message for a layout channel that is not associated \
              with this script task. This is a bug.").page();
-        let last_reflow_id = page.last_reflow_id.borrow();
+        let last_reflow_id = page.last_reflow_id.deref().borrow();
         if *last_reflow_id == reflow_id {
-            let mut layout_join_port = page.layout_join_port.borrow_mut();
+            let mut layout_join_port = page.layout_join_port.deref().borrow_mut();
             *layout_join_port = None;
         }
         self.compositor.set_ready_state(FinishedLoading);
@@ -715,7 +711,7 @@ impl ScriptTask {
         let mut page_tree = self.page_tree.borrow_mut();
         let page = page_tree.find(id).expect("Received resize message for PipelineId not associated
             with a page in the page tree. This is a bug.").page();
-        let mut window_size = page.window_size.borrow_mut();
+        let mut window_size = page.window_size.deref().borrow_mut();
         *window_size = new_size;
         let mut page_url = page.mut_url();
         let last_loaded_url = replace(&mut *page_url, None);
@@ -845,12 +841,12 @@ impl ScriptTask {
                     js_scripts = Some(scripts);
                 }
                 Some(HtmlDiscoveredStyle(sheet)) => {
-                    let LayoutChan(ref chan) = page.layout_chan;
+                    let LayoutChan(ref chan) = *page.layout_chan;
                     chan.send(AddStylesheetMsg(sheet));
                 }
                 Some(HtmlDiscoveredIFrame((iframe_url, subpage_id, sandboxed))) => {
                     let SubpageId(num) = subpage_id;
-                    page.next_subpage_id.set(SubpageId(num + 1));
+                    page.next_subpage_id.deref().set(SubpageId(num + 1));
                     let sandboxed = if sandboxed {
                         IFrameSandboxed
                     } else {
@@ -886,9 +882,9 @@ impl ScriptTask {
         let cx = {
             let js_info = page.js_info();
             let js_info = js_info.get_ref();
-            assert!(js_info.js_compartment.define_functions(DEBUG_FNS).is_ok());
+            assert!(js_info.js_compartment.deref().define_functions(DEBUG_FNS).is_ok());
 
-            js_info.js_context.deref().ptr
+            js_info.js_context.deref().deref().ptr
         };
 
         // Evaluate every script in the document.
@@ -896,7 +892,7 @@ impl ScriptTask {
             with_gc_enabled(cx, || {
                 let (cx, global_obj) = {
                     let js_info = page.js_info();
-                    (js_info.get_ref().js_context.clone(),
+                    (js_info.get_ref().js_context.deref().clone(),
                      js_info.get_ref().js_compartment.global_obj)
                 };
                 //FIXME: this should have some kind of error handling, or explicitly
@@ -918,7 +914,7 @@ impl ScriptTask {
         let winclone = wintarget.clone();
         let _ = wintarget.get_mut().dispatch_event_with_target(&winclone, Some(doctarget), &mut event);
 
-        let mut fragment_node = page.fragment_node.borrow_mut();
+        let mut fragment_node = page.fragment_node.deref().borrow_mut();
         *fragment_node = fragment.map_or(None, |fragid| page.find_fragment_node(fragid));
 
         let ConstellationChan(ref chan) = self.constellation_chan;
@@ -953,7 +949,7 @@ impl ScriptTask {
                 debug!("script got resize event: {:u}, {:u}", new_width, new_height);
 
                 {
-                    let mut window_size = page.window_size.borrow_mut();
+                    let mut window_size = page.window_size.deref().borrow_mut();
                     *window_size = Size2D(new_width, new_height);
                 }
 
@@ -965,7 +961,7 @@ impl ScriptTask {
                     }
                 }
 
-                let mut fragment_node = page.fragment_node.borrow_mut();
+                let mut fragment_node = page.fragment_node.deref().borrow_mut();
                 match fragment_node.take() {
                     Some(node) => self.scroll_fragment_point(pipeline_id, page, node),
                     None => {}
@@ -1145,7 +1141,7 @@ fn shut_down_layout(page: &Page) {
 
     // Tell the layout task to begin shutting down.
     let (response_chan, response_port) = channel();
-    let LayoutChan(ref chan) = page.layout_chan;
+    let LayoutChan(ref chan) = *page.layout_chan;
     chan.send(layout_interface::PrepareToExitMsg(response_chan));
     response_port.recv();
 
@@ -1154,7 +1150,7 @@ fn shut_down_layout(page: &Page) {
 
     let mut js_info = page.mut_js_info();
     unsafe {
-        JS_AllowGC(js_info.get_ref().js_context.deref().ptr);
+        JS_AllowGC(js_info.get_ref().js_context.deref().deref().ptr);
     }
 
     let mut frame = page.mut_frame();