Allow refcounting arbitrary DOM objects in concert with the GC to enable safe, asynchronous/cross-task references to pinned objects.

components/script/dom/bindings/js.rs

@@ -48,8 +48,6 @@
 use dom::bindings::trace::JSTraceable;
 use dom::bindings::utils::{Reflector, Reflectable};
 use dom::node::Node;
-use dom::xmlhttprequest::{XMLHttpRequest, TrustedXHRAddress};
-use dom::worker::{Worker, TrustedWorkerAddress};
 use js::jsapi::JSObject;
 use js::jsval::JSVal;
 use layout_interface::TrustedNodeAddress;
@@ -142,24 +140,6 @@ impl JS<Node> {
     }
 }
 
-impl JS<XMLHttpRequest> {
-    pub unsafe fn from_trusted_xhr_address(inner: TrustedXHRAddress) -> JS<XMLHttpRequest> {
-        let TrustedXHRAddress(addr) = inner;
-        JS {
-            ptr: addr as *const XMLHttpRequest
-        }
-    }
-}
-
-impl JS<Worker> {
-    pub unsafe fn from_trusted_worker_address(inner: TrustedWorkerAddress) -> JS<Worker> {
-        let TrustedWorkerAddress(addr) = inner;
-        JS {
-            ptr: addr as *const Worker
-        }
-    }
-}
-
 impl<T: Reflectable> JS<T> {
     /// Create a new JS-owned value wrapped from a raw Rust pointer.
     pub unsafe fn from_raw(raw: *const T) -> JS<T> {

components/script/dom/bindings/refcounted.rs

@@ -0,0 +1,174 @@
+/* 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/. */
+
+#![deny(missing_docs)]
+
+//! A generic, safe mechnanism by which DOM objects can be pinned and transferred
+//! between tasks (or intra-task for asynchronous events). Akin to Gecko's
+//! nsMainThreadPtrHandle, this uses thread-safe reference counting and ensures
+//! that the actual SpiderMonkey GC integration occurs on the script task via
+//! message passing. Ownership of a `Trusted<T>` object means the DOM object of
+//! type T to which it points remains alive. Any other behaviour is undefined.
+//! To guarantee the lifetime of a DOM object when performing asynchronous operations,
+//! obtain a `Trusted<T>` from that object and pass it along with each operation.
+//! A usable pointer to the original DOM object can be obtained on the script task
+//! from a `Trusted<T>` via the `to_temporary` method.
+//!
+//! The implementation of Trusted<T> is as follows:
+//! A hashtable resides in the script task, keyed on the pointer to the Rust DOM object.
+//! The values in this hashtable are atomic reference counts. When a Trusted<T> object is
+//! created or cloned, this count is increased. When a Trusted<T> is dropped, the count
+//! decreases. If the count hits zero, a message is dispatched to the script task to remove
+//! the entry from the hashmap if the count is still zero. The JS reflector for the DOM object
+//! is rooted when a hashmap entry is first created, and unrooted when the hashmap entry
+//! is removed.
+
+use dom::bindings::js::{Temporary, JS, JSRef};
+use dom::bindings::utils::{Reflector, Reflectable};
+use script_task::{ScriptMsg, ScriptChan};
+
+use js::jsapi::{JS_AddObjectRoot, JS_RemoveObjectRoot, JSContext};
+
+use libc;
+use std::cell::RefCell;
+use std::collections::hash_map::{HashMap, Vacant, Occupied};
+use std::sync::{Arc, Mutex};
+
+local_data_key!(pub LiveReferences: LiveDOMReferences)
+
+/// A safe wrapper around a raw pointer to a DOM object that can be
+/// shared among tasks for use in asynchronous operations. The underlying
+/// DOM object is guaranteed to live at least as long as the last outstanding
+/// `Trusted<T>` instance.
+pub struct Trusted<T> {
+    cx: *mut JSContext,
+    /// A pointer to the Rust DOM object of type T, but void to allow
+    /// sending `Trusted<T>` between tasks, regardless of T's sendability.
+    ptr: *const libc::c_void,
+    refcount: Arc<Mutex<uint>>,
+    script_chan: ScriptChan,
+}
+
+impl<T: Reflectable> Trusted<T> {
+    /// Create a new `Trusted<T>` instance from an existing DOM pointer. The DOM object will
+    /// be prevented from being GCed for the duration of the resulting `Trusted<T>` object's
+    /// lifetime.
+    pub fn new(cx: *mut JSContext, ptr: JSRef<T>, script_chan: ScriptChan) -> Trusted<T> {
+        let live_references = LiveReferences.get().unwrap();
+        let refcount = live_references.addref(cx, &*ptr as *const T);
+        Trusted {
+            cx: cx,
+            ptr: &*ptr as *const T as *const libc::c_void,
+            refcount: refcount,
+            script_chan: script_chan,
+        }
+    }
+
+    /// Obtain a usable DOM pointer from a pinned `Trusted<T>` value. Attempts to use the
+    /// resulting `Temporary<T>` off of the script thread will fail.
+    pub fn to_temporary(&self) -> Temporary<T> {
+        unsafe {
+            Temporary::new(JS::from_raw(self.ptr as *const T))
+        }
+    }
+}
+
+impl<T: Reflectable> Clone for Trusted<T> {
+    fn clone(&self) -> Trusted<T> {
+        {
+            let mut refcount = self.refcount.lock();
+            *refcount += 1;
+        }
+
+        Trusted {
+            cx: self.cx,
+            ptr: self.ptr,
+            refcount: self.refcount.clone(),
+            script_chan: self.script_chan.clone(),
+        }
+    }
+}
+
+#[unsafe_destructor]
+impl<T: Reflectable> Drop for Trusted<T> {
+    fn drop(&mut self) {
+        let mut refcount = self.refcount.lock();
+        assert!(*refcount > 0);
+        *refcount -= 1;
+        if *refcount == 0 {
+            let ScriptChan(ref chan) = self.script_chan;
+            chan.send(ScriptMsg::RefcountCleanup(self.ptr));
+        }
+    }
+}
+
+/// The set of live, pinned DOM objects that are currently prevented
+/// from being garbage collected due to outstanding references.
+pub struct LiveDOMReferences {
+    // keyed on pointer to Rust DOM object
+    table: RefCell<HashMap<*const libc::c_void, Arc<Mutex<uint>>>>
+}
+
+impl LiveDOMReferences {
+    /// Set up the task-local data required for storing the outstanding DOM references.
+    pub fn initialize() {
+        LiveReferences.replace(Some(LiveDOMReferences {
+            table: RefCell::new(HashMap::new()),
+        }));
+    }
+
+    fn addref<T: Reflectable>(&self, cx: *mut JSContext, ptr: *const T) -> Arc<Mutex<uint>> {
+        let mut table = self.table.borrow_mut();
+        match table.entry(ptr as *const libc::c_void) {
+            Occupied(mut entry) => {
+                let refcount = entry.get_mut();
+                *refcount.lock() += 1;
+                refcount.clone()
+            }
+            Vacant(entry) => {
+                unsafe {
+                    let rootable = (*ptr).reflector().rootable();
+                    JS_AddObjectRoot(cx, rootable);
+                }
+                let refcount = Arc::new(Mutex::new(1));
+                entry.set(refcount.clone());
+                refcount
+            }
+        }
+    }
+
+    /// Unpin the given DOM object if its refcount is 0.
+    pub fn cleanup(cx: *mut JSContext, raw_reflectable: *const libc::c_void) {
+        let live_references = LiveReferences.get().unwrap();
+        let reflectable = raw_reflectable as *const Reflector;
+        let mut table = live_references.table.borrow_mut();
+        match table.entry(raw_reflectable) {
+            Occupied(entry) => {
+                if *entry.get().lock() != 0 {
+                    // there could have been a new reference taken since
+                    // this message was dispatched.
+                    return;
+                }
+
+                unsafe {
+                    JS_RemoveObjectRoot(cx, (*reflectable).rootable());
+                }
+                let _ = entry.take();
+            }
+            Vacant(_) => {
+                // there could be a cleanup message dispatched, then a new
+                // pinned reference obtained and released before the message
+                // is processed, at which point there would be no matching
+                // hashtable entry.
+                info!("attempt to cleanup an unrecognized reflector");
+            }
+        }
+    }
+}
+
+impl Drop for LiveDOMReferences {
+    fn drop(&mut self) {
+        assert!(self.table.borrow().keys().count() == 0);
+    }
+}

components/script/dom/bindings/trace.rs

@@ -28,6 +28,7 @@
 //! a datatype.
 
 use dom::bindings::js::JS;
+use dom::bindings::refcounted::Trusted;
 use dom::bindings::utils::{Reflectable, Reflector, WindowProxyHandler};
 use dom::node::{Node, TrustedNodeAddress};
 
@@ -203,6 +204,7 @@ no_jsmanaged_fields!(Receiver<T>)
 no_jsmanaged_fields!(Rect<T>)
 no_jsmanaged_fields!(ImageCacheTask, ScriptControlChan)
 no_jsmanaged_fields!(Atom, Namespace, Timer)
+no_jsmanaged_fields!(Trusted<T>)
 no_jsmanaged_fields!(PropertyDeclarationBlock)
 // These three are interdependent, if you plan to put jsmanaged data
 // in one of these make sure it is propagated properly to containing structs

components/script/dom/dedicatedworkerglobalscope.rs

@@ -11,6 +11,7 @@ use dom::bindings::error::ErrorResult;
 use dom::bindings::error::Error::DataClone;
 use dom::bindings::global::GlobalRef;
 use dom::bindings::js::{JSRef, Temporary, RootCollection};
+use dom::bindings::refcounted::LiveDOMReferences;
 use dom::bindings::utils::Reflectable;
 use dom::eventtarget::{EventTarget, EventTargetHelpers, EventTargetTypeId};
 use dom::messageevent::MessageEvent;
@@ -110,7 +111,6 @@ impl DedicatedWorkerGlobalScope {
                 Ok(_) => (),
                 Err(_) => println!("evaluate_script failed")
             }
-            global.delayed_release_worker();
 
             let scope: JSRef<WorkerGlobalScope> =
                 WorkerGlobalScopeCast::from_ref(*global);
@@ -118,7 +118,7 @@ impl DedicatedWorkerGlobalScope {
                 EventTargetCast::from_ref(*global);
             loop {
                 match global.receiver.recv_opt() {
-                    Ok(ScriptMsg::DOMMessage(data, nbytes)) => {
+                    Ok(ScriptMsg::DOMMessage(_addr, data, nbytes)) => {
                         let mut message = UndefinedValue();
                         unsafe {
                             assert!(JS_ReadStructuredClone(
@@ -128,7 +128,6 @@ impl DedicatedWorkerGlobalScope {
                         }
 
                         MessageEvent::dispatch_jsval(target, GlobalRef::Worker(scope), message);
-                        global.delayed_release_worker();
                     },
                     Ok(ScriptMsg::RunnableMsg(runnable)) => {
                         runnable.handler()
@@ -136,9 +135,9 @@ impl DedicatedWorkerGlobalScope {
                     Ok(ScriptMsg::WorkerPostMessage(addr, data, nbytes)) => {
                         Worker::handle_message(addr, data, nbytes);
                     },
-                    Ok(ScriptMsg::WorkerRelease(addr)) => {
-                        Worker::handle_release(addr)
-                    },
+                    Ok(ScriptMsg::RefcountCleanup(addr)) => {
+                        LiveDOMReferences::cleanup(js_context.ptr, addr);
+                    }
                     Ok(ScriptMsg::FireTimer(TimerSource::FromWorker, timer_id)) => {
                         scope.handle_fire_timer(timer_id);
                     }
@@ -164,24 +163,13 @@ impl<'a> DedicatedWorkerGlobalScopeMethods for JSRef<'a, DedicatedWorkerGlobalSc
         }
 
         let ScriptChan(ref sender) = self.parent_sender;
-        sender.send(ScriptMsg::WorkerPostMessage(self.worker, data, nbytes));
+        sender.send(ScriptMsg::WorkerPostMessage(self.worker.clone(), data, nbytes));
         Ok(())
     }
 
     event_handler!(message, GetOnmessage, SetOnmessage)
 }
 
-trait PrivateDedicatedWorkerGlobalScopeHelpers {
-    fn delayed_release_worker(self);
-}
-
-impl<'a> PrivateDedicatedWorkerGlobalScopeHelpers for JSRef<'a, DedicatedWorkerGlobalScope> {
-    fn delayed_release_worker(self) {
-        let ScriptChan(ref sender) = self.parent_sender;
-        sender.send(ScriptMsg::WorkerRelease(self.worker));
-    }
-}
-
 impl DedicatedWorkerGlobalScopeDerived for EventTarget {
     fn is_dedicatedworkerglobalscope(&self) -> bool {
         match *self.type_id() {

components/script/dom/worker.rs

@@ -9,7 +9,8 @@ use dom::bindings::codegen::InheritTypes::EventTargetCast;
 use dom::bindings::error::{Fallible, ErrorResult};
 use dom::bindings::error::Error::{Syntax, DataClone};
 use dom::bindings::global::{GlobalRef, GlobalField};
-use dom::bindings::js::{JS, JSRef, Temporary};
+use dom::bindings::js::{JSRef, Temporary};
+use dom::bindings::refcounted::Trusted;
 use dom::bindings::trace::JSTraceable;
 use dom::bindings::utils::{Reflectable, reflect_dom_object};
 use dom::dedicatedworkerglobalscope::DedicatedWorkerGlobalScope;
@@ -20,17 +21,16 @@ use script_task::{ScriptChan, ScriptMsg};
 use servo_util::str::DOMString;
 
 use js::glue::JS_STRUCTURED_CLONE_VERSION;
-use js::jsapi::{JSContext, JS_AddObjectRoot, JS_RemoveObjectRoot, JSTracer};
+use js::jsapi::JSContext;
 use js::jsapi::{JS_ReadStructuredClone, JS_WriteStructuredClone, JS_ClearPendingException};
 use js::jsval::{JSVal, UndefinedValue};
 use url::UrlParser;
 
-use libc::{c_void, size_t};
+use libc::size_t;
 use std::cell::Cell;
 use std::ptr;
 
-pub struct TrustedWorkerAddress(pub *const c_void);
-no_jsmanaged_fields!(TrustedWorkerAddress)
+pub type TrustedWorkerAddress = Trusted<Worker>;
 
 #[dom_struct]
 pub struct Worker {
@@ -71,7 +71,7 @@ impl Worker {
         let (receiver, sender) = ScriptChan::new();
 
         let worker = Worker::new(global, sender.clone()).root();
-        let worker_ref = worker.addref();
+        let worker_ref = Trusted::new(global.get_cx(), *worker, global.script_chan().clone());
 
         DedicatedWorkerGlobalScope::run_worker_scope(
             worker_url, worker_ref, resource_task, global.script_chan().clone(),
@@ -82,7 +82,7 @@ impl Worker {
 
     pub fn handle_message(address: TrustedWorkerAddress,
                           data: *mut u64, nbytes: size_t) {
-        let worker = unsafe { JS::from_trusted_worker_address(address).root() };
+        let worker = address.to_temporary().root();
 
         let global = worker.global.root();
 
@@ -99,38 +99,6 @@ impl Worker {
     }
 }
 
-impl Worker {
-    // Creates a trusted address to the object, and roots it. Always pair this with a release()
-    pub fn addref(&self) -> TrustedWorkerAddress {
-        let refcount = self.refcount.get();
-        if refcount == 0 {
-            let cx = self.global.root().root_ref().get_cx();
-            unsafe {
-                JS_AddObjectRoot(cx, self.reflector().rootable());
-            }
-        }
-        self.refcount.set(refcount + 1);
-        TrustedWorkerAddress(self as *const Worker as *const c_void)
-    }
-
-    pub fn release(&self) {
-        let refcount = self.refcount.get();
-        assert!(refcount > 0)
-        self.refcount.set(refcount - 1);
-        if refcount == 1 {
-            let cx = self.global.root().root_ref().get_cx();
-            unsafe {
-                JS_RemoveObjectRoot(cx, self.reflector().rootable());
-            }
-        }
-    }
-
-    pub fn handle_release(address: TrustedWorkerAddress) {
-        let worker = unsafe { JS::from_trusted_worker_address(address).root() };
-        worker.release();
-    }
-}
-
 impl<'a> WorkerMethods for JSRef<'a, Worker> {
     fn PostMessage(self, cx: *mut JSContext, message: JSVal) -> ErrorResult {
         let mut data = ptr::null_mut();
@@ -144,9 +112,9 @@ impl<'a> WorkerMethods for JSRef<'a, Worker> {
             return Err(DataClone);
         }
 
-        self.addref();
+        let addr = Trusted::new(cx, self, self.global.root().root_ref().script_chan().clone());
         let ScriptChan(ref sender) = self.sender;
-        sender.send(ScriptMsg::DOMMessage(data, nbytes));
+        sender.send(ScriptMsg::DOMMessage(addr, data, nbytes));
         Ok(())
     }
 

components/script/dom/xmlhttprequest.rs

@@ -15,6 +15,7 @@ use dom::bindings::error::Error::{InvalidState, InvalidAccess};
 use dom::bindings::error::Error::{Network, Syntax, Security, Abort, Timeout};
 use dom::bindings::global::{GlobalField, GlobalRef, GlobalRoot};
 use dom::bindings::js::{MutNullableJS, JS, JSRef, Temporary, OptionalRootedRootable};
+use dom::bindings::refcounted::Trusted;
 use dom::bindings::str::ByteString;
 use dom::bindings::utils::{Reflectable, reflect_dom_object};
 use dom::document::Document;
@@ -37,13 +38,10 @@ use hyper::http::RawStatus;
 use hyper::mime::{mod, Mime};
 use hyper::method::{Method, Get, Head, Connect, Trace, Extension};
 
-use js::jsapi::{JS_AddObjectRoot, JS_ParseJSON, JS_RemoveObjectRoot, JSContext};
+use js::jsapi::{JS_ParseJSON, JSContext};
 use js::jsapi::JS_ClearPendingException;
 use js::jsval::{JSVal, NullValue, UndefinedValue};
 
-use libc;
-use libc::c_void;
-
 use net::resource_task::{ResourceTask, ResourceCORSData, Load, LoadData, LoadResponse, Payload, Done};
 use cors::{allow_cross_origin_request, CORSRequest, RequestMode};
 use servo_util::str::DOMString;
@@ -73,15 +71,6 @@ enum XMLHttpRequestState {
     XHRDone = 4, // So as not to conflict with the ProgressMsg `Done`
 }
 
-struct XHRReleaseHandler(TrustedXHRAddress);
-
-impl Runnable for XHRReleaseHandler {
-    fn handler(&self) {
-        let XHRReleaseHandler(addr) = *self;
-        XMLHttpRequest::handle_release(addr);
-    }
-}
-
 struct XHRProgressHandler {
     addr: TrustedXHRAddress,
     progress: XHRProgress,
@@ -95,7 +84,7 @@ impl XHRProgressHandler {
 
 impl Runnable for XHRProgressHandler {
     fn handler(&self) {
-        XMLHttpRequest::handle_progress(self.addr, self.progress.clone());
+        XMLHttpRequest::handle_progress(self.addr.clone(), self.progress.clone());
     }
 }
 
@@ -162,7 +151,6 @@ pub struct XMLHttpRequest {
     send_flag: Cell<bool>,
 
     global: GlobalField,
-    pinned_count: Cell<uint>,
     timer: DOMRefCell<Timer>,
     fetch_time: Cell<i64>,
     terminate_sender: DOMRefCell<Option<Sender<TerminateReason>>>,
@@ -196,7 +184,6 @@ impl XMLHttpRequest {
             upload_events: Cell::new(false),
 
             global: GlobalField::from_rooted(global),
-            pinned_count: Cell::new(0),
             timer: DOMRefCell::new(Timer::new().unwrap()),
             fetch_time: Cell::new(0),
             terminate_sender: DOMRefCell::new(None),
@@ -213,14 +200,8 @@ impl XMLHttpRequest {
     }
 
     pub fn handle_progress(addr: TrustedXHRAddress, progress: XHRProgress) {
-        unsafe {
-            let xhr = JS::from_trusted_xhr_address(addr).root();
-            xhr.process_partial_response(progress);
-        }
-    }
-
-    pub fn handle_release(addr: TrustedXHRAddress) {
-        addr.release_once();
+        let xhr = addr.to_temporary().root();
+        xhr.process_partial_response(progress);
     }
 
     fn fetch(fetch_type: &SyncOrAsync, resource_task: ResourceTask,
@@ -233,9 +214,9 @@ impl XMLHttpRequest {
                 SyncOrAsync::Sync(xhr) => {
                     xhr.process_partial_response(msg);
                 },
-                SyncOrAsync::Async(addr, script_chan) => {
+                SyncOrAsync::Async(ref addr, script_chan) => {
                     let ScriptChan(ref chan) = *script_chan;
-                    chan.send(ScriptMsg::RunnableMsg(box XHRProgressHandler::new(addr, msg)));
+                    chan.send(ScriptMsg::RunnableMsg(box XHRProgressHandler::new(addr.clone(), msg)));
                 }
             }
         }
@@ -639,9 +620,8 @@ impl<'a> XMLHttpRequestMethods for JSRef<'a, XMLHttpRequest> {
             // unpin it. This is to ensure that the object will stay alive
             // as long as there are (possibly cancelled) inflight events queued up
             // in the script task's port
-            let addr = unsafe {
-                self.to_trusted()
-            };
+            let addr = Trusted::new(self.global.root().root_ref().get_cx(), self,
+                                    script_chan.clone());
             spawn_named("XHRTask", proc() {
                 let _ = XMLHttpRequest::fetch(&mut SyncOrAsync::Async(addr, &script_chan),
                                               resource_task,
@@ -650,8 +630,6 @@ impl<'a> XMLHttpRequestMethods for JSRef<'a, XMLHttpRequest> {
                                               cors_request,
                                               gen_id,
                                               start_port);
-                let ScriptChan(ref chan) = script_chan;
-                chan.send(ScriptMsg::RunnableMsg(box XHRReleaseHandler(addr)));
             });
             let timeout = self.timeout.get();
             if timeout > 0 {
@@ -768,20 +746,9 @@ impl XMLHttpRequestDerived for EventTarget {
     }
 }
 
-pub struct TrustedXHRAddress(pub *const c_void);
-
-impl TrustedXHRAddress {
-    pub fn release_once(self) {
-        unsafe {
-            JS::from_trusted_xhr_address(self).root().release_once();
-        }
-    }
-}
-
+pub type TrustedXHRAddress = Trusted<XMLHttpRequest>;
 
 trait PrivateXMLHttpRequestHelpers {
-    unsafe fn to_trusted(self) -> TrustedXHRAddress;
-    fn release_once(self);
     fn change_ready_state(self, XMLHttpRequestState);
     fn process_partial_response(self, progress: XHRProgress);
     fn terminate_ongoing_fetch(self);
@@ -796,33 +763,6 @@ trait PrivateXMLHttpRequestHelpers {
 }
 
 impl<'a> PrivateXMLHttpRequestHelpers for JSRef<'a, XMLHttpRequest> {
-    // Creates a trusted address to the object, and roots it. Always pair this with a release()
-    unsafe fn to_trusted(self) -> TrustedXHRAddress {
-        if self.pinned_count.get() == 0 {
-            JS_AddObjectRoot(self.global.root().root_ref().get_cx(), self.reflector().rootable());
-        }
-        let pinned_count = self.pinned_count.get();
-        self.pinned_count.set(pinned_count + 1);
-        TrustedXHRAddress(self.deref() as *const XMLHttpRequest as *const libc::c_void)
-    }
-
-    fn release_once(self) {
-        if self.sync.get() {
-            // Lets us call this at various termination cases without having to
-            // check self.sync every time, since the pinning mechanism only is
-            // meaningful during an async fetch
-            return;
-        }
-        assert!(self.pinned_count.get() > 0)
-        let pinned_count = self.pinned_count.get();
-        self.pinned_count.set(pinned_count - 1);
-        if self.pinned_count.get() == 0 {
-            unsafe {
-                JS_RemoveObjectRoot(self.global.root().root_ref().get_cx(), self.reflector().rootable());
-            }
-        }
-    }
-
     fn change_ready_state(self, rs: XMLHttpRequestState) {
         assert!(self.ready_state.get() != rs)
         self.ready_state.set(rs);

components/script/lib.rs

@@ -59,6 +59,7 @@ pub mod dom {
         pub mod cell;
         pub mod global;
         pub mod js;
+        pub mod refcounted;
         pub mod utils;
         pub mod callback;
         pub mod error;

components/script/script_task.rs

@@ -15,6 +15,7 @@ use dom::bindings::conversions::FromJSValConvertible;
 use dom::bindings::conversions::StringificationBehavior;
 use dom::bindings::global::GlobalRef;
 use dom::bindings::js::{JS, JSRef, RootCollection, Temporary, OptionalRootable};
+use dom::bindings::refcounted::LiveDOMReferences;
 use dom::bindings::trace::JSTraceable;
 use dom::bindings::utils::{wrap_for_same_compartment, pre_wrap};
 use dom::document::{Document, IsHTMLDocument, DocumentHelpers, DocumentSource};
@@ -70,6 +71,7 @@ use js::rust::{Cx, RtUtils};
 use js;
 use url::Url;
 
+use libc;
 use libc::size_t;
 use std::any::{Any, AnyRefExt};
 use std::comm::{channel, Sender, Receiver, Select};
@@ -111,13 +113,13 @@ pub enum ScriptMsg {
     ExitWindow(PipelineId),
     /// Message sent through Worker.postMessage (only dispatched to
     /// DedicatedWorkerGlobalScope).
-    DOMMessage(*mut u64, size_t),
+    DOMMessage(TrustedWorkerAddress, *mut u64, size_t),
     /// Posts a message to the Worker object (dispatched to all tasks).
     WorkerPostMessage(TrustedWorkerAddress, *mut u64, size_t),
-    /// Releases one reference to the Worker object (dispatched to all tasks).
-    WorkerRelease(TrustedWorkerAddress),
     /// Generic message that encapsulates event handling.
     RunnableMsg(Box<Runnable+Send>),
+    /// A DOM object's last pinned reference was removed (dispatched to all tasks).
+    RefcountCleanup(*const libc::c_void),
 }
 
 /// Encapsulates internal communication within the script task.
@@ -368,6 +370,7 @@ impl ScriptTask {
     }
 
     pub fn new_rt_and_cx() -> (js::rust::rt, Rc<Cx>) {
+        LiveDOMReferences::initialize();
         let js_runtime = js::rust::rt();
         assert!({
             let ptr: *mut JSRuntime = (*js_runtime).ptr;
@@ -577,10 +580,10 @@ impl ScriptTask {
                 panic!("unexpected message"),
             ScriptMsg::WorkerPostMessage(addr, data, nbytes) =>
                 Worker::handle_message(addr, data, nbytes),
-            ScriptMsg::WorkerRelease(addr) =>
-                Worker::handle_release(addr),
             ScriptMsg::RunnableMsg(runnable) =>
                 runnable.handler(),
+            ScriptMsg::RefcountCleanup(addr) =>
+                LiveDOMReferences::cleanup(self.js_context.borrow().as_ref().unwrap().ptr, addr),
         }
     }