auto merge of #2331 : Ms2ger/servo/global-cx-3, r=jdm

The long-term plan for SpiderMonkey is to eliminate JSContexts by merging
(most of) it into JSRuntime, so to future-proof our code, we should avoid
creating multiple JSContexts for the same JSRuntime.

However, this implies we'll have to use the same JSContext for objects in
different compartments, so we need to enter compartments. This is done by
using the with_compartment function.

1 files changed, 108 insertions, 76 deletions

diff --git a/src/components/script/script_task.rs b/src/components/script/script_task.rs
index 09d9ee59aa6..249d13d6a99 100644
--- a/src/components/script/script_task.rs
+++ b/src/components/script/script_task.rs
@@ -35,10 +35,12 @@ use layout_interface;
 use geom::point::Point2D;
 use geom::size::Size2D;
 use js::global::DEBUG_FNS;
-use js::jsapi::{JSObject, JS_CallFunctionValue, JS_DefineFunctions};
+use js::jsapi::{JS_CallFunctionValue, JS_DefineFunctions};
 use js::jsapi::{JS_SetWrapObjectCallbacks, JS_SetGCZeal, JS_DEFAULT_ZEAL_FREQ};
+use js::jsapi::{JSContext, JSRuntime};
 use js::jsval::NullValue;
 use js::rust::{Cx, RtUtils};
+use js::rust::with_compartment;
 use js;
 use servo_msg::compositor_msg::{FinishedLoading, LayerId, Loading, PerformingLayout};
 use servo_msg::compositor_msg::{ScriptListener};
@@ -426,21 +428,8 @@ impl Page {
         }
     }
 
-    pub fn initialize_js_info(&self, js_context: Rc<Cx>, global: *JSObject) {
-        assert!(global.is_not_null());
-
-        // Note that the order that these variables are initialized is _not_ arbitrary. Switching
-        // them around can -- and likely will -- lead to things breaking.
-
-        unsafe {
-            JS_SetGCZeal(js_context.deref().ptr, 0, JS_DEFAULT_ZEAL_FREQ);
-        }
-
-        js_context.set_default_options_and_version();
-        js_context.set_logging_error_reporter();
-
-        let mut js_info = self.mut_js_info();
-        *js_info = Some(JSPageInfo {
+    pub fn initialize_js_info(&self, js_context: Rc<Cx>) {
+        *self.mut_js_info() = Some(JSPageInfo {
             dom_static: GlobalStaticData(),
             js_context: Untraceable::new(js_context),
         });
@@ -548,6 +537,8 @@ pub struct ScriptTask {
 
     /// The JavaScript runtime.
     pub js_runtime: js::rust::rt,
+    /// The JSContext.
+    pub js_context: RefCell<Option<Rc<Cx>>>,
 
     pub mouse_over_targets: RefCell<Option<Vec<JS<Node>>>>
 }
@@ -581,6 +572,7 @@ impl<'a> Drop for ScriptMemoryFailsafe<'a> {
                 for page in page_tree.iter() {
                     *page.mut_js_info() = None;
                 }
+                *owner.js_context.borrow_mut() = None;
             }
             None => (),
         }
@@ -599,15 +591,7 @@ impl ScriptTask {
                img_cache_task: ImageCacheTask,
                window_size: Size2D<uint>)
                -> Rc<ScriptTask> {
-        let js_runtime = js::rust::rt();
-
-        unsafe {
-            JS_SetWrapObjectCallbacks(js_runtime.deref().ptr,
-                                      ptr::null(),
-                                      wrap_for_same_compartment,
-                                      ptr::null());
-        }
-
+        let (js_runtime, js_context) = ScriptTask::new_rt_and_cx();
         Rc::new(ScriptTask {
             page_tree: RefCell::new(PageTree::new(id, layout_chan, window_size)),
 
@@ -620,10 +604,50 @@ impl ScriptTask {
             compositor: compositor,
 
             js_runtime: js_runtime,
+            js_context: RefCell::new(Some(js_context)),
             mouse_over_targets: RefCell::new(None)
         })
     }
 
+    fn new_rt_and_cx() -> (js::rust::rt, Rc<Cx>) {
+        let js_runtime = js::rust::rt();
+        assert!({
+            let ptr: *JSRuntime = (*js_runtime).ptr;
+            ptr.is_not_null()
+        });
+        unsafe {
+            // JS_SetWrapObjectCallbacks clobbers the existing wrap callback,
+            // and JSCompartment::wrap crashes if that happens. The only way
+            // to retrieve the default callback is as the result of
+            // JS_SetWrapObjectCallbacks, which is why we call it twice.
+            let callback = JS_SetWrapObjectCallbacks((*js_runtime).ptr,
+                                                     ptr::null(),
+                                                     wrap_for_same_compartment,
+                                                     ptr::null());
+            JS_SetWrapObjectCallbacks((*js_runtime).ptr,
+                                      callback,
+                                      wrap_for_same_compartment,
+                                      ptr::null());
+        }
+
+        let js_context = js_runtime.cx();
+        assert!({
+            let ptr: *JSContext = (*js_context).ptr;
+            ptr.is_not_null()
+        });
+        js_context.set_default_options_and_version();
+        js_context.set_logging_error_reporter();
+        unsafe {
+            JS_SetGCZeal((*js_context).ptr, 0, JS_DEFAULT_ZEAL_FREQ);
+        }
+
+        (js_runtime, js_context)
+    }
+
+    pub fn get_cx(&self) -> *JSContext {
+        (**self.js_context.borrow().get_ref()).ptr
+    }
+
     /// Starts the script task. After calling this method, the script task will loop receiving
     /// messages on its port.
     pub fn start(&self) {
@@ -771,13 +795,15 @@ impl ScriptTask {
             None => return,
             Some(timer_handle) => {
                 // TODO: Support extra arguments. This requires passing a `*JSVal` array as `argv`.
-                let rval = NullValue();
-                let js_info = page.js_info();
-                let cx = js_info.get_ref().js_context.deref().deref().ptr;
-                unsafe {
-                    JS_CallFunctionValue(cx, this_value, *timer_handle.data.funval,
-                                         0, ptr::null(), &rval);
-                }
+                let cx = self.get_cx();
+                with_compartment(cx, this_value, || {
+                    let rval = NullValue();
+                    unsafe {
+                        JS_CallFunctionValue(cx, this_value,
+                                             *timer_handle.data.funval,
+                                             0, ptr::null(), &rval);
+                    }
+                });
 
                 is_interval = timer_handle.data.is_interval;
             }
@@ -844,20 +870,16 @@ impl ScriptTask {
         // If root is being exited, shut down all pages
         let mut page_tree = self.page_tree.borrow_mut();
         if page_tree.page().id == id {
-            for page in page_tree.iter() {
-                debug!("shutting down layout for root page {:?}", page.id);
-                shut_down_layout(&*page)
-            }
+            debug!("shutting down layout for root page {:?}", id);
+            *self.js_context.borrow_mut() = None;
+            shut_down_layout(&mut *page_tree);
             return true
         }
 
         // otherwise find just the matching page and exit all sub-pages
         match page_tree.remove(id) {
             Some(ref mut page_tree) => {
-                for page in page_tree.iter() {
-                    debug!("shutting down layout for page {:?}", page.id);
-                    shut_down_layout(&*page)
-                }
+                shut_down_layout(&mut *page_tree);
                 false
             }
             // TODO(tkuehn): pipeline closing is currently duplicated across
@@ -892,21 +914,22 @@ impl ScriptTask {
             }
         }
 
-        let cx = self.js_runtime.cx();
+        let cx = self.js_context.borrow();
+        let cx = cx.get_ref();
         // Create the window and document objects.
         let mut window = Window::new(cx.deref().ptr,
                                      page_tree.page.clone(),
                                      self.chan.clone(),
                                      self.compositor.dup(),
                                      self.image_cache_task.clone()).root();
-        page.initialize_js_info(cx.clone(), window.reflector().get_jsobject());
+        page.initialize_js_info(cx.clone());
         let mut document = Document::new(&*window, Some(url.clone()), HTMLDocument, None).root();
         window.deref_mut().init_browser_context(&*document);
 
-        {
+        with_compartment((**cx).ptr, window.reflector().get_jsobject(), || {
             let mut js_info = page.mut_js_info();
             RegisterBindings::Register(&window.unrooted(), js_info.get_mut_ref());
-        }
+        });
 
         self.compositor.set_ready_state(Loading);
         // Parse HTML.
@@ -980,23 +1003,25 @@ impl ScriptTask {
         let js_scripts = js_scripts.take_unwrap();
         debug!("js_scripts: {:?}", js_scripts);
 
-        // Define debug functions.
-        unsafe {
-            assert!(JS_DefineFunctions((*cx).ptr,
-                                       window.reflector().get_jsobject(),
-                                       DEBUG_FNS.as_ptr()) != 0);
-        }
+        with_compartment((**cx).ptr, window.reflector().get_jsobject(), || {
+            // Define debug functions.
+            unsafe {
+                assert!(JS_DefineFunctions((**cx).ptr,
+                                           window.reflector().get_jsobject(),
+                                           DEBUG_FNS.as_ptr()) != 0);
+            }
 
-        // Evaluate every script in the document.
-        for file in js_scripts.iter() {
-            let global_obj = window.reflector().get_jsobject();
-            //FIXME: this should have some kind of error handling, or explicitly
-            //       drop an exception on the floor.
-            match cx.evaluate_script(global_obj, file.data.clone(), file.url.to_str(), 1) {
-                Ok(_) => (),
-                Err(_) => println!("evaluate_script failed")
+            // Evaluate every script in the document.
+            for file in js_scripts.iter() {
+                let global_obj = window.reflector().get_jsobject();
+                //FIXME: this should have some kind of error handling, or explicitly
+                //       drop an exception on the floor.
+                match cx.evaluate_script(global_obj, file.data.clone(), file.url.to_str(), 1) {
+                    Ok(_) => (),
+                    Err(_) => println!("evaluate_script failed")
+                }
             }
-        }
+        });
 
         // We have no concept of a document loader right now, so just dispatch the
         // "load" event as soon as we've finished executing all scripts parsed during
@@ -1221,25 +1246,32 @@ impl ScriptTask {
     }
 }
 
-/// Shuts down layout for the given page.
-fn shut_down_layout(page: &Page) {
-    page.join_layout();
-
-    // Tell the layout task to begin shutting down.
-    let (response_chan, response_port) = channel();
-    let LayoutChan(ref chan) = *page.layout_chan;
-    chan.send(layout_interface::PrepareToExitMsg(response_chan));
-    response_port.recv();
-
-    // Destroy all nodes. Setting frame and js_info to None will trigger our
-    // compartment to shutdown, run GC, etc.
+/// Shuts down layout for the given page tree.
+fn shut_down_layout(page_tree: &mut PageTree) {
+    for page in page_tree.iter() {
+        page.join_layout();
+
+        // Tell the layout task to begin shutting down, and wait until it
+        // processed this message.
+        let (response_chan, response_port) = channel();
+        let LayoutChan(ref chan) = *page.layout_chan;
+        chan.send(layout_interface::PrepareToExitMsg(response_chan));
+        response_port.recv();
+    }
 
-    let mut js_info = page.mut_js_info();
+    // Remove our references to the DOM objects in this page tree.
+    for page in page_tree.iter() {
+        *page.mut_frame() = None;
+    }
 
-    let mut frame = page.mut_frame();
-    *frame = None;
-    *js_info = None;
+    // Drop our references to the JSContext, potentially triggering a GC.
+    for page in page_tree.iter() {
+        *page.mut_js_info() = None;
+    }
 
     // Destroy the layout task. If there were node leaks, layout will now crash safely.
-    chan.send(layout_interface::ExitNowMsg);
+    for page in page_tree.iter() {
+        let LayoutChan(ref chan) = *page.layout_chan;
+        chan.send(layout_interface::ExitNowMsg);
+    }
 }