servo: Merge #2331 - Use a single JSContext per JSRuntime (from Ms2ger: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.

Source-Repo: https://github.com/servo/servo
Source-Revision: d66197ae406e252c51bda48611ddfce78ecedb02

servo/src/components/script/dom/bindings/codegen/CodegenRust.py

@@ -1755,22 +1755,26 @@ def CreateBindingJSObject(descriptor, parent=None):
     create = "  let mut raw: JS<%s> = JS::from_raw(&mut *aObject);\n" % descriptor.concreteType
     if descriptor.proxy:
         assert not descriptor.createGlobal
-        handler = """
+        create += """
   let js_info = aScope.deref().page().js_info();
   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),
+  let private = PrivateValue(squirrel_away_unique(aObject) as *libc::c_void);
+  let obj = with_compartment(aCx, proto, || {
+    NewProxyObject(aCx, *handler,
+                   &private,
                    proto, %s,
-                           ptr::null(), ptr::null());
+                   ptr::null(), ptr::null())
+  });
   assert!(obj.is_not_null());
 
-""" % (parent)
+""" % (descriptor.name, parent)
     else:
         if descriptor.createGlobal:
             create += "  let obj = CreateDOMGlobal(aCx, &Class.base as *js::Class as *JSClass);\n"
         else:
-            create += "  let obj = JS_NewObject(aCx, &Class.base as *js::Class as *JSClass, proto, %s);\n" % parent
+            create += ("  let obj = with_compartment(aCx, proto, || {\n"
+                       "    JS_NewObject(aCx, &Class.base as *js::Class as *JSClass, proto, %s)\n"
+                       "  });\n" % parent)
         create += """  assert!(obj.is_not_null());
 
   JS_SetReservedSlot(obj, DOM_OBJECT_SLOT as u32,
@@ -1797,8 +1801,7 @@ class CGWrapMethod(CGAbstractMethod):
   assert!(scope.is_not_null());
   assert!(((*JS_GetClass(scope)).flags & JSCLASS_IS_GLOBAL) != 0);
 
-  //JSAutoCompartment ac(aCx, scope);
-  let proto = GetProtoObject(aCx, scope, scope);
+  let proto = with_compartment(aCx, scope, || GetProtoObject(aCx, scope, scope));
   assert!(proto.is_not_null());
 
 %s
@@ -1809,8 +1812,10 @@ class CGWrapMethod(CGAbstractMethod):
         else:
             return """
 %s
+  with_compartment(aCx, obj, || {
     let proto = GetProtoObject(aCx, obj, obj);
     JS_SetPrototype(aCx, obj, proto);
+  });
   raw.mut_reflector().set_jsobject(obj);
   return raw;""" % CreateBindingJSObject(self.descriptor)
 
@@ -4241,6 +4246,7 @@ class CGBindingRoot(CGThing):
             'js::glue::{GetProxyPrivate, NewProxyObject, ProxyTraps}',
             'js::glue::{RUST_FUNCTION_VALUE_TO_JITINFO}',
             'js::glue::{RUST_JS_NumberValue, RUST_JSID_IS_STRING}',
+            'js::rust::with_compartment',
             'dom::types::*',
             'dom::bindings',
             'dom::bindings::js::{JS, JSRef, Root, RootedReference, Temporary}',
@@ -4853,14 +4859,21 @@ class CallbackMember(CGNativeMember):
             # Avoid weird 0-sized arrays
             replacements["argvDecl"] = ""
 
-        return string.Template(
         # Newlines and semicolons are in the values
+        pre = string.Template(
             "${setupCall}"
             "${declRval}"
-            "${argvDecl}"
+            "${argvDecl}").substitute(replacements)
+        body = string.Template(
             "${convertArgs}"
             "${doCall}"
             "${returnResult}").substitute(replacements)
+        return CGList([
+            CGGeneric(pre),
+            CGWrapper(CGIndenter(CGGeneric(body)),
+                      pre="with_compartment(cx, self.parent.callback, || {\n",
+                      post="})")
+        ], "\n").define()
 
     def getResultConversion(self):
         replacements = {
@@ -4883,7 +4896,7 @@ class CallbackMember(CGNativeMember):
         assignRetval = string.Template(
             self.getRetvalInfo(self.retvalType,
                                False)[2]).substitute(replacements)
-        return convertType.define() + "\n" + assignRetval
+        return convertType.define() + "\n" + assignRetval + "\n"
 
     def getArgConversions(self):
         # Just reget the arglist from self.originalSig, because our superclasses

servo/src/components/script/dom/bindings/utils.rs

@@ -41,6 +41,7 @@ use js::jsfriendapi::bindgen::JS_NewObjectWithUniqueType;
 use js::jsval::JSVal;
 use js::jsval::{PrivateValue, ObjectValue, NullValue, ObjectOrNullValue};
 use js::jsval::{Int32Value, UInt32Value, DoubleValue, BooleanValue, UndefinedValue};
+use js::rust::with_compartment;
 use js::{JSPROP_ENUMERATE, JSCLASS_IS_GLOBAL, JSCLASS_IS_DOMJSCLASS};
 use js::JSPROP_PERMANENT;
 use js::{JSFUN_CONSTRUCTOR, JSPROP_READONLY};
@@ -583,7 +584,9 @@ pub fn CreateDOMGlobal(cx: *JSContext, class: *JSClass) -> *JSObject {
         if obj.is_null() {
             return ptr::null();
         }
+        with_compartment(cx, obj, || {
             JS_InitStandardClasses(cx, obj);
+        });
         initialize_global(obj);
         obj
     }

servo/src/components/script/dom/browsercontext.rs

@@ -10,6 +10,7 @@ use dom::window::Window;
 
 use js::jsapi::JSObject;
 use js::glue::{WrapperNew, CreateWrapperProxyHandler, ProxyTraps};
+use js::rust::with_compartment;
 
 use libc::c_void;
 use std::ptr;
@@ -56,9 +57,9 @@ impl BrowserContext {
 
         let parent = win.deref().reflector().get_jsobject();
         let cx = js_info.get_ref().js_context.deref().deref().ptr;
-        let wrapper = unsafe {
+        let wrapper = with_compartment(cx, parent, || unsafe {
             WrapperNew(cx, parent, *handler.deref())
-        };
+        });
         assert!(wrapper.is_not_null());
         wrapper
     }

servo/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 cx = self.get_cx();
+                with_compartment(cx, this_value, || {
                     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,
+                        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.
@@ -980,9 +1003,10 @@ impl ScriptTask {
         let js_scripts = js_scripts.take_unwrap();
         debug!("js_scripts: {:?}", js_scripts);
 
+        with_compartment((**cx).ptr, window.reflector().get_jsobject(), || {
             // Define debug functions.
             unsafe {
-            assert!(JS_DefineFunctions((*cx).ptr,
+                assert!(JS_DefineFunctions((**cx).ptr,
                                            window.reflector().get_jsobject(),
                                            DEBUG_FNS.as_ptr()) != 0);
             }
@@ -997,6 +1021,7 @@ impl ScriptTask {
                     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) {
+/// 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.
+        // 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();
+    }
 
-    // Destroy all nodes. Setting frame and js_info to None will trigger our
-    // compartment to shutdown, run GC, etc.
+    // Remove our references to the DOM objects in this page tree.
+    for page in page_tree.iter() {
+        *page.mut_frame() = None;
+    }
 
-    let mut js_info = page.mut_js_info();
-
-    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.
+    for page in page_tree.iter() {
+        let LayoutChan(ref chan) = *page.layout_chan;
         chan.send(layout_interface::ExitNowMsg);
     }
+}