Auto merge of #11373 - servo:threadfactory, r=larsbergstrom

Use associated types to improve LayoutThreadFactory and ScriptThreadFactory.

Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data:
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy --faster` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

Either:
- [ ] There are tests for these changes OR
- [x] These changes do not require tests because refactoring

Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process.

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components/script/layout_interface.rs

@@ -16,8 +16,7 @@ use msg::constellation_msg::{PanicMsg, PipelineId, WindowSizeData};
 use net_traits::image_cache_thread::ImageCacheThread;
 use profile_traits::mem::ReportsChan;
 use script_traits::{ConstellationControlMsg, LayoutControlMsg, LayoutMsg as ConstellationMsg};
-use script_traits::{OpaqueScriptLayoutChannel, UntrustedNodeAddress};
-use std::any::Any;
+use script_traits::{UntrustedNodeAddress};
 use std::sync::Arc;
 use std::sync::mpsc::{Receiver, Sender, channel};
 use string_cache::Atom;
@@ -230,36 +229,11 @@ impl LayoutChan {
     }
 }
 
-/// A trait to manage opaque references to script<->layout channels without needing
-/// to expose the message type to crates that don't need to know about them.
-pub trait ScriptLayoutChan {
-    fn new(sender: Sender<Msg>, receiver: Receiver<Msg>) -> Self;
-    fn sender(&self) -> Sender<Msg>;
-    fn receiver(self) -> Receiver<Msg>;
-}
-
-impl ScriptLayoutChan for OpaqueScriptLayoutChannel {
-    fn new(sender: Sender<Msg>, receiver: Receiver<Msg>) -> OpaqueScriptLayoutChannel {
-        let inner = (box sender as Box<Any + Send>, box receiver as Box<Any + Send>);
-        OpaqueScriptLayoutChannel(inner)
-    }
-
-    fn sender(&self) -> Sender<Msg> {
-        let &OpaqueScriptLayoutChannel((ref sender, _)) = self;
-        (*sender.downcast_ref::<Sender<Msg>>().unwrap()).clone()
-    }
-
-    fn receiver(self) -> Receiver<Msg> {
-        let OpaqueScriptLayoutChannel((_, receiver)) = self;
-        *receiver.downcast::<Receiver<Msg>>().unwrap()
-    }
-}
-
 pub struct NewLayoutThreadInfo {
     pub id: PipelineId,
     pub url: Url,
     pub is_parent: bool,
-    pub layout_pair: OpaqueScriptLayoutChannel,
+    pub layout_pair: (Sender<Msg>, Receiver<Msg>),
     pub pipeline_port: IpcReceiver<LayoutControlMsg>,
     pub constellation_chan: IpcSender<ConstellationMsg>,
     pub panic_chan: IpcSender<PanicMsg>,

components/script/script_thread.rs

@@ -58,7 +58,7 @@ use js::jsapi::{JSContext, JS_SetWrapObjectCallbacks, JSTracer, SetWindowProxyCl
 use js::jsval::UndefinedValue;
 use js::rust::Runtime;
 use layout_interface::{ReflowQueryType};
-use layout_interface::{self, LayoutChan, NewLayoutThreadInfo, ScriptLayoutChan};
+use layout_interface::{self, LayoutChan, NewLayoutThreadInfo};
 use mem::heap_size_of_self_and_children;
 use msg::constellation_msg::{LoadData, PanicMsg, PipelineId, PipelineNamespace};
 use msg::constellation_msg::{SubpageId, WindowSizeData, WindowSizeType};
@@ -80,10 +80,9 @@ use script_traits::CompositorEvent::{KeyEvent, MouseButtonEvent, MouseMoveEvent,
 use script_traits::CompositorEvent::{TouchEvent, TouchpadPressureEvent};
 use script_traits::{CompositorEvent, ConstellationControlMsg, EventResult};
 use script_traits::{InitialScriptState, MouseButton, MouseEventType, MozBrowserEvent, NewLayoutInfo};
-use script_traits::{LayoutMsg, OpaqueScriptLayoutChannel, ScriptMsg as ConstellationMsg};
+use script_traits::{LayoutMsg, ScriptMsg as ConstellationMsg};
 use script_traits::{ScriptThreadFactory, ScriptToCompositorMsg, TimerEvent, TimerEventRequest, TimerSource};
 use script_traits::{TouchEventType, TouchId};
-use std::any::Any;
 use std::borrow::ToOwned;
 use std::cell::{Cell, RefCell};
 use std::collections::HashSet;
@@ -428,22 +427,16 @@ impl<'a> Drop for ScriptMemoryFailsafe<'a> {
 }
 
 impl ScriptThreadFactory for ScriptThread {
-    fn create_layout_channel() -> OpaqueScriptLayoutChannel {
-        let (chan, port) = channel();
-        ScriptLayoutChan::new(chan, port)
-    }
-
-    fn clone_layout_channel(pair: &OpaqueScriptLayoutChannel)
-                            -> Box<Any + Send> {
-        box pair.sender() as Box<Any + Send>
-    }
+    type Message = layout_interface::Msg;
 
     fn create(state: InitialScriptState,
-              layout_chan: &OpaqueScriptLayoutChannel,
-              load_data: LoadData) {
+              load_data: LoadData)
+              -> (Sender<layout_interface::Msg>, Receiver<layout_interface::Msg>) {
         let panic_chan = state.panic_chan.clone();
         let (script_chan, script_port) = channel();
-        let layout_chan = LayoutChan(layout_chan.sender());
+
+        let (sender, receiver) = channel();
+        let layout_chan = LayoutChan(sender.clone());
         let pipeline_id = state.id;
         thread::spawn_named_with_send_on_panic(format!("ScriptThread {:?}", state.id),
                                                thread_state::SCRIPT,
@@ -479,6 +472,8 @@ impl ScriptThreadFactory for ScriptThread {
             // This must always be the very last operation performed before the thread completes
             failsafe.neuter();
         }, Some(pipeline_id), panic_chan);
+
+        (sender, receiver)
     }
 }
 
@@ -1103,9 +1098,8 @@ impl ScriptThread {
             content_process_shutdown_chan,
         } = new_layout_info;
 
-        let layout_pair = ScriptThread::create_layout_channel();
-        let layout_chan = LayoutChan(*ScriptThread::clone_layout_channel(
-            &layout_pair).downcast::<Sender<layout_interface::Msg>>().unwrap());
+        let layout_pair = channel();
+        let layout_chan = LayoutChan(layout_pair.0.clone());
 
         let layout_creation_info = NewLayoutThreadInfo {
             id: new_pipeline_id,