Update Servo::get_events to return drain type (#31181)

* Update Servo::get_events to return drain type to prevent constant allocation

* Remove type alias for tlwc

* Fix libsimpleservo

components/servo/lib.rs

@@ -23,6 +23,7 @@ use std::collections::HashMap;
 use std::path::PathBuf;
 use std::rc::Rc;
 use std::sync::{Arc, Mutex};
+use std::vec::Drain;
 
 use bluetooth::BluetoothThreadFactory;
 use bluetooth_traits::BluetoothRequest;
@@ -64,7 +65,7 @@ pub use gleam::gl;
 use ipc_channel::ipc::{self, IpcSender};
 use log::{error, trace, warn, Log, Metadata, Record};
 use media::{GLPlayerThreads, WindowGLContext};
-pub use msg::constellation_msg::TopLevelBrowsingContextId as BrowserId;
+pub use msg::constellation_msg::TopLevelBrowsingContextId;
 use msg::constellation_msg::{PipelineNamespace, PipelineNamespaceId};
 use net::resource_thread::new_resource_threads;
 use net_traits::IpcSend;
@@ -162,7 +163,7 @@ pub struct Servo<Window: WindowMethods + 'static + ?Sized> {
     compositor: IOCompositor<Window>,
     constellation_chan: Sender<ConstellationMsg>,
     embedder_receiver: EmbedderReceiver,
-    messages_for_embedder: Vec<(Option<BrowserId>, EmbedderMsg)>,
+    messages_for_embedder: Vec<(Option<TopLevelBrowsingContextId>, EmbedderMsg)>,
     profiler_enabled: bool,
     /// For single-process Servo instances, this field controls the initialization
     /// and deinitialization of the JS Engine. Multiprocess Servo instances have their
@@ -213,7 +214,7 @@ impl webrender_api::RenderNotifier for RenderNotifier {
 
 pub struct InitializedServo<Window: WindowMethods + 'static + ?Sized> {
     pub servo: Servo<Window>,
-    pub browser_id: BrowserId,
+    pub browser_id: TopLevelBrowsingContextId,
 }
 
 impl<Window> Servo<Window>
@@ -282,7 +283,7 @@ where
 
         // Reserving a namespace to create TopLevelBrowsingContextId.
         PipelineNamespace::install(PipelineNamespaceId(0));
-        let top_level_browsing_context_id = BrowserId::new();
+        let top_level_browsing_context_id = TopLevelBrowsingContextId::new();
 
         // Get both endpoints of a special channel for communication between
         // the client window and the compositor. This channel is unique because
@@ -722,8 +723,8 @@ where
         }
     }
 
-    pub fn get_events(&mut self) -> Vec<(Option<BrowserId>, EmbedderMsg)> {
-        ::std::mem::replace(&mut self.messages_for_embedder, Vec::new())
+    pub fn get_events(&mut self) -> Drain<'_, (Option<TopLevelBrowsingContextId>, EmbedderMsg)> {
+        self.messages_for_embedder.drain(..)
     }
 
     pub fn handle_events(&mut self, events: impl IntoIterator<Item = EmbedderEvent>) -> bool {

ports/libsimpleservo/api/src/lib.rs

@@ -40,7 +40,7 @@ pub use servo::webrender_api::units::DeviceIntRect;
 use servo::webrender_api::units::DevicePixel;
 use servo::webrender_api::ScrollLocation;
 use servo::webrender_surfman::WebrenderSurfman;
-use servo::{self, gl, BrowserId, Servo};
+use servo::{self, gl, Servo, TopLevelBrowsingContextId};
 use servo_media::player::context as MediaPlayerContext;
 use surfman::{Connection, SurfaceType};
 
@@ -336,7 +336,7 @@ pub fn deinit() {
 }
 
 impl ServoGlue {
-    fn get_browser_id(&self) -> Result<BrowserId, &'static str> {
+    fn get_browser_id(&self) -> Result<TopLevelBrowsingContextId, &'static str> {
         let webview_id = match self.focused_webview_id {
             Some(id) => id,
             None => return Err("No focused WebViewId yet."),
@@ -646,6 +646,8 @@ impl ServoGlue {
     }
 
     fn handle_servo_events(&mut self) -> Result<(), &'static str> {
+        let mut need_update = false;
+        let mut need_present = false;
         for (browser_id, event) in self.servo.get_events() {
             match event {
                 EmbedderMsg::ChangePageTitle(title) => {
@@ -660,7 +662,7 @@ impl ServoGlue {
                         let window_event =
                             EmbedderEvent::AllowNavigationResponse(pipeline_id, data);
                         self.events.push(window_event);
-                        let _ = self.perform_updates();
+                        need_update = true;
                     }
                 },
                 EmbedderMsg::HistoryChanged(entries, current) => {
@@ -824,7 +826,7 @@ impl ServoGlue {
                     self.callbacks.host_callbacks.on_panic(reason, backtrace);
                 },
                 EmbedderMsg::ReadyToPresent => {
-                    self.servo.present();
+                    need_present = true;
                 },
                 EmbedderMsg::Status(..) |
                 EmbedderMsg::SelectFiles(..) |
@@ -839,6 +841,13 @@ impl ServoGlue {
                 EmbedderMsg::EventDelivered(..) => {},
             }
         }
+
+        if need_update {
+            let _ = self.perform_updates();
+        }
+        if need_present {
+            self.servo.present();
+        }
         Ok(())
     }
 }

ports/servoshell/app.rs

@@ -462,7 +462,7 @@ impl App {
 
             // Take any new embedder messages from Servo itself.
             embedder_messages = self.servo.as_mut().unwrap().get_events();
-            if embedder_messages.is_empty() {
+            if embedder_messages.len() == 0 {
                 break;
             }
         }

ports/servoshell/webview.rs

@@ -7,6 +7,7 @@ use std::fs::File;
 use std::io::Write;
 use std::rc::Rc;
 use std::time::Duration;
+use std::vec::Drain;
 use std::{env, thread};
 
 use arboard::Clipboard;
@@ -292,7 +293,7 @@ where
     /// Returns true if the caller needs to manually present a new frame.
     pub fn handle_servo_events(
         &mut self,
-        events: Vec<(Option<WebViewId>, EmbedderMsg)>,
+        events: Drain<'_, (Option<WebViewId>, EmbedderMsg)>,
     ) -> ServoEventResponse {
         let mut need_present = false;
         let mut history_changed = false;