compositor: Wait for both Script and the Constellation when shutting down Pipelines (#37505)

Previously, the Constellation would immediately ask the Compositor to
shut down a pipeline, even before the ScriptThread finished shutting it
down. This meant that the Compositor might remove a Pipeline and then
re-add it if the ScriptThread sent a Pipeline-related message (such as a
new display list) in the meantime.

This change makes it so that the Compositor waits for both the
Constellation and the ScriptThread to finish shutting down a Pipeline
before removing its data. In addition, the Constellation no longer
synchronously waits on the Compositor when shutting down Pipelines. This
was important when the Compositor would talk to the ScriptThread
directly, but isn't necessary any longer.

Testing: This is very hard to test, because it depends on the creation
and destruction of many iframes and the particular timing of of all
the messaging between Servo bits. That said, this was tested manually
by observing the completion of Speedometer 2.1.
Fixes: #37458.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>

components/script/script_thread.rs

@@ -36,7 +36,7 @@ use base::cross_process_instant::CrossProcessInstant;
 use base::id::{BrowsingContextId, HistoryStateId, PipelineId, PipelineNamespace, WebViewId};
 use canvas_traits::webgl::WebGLPipeline;
 use chrono::{DateTime, Local};
-use compositing_traits::CrossProcessCompositorApi;
+use compositing_traits::{CompositorMsg, CrossProcessCompositorApi, PipelineExitSource};
 use constellation_traits::{
     JsEvalResult, LoadData, LoadOrigin, NavigationHistoryBehavior, ScriptToConstellationChan,
     ScriptToConstellationMessage, StructuredSerializedData, WindowSizeType,
@@ -1605,10 +1605,12 @@ impl ScriptThread {
                         return false;
                     },
                     MixedMessage::FromConstellation(ScriptThreadMessage::ExitPipeline(
+                        webview_id,
                         pipeline_id,
                         discard_browsing_context,
                     )) => {
                         self.handle_exit_pipeline_msg(
+                            webview_id,
                             pipeline_id,
                             discard_browsing_context,
                             can_gc,
@@ -1970,9 +1972,16 @@ impl ScriptThread {
                 self.handle_css_error_reporting(pipeline_id, filename, line, column, msg)
             },
             ScriptThreadMessage::Reload(pipeline_id) => self.handle_reload(pipeline_id, can_gc),
-            ScriptThreadMessage::ExitPipeline(pipeline_id, discard_browsing_context) => {
-                self.handle_exit_pipeline_msg(pipeline_id, discard_browsing_context, can_gc)
-            },
+            ScriptThreadMessage::ExitPipeline(
+                webview_id,
+                pipeline_id,
+                discard_browsing_context,
+            ) => self.handle_exit_pipeline_msg(
+                webview_id,
+                pipeline_id,
+                discard_browsing_context,
+                can_gc,
+            ),
             ScriptThreadMessage::PaintMetric(
                 pipeline_id,
                 metric_type,
@@ -2975,6 +2984,7 @@ impl ScriptThread {
     /// Handles a request to exit a pipeline and shut down layout.
     fn handle_exit_pipeline_msg(
         &self,
+        webview_id: WebViewId,
         id: PipelineId,
         discard_bc: DiscardBrowsingContext,
         can_gc: CanGc,
@@ -3032,6 +3042,15 @@ impl ScriptThread {
             .send((id, ScriptToConstellationMessage::PipelineExited))
             .ok();
 
+        self.compositor_api
+            .sender()
+            .send(CompositorMsg::PipelineExited(
+                webview_id,
+                id,
+                PipelineExitSource::Script,
+            ))
+            .ok();
+
         debug!("{id}: Finished pipeline exit");
     }
 
@@ -3039,24 +3058,29 @@ impl ScriptThread {
     fn handle_exit_script_thread_msg(&self, can_gc: CanGc) {
         debug!("Exiting script thread.");
 
-        let mut pipeline_ids = Vec::new();
-        pipeline_ids.extend(
+        let mut webview_and_pipeline_ids = Vec::new();
+        webview_and_pipeline_ids.extend(
             self.incomplete_loads
                 .borrow()
                 .iter()
                 .next()
-                .map(|load| load.pipeline_id),
+                .map(|load| (load.webview_id, load.pipeline_id)),
         );
-        pipeline_ids.extend(
+        webview_and_pipeline_ids.extend(
             self.documents
                 .borrow()
                 .iter()
                 .next()
-                .map(|(pipeline_id, _)| pipeline_id),
+                .map(|(pipeline_id, document)| (document.webview_id(), pipeline_id)),
         );
 
-        for pipeline_id in pipeline_ids {
-            self.handle_exit_pipeline_msg(pipeline_id, DiscardBrowsingContext::Yes, can_gc);
+        for (webview_id, pipeline_id) in webview_and_pipeline_ids {
+            self.handle_exit_pipeline_msg(
+                webview_id,
+                pipeline_id,
+                DiscardBrowsingContext::Yes,
+                can_gc,
+            );
         }
 
         self.background_hang_monitor.unregister();