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script: Do not run layout in a thread (#31346)

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* script: Do not run layout in a thread

Instead of spawning a thread for layout that almost always runs
synchronously with script, simply run layout in the script thread.

This is a resurrection of #28708, taking just the bits that remove the
layout thread. It's a complex change and thus is just a first step
toward cleaning up the interface between script and layout. Messages are
still passed from script to layout via a `process()` method and script
proxies some messages to layout from other threads as well.

Big changes:

1. Layout is created in the script thread on Document load, thus every
   live document is guaranteed to have a layout. This isn't completely
   hidden in the interface, but we can safely `unwrap()` on a Document's
   layout.
2. Layout configuration is abstracted away into a LayoutConfig struct
   and the LayoutFactory is a struct passed around by the Constellation.
   This is to avoid having to monomorphize the entire script thread
   for each layout.
3. Instead of having the Constellation block on the layout thread to
   figure out the current epoch and whether there are pending web fonts
   loading, updates are sent synchronously to the Constellation when
   rendering to a screenshot. This practically only used by the WPT.

A couple tests start to fail, which is probably inevitable since removing
the layout thread has introduced timing changes in "exit after load" and
screenshot behavior.

Co-authored-by: Josh Matthews <josh@joshmatthews.net>

* Update test expectations

* Fix some issues found during review

* Clarify some comments

* Address review comments

---------

Co-authored-by: Josh Matthews <josh@joshmatthews.net>
This commit is contained in:
Martin Robinson 2024-02-23 09:14:10 +01:00 • committed by GitHub
parent 4849ba901e
commit 9c0561536d
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GPG key ID: B5690EEEBB952194
44 changed files with 636 additions and 1253 deletions
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37
components/compositing/compositor.rs
View file

@ -37,9 +37,9 @@ use profile_traits::time::{self as profile_time, profile, ProfilerCategory};
use script_traits::compositor::{HitTestInfo, ScrollTree};
use script_traits::CompositorEvent::{MouseButtonEvent, MouseMoveEvent, TouchEvent, WheelEvent};
use script_traits::{
AnimationState, AnimationTickType, CompositorHitTestResult, LayoutControlMsg, MouseButton,
MouseEventType, ScrollState, TouchEventType, TouchId, UntrustedNodeAddress, WheelDelta,
WindowSizeData, WindowSizeType,
AnimationState, AnimationTickType, CompositorHitTestResult, ConstellationControlMsg,
LayoutControlMsg, MouseButton, MouseEventType, ScrollState, TouchEventType, TouchId,
UntrustedNodeAddress, WheelDelta, WindowSizeData, WindowSizeType,
};
use servo_geometry::{DeviceIndependentPixel, FramebufferUintLength};
use style_traits::{CSSPixel, DevicePixel, PinchZoomFactor};
@ -207,11 +207,11 @@ pub struct IOCompositor<Window: WindowMethods + ?Sized> {
/// Some XR devices want to run on the main thread.
pub webxr_main_thread: webxr::MainThreadRegistry,
/// Map of the pending paint metrics per layout thread.
/// The layout thread for each specific pipeline expects the compositor to
/// Map of the pending paint metrics per Layout.
/// The Layout for each specific pipeline expects the compositor to
/// paint frames with specific given IDs (epoch). Once the compositor paints
/// these frames, it records the paint time for each of them and sends the
/// metric to the corresponding layout thread.
/// metric to the corresponding Layout.
pending_paint_metrics: HashMap<PipelineId, Epoch>,
/// The coordinates of the native window, its view and the screen.
@ -1606,9 +1606,11 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
});
if let Some(pipeline) = details.pipeline.as_ref() {
let _ = pipeline
.layout_chan
.send(LayoutControlMsg::SetScrollStates(scroll_states));
let message = ConstellationControlMsg::ForLayoutFromConstellation(
LayoutControlMsg::SetScrollStates(scroll_states),
*pipeline_id,
);
let _ = pipeline.script_chan.send(message);
}
}
@ -1792,10 +1794,9 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
},
);
// If there are pending paint metrics, we check if any of the painted epochs is
// one of the ones that the paint metrics recorder is expecting . In that case,
// we get the current time, inform the layout thread about it and remove the
// pending metric from the list.
// If there are pending paint metrics, we check if any of the painted epochs is one of the
// ones that the paint metrics recorder is expecting. In that case, we get the current
// time, inform layout about it and remove the pending metric from the list.
if !self.pending_paint_metrics.is_empty() {
let paint_time = SystemTime::now()
.duration_since(UNIX_EPOCH)
@ -1809,7 +1810,7 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
.webrender
.current_epoch(self.webrender_document, id.to_webrender())
{
// and check if it is the one the layout thread is expecting,
// and check if it is the one layout is expecting,
let epoch = Epoch(epoch);
if *pending_epoch != epoch {
continue;
@ -1817,9 +1818,11 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
// in which case, we remove it from the list of pending metrics,
to_remove.push(id.clone());
if let Some(pipeline) = self.pipeline(*id) {
// and inform the layout thread with the measured paint time.
let msg = LayoutControlMsg::PaintMetric(epoch, paint_time);
if let Err(e) = pipeline.layout_chan.send(msg) {
// and inform layout with the measured paint time.
let message = LayoutControlMsg::PaintMetric(epoch, paint_time);
let message =
ConstellationControlMsg::ForLayoutFromConstellation(message, *id);
if let Err(e) = pipeline.script_chan.send(message) {
warn!("Sending PaintMetric message to layout failed ({:?}).", e);
}
}