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LibWeb: Do not spin the event loop awaiting text track state changes
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Browse source 
The text track processing model would previously spin forever waiting
for the track URL to change. It would then recursively invoke itself
to handle the new URL, again entering the spin loop. This meant that
tracks could easily cause event loop hangs.

We now have an observer system to be notified when the track state
changes instead. This lets us exit the processing model and move on.
This commit is contained in:
Timothy Flynn 2025-06-12 08:51:45 -04:00 • committed by Tim Flynn
parent 24ac860998
commit de34143a4e
Notes: github-actions[bot] 2025-06-12 16:26:50 +00:00
11 changed files with 182 additions and 17 deletions
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49
Libraries/LibWeb/HTML/HTMLTrackElement.cpp
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@ -18,6 +18,7 @@
#include <LibWeb/HTML/HTMLTrackElement.h>
#include <LibWeb/HTML/PotentialCORSRequest.h>
#include <LibWeb/HTML/TextTrack.h>
#include <LibWeb/HTML/TextTrackObserver.h>
#include <LibWeb/Platform/EventLoopPlugin.h>
namespace Web::HTML {
@ -37,12 +38,14 @@ void HTMLTrackElement::initialize(JS::Realm& realm)
Base::initialize(realm);
m_track = TextTrack::create(realm);
m_track_observer = realm.create<TextTrackObserver>(realm, *m_track);
}
void HTMLTrackElement::visit_edges(Cell::Visitor& visitor)
{
Base::visit_edges(visitor);
visitor.visit(m_track);
visitor.visit(m_track_observer);
visitor.visit(m_fetch_algorithms);
visitor.visit(m_fetch_controller);
}
@ -132,16 +135,28 @@ void HTMLTrackElement::set_track_url(String track_url)
m_track_url = move(track_url);
auto track_is_hidden_or_showing = first_is_one_of(m_track->mode(), Bindings::TextTrackMode::Hidden, Bindings::TextTrackMode::Showing);
// https://html.spec.whatwg.org/multipage/media.html#start-the-track-processing-model
if (m_loading && m_fetch_controller && first_is_one_of(m_track->mode(), Bindings::TextTrackMode::Hidden, Bindings::TextTrackMode::Showing)) {
if (m_loading && m_fetch_controller && track_is_hidden_or_showing) {
m_loading = false;
m_fetch_controller->abort(realm(), {});
}
// https://html.spec.whatwg.org/multipage/media.html#start-the-track-processing-model
if (m_awaiting_track_url_change && track_is_hidden_or_showing) {
m_awaiting_track_url_change = false;
// 13. Jump to the step labeled top.
start_the_track_processing_model_parallel_steps();
}
}
// https://html.spec.whatwg.org/multipage/media.html#start-the-track-processing-model
void HTMLTrackElement::start_the_track_processing_model()
{
auto& realm = this->realm();
// 1. If another occurrence of this algorithm is already running for this text track and its track element, return,
// letting that other algorithm take care of this element.
if (m_loading)
@ -158,14 +173,15 @@ void HTMLTrackElement::start_the_track_processing_model()
m_loading = true;
// 4. Run the remainder of these steps in parallel, allowing whatever caused these steps to run to continue.
auto& realm = this->realm();
Platform::EventLoopPlugin::the().deferred_invoke(GC::create_function(realm.heap(), [this, &realm] {
start_the_track_processing_model_parallel_steps(realm);
Platform::EventLoopPlugin::the().deferred_invoke(GC::create_function(realm.heap(), [this]() {
start_the_track_processing_model_parallel_steps();
}));
}
void HTMLTrackElement::start_the_track_processing_model_parallel_steps(JS::Realm& realm)
void HTMLTrackElement::start_the_track_processing_model_parallel_steps()
{
auto& realm = this->realm();
// 5. Top: Await a stable state. The synchronous section consists of the following steps.
// 6. ⌛ Set the text track readiness state to loading.
@ -236,17 +252,22 @@ void HTMLTrackElement::start_the_track_processing_model_parallel_steps(JS::Realm
}
// 11. Wait until the text track readiness state is no longer set to loading.
HTML::main_thread_event_loop().spin_until(GC::create_function(realm.heap(), [this] {
return m_track->readiness_state() != TextTrack::ReadinessState::Loading;
}));
if (m_track->readiness_state() == TextTrack::ReadinessState::Loading) {
m_track_observer->set_track_readiness_observer([this, url = move(url)](TextTrack::ReadinessState) mutable {
if (m_track->readiness_state() != TextTrack::ReadinessState::Loading)
track_became_ready();
});
} else {
track_became_ready();
}
}
void HTMLTrackElement::track_became_ready()
{
m_track_observer->set_track_readiness_observer({});
// 12. Wait until the track URL is no longer equal to URL, at the same time as the text track mode is set to hidden or showing.
HTML::main_thread_event_loop().spin_until(GC::create_function(realm.heap(), [this, url = move(url)] {
return track_url() != url && first_is_one_of(m_track->mode(), Bindings::TextTrackMode::Hidden, Bindings::TextTrackMode::Showing);
}));
// 13. Jump to the step labeled top.
start_the_track_processing_model_parallel_steps(realm);
m_awaiting_track_url_change = true;
}
void HTMLTrackElement::track_failed_to_load()