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LibWeb+AK: Use AK::Queue for the microtask queue

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The microtask queue is a pure FIFO (enqueue at back, dequeue from
front) but was using a Vector, making every dequeue O(n) due to
element shifting.

Replace it with AK::Queue which has O(1) dequeue. This makes a huge
difference when processing large numbers of microtasks, e.g. during
async-heavy JavaScript workloads where each `await` generates a
microtask.

Also add a for_each() method to AK::Queue so the GC can visit the
queued tasks.
This commit is contained in:
Andreas Kling 2026-03-15 12:02:25 -05:00 • committed by Shannon Booth
parent 0e2d8ff43a
commit a141c2c492
Notes: github-actions[bot] 2026-03-16 08:39:17 +00:00
3 changed files with 26 additions and 12 deletions
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18
Libraries/LibWeb/HTML/EventLoop/EventLoop.cpp
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@ -38,7 +38,6 @@ EventLoop::EventLoop(Type type)
: m_type(type)
{
m_task_queue = heap().allocate<TaskQueue>(*this);
m_microtask_queue = heap().allocate<TaskQueue>(*this);
m_rendering_task_function = GC::create_function(heap(), [this] {
update_the_rendering();
@ -52,7 +51,7 @@ void EventLoop::visit_edges(Visitor& visitor)
Base::visit_edges(visitor);
visitor.visit(m_reached_step_1_tasks);
visitor.visit(m_task_queue);
visitor.visit(m_microtask_queue);
m_microtask_queue.for_each([&](auto& task) { visitor.visit(task); });
visitor.visit(m_currently_running_task);
visitor.visit(m_backup_incumbent_realm_stack);
visitor.visit(m_rendering_task_function);
@ -227,7 +226,7 @@ void EventLoop::process()
}
// If there are eligible tasks in the queue, schedule a new round of processing. :^)
if (m_task_queue->has_runnable_tasks() || (!m_microtask_queue->is_empty() && !m_performing_a_microtask_checkpoint)) {
if (m_task_queue->has_runnable_tasks() || (!m_microtask_queue.is_empty() && !m_performing_a_microtask_checkpoint)) {
schedule();
}
}
@ -574,10 +573,11 @@ TaskID queue_a_task(HTML::Task::Source source, GC::Ptr<EventLoop> event_loop, GC
auto task = HTML::Task::create(event_loop->vm(), source, document, steps);
// 8. Let queue be the task queue to which source is associated on event loop.
auto& queue = source == HTML::Task::Source::Microtask ? event_loop->microtask_queue() : event_loop->task_queue();
// 9. Append task to queue.
queue.add(task);
if (source == HTML::Task::Source::Microtask)
event_loop->enqueue_microtask(task);
else
event_loop->task_queue().add(task);
return task->id();
}
@ -615,7 +615,7 @@ void queue_a_microtask(DOM::Document const* document, GC::Ref<GC::Function<void(
// FIXME: 7. Set microtask's script evaluation environment settings object set to an empty set.
// 8. Enqueue microtask on event loop's microtask queue.
(void)event_loop.microtask_queue().enqueue(microtask);
event_loop.enqueue_microtask(microtask);
}
void perform_a_microtask_checkpoint()
@ -641,9 +641,9 @@ void EventLoop::perform_a_microtask_checkpoint()
m_performing_a_microtask_checkpoint = true;
// 3. While the event loop's microtask queue is not empty:
while (!m_microtask_queue->is_empty()) {
while (!m_microtask_queue.is_empty()) {
// 1. Let oldestMicrotask be the result of dequeuing from the event loop's microtask queue.
auto oldest_microtask = m_microtask_queue->dequeue();
auto oldest_microtask = m_microtask_queue.dequeue();
// 2. Set the event loop's currently running task to oldestMicrotask.
m_currently_running_task = oldest_microtask;