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LibWeb: Unregister ResizeObserver from Document when it has no targets

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According to the spec, `ResizeObserver` needs to live for as long as
it's referenced from script or has observation targets. With this change
we make sure that `ResizeObserver` is unregistered from the `Document`
when it has no target.

Fixes GC leak that caused us to keep all resize observers alive until
document they belong to is destroyed.
This commit is contained in:
Aliaksandr Kalenik
2025-07-30 00:25:12 +02:00
committed by Andreas Kling
parent 40fd2643cc
commit 4cbf47dcd2
Notes: github-actions[bot] 2025-07-29 22:56:18 +00:00 
Author: https://github.com/kalenikaliaksandr
Commit: https://github.com/LadybirdBrowser/ladybird/commit/4cbf47dcd2f
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5646
4 changed files with 53 additions and 20 deletions
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28
Libraries/LibWeb/ResizeObserver/ResizeObserver.cpp
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@@ -1,6 +1,6 @@
/*
* Copyright (c) 2021, Andreas Kling <andreas@ladybird.org>
* Copyright (c) 2024, Aliaksandr Kalenik <kalenik.aliaksandr@gmail.com>
* Copyright (c) 2024-2025, Aliaksandr Kalenik <kalenik.aliaksandr@gmail.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@@ -29,7 +29,6 @@ ResizeObserver::ResizeObserver(JS::Realm& realm, WebIDL::CallbackType* callback)
{
auto navigable = as<HTML::Window>(HTML::relevant_global_object(*this)).navigable();
m_document = navigable->active_document().ptr();
m_document->register_resize_observer({}, *this);
}
ResizeObserver::~ResizeObserver() = default;
@@ -51,7 +50,7 @@ void ResizeObserver::visit_edges(JS::Cell::Visitor& visitor)
void ResizeObserver::finalize()
{
if (m_document)
if (m_document && m_list_node.is_in_list())
m_document->unregister_resize_observer({}, *this);
}
@@ -71,6 +70,10 @@ void ResizeObserver::observe(DOM::Element& target, ResizeObserverOptions options
// 4. Add the resizeObservation to the [[observationTargets]] slot.
m_observation_targets.append(resize_observation);
if (!m_list_node.is_in_list()) {
m_document->register_resize_observer({}, *this);
}
}
// https://drafts.csswg.org/resize-observer-1/#dom-resizeobserver-unobserve
@@ -85,6 +88,8 @@ void ResizeObserver::unobserve(DOM::Element& target)
// 3. Remove observation from [[observationTargets]].
m_observation_targets.remove(observation.index());
unregister_observer_if_needed();
}
// https://drafts.csswg.org/resize-observer-1/#dom-resizeobserver-disconnect
@@ -95,6 +100,8 @@ void ResizeObserver::disconnect()
// 2. Clear the [[activeTargets]] list.
m_active_targets.clear();
unregister_observer_if_needed();
}
void ResizeObserver::invoke_callback(ReadonlySpan<GC::Ref<ResizeObserverEntry>> entries) const
@@ -112,4 +119,19 @@ void ResizeObserver::invoke_callback(ReadonlySpan<GC::Ref<ResizeObserverEntry>>
(void)WebIDL::invoke_callback(callback, JS::js_undefined(), WebIDL::ExceptionBehavior::Report, { { wrapped_records } });
}
void ResizeObserver::unregister_observer_if_needed()
{
// https://drafts.csswg.org/resize-observer/#lifetime
// A ResizeObserver will remain alive until both of these conditions are met:
// - there are no scripting references to the observer.
// - the observer is not observing any targets.
// The first condition from the spec is handled by visiting ResizeObserver from
// JS environment that holds a reference to ResizeObserver.
// Here we handle the second condition.
if (m_observation_targets.is_empty() && m_list_node.is_in_list() && m_document) {
m_document->unregister_resize_observer({}, *this);
}
}
}