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ladybird/Libraries/LibWeb/DOM/MutationObserver.h
Andreas Kling 53c9c6f3ee LibWeb: Make Agent's MutationObserver list weak
Before this change, Agent held on to all of the live MutationObserver
objects via GC::Root. This prevented them from ever getting
garbage-collected.

Instead of roots, we now use a simple IntrusiveList and remove them
from it in the finalizer for MutationObserver.

This fixes a massive GC leak on Speedometer.
2025-02-07 16:53:11 +01:00

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/*
* Copyright (c) 2022, Luke Wilde <lukew@serenityos.org>
* Copyright (c) 2022, Andreas Kling <andreas@ladybird.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <LibGC/Root.h>
#include <LibWeb/DOM/MutationRecord.h>
#include <LibWeb/WebIDL/CallbackType.h>
#include <LibWeb/WebIDL/ExceptionOr.h>
namespace Web::DOM {
// https://dom.spec.whatwg.org/#dictdef-mutationobserverinit
struct MutationObserverInit {
bool child_list { false };
Optional<bool> attributes;
Optional<bool> character_data;
bool subtree { false };
Optional<bool> attribute_old_value;
Optional<bool> character_data_old_value;
Optional<Vector<String>> attribute_filter;
};
// https://dom.spec.whatwg.org/#mutationobserver
class MutationObserver final : public Bindings::PlatformObject {
WEB_PLATFORM_OBJECT(MutationObserver, Bindings::PlatformObject);
GC_DECLARE_ALLOCATOR(MutationObserver);
public:
static WebIDL::ExceptionOr<GC::Ref<MutationObserver>> construct_impl(JS::Realm&, GC::Ptr<WebIDL::CallbackType>);
virtual ~MutationObserver() override;
WebIDL::ExceptionOr<void> observe(Node& target, MutationObserverInit options = {});
void disconnect();
Vector<GC::Root<MutationRecord>> take_records();
Vector<WeakPtr<Node>>& node_list() { return m_node_list; }
Vector<WeakPtr<Node>> const& node_list() const { return m_node_list; }
WebIDL::CallbackType& callback() { return *m_callback; }
void enqueue_record(Badge<Node>, GC::Ref<MutationRecord> mutation_record)
{
m_record_queue.append(*mutation_record);
}
private:
MutationObserver(JS::Realm&, GC::Ptr<WebIDL::CallbackType>);
virtual void initialize(JS::Realm&) override;
virtual void visit_edges(Cell::Visitor&) override;
virtual void finalize() override;
// https://dom.spec.whatwg.org/#concept-mo-callback
GC::Ptr<WebIDL::CallbackType> m_callback;
// https://dom.spec.whatwg.org/#mutationobserver-node-list
// NOTE: These are weak, per https://dom.spec.whatwg.org/#garbage-collection
// Registered observers in a nodes registered observer list have a weak reference to the node.
Vector<WeakPtr<Node>> m_node_list;
// https://dom.spec.whatwg.org/#concept-mo-queue
Vector<GC::Ref<MutationRecord>> m_record_queue;
IntrusiveListNode<MutationObserver> m_list_node;
public:
using List = IntrusiveList<&MutationObserver::m_list_node>;
};
// https://dom.spec.whatwg.org/#registered-observer
class RegisteredObserver : public JS::Cell {
GC_CELL(RegisteredObserver, JS::Cell);
public:
static GC::Ref<RegisteredObserver> create(MutationObserver&, MutationObserverInit const&);
virtual ~RegisteredObserver() override;
GC::Ref<MutationObserver> observer() const { return m_observer; }
MutationObserverInit const& options() const { return m_options; }
void set_options(MutationObserverInit options) { m_options = move(options); }
protected:
RegisteredObserver(MutationObserver& observer, MutationObserverInit const& options);
virtual void visit_edges(Cell::Visitor&) override;
private:
GC::Ref<MutationObserver> m_observer;
MutationObserverInit m_options;
};
// https://dom.spec.whatwg.org/#transient-registered-observer
class TransientRegisteredObserver final : public RegisteredObserver {
GC_CELL(TransientRegisteredObserver, RegisteredObserver);
GC_DECLARE_ALLOCATOR(TransientRegisteredObserver);
public:
static GC::Ref<TransientRegisteredObserver> create(MutationObserver&, MutationObserverInit const&, RegisteredObserver& source);
virtual ~TransientRegisteredObserver() override;
GC::Ref<RegisteredObserver> source() const { return m_source; }
private:
TransientRegisteredObserver(MutationObserver& observer, MutationObserverInit const& options, RegisteredObserver& source);
virtual void visit_edges(Cell::Visitor&) override;
GC::Ref<RegisteredObserver> m_source;
};
}