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e0493c509e
Before this patch, every shape would permanently remember every other shape it had ever transitioned to. This could lead to pathological accumulation of unused shape objects in some cases. Fix this by using WeakPtr instead of a strongly visited Shape* in the the forward transition chain map. This means that we will now miss out on some shape sharing opportunities, but since this is not required for correctness it doesn't matter. Note that the backward transition chain is still strongly cached, as it's necessary for the reification of property tables. An interesting future optimization could be to allow property tables to get garbage collected (by detaching them from the shape object) and then reconstituted from the backwards transition chain (if needed.)
117 lines
3.5 KiB
C++
117 lines
3.5 KiB
C++
/*
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* Copyright (c) 2020-2021, Andreas Kling <kling@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/HashMap.h>
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#include <AK/OwnPtr.h>
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#include <AK/WeakPtr.h>
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#include <AK/Weakable.h>
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#include <LibJS/Forward.h>
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#include <LibJS/Heap/Cell.h>
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#include <LibJS/Runtime/PropertyAttributes.h>
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#include <LibJS/Runtime/StringOrSymbol.h>
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#include <LibJS/Runtime/Value.h>
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namespace JS {
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struct PropertyMetadata {
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size_t offset { 0 };
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PropertyAttributes attributes { 0 };
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};
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struct TransitionKey {
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StringOrSymbol property_name;
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PropertyAttributes attributes { 0 };
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bool operator==(const TransitionKey& other) const
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{
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return property_name == other.property_name && attributes == other.attributes;
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}
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};
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class Shape final
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: public Cell
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, public Weakable<Shape> {
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public:
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virtual ~Shape() override;
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enum class TransitionType {
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Invalid,
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Put,
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Configure,
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Prototype,
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};
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enum class ShapeWithoutGlobalObjectTag { Tag };
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explicit Shape(ShapeWithoutGlobalObjectTag);
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explicit Shape(Object& global_object);
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Shape(Shape& previous_shape, const StringOrSymbol& property_name, PropertyAttributes attributes, TransitionType);
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Shape(Shape& previous_shape, Object* new_prototype);
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Shape* create_put_transition(const StringOrSymbol&, PropertyAttributes attributes);
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Shape* create_configure_transition(const StringOrSymbol&, PropertyAttributes attributes);
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Shape* create_prototype_transition(Object* new_prototype);
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void add_property_without_transition(const StringOrSymbol&, PropertyAttributes);
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bool is_unique() const { return m_unique; }
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Shape* create_unique_clone() const;
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GlobalObject* global_object() const;
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Object* prototype() { return m_prototype; }
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const Object* prototype() const { return m_prototype; }
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Optional<PropertyMetadata> lookup(const StringOrSymbol&) const;
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const HashMap<StringOrSymbol, PropertyMetadata>& property_table() const;
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size_t property_count() const;
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struct Property {
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StringOrSymbol key;
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PropertyMetadata value;
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};
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Vector<Property> property_table_ordered() const;
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void set_prototype_without_transition(Object* new_prototype) { m_prototype = new_prototype; }
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void remove_property_from_unique_shape(const StringOrSymbol&, size_t offset);
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void add_property_to_unique_shape(const StringOrSymbol&, PropertyAttributes attributes);
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void reconfigure_property_in_unique_shape(const StringOrSymbol& property_name, PropertyAttributes attributes);
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private:
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virtual const char* class_name() const override { return "Shape"; }
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virtual void visit_edges(Visitor&) override;
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Shape* get_or_prune_cached_forward_transition(TransitionKey const&);
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void ensure_property_table() const;
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PropertyAttributes m_attributes { 0 };
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TransitionType m_transition_type : 6 { TransitionType::Invalid };
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bool m_unique : 1 { false };
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Object* m_global_object { nullptr };
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mutable OwnPtr<HashMap<StringOrSymbol, PropertyMetadata>> m_property_table;
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HashMap<TransitionKey, WeakPtr<Shape>> m_forward_transitions;
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Shape* m_previous { nullptr };
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StringOrSymbol m_property_name;
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Object* m_prototype { nullptr };
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size_t m_property_count { 0 };
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};
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}
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template<>
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struct AK::Traits<JS::TransitionKey> : public GenericTraits<JS::TransitionKey> {
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static unsigned hash(const JS::TransitionKey& key)
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{
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return pair_int_hash(key.attributes.bits(), Traits<JS::StringOrSymbol>::hash(key.property_name));
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}
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};
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