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LibWeb: Make LayoutState use HashMap instead of potentially huge Vector

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Before this change, LayoutState essentially had a Vector<UsedValues*>
resized to the exact number of layout nodes in the current document.

When a nested layout is performed (to calculate the intrinsic size of
something), we make a new LayoutState with its own Vector. If an entry
is missing in a nested LayoutState, we check the parent chain all the
way up to the root.

Because each nested LayoutState had to allocate a new Vector with space
for all layout nodes, this could get really nasty on very large pages
(such as the ECMA262 specification).

This patch replaces the Vector with a HashMap. There's now a small cost
to lookups, but what we get in return is the ability to handle huge
layout trees without spending eternity in page faults.
This commit is contained in:
Andreas Kling 2023-05-23 07:47:37 +02:00
parent e83681ee34
commit e2c72922f6
Notes: sideshowbarker 2024-07-16 23:55:09 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/e2c72922f6
Pull-request: https://github.com/SerenityOS/serenity/pull/18996
6 changed files with 35 additions and 42 deletions
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2
Userland/Libraries/LibWeb/DOM/Document.cpp
View file

@ -859,13 +859,11 @@ void Document::update_layout()
auto viewport_rect = browsing_context()->viewport_rect();
if (!m_layout_root) {
m_next_layout_node_serial_id = 0;
Layout::TreeBuilder tree_builder;
m_layout_root = verify_cast<Layout::Viewport>(*tree_builder.build(*this));
}
Layout::LayoutState layout_state;
layout_state.used_values_per_layout_node.resize(layout_node_count());
{
Layout::BlockFormattingContext root_formatting_context(layout_state, *m_layout_root, nullptr);

5
Userland/Libraries/LibWeb/DOM/Document.h
View file

@ -97,9 +97,6 @@ public:
JS::GCPtr<Selection::Selection> get_selection() const;
size_t next_layout_node_serial_id(Badge<Layout::Node>) { return m_next_layout_node_serial_id++; }
size_t layout_node_count() const { return m_next_layout_node_serial_id; }
DeprecatedString cookie(Cookie::Source = Cookie::Source::NonHttp);
void set_cookie(DeprecatedString const&, Cookie::Source = Cookie::Source::NonHttp);
@ -493,8 +490,6 @@ private:
WebIDL::ExceptionOr<void> run_the_document_write_steps(DeprecatedString);
size_t m_next_layout_node_serial_id { 0 };
OwnPtr<CSS::StyleComputer> m_style_computer;
JS::GCPtr<CSS::StyleSheetList> m_style_sheets;
JS::GCPtr<Node> m_hovered_node;

54
Userland/Libraries/LibWeb/Layout/LayoutState.cpp
View file

@ -11,44 +11,56 @@
namespace Web::Layout {
LayoutState::LayoutState(LayoutState const* parent)
: m_parent(parent)
, m_root(find_root())
{
}
LayoutState::~LayoutState()
{
}
LayoutState::UsedValues& LayoutState::get_mutable(NodeWithStyleAndBoxModelMetrics const& box)
{
auto serial_id = box.serial_id();
if (used_values_per_layout_node[serial_id])
return *used_values_per_layout_node[serial_id];
if (auto* used_values = used_values_per_layout_node.get(&box).value_or(nullptr))
return *used_values;
for (auto const* ancestor = m_parent; ancestor; ancestor = ancestor->m_parent) {
if (ancestor->used_values_per_layout_node[serial_id]) {
auto cow_used_values = adopt_own(*new UsedValues(*ancestor->used_values_per_layout_node[serial_id]));
if (auto* ancestor_used_values = ancestor->used_values_per_layout_node.get(&box).value_or(nullptr)) {
auto cow_used_values = adopt_own(*new UsedValues(*ancestor_used_values));
auto* cow_used_values_ptr = cow_used_values.ptr();
used_values_per_layout_node[serial_id] = move(cow_used_values);
used_values_per_layout_node.set(&box, move(cow_used_values));
return *cow_used_values_ptr;
}
}
auto const* containing_block_used_values = box.is_viewport() ? nullptr : &get(*box.containing_block());
used_values_per_layout_node[serial_id] = adopt_own(*new UsedValues);
used_values_per_layout_node[serial_id]->set_node(const_cast<NodeWithStyleAndBoxModelMetrics&>(box), containing_block_used_values);
return *used_values_per_layout_node[serial_id];
auto new_used_values = adopt_own(*new UsedValues);
auto* new_used_values_ptr = new_used_values.ptr();
new_used_values->set_node(const_cast<NodeWithStyleAndBoxModelMetrics&>(box), containing_block_used_values);
used_values_per_layout_node.set(&box, move(new_used_values));
return *new_used_values_ptr;
}
LayoutState::UsedValues const& LayoutState::get(NodeWithStyleAndBoxModelMetrics const& box) const
{
auto serial_id = box.serial_id();
if (used_values_per_layout_node[serial_id])
return *used_values_per_layout_node[serial_id];
if (auto const* used_values = used_values_per_layout_node.get(&box).value_or(nullptr))
return *used_values;
for (auto* ancestor = m_parent; ancestor; ancestor = ancestor->m_parent) {
if (ancestor->used_values_per_layout_node[serial_id])
return *ancestor->used_values_per_layout_node[serial_id];
for (auto const* ancestor = m_parent; ancestor; ancestor = ancestor->m_parent) {
if (auto const* ancestor_used_values = ancestor->used_values_per_layout_node.get(&box).value_or(nullptr))
return *ancestor_used_values;
}
auto const* containing_block_used_values = box.is_viewport() ? nullptr : &get(*box.containing_block());
const_cast<LayoutState*>(this)->used_values_per_layout_node[serial_id] = adopt_own(*new UsedValues);
const_cast<LayoutState*>(this)->used_values_per_layout_node[serial_id]->set_node(const_cast<NodeWithStyleAndBoxModelMetrics&>(box), containing_block_used_values);
return *used_values_per_layout_node[serial_id];
auto new_used_values = adopt_own(*new UsedValues);
auto* new_used_values_ptr = new_used_values.ptr();
new_used_values->set_node(const_cast<NodeWithStyleAndBoxModelMetrics&>(box), containing_block_used_values);
const_cast<LayoutState*>(this)->used_values_per_layout_node.set(&box, move(new_used_values));
return *new_used_values_ptr;
}
void LayoutState::commit()
@ -58,10 +70,8 @@ void LayoutState::commit()
HashTable<Layout::TextNode*> text_nodes;
for (auto& used_values_ptr : used_values_per_layout_node) {
if (!used_values_ptr)
continue;
auto& used_values = *used_values_ptr;
for (auto& it : used_values_per_layout_node) {
auto& used_values = *it.value;
auto& node = const_cast<NodeWithStyleAndBoxModelMetrics&>(used_values.node());
// Transfer box model metrics.

10
Userland/Libraries/LibWeb/Layout/LayoutState.h
View file

@ -29,12 +29,8 @@ struct LayoutState {
{
}
explicit LayoutState(LayoutState const* parent)
: m_parent(parent)
, m_root(find_root())
{
used_values_per_layout_node.resize(m_root.used_values_per_layout_node.size());
}
explicit LayoutState(LayoutState const* parent);
~LayoutState();
LayoutState const& find_root() const
{
@ -153,7 +149,7 @@ struct LayoutState {
// NOTE: get() will not CoW the UsedValues.
UsedValues const& get(NodeWithStyleAndBoxModelMetrics const&) const;
Vector<OwnPtr<UsedValues>> used_values_per_layout_node;
HashMap<Layout::Node const*, NonnullOwnPtr<UsedValues>> used_values_per_layout_node;
// We cache intrinsic sizes once determined, as they will not change over the course of a full layout.
// This avoids computing them several times while performing flex layout.

2
Userland/Libraries/LibWeb/Layout/Node.cpp
View file

@ -32,8 +32,6 @@ Node::Node(DOM::Document& document, DOM::Node* node)
, m_browsing_context(*document.browsing_context())
, m_anonymous(node == nullptr)
{
m_serial_id = document.next_layout_node_serial_id({});
if (node)
node->set_layout_node({}, *this);
}

4
Userland/Libraries/LibWeb/Layout/Node.h
View file

@ -42,8 +42,6 @@ class Node
public:
virtual ~Node();
size_t serial_id() const { return m_serial_id; }
bool is_anonymous() const;
DOM::Node const* dom_node() const;
DOM::Node* dom_node();
@ -165,8 +163,6 @@ private:
JS::NonnullGCPtr<HTML::BrowsingContext> m_browsing_context;
size_t m_serial_id { 0 };
bool m_anonymous { false };
bool m_has_style { false };
bool m_visible { true };