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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
6 changed files with 35 additions and 42 deletions
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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.