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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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10
Userland/Libraries/LibWeb/Layout/LayoutState.h
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@ -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.