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LibWeb: Break reference cycles so DOM::Document actually gets deleted

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When a document reaches ref_count==0, we will now remove all of the
descendant nodes from the document, and also break all the explicit
links (such as the currently hovered element.)

Basically, DOM nodes will keep the document alive even after the
document reaches ref_count==0. This allows JS wrappers to stay alive
and keep the document alive as well. This matches the behavior of
at least some other browsers.

This patch also adds a bunch of sanity checking assertions around
DOM teardown, to help catch mistakes in the future.

Fixes #3771.
This commit is contained in:
Andreas Kling 2020-10-22 23:38:14 +02:00
parent 018b458962
commit f79e28bd65
4 changed files with 79 additions and 14 deletions
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48
Libraries/LibWeb/DOM/Document.cpp
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@ -81,10 +81,51 @@ Document::~Document()
void Document::removed_last_ref()
{
ASSERT(!ref_count());
ASSERT(!m_deletion_has_begun);
if (m_referencing_node_count)
if (m_referencing_node_count) {
// The document has reached ref_count==0 but still has nodes keeping it alive.
// At this point, sever all the node links we control.
// If nodes remain elsewhere (e.g JS wrappers), they will keep the document alive.
// NOTE: This makes sure we stay alive across for the duration of the cleanup below.
increment_referencing_node_count();
m_focused_element = nullptr;
m_hovered_node = nullptr;
m_pending_parsing_blocking_script = nullptr;
m_inspected_node = nullptr;
m_scripts_to_execute_when_parsing_has_finished.clear();
m_scripts_to_execute_as_soon_as_possible.clear();
m_associated_inert_template_document = nullptr;
m_interpreter = nullptr;
{
// Gather up all the descendants of this document and prune them from the tree.
// FIXME: This could definitely be more elegant.
NonnullRefPtrVector<Node> descendants;
for_each_in_subtree([&](auto& node) {
if (&node != this)
descendants.append(node);
return IterationDecision::Continue;
});
for (auto& node : descendants) {
ASSERT(&node.document() == this);
ASSERT(!node.is_document());
if (node.parent())
node.parent()->remove_child(node);
}
}
m_in_removed_last_ref = false;
decrement_referencing_node_count();
return;
}
m_in_removed_last_ref = false;
m_deletion_has_begun = true;
delete this;
}
@ -222,9 +263,8 @@ void Document::tear_down_layout_tree()
NonnullRefPtrVector<LayoutNode> layout_nodes;
for_each_in_subtree([&](auto& node) {
if (node.layout_node())
layout_nodes.append(*node.layout_node());
m_layout_root->for_each_in_subtree([&](auto& layout_node) {
layout_nodes.append(layout_node);
return IterationDecision::Continue;
});