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BTreeMap: declare clear_parent_link directly on the root it needs #80005

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Dec 14, 2020
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BTreeMap: declare clear_parent_link directly on the root it needs #80005

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21 changes: 11 additions & 10 deletions library/alloc/src/collections/btree/node.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -150,7 +150,7 @@ impl<K, V, Type> NodeRef<marker::Owned, K, V, Type> {
/// Mutably borrows the owned node. Unlike `reborrow_mut`, this is safe,
/// because the return value cannot be used to destroy the node itself,
/// and there cannot be other references to the tree (except during the
/// process of `into_iter` or `drop`, but that is a horrific already).
/// process of `into_iter` or `drop`, but that is horrific already).
pub fn borrow_mut(&mut self) -> NodeRef<marker::Mut<'_>, K, V, Type> {
NodeRef { height: self.height, node: self.node, _marker: PhantomData }
}
Expand Down Expand Up @@ -192,7 +192,7 @@ impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {

let internal_node = NodeRef { height: self.height, node: top, _marker: PhantomData };
*self = internal_node.first_edge().descend();
self.borrow_mut().clear_parent_link();
self.clear_parent_link();

unsafe {
Global.deallocate(top.cast(), Layout::new::<InternalNode<K, V>>());
Expand Down Expand Up @@ -611,18 +611,19 @@ impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
}

impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
/// Set or clear the node's link to its parent edge,
/// Sets the node's link to its parent edge,
/// without invalidating other references to the node.
fn set_parent_link(&mut self, parent: NonNull<InternalNode<K, V>>, parent_idx: usize) {
let leaf = Self::as_leaf_ptr(self);
unsafe { (*leaf).parent = Some(parent) };
unsafe { (*leaf).parent_idx.write(parent_idx as u16) };
}
}

/// Clear the node's link to its parent edge.
/// This only makes sense when there are no other references to the node.
impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
/// Clears the root's link to its parent edge.
fn clear_parent_link(&mut self) {
let leaf = Self::as_leaf_mut(self);
let leaf = NodeRef::as_leaf_mut(&mut self.borrow_mut());
leaf.parent = None;
}
}
Expand Down Expand Up @@ -720,9 +721,9 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
ForceResult::Internal(internal) => {
let node = ptr::read(internal.reborrow().edge_at(idx + 1));
let mut edge = Root { node, height: internal.height - 1, _marker: PhantomData };
// In practice, clearing the parent is a waste of time, because we will
// Currently, clearing the parent link is superfluous, because we will
// insert the node elsewhere and set its parent link again.
edge.borrow_mut().clear_parent_link();
edge.clear_parent_link();
Some(edge)
}
};
Expand All @@ -748,9 +749,9 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
ForceResult::Internal(mut internal) => {
let node = slice_remove(internal.reborrow_mut().into_edge_area_slice(), 0);
let mut edge = Root { node, height: internal.height - 1, _marker: PhantomData };
// In practice, clearing the parent is a waste of time, because we will
// Currently, clearing the parent link is superfluous, because we will
// insert the node elsewhere and set its parent link again.
edge.borrow_mut().clear_parent_link();
edge.clear_parent_link();

internal.correct_childrens_parent_links(0..old_len);

Expand Down