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BTreeMap: more refactoring around edges #77244

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merged 2 commits into from
Oct 21, 2020
Merged

BTreeMap: more refactoring around edges #77244

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7829e18
BTreeMap: reuse BoxedNode instances directly instead of their contents
ssomers Oct 1, 2020
76c466a
BTreeMap: less sharing, more similarity between leaf and internal nodes
ssomers Sep 26, 2020
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91 changes: 39 additions & 52 deletions library/alloc/src/collections/btree/node.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -127,10 +127,6 @@ impl<K, V> BoxedNode<K, V> {
BoxedNode { ptr: Unique::from(&mut Box::leak(node).data) }
}

unsafe fn from_ptr(ptr: NonNull<LeafNode<K, V>>) -> Self {
BoxedNode { ptr: unsafe { Unique::new_unchecked(ptr.as_ptr()) } }
}

fn as_ptr(&self) -> NonNull<LeafNode<K, V>> {
NonNull::from(self.ptr)
}
Expand Down Expand Up @@ -198,7 +194,7 @@ impl<K, V> Root<K, V> {
/// and is the opposite of `pop_internal_level`.
pub fn push_internal_level(&mut self) -> NodeRef<marker::Mut<'_>, K, V, marker::Internal> {
let mut new_node = Box::new(unsafe { InternalNode::new() });
new_node.edges[0].write(unsafe { BoxedNode::from_ptr(self.node.as_ptr()) });
new_node.edges[0].write(unsafe { ptr::read(&mut self.node) });

self.node = BoxedNode::from_internal(new_node);
self.height += 1;
Expand All @@ -224,8 +220,8 @@ impl<K, V> Root<K, V> {

let top = self.node.ptr;

let internal_node = unsafe { self.internal_node_as_mut() };
self.node = unsafe { BoxedNode::from_ptr(internal_node.first_edge().descend().node) };
let mut internal_node = unsafe { self.internal_node_as_mut() };
self.node = unsafe { internal_node.as_internal_mut().edges[0].assume_init_read() };
self.height -= 1;
self.node_as_mut().as_leaf_mut().parent = None;

Expand Down Expand Up @@ -615,7 +611,7 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {

/// Adds a key/value pair to the beginning of the node.
fn push_front(&mut self, key: K, val: V) {
debug_assert!(self.len() < CAPACITY);
assert!(self.len() < CAPACITY);

unsafe {
slice_insert(self.keys_mut(), 0, key);
Expand Down Expand Up @@ -668,14 +664,7 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
unsafe {
slice_insert(self.keys_mut(), 0, key);
slice_insert(self.vals_mut(), 0, val);
slice_insert(
slice::from_raw_parts_mut(
MaybeUninit::slice_as_mut_ptr(&mut self.as_internal_mut().edges),
self.len() + 1,
),
0,
edge.node,
);
slice_insert(self.edges_mut(), 0, edge.node);
}

self.as_leaf_mut().len += 1;
Expand Down Expand Up @@ -925,33 +914,22 @@ fn splitpoint(edge_idx: usize) -> (usize, InsertionPlace) {
}
}

impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::Edge> {
/// Helps implementations of `insert_fit` for a particular `NodeType`,
/// by taking care of leaf data.
impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
/// Inserts a new key/value pair between the key/value pairs to the right and left of
/// this edge. This method assumes that there is enough space in the node for the new
/// pair to fit.
fn leafy_insert_fit(&mut self, key: K, val: V) {
///
/// The returned pointer points to the inserted value.
fn insert_fit(&mut self, key: K, val: V) -> *mut V {
debug_assert!(self.node.len() < CAPACITY);

unsafe {
slice_insert(self.node.keys_mut(), self.idx, key);
slice_insert(self.node.vals_mut(), self.idx, val);

self.node.as_leaf_mut().len += 1;
}
}
}

impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
/// Inserts a new key/value pair between the key/value pairs to the right and left of
/// this edge. This method assumes that there is enough space in the node for the new
/// pair to fit.
///
/// The returned pointer points to the inserted value.
fn insert_fit(&mut self, key: K, val: V) -> *mut V {
self.leafy_insert_fit(key, val);
unsafe { self.node.val_mut_at(self.idx) }
self.node.val_mut_at(self.idx)
}
}
}

Expand Down Expand Up @@ -1000,11 +978,14 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
/// between this edge and the key/value pair to the right of this edge. This method assumes
/// that there is enough space in the node for the new pair to fit.
fn insert_fit(&mut self, key: K, val: V, edge: Root<K, V>) {
debug_assert!(self.node.len() < CAPACITY);
debug_assert!(edge.height == self.node.height - 1);

unsafe {
slice_insert(self.node.keys_mut(), self.idx, key);
slice_insert(self.node.vals_mut(), self.idx, val);
slice_insert(self.node.edges_mut(), self.idx + 1, edge.node);
self.leafy_insert_fit(key, val);
self.node.as_leaf_mut().len += 1;

self.node.correct_childrens_parent_links((self.idx + 1)..=self.node.len());
}
Expand Down Expand Up @@ -1135,15 +1116,21 @@ impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>
}

impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
/// Helps implementations of `split` for a particular `NodeType`,
/// by calculating the length of the new node.
fn split_new_node_len(&self) -> usize {
debug_assert!(self.idx < self.node.len());
self.node.len() - self.idx - 1
}

/// Helps implementations of `split` for a particular `NodeType`,
/// by taking care of leaf data.
fn leafy_split(&mut self, new_node: &mut LeafNode<K, V>) -> (K, V, usize) {
fn split_leaf_data(&mut self, new_node: &mut LeafNode<K, V>) -> (K, V) {
let new_len = self.split_new_node_len();
unsafe {
let k = ptr::read(self.node.key_at(self.idx));
let v = ptr::read(self.node.val_at(self.idx));

let new_len = self.node.len() - self.idx - 1;

ptr::copy_nonoverlapping(
self.node.key_at(self.idx + 1),
MaybeUninit::slice_as_mut_ptr(&mut new_node.keys),
Expand All @@ -1157,15 +1144,15 @@ impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>

self.node.as_leaf_mut().len = self.idx as u16;
new_node.len = new_len as u16;
(k, v, new_len)
(k, v)
}
}
}

impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV> {
/// Splits the underlying node into three parts:
///
/// - The node is truncated to only contain the key/value pairs to the right of
/// - The node is truncated to only contain the key/value pairs to the left of
/// this handle.
/// - The key and value pointed to by this handle are extracted.
/// - All the key/value pairs to the right of this handle are put into a newly
Expand All @@ -1174,9 +1161,10 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, mark
unsafe {
let mut new_node = Box::new(LeafNode::new());

let (k, v, _) = self.leafy_split(&mut new_node);
let (k, v) = self.split_leaf_data(&mut new_node);

(self.node, k, v, Root { node: BoxedNode::from_leaf(new_node), height: 0 })
let right = Root { node: BoxedNode::from_leaf(new_node), height: 0 };
(self.node, k, v, right)
}
}

Expand Down Expand Up @@ -1210,29 +1198,28 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
/// Splits the underlying node into three parts:
///
/// - The node is truncated to only contain the edges and key/value pairs to the
/// right of this handle.
/// left of this handle.
/// - The key and value pointed to by this handle are extracted.
/// - All the edges and key/value pairs to the right of this handle are put into
/// a newly allocated node.
pub fn split(mut self) -> (NodeRef<marker::Mut<'a>, K, V, marker::Internal>, K, V, Root<K, V>) {
unsafe {
let mut new_node = Box::new(InternalNode::new());

let (k, v, new_len) = self.leafy_split(&mut new_node.data);
let height = self.node.height;
let old_node = &*self.node.as_internal_ptr();

// Move edges out before reducing length:
let new_len = self.split_new_node_len();
ptr::copy_nonoverlapping(
old_node.edges.as_ptr().add(self.idx + 1),
new_node.edges.as_mut_ptr(),
self.node.edge_at(self.idx + 1),
MaybeUninit::slice_as_mut_ptr(&mut new_node.edges),
new_len + 1,
);
let (k, v) = self.split_leaf_data(&mut new_node.data);

let mut new_root = Root { node: BoxedNode::from_internal(new_node), height };
let height = self.node.height;
let mut right = Root { node: BoxedNode::from_internal(new_node), height };

new_root.internal_node_as_mut().correct_childrens_parent_links(0..=new_len);
right.internal_node_as_mut().correct_childrens_parent_links(0..=new_len);

(self.node, k, v, new_root)
(self.node, k, v, right)
}
}

Expand Down