0ab37e1541
treap recycle nodes consistently. Rework Immutable treap node recycling attempting to make it safer in the presence of code that takes snapshots (dbCacheSnapshot) of the treap. Add special mutable PutM and DeleteM methods which DB transaction can use to apply changes more efficiently without creating lots of garbage memory.
301 lines
8.1 KiB
Go
301 lines
8.1 KiB
Go
// Copyright (c) 2015-2016 The btcsuite developers
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// Use of this source code is governed by an ISC
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// license that can be found in the LICENSE file.
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package treap
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import (
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"bytes"
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"math/rand"
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)
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// Mutable represents a treap data structure which is used to hold ordered
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// key/value pairs using a combination of binary search tree and heap semantics.
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// It is a self-organizing and randomized data structure that doesn't require
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// complex operations to maintain balance. Search, insert, and delete
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// operations are all O(log n).
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type Mutable struct {
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root *treapNode
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count int
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// totalSize is the best estimate of the total size of of all data in
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// the treap including the keys, values, and node sizes.
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totalSize uint64
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}
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// Len returns the number of items stored in the treap.
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func (t *Mutable) Len() int {
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return t.count
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}
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// Size returns a best estimate of the total number of bytes the treap is
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// consuming including all of the fields used to represent the nodes as well as
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// the size of the keys and values. Shared values are not detected, so the
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// returned size assumes each value is pointing to different memory.
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func (t *Mutable) Size() uint64 {
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return t.totalSize
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}
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// get returns the treap node that contains the passed key and its parent. When
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// the found node is the root of the tree, the parent will be nil. When the key
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// does not exist, both the node and the parent will be nil.
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func (t *Mutable) get(key []byte) (*treapNode, *treapNode) {
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var parent *treapNode
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for node := t.root; node != nil; {
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// Traverse left or right depending on the result of the
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// comparison.
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compareResult := bytes.Compare(key, node.key)
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if compareResult < 0 {
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parent = node
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node = node.left
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continue
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}
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if compareResult > 0 {
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parent = node
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node = node.right
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continue
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}
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// The key exists.
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return node, parent
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}
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// A nil node was reached which means the key does not exist.
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return nil, nil
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}
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// Has returns whether or not the passed key exists.
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func (t *Mutable) Has(key []byte) bool {
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if node, _ := t.get(key); node != nil {
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return true
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}
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return false
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}
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// Get returns the value for the passed key. The function will return nil when
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// the key does not exist.
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func (t *Mutable) Get(key []byte) []byte {
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if node, _ := t.get(key); node != nil {
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return node.value
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}
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return nil
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}
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// relinkGrandparent relinks the node into the treap after it has been rotated
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// by changing the passed grandparent's left or right pointer, depending on
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// where the old parent was, to point at the passed node. Otherwise, when there
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// is no grandparent, it means the node is now the root of the tree, so update
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// it accordingly.
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func (t *Mutable) relinkGrandparent(node, parent, grandparent *treapNode) {
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// The node is now the root of the tree when there is no grandparent.
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if grandparent == nil {
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t.root = node
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return
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}
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// Relink the grandparent's left or right pointer based on which side
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// the old parent was.
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if grandparent.left == parent {
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grandparent.left = node
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} else {
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grandparent.right = node
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}
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}
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// Put inserts the passed key/value pair.
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func (t *Mutable) Put(key, value []byte) {
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// Use an empty byte slice for the value when none was provided. This
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// ultimately allows key existence to be determined from the value since
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// an empty byte slice is distinguishable from nil.
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if value == nil {
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value = emptySlice
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}
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// The node is the root of the tree if there isn't already one.
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if t.root == nil {
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node := getTreapNode(key, value, rand.Int(), MutableGeneration)
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t.count = 1
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t.totalSize = nodeSize(node)
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t.root = node
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return
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}
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// Find the binary tree insertion point and construct a list of parents
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// while doing so. When the key matches an entry already in the treap,
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// just update its value and return.
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var parents parentStack
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var compareResult int
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for node := t.root; node != nil; {
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parents.Push(node)
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compareResult = bytes.Compare(key, node.key)
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if compareResult < 0 {
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node = node.left
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continue
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}
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if compareResult > 0 {
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node = node.right
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continue
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}
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// The key already exists, so update its value.
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t.totalSize -= uint64(len(node.value))
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t.totalSize += uint64(len(value))
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node.value = value
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return
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}
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// Link the new node into the binary tree in the correct position.
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node := getTreapNode(key, value, rand.Int(), MutableGeneration)
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t.count++
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t.totalSize += nodeSize(node)
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parent := parents.At(0)
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if compareResult < 0 {
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parent.left = node
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} else {
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parent.right = node
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}
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// Perform any rotations needed to maintain the min-heap.
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for parents.Len() > 0 {
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// There is nothing left to do when the node's priority is
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// greater than or equal to its parent's priority.
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parent = parents.Pop()
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if node.priority >= parent.priority {
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break
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}
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// Perform a right rotation if the node is on the left side or
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// a left rotation if the node is on the right side.
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if parent.left == node {
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node.right, parent.left = parent, node.right
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} else {
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node.left, parent.right = parent, node.left
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}
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t.relinkGrandparent(node, parent, parents.At(0))
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}
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}
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// Delete removes the passed key if it exists.
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func (t *Mutable) Delete(key []byte) {
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// Find the node for the key along with its parent. There is nothing to
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// do if the key does not exist.
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node, parent := t.get(key)
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if node == nil {
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return
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}
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// When the only node in the tree is the root node and it is the one
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// being deleted, there is nothing else to do besides removing it.
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if parent == nil && node.left == nil && node.right == nil {
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t.root = nil
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t.count = 0
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t.totalSize = 0
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putTreapNode(node)
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return
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}
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// Perform rotations to move the node to delete to a leaf position while
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// maintaining the min-heap.
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var isLeft bool
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var child *treapNode
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for node.left != nil || node.right != nil {
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// Choose the child with the higher priority.
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if node.left == nil {
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child = node.right
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isLeft = false
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} else if node.right == nil {
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child = node.left
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isLeft = true
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} else if node.left.priority >= node.right.priority {
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child = node.left
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isLeft = true
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} else {
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child = node.right
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isLeft = false
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}
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// Rotate left or right depending on which side the child node
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// is on. This has the effect of moving the node to delete
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// towards the bottom of the tree while maintaining the
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// min-heap.
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if isLeft {
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child.right, node.left = node, child.right
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} else {
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child.left, node.right = node, child.left
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}
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t.relinkGrandparent(child, node, parent)
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// The parent for the node to delete is now what was previously
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// its child.
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parent = child
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}
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// Delete the node, which is now a leaf node, by disconnecting it from
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// its parent.
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if parent.right == node {
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parent.right = nil
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} else {
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parent.left = nil
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}
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t.count--
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t.totalSize -= nodeSize(node)
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putTreapNode(node)
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}
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// ForEach invokes the passed function with every key/value pair in the treap
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// in ascending order.
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func (t *Mutable) ForEach(fn func(k, v []byte) bool) {
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// Add the root node and all children to the left of it to the list of
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// nodes to traverse and loop until they, and all of their child nodes,
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// have been traversed.
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var parents parentStack
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for node := t.root; node != nil; node = node.left {
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parents.Push(node)
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}
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for parents.Len() > 0 {
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node := parents.Pop()
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if !fn(node.key, node.value) {
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return
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}
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// Extend the nodes to traverse by all children to the left of
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// the current node's right child.
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for node := node.right; node != nil; node = node.left {
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parents.Push(node)
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}
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}
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}
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// Reset efficiently removes all items in the treap.
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func (t *Mutable) Reset() {
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t.count = 0
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t.totalSize = 0
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t.root = nil
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}
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// NewMutable returns a new empty mutable treap ready for use. See the
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// documentation for the Mutable structure for more details.
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func NewMutable() *Mutable {
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return &Mutable{}
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}
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func (t *Mutable) Recycle() {
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var parents parentStack
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for node := t.root; node != nil; node = node.left {
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parents.Push(node)
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}
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for parents.Len() > 0 {
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node := parents.Pop()
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// Extend the nodes to traverse by all children to the left of
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// the current node's right child.
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for n := node.right; n != nil; n = n.left {
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parents.Push(n)
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}
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if node.generation == MutableGeneration {
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putTreapNode(node)
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}
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}
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}
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