internal/persistent/map.go - tools - Git at Google

 // Copyright 2022 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // The persistent package defines various persistent data structures;
 // that is, data structures that can be efficiently copied and modified
 // in sublinear time.
 package persistent

 import (
 	"math/rand"
 	"sync/atomic"
 )

 // Implementation details:
 // * Each value is reference counted by nodes which hold it.
 // * Each node is reference counted by its parent nodes.
 // * Each map is considered a top-level parent node from reference counting perspective.
 // * Each change does always effectivelly produce a new top level node.
 //
 // Functions which operate directly with nodes do have a notation in form of
 // `foo(arg1:+n1, arg2:+n2) (ret1:+n3)`.
 // Each argument is followed by a delta change to its reference counter.
 // In case if no change is expected, the delta will be `-0`.

 // Map is an associative mapping from keys to values, both represented as
 // interface{}. Key comparison and iteration order is defined by a
 // client-provided function that implements a strict weak order.
 //
 // Maps can be Cloned in constant time.
 // Get, Store, and Delete operations are done on average in logarithmic time.
 // Maps can be Updated in O(m log(n/m)) time for maps of size n and m, where m < n.
 //
 // Values are reference counted, and a client-supplied release function
 // is called when a value is no longer referenced by a map or any clone.
 //
 // Internally the implementation is based on a randomized persistent treap:
 // https://en.wikipedia.org/wiki/Treap.
 type Map struct {
 	less func(a, b interface{}) bool
 	root *mapNode
 }

 type mapNode struct {
 	key         interface{}
 	value       *refValue
 	weight      uint64
 	refCount    int32
 	left, right *mapNode
 }

 type refValue struct {
 	refCount int32
 	value    interface{}
 	release  func(key, value interface{})
 }

 func newNodeWithRef(key, value interface{}, release func(key, value interface{})) *mapNode {
 	return &mapNode{
 		key: key,
 		value: &refValue{
 			value:    value,
 			release:  release,
 			refCount: 1,
 		},
 		refCount: 1,
 		weight:   rand.Uint64(),
 	}
 }

 func (node *mapNode) shallowCloneWithRef() *mapNode {
 	atomic.AddInt32(&node.value.refCount, 1)
 	return &mapNode{
 		key:      node.key,
 		value:    node.value,
 		weight:   node.weight,
 		refCount: 1,
 	}
 }

 func (node *mapNode) incref() *mapNode {
 	if node != nil {
 		atomic.AddInt32(&node.refCount, 1)
 	}
 	return node
 }

 func (node *mapNode) decref() {
 	if node == nil {
 		return
 	}
 	if atomic.AddInt32(&node.refCount, -1) == 0 {
 		if atomic.AddInt32(&node.value.refCount, -1) == 0 {
 			if node.value.release != nil {
 				node.value.release(node.key, node.value.value)
 			}
 			node.value.value = nil
 			node.value.release = nil
 		}
 		node.left.decref()
 		node.right.decref()
 	}
 }

 // NewMap returns a new map whose keys are ordered by the given comparison
 // function (a strict weak order). It is the responsibility of the caller to
 // Destroy it at later time.
 func NewMap(less func(a, b interface{}) bool) *Map {
 	return &Map{
 		less: less,
 	}
 }

 // Clone returns a copy of the given map. It is a responsibility of the caller
 // to Destroy it at later time.
 func (pm *Map) Clone() *Map {
 	return &Map{
 		less: pm.less,
 		root: pm.root.incref(),
 	}
 }

 // Destroy destroys the map.
 //
 // After Destroy, the Map should not be used again.
 func (pm *Map) Destroy() {
 	// The implementation of these two functions is the same,
 	// but their intent is different.
 	pm.Clear()
 }

 // Clear removes all entries from the map.
 func (pm *Map) Clear() {
 	pm.root.decref()
 	pm.root = nil
 }

 // Range calls f sequentially in ascending key order for all entries in the map.
 func (pm *Map) Range(f func(key, value interface{})) {
 	pm.root.forEach(f)
 }

 func (node *mapNode) forEach(f func(key, value interface{})) {
 	if node == nil {
 		return
 	}
 	node.left.forEach(f)
 	f(node.key, node.value.value)
 	node.right.forEach(f)
 }

 // Get returns the map value associated with the specified key, or nil if no entry
 // is present. The ok result indicates whether an entry was found in the map.
 func (pm *Map) Get(key interface{}) (interface{}, bool) {
 	node := pm.root
 	for node != nil {
 		if pm.less(key, node.key) {
 			node = node.left
 		} else if pm.less(node.key, key) {
 			node = node.right
 		} else {
 			return node.value.value, true
 		}
 	}
 	return nil, false
 }

 // SetAll updates the map with key/value pairs from the other map, overwriting existing keys.
 // It is equivalent to calling Set for each entry in the other map but is more efficient.
 // Both maps must have the same comparison function, otherwise behavior is undefined.
 func (pm *Map) SetAll(other *Map) {
 	root := pm.root
 	pm.root = union(root, other.root, pm.less, true)
 	root.decref()
 }

 // Set updates the value associated with the specified key.
 // If release is non-nil, it will be called with entry's key and value once the
 // key is no longer contained in the map or any clone.
 func (pm *Map) Set(key, value interface{}, release func(key, value interface{})) {
 	first := pm.root
 	second := newNodeWithRef(key, value, release)
 	pm.root = union(first, second, pm.less, true)
 	first.decref()
 	second.decref()
 }

 // union returns a new tree which is a union of first and second one.
 // If overwrite is set to true, second one would override a value for any duplicate keys.
 //
 // union(first:-0, second:-0) (result:+1)
 // Union borrows both subtrees without affecting their refcount and returns a
 // new reference that the caller is expected to call decref.
 func union(first, second *mapNode, less func(a, b interface{}) bool, overwrite bool) *mapNode {
 	if first == nil {
 		return second.incref()
 	}
 	if second == nil {
 		return first.incref()
 	}

 	if first.weight < second.weight {
 		second, first, overwrite = first, second, !overwrite
 	}

 	left, mid, right := split(second, first.key, less, false)
 	var result *mapNode
 	if overwrite && mid != nil {
 		result = mid.shallowCloneWithRef()
 	} else {
 		result = first.shallowCloneWithRef()
 	}
 	result.weight = first.weight
 	result.left = union(first.left, left, less, overwrite)
 	result.right = union(first.right, right, less, overwrite)
 	left.decref()
 	mid.decref()
 	right.decref()
 	return result
 }

 // split the tree midway by the key into three different ones.
 // Return three new trees: left with all nodes with smaller than key, mid with
 // the node matching the key, right with all nodes larger than key.
 // If there are no nodes in one of trees, return nil instead of it.
 // If requireMid is set (such as during deletion), then all return arguments
 // are nil if mid is not found.
 //
 // split(n:-0) (left:+1, mid:+1, right:+1)
 // Split borrows n without affecting its refcount, and returns three
 // new references that that caller is expected to call decref.
 func split(n *mapNode, key interface{}, less func(a, b interface{}) bool, requireMid bool) (left, mid, right *mapNode) {
 	if n == nil {
 		return nil, nil, nil
 	}

 	if less(n.key, key) {
 		left, mid, right := split(n.right, key, less, requireMid)
 		if requireMid && mid == nil {
 			return nil, nil, nil
 		}
 		newN := n.shallowCloneWithRef()
 		newN.left = n.left.incref()
 		newN.right = left
 		return newN, mid, right
 	} else if less(key, n.key) {
 		left, mid, right := split(n.left, key, less, requireMid)
 		if requireMid && mid == nil {
 			return nil, nil, nil
 		}
 		newN := n.shallowCloneWithRef()
 		newN.left = right
 		newN.right = n.right.incref()
 		return left, mid, newN
 	}
 	mid = n.shallowCloneWithRef()
 	return n.left.incref(), mid, n.right.incref()
 }

 // Delete deletes the value for a key.
 func (pm *Map) Delete(key interface{}) {
 	root := pm.root
 	left, mid, right := split(root, key, pm.less, true)
 	if mid == nil {
 		return
 	}
 	pm.root = merge(left, right)
 	left.decref()
 	mid.decref()
 	right.decref()
 	root.decref()
 }

 // merge two trees while preserving the weight invariant.
 // All nodes in left must have smaller keys than any node in right.
 //
 // merge(left:-0, right:-0) (result:+1)
 // Merge borrows its arguments without affecting their refcount
 // and returns a new reference that the caller is expected to call decref.
 func merge(left, right *mapNode) *mapNode {
 	switch {
 	case left == nil:
 		return right.incref()
 	case right == nil:
 		return left.incref()
 	case left.weight > right.weight:
 		root := left.shallowCloneWithRef()
 		root.left = left.left.incref()
 		root.right = merge(left.right, right)
 		return root
 	default:
 		root := right.shallowCloneWithRef()
 		root.left = merge(left, right.left)
 		root.right = right.right.incref()
 		return root
 	}
 }
	// Copyright 2022 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// The persistent package defines various persistent data structures;
	// that is, data structures that can be efficiently copied and modified
	// in sublinear time.
	package persistent

	import (
	"math/rand"
	"sync/atomic"
	)

	// Implementation details:
	// * Each value is reference counted by nodes which hold it.
	// * Each node is reference counted by its parent nodes.
	// * Each map is considered a top-level parent node from reference counting perspective.
	// * Each change does always effectivelly produce a new top level node.
	//
	// Functions which operate directly with nodes do have a notation in form of
	// `foo(arg1:+n1, arg2:+n2) (ret1:+n3)`.
	// Each argument is followed by a delta change to its reference counter.
	// In case if no change is expected, the delta will be `-0`.

	// Map is an associative mapping from keys to values, both represented as
	// interface{}. Key comparison and iteration order is defined by a
	// client-provided function that implements a strict weak order.
	//
	// Maps can be Cloned in constant time.
	// Get, Store, and Delete operations are done on average in logarithmic time.
	// Maps can be Updated in O(m log(n/m)) time for maps of size n and m, where m < n.
	//
	// Values are reference counted, and a client-supplied release function
	// is called when a value is no longer referenced by a map or any clone.
	//
	// Internally the implementation is based on a randomized persistent treap:
	// https://en.wikipedia.org/wiki/Treap.
	type Map struct {
	less func(a, b interface{}) bool
	root *mapNode
	}

	type mapNode struct {
	key interface{}
	value *refValue
	weight uint64
	refCount int32
	left, right *mapNode
	}

	type refValue struct {
	refCount int32
	value interface{}
	release func(key, value interface{})
	}

	func newNodeWithRef(key, value interface{}, release func(key, value interface{})) *mapNode {
	return &mapNode{
	key: key,
	value: &refValue{
	value: value,
	release: release,
	refCount: 1,
	},
	refCount: 1,
	weight: rand.Uint64(),
	}
	}

	func (node mapNode) shallowCloneWithRef() mapNode {
	atomic.AddInt32(&node.value.refCount, 1)
	return &mapNode{
	key: node.key,
	value: node.value,
	weight: node.weight,
	refCount: 1,
	}
	}

	func (node mapNode) incref() mapNode {
	if node != nil {
	atomic.AddInt32(&node.refCount, 1)
	}
	return node
	}

	func (node *mapNode) decref() {
	if node == nil {
	return
	}
	if atomic.AddInt32(&node.refCount, -1) == 0 {
	if atomic.AddInt32(&node.value.refCount, -1) == 0 {
	if node.value.release != nil {
	node.value.release(node.key, node.value.value)
	}
	node.value.value = nil
	node.value.release = nil
	}
	node.left.decref()
	node.right.decref()
	}
	}

	// NewMap returns a new map whose keys are ordered by the given comparison
	// function (a strict weak order). It is the responsibility of the caller to
	// Destroy it at later time.
	func NewMap(less func(a, b interface{}) bool) *Map {
	return &Map{
	less: less,
	}
	}

	// Clone returns a copy of the given map. It is a responsibility of the caller
	// to Destroy it at later time.
	func (pm Map) Clone() Map {
	return &Map{
	less: pm.less,
	root: pm.root.incref(),
	}
	}

	// Destroy destroys the map.
	//
	// After Destroy, the Map should not be used again.
	func (pm *Map) Destroy() {
	// The implementation of these two functions is the same,
	// but their intent is different.
	pm.Clear()
	}

	// Clear removes all entries from the map.
	func (pm *Map) Clear() {
	pm.root.decref()
	pm.root = nil
	}

	// Range calls f sequentially in ascending key order for all entries in the map.
	func (pm *Map) Range(f func(key, value interface{})) {
	pm.root.forEach(f)
	}

	func (node *mapNode) forEach(f func(key, value interface{})) {
	if node == nil {
	return
	}
	node.left.forEach(f)
	f(node.key, node.value.value)
	node.right.forEach(f)
	}

	// Get returns the map value associated with the specified key, or nil if no entry
	// is present. The ok result indicates whether an entry was found in the map.
	func (pm *Map) Get(key interface{}) (interface{}, bool) {
	node := pm.root
	for node != nil {
	if pm.less(key, node.key) {
	node = node.left
	} else if pm.less(node.key, key) {
	node = node.right
	} else {
	return node.value.value, true
	}
	}
	return nil, false
	}

	// SetAll updates the map with key/value pairs from the other map, overwriting existing keys.
	// It is equivalent to calling Set for each entry in the other map but is more efficient.
	// Both maps must have the same comparison function, otherwise behavior is undefined.
	func (pm Map) SetAll(other Map) {
	root := pm.root
	pm.root = union(root, other.root, pm.less, true)
	root.decref()
	}

	// Set updates the value associated with the specified key.
	// If release is non-nil, it will be called with entry's key and value once the
	// key is no longer contained in the map or any clone.
	func (pm *Map) Set(key, value interface{}, release func(key, value interface{})) {
	first := pm.root
	second := newNodeWithRef(key, value, release)
	pm.root = union(first, second, pm.less, true)
	first.decref()
	second.decref()
	}

	// union returns a new tree which is a union of first and second one.
	// If overwrite is set to true, second one would override a value for any duplicate keys.
	//
	// union(first:-0, second:-0) (result:+1)
	// Union borrows both subtrees without affecting their refcount and returns a
	// new reference that the caller is expected to call decref.
	func union(first, second mapNode, less func(a, b interface{}) bool, overwrite bool) mapNode {
	if first == nil {
	return second.incref()
	}
	if second == nil {
	return first.incref()
	}

	if first.weight < second.weight {
	second, first, overwrite = first, second, !overwrite
	}

	left, mid, right := split(second, first.key, less, false)
	var result *mapNode
	if overwrite && mid != nil {
	result = mid.shallowCloneWithRef()
	} else {
	result = first.shallowCloneWithRef()
	}
	result.weight = first.weight
	result.left = union(first.left, left, less, overwrite)
	result.right = union(first.right, right, less, overwrite)
	left.decref()
	mid.decref()
	right.decref()
	return result
	}

	// split the tree midway by the key into three different ones.
	// Return three new trees: left with all nodes with smaller than key, mid with
	// the node matching the key, right with all nodes larger than key.
	// If there are no nodes in one of trees, return nil instead of it.
	// If requireMid is set (such as during deletion), then all return arguments
	// are nil if mid is not found.
	//
	// split(n:-0) (left:+1, mid:+1, right:+1)
	// Split borrows n without affecting its refcount, and returns three
	// new references that that caller is expected to call decref.
	func split(n mapNode, key interface{}, less func(a, b interface{}) bool, requireMid bool) (left, mid, right mapNode) {
	if n == nil {
	return nil, nil, nil
	}

	if less(n.key, key) {
	left, mid, right := split(n.right, key, less, requireMid)
	if requireMid && mid == nil {
	return nil, nil, nil
	}
	newN := n.shallowCloneWithRef()
	newN.left = n.left.incref()
	newN.right = left
	return newN, mid, right
	} else if less(key, n.key) {
	left, mid, right := split(n.left, key, less, requireMid)
	if requireMid && mid == nil {
	return nil, nil, nil
	}
	newN := n.shallowCloneWithRef()
	newN.left = right
	newN.right = n.right.incref()
	return left, mid, newN
	}
	mid = n.shallowCloneWithRef()
	return n.left.incref(), mid, n.right.incref()
	}

	// Delete deletes the value for a key.
	func (pm *Map) Delete(key interface{}) {
	root := pm.root
	left, mid, right := split(root, key, pm.less, true)
	if mid == nil {
	return
	}
	pm.root = merge(left, right)
	left.decref()
	mid.decref()
	right.decref()
	root.decref()
	}

	// merge two trees while preserving the weight invariant.
	// All nodes in left must have smaller keys than any node in right.
	//
	// merge(left:-0, right:-0) (result:+1)
	// Merge borrows its arguments without affecting their refcount
	// and returns a new reference that the caller is expected to call decref.
	func merge(left, right mapNode) mapNode {
	switch {
	case left == nil:
	return right.incref()
	case right == nil:
	return left.incref()
	case left.weight > right.weight:
	root := left.shallowCloneWithRef()
	root.left = left.left.incref()
	root.right = merge(left.right, right)
	return root
	default:
	root := right.shallowCloneWithRef()
	root.left = merge(left, right.left)
	root.right = right.right.incref()
	return root
	}
	}