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143 lines
3.8 KiB
Go
143 lines
3.8 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE_list file.
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package internal
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import "time"
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// Entry is an LRU Entry
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type Entry[K comparable, V any] struct {
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// Next and previous pointers in the doubly-linked list of elements.
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// To simplify the implementation, internally a list l is implemented
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// as a ring, such that &l.root is both the next element of the last
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// list element (l.Back()) and the previous element of the first list
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// element (l.Front()).
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next, prev *Entry[K, V]
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// The list to which this element belongs.
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list *LruList[K, V]
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// The LRU Key of this element.
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Key K
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// The Value stored with this element.
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Value V
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// The time this element would be cleaned up, optional
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ExpiresAt time.Time
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// The expiry bucket item was put in, optional
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ExpireBucket uint8
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}
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// PrevEntry returns the previous list element or nil.
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func (e *Entry[K, V]) PrevEntry() *Entry[K, V] {
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if p := e.prev; e.list != nil && p != &e.list.root {
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return p
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}
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return nil
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}
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// LruList represents a doubly linked list.
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// The zero Value for LruList is an empty list ready to use.
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type LruList[K comparable, V any] struct {
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root Entry[K, V] // sentinel list element, only &root, root.prev, and root.next are used
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len int // current list Length excluding (this) sentinel element
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}
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// Init initializes or clears list l.
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func (l *LruList[K, V]) Init() *LruList[K, V] {
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l.root.next = &l.root
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l.root.prev = &l.root
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l.len = 0
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return l
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}
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// NewList returns an initialized list.
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func NewList[K comparable, V any]() *LruList[K, V] { return new(LruList[K, V]).Init() }
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// Length returns the number of elements of list l.
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// The complexity is O(1).
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func (l *LruList[K, V]) Length() int { return l.len }
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// Back returns the last element of list l or nil if the list is empty.
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func (l *LruList[K, V]) Back() *Entry[K, V] {
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if l.len == 0 {
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return nil
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}
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return l.root.prev
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}
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// lazyInit lazily initializes a zero List Value.
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func (l *LruList[K, V]) lazyInit() {
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if l.root.next == nil {
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l.Init()
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}
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}
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// insert inserts e after at, increments l.len, and returns e.
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func (l *LruList[K, V]) insert(e, at *Entry[K, V]) *Entry[K, V] {
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e.prev = at
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e.next = at.next
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e.prev.next = e
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e.next.prev = e
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e.list = l
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l.len++
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return e
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}
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// insertValue is a convenience wrapper for insert(&Entry{Value: v, ExpiresAt: ExpiresAt}, at).
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func (l *LruList[K, V]) insertValue(k K, v V, expiresAt time.Time, at *Entry[K, V]) *Entry[K, V] {
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return l.insert(&Entry[K, V]{Value: v, Key: k, ExpiresAt: expiresAt}, at)
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}
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// Remove removes e from its list, decrements l.len
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func (l *LruList[K, V]) Remove(e *Entry[K, V]) V {
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e.prev.next = e.next
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e.next.prev = e.prev
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e.next = nil // avoid memory leaks
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e.prev = nil // avoid memory leaks
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e.list = nil
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l.len--
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return e.Value
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}
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// move moves e to next to at.
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func (l *LruList[K, V]) move(e, at *Entry[K, V]) {
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if e == at {
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return
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}
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e.prev.next = e.next
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e.next.prev = e.prev
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e.prev = at
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e.next = at.next
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e.prev.next = e
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e.next.prev = e
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}
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// PushFront inserts a new element e with value v at the front of list l and returns e.
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func (l *LruList[K, V]) PushFront(k K, v V) *Entry[K, V] {
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l.lazyInit()
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return l.insertValue(k, v, time.Time{}, &l.root)
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}
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// PushFrontExpirable inserts a new expirable element e with Value v at the front of list l and returns e.
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func (l *LruList[K, V]) PushFrontExpirable(k K, v V, expiresAt time.Time) *Entry[K, V] {
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l.lazyInit()
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return l.insertValue(k, v, expiresAt, &l.root)
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}
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// MoveToFront moves element e to the front of list l.
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// If e is not an element of l, the list is not modified.
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// The element must not be nil.
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func (l *LruList[K, V]) MoveToFront(e *Entry[K, V]) {
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if e.list != l || l.root.next == e {
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return
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}
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// see comment in List.Remove about initialization of l
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l.move(e, &l.root)
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}
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