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| 1 | +// Copyright 2022 The go-ethereum Authors |
| 2 | +// (original work) |
| 3 | +// Copyright 2024 The Erigon Authors |
| 4 | +// (modifications) |
| 5 | +// This file is part of Erigon. |
| 6 | +// |
| 7 | +// Erigon is free software: you can redistribute it and/or modify |
| 8 | +// it under the terms of the GNU Lesser General Public License as published by |
| 9 | +// the Free Software Foundation, either version 3 of the License, or |
| 10 | +// (at your option) any later version. |
| 11 | +// |
| 12 | +// Erigon is distributed in the hope that it will be useful, |
| 13 | +// but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 14 | +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 15 | +// GNU Lesser General Public License for more details. |
| 16 | +// |
| 17 | +// You should have received a copy of the GNU Lesser General Public License |
| 18 | +// along with Erigon. If not, see <http://www.gnu.org/licenses/>. |
| 19 | + |
| 20 | +// Package lru implements generically-typed LRU caches. |
| 21 | +package lru |
| 22 | + |
| 23 | +// BasicLRU is a simple LRU cache. |
| 24 | +// |
| 25 | +// This type is not safe for concurrent use. |
| 26 | +// The zero value is not valid, instances must be created using NewCache. |
| 27 | +type BasicLRU[K comparable, V any] struct { |
| 28 | + list *list[K] |
| 29 | + items map[K]cacheItem[K, V] |
| 30 | + cap int |
| 31 | +} |
| 32 | + |
| 33 | +type cacheItem[K any, V any] struct { |
| 34 | + elem *listElem[K] |
| 35 | + value V |
| 36 | +} |
| 37 | + |
| 38 | +// NewBasicLRU creates a new LRU cache. |
| 39 | +func NewBasicLRU[K comparable, V any](capacity int) BasicLRU[K, V] { |
| 40 | + if capacity <= 0 { |
| 41 | + capacity = 1 |
| 42 | + } |
| 43 | + c := BasicLRU[K, V]{ |
| 44 | + items: make(map[K]cacheItem[K, V]), |
| 45 | + list: newList[K](), |
| 46 | + cap: capacity, |
| 47 | + } |
| 48 | + return c |
| 49 | +} |
| 50 | + |
| 51 | +// Add adds a value to the cache. Returns true if an item was evicted to store the new item. |
| 52 | +func (c *BasicLRU[K, V]) Add(key K, value V) (evicted bool) { |
| 53 | + _, _, evicted = c.Add3(key, value) |
| 54 | + return evicted |
| 55 | +} |
| 56 | + |
| 57 | +// Add3 adds a value to the cache. If an item was evicted to store the new one, it returns the evicted item. |
| 58 | +func (c *BasicLRU[K, V]) Add3(key K, value V) (ek K, ev V, evicted bool) { |
| 59 | + item, ok := c.items[key] |
| 60 | + if ok { |
| 61 | + item.value = value |
| 62 | + c.items[key] = item |
| 63 | + c.list.moveToFront(item.elem) |
| 64 | + return ek, ev, false |
| 65 | + } |
| 66 | + |
| 67 | + var elem *listElem[K] |
| 68 | + if c.Len() >= c.cap { |
| 69 | + elem = c.list.removeLast() |
| 70 | + evicted = true |
| 71 | + ek = elem.v |
| 72 | + ev = c.items[ek].value |
| 73 | + delete(c.items, ek) |
| 74 | + } else { |
| 75 | + elem = new(listElem[K]) |
| 76 | + } |
| 77 | + |
| 78 | + // Store the new item. |
| 79 | + // Note that if another item was evicted, we re-use its list element here. |
| 80 | + elem.v = key |
| 81 | + c.items[key] = cacheItem[K, V]{elem, value} |
| 82 | + c.list.pushElem(elem) |
| 83 | + return ek, ev, evicted |
| 84 | +} |
| 85 | + |
| 86 | +// Contains reports whether the given key exists in the cache. |
| 87 | +func (c *BasicLRU[K, V]) Contains(key K) bool { |
| 88 | + _, ok := c.items[key] |
| 89 | + return ok |
| 90 | +} |
| 91 | + |
| 92 | +// Get retrieves a value from the cache. This marks the key as recently used. |
| 93 | +func (c *BasicLRU[K, V]) Get(key K) (value V, ok bool) { |
| 94 | + item, ok := c.items[key] |
| 95 | + if !ok { |
| 96 | + return value, false |
| 97 | + } |
| 98 | + c.list.moveToFront(item.elem) |
| 99 | + return item.value, true |
| 100 | +} |
| 101 | + |
| 102 | +// GetOldest retrieves the least-recently-used item. |
| 103 | +// Note that this does not update the item's recency. |
| 104 | +func (c *BasicLRU[K, V]) GetOldest() (key K, value V, ok bool) { |
| 105 | + lastElem := c.list.last() |
| 106 | + if lastElem == nil { |
| 107 | + return key, value, false |
| 108 | + } |
| 109 | + key = lastElem.v |
| 110 | + item := c.items[key] |
| 111 | + return key, item.value, true |
| 112 | +} |
| 113 | + |
| 114 | +// Len returns the current number of items in the cache. |
| 115 | +func (c *BasicLRU[K, V]) Len() int { |
| 116 | + return len(c.items) |
| 117 | +} |
| 118 | + |
| 119 | +// Peek retrieves a value from the cache, but does not mark the key as recently used. |
| 120 | +func (c *BasicLRU[K, V]) Peek(key K) (value V, ok bool) { |
| 121 | + item, ok := c.items[key] |
| 122 | + return item.value, ok |
| 123 | +} |
| 124 | + |
| 125 | +// Purge empties the cache. |
| 126 | +func (c *BasicLRU[K, V]) Purge() { |
| 127 | + c.list.init() |
| 128 | + clear(c.items) |
| 129 | +} |
| 130 | + |
| 131 | +// Remove drops an item from the cache. Returns true if the key was present in cache. |
| 132 | +func (c *BasicLRU[K, V]) Remove(key K) bool { |
| 133 | + item, ok := c.items[key] |
| 134 | + if ok { |
| 135 | + delete(c.items, key) |
| 136 | + c.list.remove(item.elem) |
| 137 | + } |
| 138 | + return ok |
| 139 | +} |
| 140 | + |
| 141 | +// RemoveOldest drops the least recently used item. |
| 142 | +func (c *BasicLRU[K, V]) RemoveOldest() (key K, value V, ok bool) { |
| 143 | + lastElem := c.list.last() |
| 144 | + if lastElem == nil { |
| 145 | + return key, value, false |
| 146 | + } |
| 147 | + |
| 148 | + key = lastElem.v |
| 149 | + item := c.items[key] |
| 150 | + delete(c.items, key) |
| 151 | + c.list.remove(lastElem) |
| 152 | + return key, item.value, true |
| 153 | +} |
| 154 | + |
| 155 | +// Keys returns all keys in the cache. |
| 156 | +func (c *BasicLRU[K, V]) Keys() []K { |
| 157 | + keys := make([]K, 0, len(c.items)) |
| 158 | + return c.list.appendTo(keys) |
| 159 | +} |
| 160 | + |
| 161 | +// list is a doubly-linked list holding items of type he. |
| 162 | +// The zero value is not valid, use newList to create lists. |
| 163 | +type list[T any] struct { |
| 164 | + root listElem[T] |
| 165 | +} |
| 166 | + |
| 167 | +type listElem[T any] struct { |
| 168 | + next *listElem[T] |
| 169 | + prev *listElem[T] |
| 170 | + v T |
| 171 | +} |
| 172 | + |
| 173 | +func newList[T any]() *list[T] { |
| 174 | + l := new(list[T]) |
| 175 | + l.init() |
| 176 | + return l |
| 177 | +} |
| 178 | + |
| 179 | +// init reinitializes the list, making it empty. |
| 180 | +func (l *list[T]) init() { |
| 181 | + l.root.next = &l.root |
| 182 | + l.root.prev = &l.root |
| 183 | +} |
| 184 | + |
| 185 | +// pushElem adds an element to the front of the list. |
| 186 | +func (l *list[T]) pushElem(e *listElem[T]) { |
| 187 | + e.prev = &l.root |
| 188 | + e.next = l.root.next |
| 189 | + l.root.next = e |
| 190 | + e.next.prev = e |
| 191 | +} |
| 192 | + |
| 193 | +// moveToFront makes 'node' the head of the list. |
| 194 | +func (l *list[T]) moveToFront(e *listElem[T]) { |
| 195 | + e.prev.next = e.next |
| 196 | + e.next.prev = e.prev |
| 197 | + l.pushElem(e) |
| 198 | +} |
| 199 | + |
| 200 | +// remove removes an element from the list. |
| 201 | +func (l *list[T]) remove(e *listElem[T]) { |
| 202 | + e.prev.next = e.next |
| 203 | + e.next.prev = e.prev |
| 204 | + e.next, e.prev = nil, nil |
| 205 | +} |
| 206 | + |
| 207 | +// removeLast removes the last element of the list. |
| 208 | +func (l *list[T]) removeLast() *listElem[T] { |
| 209 | + last := l.last() |
| 210 | + if last != nil { |
| 211 | + l.remove(last) |
| 212 | + } |
| 213 | + return last |
| 214 | +} |
| 215 | + |
| 216 | +// last returns the last element of the list, or nil if the list is empty. |
| 217 | +func (l *list[T]) last() *listElem[T] { |
| 218 | + e := l.root.prev |
| 219 | + if e == &l.root { |
| 220 | + return nil |
| 221 | + } |
| 222 | + return e |
| 223 | +} |
| 224 | + |
| 225 | +// appendTo appends all list elements to a slice. |
| 226 | +func (l *list[T]) appendTo(slice []T) []T { |
| 227 | + for e := l.root.prev; e != &l.root; e = e.prev { |
| 228 | + slice = append(slice, e.v) |
| 229 | + } |
| 230 | + return slice |
| 231 | +} |
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