lru.go
| 1 | package service |
| 2 | |
| 3 | import ( |
| 4 | "container/list" |
| 5 | "sync" |
| 6 | ) |
| 7 | |
| 8 | // lru is a fixed-size map keyed by path, dropping the least recently used entry |
| 9 | // when it is full. |
| 10 | // |
| 11 | // Only use it for values that are safe to lose: an eviction means the work is |
| 12 | // redone, never that correctness changes. |
| 13 | type lru[V any] struct { |
| 14 | mu sync.Mutex |
| 15 | maxSize int |
| 16 | order *list.List // front is most recently used |
| 17 | entries map[string]*list.Element |
| 18 | } |
| 19 | |
| 20 | type lruEntry[V any] struct { |
| 21 | key string |
| 22 | val V |
| 23 | } |
| 24 | |
| 25 | func newLRU[V any](maxSize int) *lru[V] { |
| 26 | // A size below 1 would evict each entry as it is stored, turning the cache |
| 27 | // into a silent miss on every lookup. |
| 28 | return &lru[V]{ |
| 29 | maxSize: max(maxSize, 1), |
| 30 | order: list.New(), |
| 31 | entries: make(map[string]*list.Element), |
| 32 | } |
| 33 | } |
| 34 | |
| 35 | func (c *lru[V]) Get(key string) (V, bool) { |
| 36 | c.mu.Lock() |
| 37 | defer c.mu.Unlock() |
| 38 | |
| 39 | el, ok := c.entries[key] |
| 40 | if !ok { |
| 41 | var zero V |
| 42 | return zero, false |
| 43 | } |
| 44 | c.order.MoveToFront(el) |
| 45 | return el.Value.(*lruEntry[V]).val, true |
| 46 | } |
| 47 | |
| 48 | func (c *lru[V]) Put(key string, val V) { |
| 49 | c.mu.Lock() |
| 50 | defer c.mu.Unlock() |
| 51 | |
| 52 | if el, ok := c.entries[key]; ok { |
| 53 | el.Value.(*lruEntry[V]).val = val |
| 54 | c.order.MoveToFront(el) |
| 55 | return |
| 56 | } |
| 57 | |
| 58 | c.entries[key] = c.order.PushFront(&lruEntry[V]{key: key, val: val}) |
| 59 | |
| 60 | if c.order.Len() > c.maxSize { |
| 61 | oldest := c.order.Back() |
| 62 | c.order.Remove(oldest) |
| 63 | delete(c.entries, oldest.Value.(*lruEntry[V]).key) |
| 64 | } |
| 65 | } |
| 66 | |
| 67 | func (c *lru[V]) Delete(key string) { |
| 68 | c.mu.Lock() |
| 69 | defer c.mu.Unlock() |
| 70 | |
| 71 | if el, ok := c.entries[key]; ok { |
| 72 | c.order.Remove(el) |
| 73 | delete(c.entries, key) |
| 74 | } |
| 75 | } |
| 76 |