| 1 | package sumdb |
| 2 | |
| 3 | import "sync" |
| 4 | |
| 5 | // lruCache is a simple fixed-size LRU cache safe for concurrent use. |
| 6 | // Keys are int64 (record/hash IDs), values are []byte. |
| 7 | type lruCache struct { |
| 8 | mu sync.Mutex |
| 9 | cap int |
| 10 | items map[int64]*lruEntry |
| 11 | head *lruEntry // most recent |
| 12 | tail *lruEntry // least recent |
| 13 | } |
| 14 | |
| 15 | type lruEntry struct { |
| 16 | key int64 |
| 17 | value []byte |
| 18 | prev, next *lruEntry |
| 19 | } |
| 20 | |
| 21 | func newLRUCache(cap int) *lruCache { |
| 22 | return &lruCache{ |
| 23 | cap: cap, |
| 24 | items: make(map[int64]*lruEntry, cap), |
| 25 | } |
| 26 | } |
| 27 | |
| 28 | func (c *lruCache) get(key int64) ([]byte, bool) { |
| 29 | c.mu.Lock() |
| 30 | defer c.mu.Unlock() |
| 31 | |
| 32 | e, ok := c.items[key] |
| 33 | if !ok { |
| 34 | return nil, false |
| 35 | } |
| 36 | c.moveToFront(e) |
| 37 | return e.value, true |
| 38 | } |
| 39 | |
| 40 | func (c *lruCache) put(key int64, value []byte) { |
| 41 | c.mu.Lock() |
| 42 | defer c.mu.Unlock() |
| 43 | |
| 44 | if e, ok := c.items[key]; ok { |
| 45 | e.value = value |
| 46 | c.moveToFront(e) |
| 47 | return |
| 48 | } |
| 49 | |
| 50 | e := &lruEntry{key: key, value: value} |
| 51 | c.items[key] = e |
| 52 | c.pushFront(e) |
| 53 | |
| 54 | if len(c.items) > c.cap { |
| 55 | c.removeTail() |
| 56 | } |
| 57 | } |
| 58 | |
| 59 | func (c *lruCache) moveToFront(e *lruEntry) { |
| 60 | if c.head == e { |
| 61 | return |
| 62 | } |
| 63 | c.remove(e) |
| 64 | c.pushFront(e) |
| 65 | } |
| 66 | |
| 67 | func (c *lruCache) pushFront(e *lruEntry) { |
| 68 | e.prev = nil |
| 69 | e.next = c.head |
| 70 | if c.head != nil { |
| 71 | c.head.prev = e |
| 72 | } |
| 73 | c.head = e |
| 74 | if c.tail == nil { |
| 75 | c.tail = e |
| 76 | } |
| 77 | } |
| 78 | |
| 79 | func (c *lruCache) remove(e *lruEntry) { |
| 80 | if e.prev != nil { |
| 81 | e.prev.next = e.next |
| 82 | } else { |
| 83 | c.head = e.next |
| 84 | } |
| 85 | if e.next != nil { |
| 86 | e.next.prev = e.prev |
| 87 | } else { |
| 88 | c.tail = e.prev |
| 89 | } |
| 90 | } |
| 91 | |
| 92 | func (c *lruCache) removeTail() { |
| 93 | if c.tail == nil { |
| 94 | return |
| 95 | } |
| 96 | e := c.tail |
| 97 | c.remove(e) |
| 98 | delete(c.items, e.key) |
| 99 | } |
| 100 | |