package d2common import ( "errors" "log" "sync" ) type cacheNode struct { next *cacheNode prev *cacheNode key string value interface{} weight int } type Cache struct { head *cacheNode tail *cacheNode lookup map[string]*cacheNode weight int budget int verbose bool mutex sync.Mutex } func CreateCache(budget int) *Cache { return &Cache{lookup: make(map[string]*cacheNode), budget: budget} } func (c *Cache) SetVerbose(verbose bool) { c.verbose = verbose } func (c *Cache) GetWeight() int { return c.weight } func (c *Cache) GetBudget() int { return c.budget } func (c *Cache) Insert(key string, value interface{}, weight int) error { c.mutex.Lock() defer c.mutex.Unlock() if _, found := c.lookup[key]; found { return errors.New("key already exists in Cache") } node := &cacheNode{ key: key, value: value, weight: weight, next: c.head, } if c.head != nil { c.head.prev = node } c.head = node if c.tail == nil { c.tail = node } c.lookup[key] = node c.weight += node.weight for ; c.tail != nil && c.tail != c.head && c.weight > c.budget; c.tail = c.tail.prev { c.weight -= c.tail.weight c.tail.prev.next = nil if c.verbose { log.Printf( "warning -- Cache is evicting %s (%d) for %s (%d); spare weight is now %d", c.tail.key, c.tail.weight, key, weight, c.budget-c.weight, ) } delete(c.lookup, c.tail.key) } return nil } func (c *Cache) Retrieve(key string) (interface{}, bool) { c.mutex.Lock() defer c.mutex.Unlock() node, found := c.lookup[key] if !found { return nil, false } if node != c.head { if node.next != nil { node.next.prev = node.prev } if node.prev != nil { node.prev.next = node.next } if node == c.tail { c.tail = c.tail.prev } node.next = c.head node.prev = nil if c.head != nil { c.head.prev = node } c.head = node } return node.value, true } func (c *Cache) Clear() { c.mutex.Lock() defer c.mutex.Unlock() c.head = nil c.tail = nil c.lookup = make(map[string]*cacheNode) c.weight = 0 }