woodpecker/vendor/github.com/koding/cache/lru_nots.go

123 lines
2.9 KiB
Go
Raw Normal View History

package cache
import (
"container/list"
)
// LRUNoTS Discards the least recently used items first. This algorithm
// requires keeping track of what was used when.
type LRUNoTS struct {
// list holds all items in a linked list, for finding the `tail` of the list
list *list.List
// cache holds the all cache values
cache Cache
// size holds the limit of the LRU cache
size int
}
// kv is an helper struct for keeping track of the key for the list item. Only
// place where we need the key of a value is while removing the last item from
// linked list, for other cases, all operations alread have the key
type kv struct {
k string
v interface{}
}
// NewLRUNoTS creates a new LRU cache struct for further cache operations. Size
// is used for limiting the upper bound of the cache
func NewLRUNoTS(size int) Cache {
if size < 1 {
panic("invalid cache size")
}
return &LRUNoTS{
list: list.New(),
cache: NewMemoryNoTS(),
size: size,
}
}
// Get returns the value of a given key if it exists, every get item will be
// moved to the head of the linked list for keeping track of least recent used
// item
func (l *LRUNoTS) Get(key string) (interface{}, error) {
res, err := l.cache.Get(key)
if err != nil {
return nil, err
}
elem := res.(*list.Element)
// move found item to the head
l.list.MoveToFront(elem)
return elem.Value.(*kv).v, nil
}
// Set sets or overrides the given key with the given value, every set item will
// be moved or prepended to the head of the linked list for keeping track of
// least recent used item. When the cache is full, last item of the linked list
// will be evicted from the cache
func (l *LRUNoTS) Set(key string, val interface{}) error {
// try to get item
res, err := l.cache.Get(key)
if err != nil && err != ErrNotFound {
return err
}
var elem *list.Element
// if elem is not in the cache, push it to front of the list
if err == ErrNotFound {
elem = l.list.PushFront(&kv{k: key, v: val})
} else {
// if elem is in the cache, update the data and move it the front
elem = res.(*list.Element)
// update the data
elem.Value.(*kv).v = val
// item already exists, so move it to the front of the list
l.list.MoveToFront(elem)
}
// in any case, set the item to the cache
err = l.cache.Set(key, elem)
if err != nil {
return err
}
// if the cache is full, evict last entry
if l.list.Len() > l.size {
// remove last element from cache
return l.removeElem(l.list.Back())
}
return nil
}
// Delete deletes the given key-value pair from cache, this function doesnt
// return an error if item is not in the cache
func (l *LRUNoTS) Delete(key string) error {
res, err := l.cache.Get(key)
if err != nil && err != ErrNotFound {
return err
}
// item already deleted
if err == ErrNotFound {
// surpress not found errors
return nil
}
elem := res.(*list.Element)
return l.removeElem(elem)
}
func (l *LRUNoTS) removeElem(e *list.Element) error {
l.list.Remove(e)
return l.cache.Delete(e.Value.(*kv).k)
}