134 lines
3 KiB
Go
134 lines
3 KiB
Go
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/*
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Copyright 2013 Google Inc.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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// Package lru implements an LRU cache.
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package lru
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import "container/list"
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// Cache is an LRU cache. It is not safe for concurrent access.
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type Cache struct {
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// MaxEntries is the maximum number of cache entries before
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// an item is evicted. Zero means no limit.
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MaxEntries int
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// OnEvicted optionally specificies a callback function to be
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// executed when an entry is purged from the cache.
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OnEvicted func(key Key, value interface{})
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ll *list.List
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cache map[interface{}]*list.Element
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}
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// A Key may be any value that is comparable. See http://golang.org/ref/spec#Comparison_operators
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type Key interface{}
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type entry struct {
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key Key
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value interface{}
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}
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// New creates a new Cache.
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// If maxEntries is zero, the cache has no limit and it's assumed
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// that eviction is done by the caller.
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func New(maxEntries int) *Cache {
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return &Cache{
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MaxEntries: maxEntries,
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ll: list.New(),
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cache: make(map[interface{}]*list.Element),
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}
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}
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// Add adds a value to the cache.
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func (c *Cache) Add(key Key, value interface{}) {
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if c.cache == nil {
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c.cache = make(map[interface{}]*list.Element)
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c.ll = list.New()
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}
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if ee, ok := c.cache[key]; ok {
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c.ll.MoveToFront(ee)
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ee.Value.(*entry).value = value
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return
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}
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ele := c.ll.PushFront(&entry{key, value})
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c.cache[key] = ele
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if c.MaxEntries != 0 && c.ll.Len() > c.MaxEntries {
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c.RemoveOldest()
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}
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}
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// Get looks up a key's value from the cache.
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func (c *Cache) Get(key Key) (value interface{}, ok bool) {
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if c.cache == nil {
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return
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}
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if ele, hit := c.cache[key]; hit {
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c.ll.MoveToFront(ele)
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return ele.Value.(*entry).value, true
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}
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return
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}
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// Remove removes the provided key from the cache.
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func (c *Cache) Remove(key Key) {
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if c.cache == nil {
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return
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}
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if ele, hit := c.cache[key]; hit {
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c.removeElement(ele)
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}
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}
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// RemoveOldest removes the oldest item from the cache.
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func (c *Cache) RemoveOldest() {
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if c.cache == nil {
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return
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}
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ele := c.ll.Back()
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if ele != nil {
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c.removeElement(ele)
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}
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}
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func (c *Cache) removeElement(e *list.Element) {
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c.ll.Remove(e)
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kv := e.Value.(*entry)
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delete(c.cache, kv.key)
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if c.OnEvicted != nil {
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c.OnEvicted(kv.key, kv.value)
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}
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}
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// Len returns the number of items in the cache.
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func (c *Cache) Len() int {
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if c.cache == nil {
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return 0
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}
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return c.ll.Len()
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}
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// Clear purges all stored items from the cache.
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func (c *Cache) Clear() {
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if c.OnEvicted != nil {
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for _, e := range c.cache {
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kv := e.Value.(*entry)
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c.OnEvicted(kv.key, kv.value)
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}
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}
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c.ll = nil
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c.cache = nil
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}
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