C# 實現Lru緩存

LRU 算法全稱是最近最少使用算法（Least Recently Use），是一種簡單的緩存策略。
通常用在對象池等需要頻繁獲取但是又需要釋放不用的地方。

代碼實現的基本原理就是使用鏈表，當某個元素被訪問時（Get或Set）就將該元素放到鏈表的頭部或者尾部（根據用戶自己定義規則即可）當達到了緩存的最大容量時對最不常使用的元素進行移除（移除的時候可以定義一系列的規則，用于判讀如何移除，是否移除）

下面直接貼出來代碼供大家參考

using System;
using System.Collections;
using System.Collections.Generic;
using System.Threading;namespace ET
{public class LruCache<TKey, TValue>: IEnumerable<KeyValuePair<TKey, TValue>>{private const int DEFAULT_CAPACITY = 255;private int capacity;private ReaderWriterLockSlim locker;private Dictionary<TKey, TValue> dictionary;private LinkedList<TKey> linkedList;private Func<TKey, TValue, bool> checkCanPopFunc;private Action<TKey, TValue> popCb;public LruCache(): this(DEFAULT_CAPACITY){}public LruCache(int capacity){this.locker = new ReaderWriterLockSlim();this.capacity = capacity > 0? capacity : DEFAULT_CAPACITY;this.dictionary = new Dictionary<TKey, TValue>(DEFAULT_CAPACITY);this.linkedList = new LinkedList<TKey>();}/// <summary>/// 設置檢測什么條件可以釋放/// </summary>/// <param name="func"></param>public void SetCheckCanPopCallBack(Func<TKey, TValue, bool> func){this.checkCanPopFunc = func;}/// <summary>/// 設置如何釋放/// </summary>/// <param name="action"></param>public void SetPopCallBack(Action<TKey, TValue> action){this.popCb = action;}public TValue this[TKey t]{get{if (TryGet(t, out TValue val))return val;throw new ArgumentException();}set{Set(t,value);}}public bool TryGet(TKey key, out TValue value){this.locker.EnterUpgradeableReadLock();try{bool b = this.dictionary.TryGetValue(key, out value);if (b){this.locker.EnterWriteLock();try{this.linkedList.Remove(key);this.linkedList.AddFirst(key);}finally{this.locker.ExitWriteLock();}}return b;}finally{this.locker.ExitUpgradeableReadLock();}}public void Set(TKey key, TValue value){this.locker.EnterWriteLock();try{if (this.checkCanPopFunc != null)this.MakeFreeSpace();this.dictionary[key] = value;this.linkedList.Remove(key);this.linkedList.AddFirst(key);//沒有設置檢測釋放條件的話，容量超載了就移除if (this.checkCanPopFunc == null && this.linkedList.Count > this.capacity){this.dictionary.Remove(this.linkedList.Last.Value);this.linkedList.RemoveLast();}}finally{this.locker.ExitWriteLock();}}public Dictionary<TKey, TValue> GetAll(){return this.dictionary;}public void Remove(TKey key){this.locker.EnterWriteLock();try{this.dictionary.Remove(key);this.linkedList.Remove(key);}finally{this.locker.ExitWriteLock();}}public bool TryOnlyGet(TKey key, out TValue value){bool b = this.dictionary.TryGetValue(key, out value);return b;}public bool ContainsKey(TKey key){this.locker.EnterReadLock();try{return this.dictionary.ContainsKey(key);}finally{this.locker.ExitReadLock();}}public int Count{get{this.locker.EnterReadLock();try{return this.dictionary.Count;}finally{this.locker.ExitReadLock();}}}public int Capacity{get{this.locker.EnterReadLock();try{return this.capacity;}finally{this.locker.ExitReadLock();}}set{this.locker.EnterUpgradeableReadLock();try{if (value > 0 && this.capacity != value){this.locker.EnterWriteLock();try{this.capacity = value;while (this.linkedList.Count > this.capacity){this.linkedList.RemoveLast();}}finally{this.locker.ExitWriteLock();}}}finally{this.locker.ExitUpgradeableReadLock();}}}public ICollection<TKey> Keys{get{this.locker.EnterReadLock();try{return this.dictionary.Keys;}finally{this.locker.ExitReadLock();}}}public ICollection<TValue> Values{get{this.locker.EnterReadLock();try{return this.dictionary.Values;}finally{this.locker.ExitReadLock();}}}public void Clear(){this.dictionary.Clear();this.linkedList.Clear();}private void MakeFreeSpace(){LinkedListNode<TKey> node = this.linkedList.Last;//檢測最不常用的10個int max_check_free_times = 10; //最大檢測空閑次數int cur_check_free_time = 0; //當前檢測空閑次數while (this.linkedList.Count + 1 > this.capacity){if (node == null)break;LinkedListNode<TKey> tuple_prev = node.Previous;if (this.checkCanPopFunc == null || this.checkCanPopFunc(node.Value, this.dictionary[node.Value])){//可以釋放var value = this.dictionary[node.Value];this.dictionary.Remove(node.Value);this.linkedList.RemoveLast();this.popCb?.Invoke(node.Value, value);}else{cur_check_free_time++;if (cur_check_free_time >= max_check_free_times){break;}}node = tuple_prev;}}public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator(){foreach (var item in this.dictionary){yield return item;}}IEnumerator IEnumerable.GetEnumerator(){foreach (var item in this.dictionary){yield return item;}}}
}