c#实现的LRU算法

using System.Collections.Generic;using System.Threading;namespace Lru{    public class LRUCache<TKey, TValue>    {        const int DEFAULT_CAPACITY = 255;        int _capacity;        ReaderWriterLockSlim _locker;        IDictionary<TKey, TValue> _dictionary;        LinkedList<TKey> _linkedList;        public LRUCache() : this(DEFAULT_CAPACITY) { }        public LRUCache(int capacity)        {            _locker = new ReaderWriterLockSlim();            _capacity = capacity > 0 ? capacity : DEFAULT_CAPACITY;            _dictionary = new Dictionary<TKey, TValue>();            _linkedList = new LinkedList<TKey>();        }        public void Set(TKey key, TValue value)        {            _locker.EnterWriteLock();            try            {                _dictionary[key] = value;                _linkedList.Remove(key);                _linkedList.AddFirst(key);                if (_linkedList.Count > _capacity)                {                    _dictionary.Remove(_linkedList.Last.Value);                    _linkedList.RemoveLast();                }            }            finally { _locker.ExitWriteLock(); }        }        public bool TryGet(TKey key, out TValue value)        {            _locker.EnterUpgradeableReadLock();            try            {                bool b = _dictionary.TryGetValue(key, out value);                if (b)                {                    _locker.EnterWriteLock();                    try                    {                        _linkedList.Remove(key);                        _linkedList.AddFirst(key);                    }                    finally { _locker.ExitWriteLock(); }                }                return b;            }            catch { throw; }            finally { _locker.ExitUpgradeableReadLock(); }        }        public bool ContainsKey(TKey key)        {            _locker.EnterReadLock();            try            {                return _dictionary.ContainsKey(key);            }            finally { _locker.ExitReadLock(); }        }        public int Count        {            get            {                _locker.EnterReadLock();                try                {                    return _dictionary.Count;                }                finally { _locker.ExitReadLock(); }            }        }        public int Capacity        {            get            {                _locker.EnterReadLock();                try                {                    return _capacity;                }                finally { _locker.ExitReadLock(); }            }            set            {                _locker.EnterUpgradeableReadLock();                try                {                    if (value > 0 && _capacity != value)                    {                        _locker.EnterWriteLock();                        try                        {                            _capacity = value;                            while (_linkedList.Count > _capacity)                            {                                _linkedList.RemoveLast();                            }                        }                        finally { _locker.ExitWriteLock(); }                    }                }                finally { _locker.ExitUpgradeableReadLock(); }            }        }        public ICollection<TKey> Keys        {            get            {                _locker.EnterReadLock();                try                {                    return _dictionary.Keys;                }                finally { _locker.ExitReadLock(); }            }        }        public ICollection<TValue> Values        {            get            {                _locker.EnterReadLock();                try                {                    return _dictionary.Values;                }                finally { _locker.ExitReadLock(); }            }        }    }}