如何更快地创建简单的.NET LRU缓存？

Question

更新:嘿家伙感谢回复.昨晚和今晚我尝试了几种不同的方法,并提出了类似于Jeff下面列出的方法(我甚至已经完成了他在更新中建议的内容,并将我自己的简单LL实现放在一起以获得额外收益).这是代码,此时它看起来并不特别干净,但是我已经多次改变了我可以做的任何事情以增强性能.

public class NewLRU2<K, V> where V : class
{
    int m_iMaxItems;
    Dictionary<K, LRUNode<K, V>> m_oMainDict;

    private LRUNode<K,V> m_oHead;
    private LRUNode<K,V> m_oTail;
    private LRUNode<K,V> m_oCurrent;

    public NewLRU2(int iSize)
    {
        m_iMaxItems = iSize;
        m_oMainDict = new Dictionary<K, LRUNode<K,V>>();

        m_oHead = null;
        m_oTail = null;
    }

    public V this[K key]
    {
        get
        {
            m_oCurrent = m_oMainDict[key];

            if (m_oCurrent == m_oHead)
            {
                //do nothing
            }
            else if (m_oCurrent == m_oTail)
            {
                m_oTail = m_oCurrent.Next;
                m_oTail.Prev = null;

                m_oHead.Next = m_oCurrent;
                m_oCurrent.Prev = m_oHead;
                m_oCurrent.Next = null;
                m_oHead = m_oCurrent;
            }
            else
            {
                m_oCurrent.Prev.Next = m_oCurrent.Next;
                m_oCurrent.Next.Prev = m_oCurrent.Prev;

                m_oHead.Next = m_oCurrent;
                m_oCurrent.Prev = m_oHead;
                m_oCurrent.Next = null;
                m_oHead = m_oCurrent;
            }

            return m_oCurrent.Value;
        }
    }

    public void Add(K key, V value)
    {
        if (m_oMainDict.Count >= m_iMaxItems)
        {   
            //remove old
            m_oMainDict.Remove(m_oTail.Key);

            //reuse old
            LRUNode<K, V> oNewNode = m_oTail;
            oNewNode.Key = key;
            oNewNode.Value = value;

            m_oTail = m_oTail.Next;
            m_oTail.Prev = null;

            //add new
            m_oHead.Next = oNewNode;
            oNewNode.Prev = m_oHead;
            oNewNode.Next = null;
            m_oHead = oNewNode;
            m_oMainDict.Add(key, oNewNode);
        }
        else
        {
            LRUNode<K, V> oNewNode = new LRUNode<K, V>(key, value);
            if (m_oHead == null)
            {
                m_oHead = oNewNode;
                m_oTail = oNewNode;
            }
            else
            {
                m_oHead.Next = oNewNode;
                oNewNode.Prev = m_oHead;
                m_oHead = oNewNode;
            }
            m_oMainDict.Add(key, oNewNode);
        }
    }

    public bool Contains(K key)
    {
        return m_oMainDict.ContainsKey(key);
    }
}


internal class LRUNode<K,V>
{
    public LRUNode(K key, V val)
    {
        Key = key;
        Value = val;
    }

    public K Key;
    public V Value;
    public LRUNode<K, V> Next;
    public LRUNode<K, V> Prev;
}

有一些部分看起来/感觉不稳定 - 比如在进行添加时重用旧节点 - 但我能够从中获得明显的性能提升.我对从节点上的实际属性切换到公共变量所产生的差异也略感惊讶,但我想这就是它与这些东西的关系.在这一点上,上面的代码几乎完全受到字典操作的性能限制,所以我不确定我是否可以通过混搭来获得更多.我将继续思考并研究一些回应.

来自原帖的解释:大家好.所以我编写了一个简单的轻量级LRU实现用于压缩库(我用它来根据散列,LZW样式在输入中查找匹配的字节串),我正在寻找制作方法它更快.

Answer 1

更新#2

这减少了对链表Remove进行列表遍历的需要。它引入了一个同时具有键和值的LruCacheNode。该密钥仅在修剪缓存时使用。如果您编写自己的链表实现，其中每个节点本质上是一个 LruCacheNode 以及 Next 和 Back 引用，那么您可以获得更好的性能。这就是 LinkedHashMap 的作用（请参阅这 两个问题）。

public class LruCache<K, V>
{
    private readonly int m_iMaxItems;
    private readonly Dictionary<K, LinkedListNode<LruCacheNode<K, V>>> m_oMainDict;
    private readonly LinkedList<LruCacheNode<K, V>> m_oMainList;

    public LruCache(int iSize)
    {
        m_iMaxItems = iSize;
        m_oMainDict = new Dictionary<K, LinkedListNode<LruCacheNode<K, V>>>();
        m_oMainList = new LinkedList<LruCacheNode<K, V>>();
    }

    public V this[K key]
    {
        get
        {
            return BumpToFront(key).Value;
        }
        set
        {
            BumpToFront(key).Value = value;
        }
    }

    public void Add(K key, V value)
    {
        LinkedListNode<LruCacheNode<K, V>> newNode = m_oMainList.AddFirst(new LruCacheNode<K, V>(key, value));
        m_oMainDict.Add(key, newNode);

        if (m_oMainList.Count > m_iMaxItems)
        {
            m_oMainDict.Remove(m_oMainList.Last.Value.Key);
            m_oMainList.RemoveLast();
        }
    }

    private LruCacheNode<K, V> BumpToFront(K key)
    {
        LinkedListNode<LruCacheNode<K, V>> node = m_oMainDict[key];
        if (m_oMainList.First != node)
        {
            m_oMainList.Remove(node);
            m_oMainList.AddFirst(node);
        }
        return node.Value;
    }

    public bool Contains(K key)
    {
        return m_oMainDict.ContainsKey(key);
    }
}

internal sealed class LruCacheNode<K, V>
{
    private readonly K m_Key;
    private V m_Value;

    public LruCacheNode(K key, V value)
    {
        m_Key = key;
        m_Value = value;
    }

    public K Key
    {
        get { return m_Key; }
    }

    public V Value
    {
        get { return m_Value; }
        set { m_Value = value; }
    }
}

您必须分析一些事情，看看这是否对您的环境有所改善。

小更新：我更新了 BumpToFront 以检查该节点是否已位于 Tim Stewart 评论的前面。