Is it there any LRU implementation of IDictionary?

Question

I would like to implement a simple in-memory LRU cache system and I was thinking about a solution based on an IDictionary implementation which could handle an hashed LRU mechanism. Coming from java, I have experiences with LinkedHashMap, which works fine for what I need: I can't find anywhere a similar solution for .NET.

Has anyone developed it or has anyone had experiences like this?

Answer 1

The Caching Application Block of EntLib has an LRU scavenging option out of the box and can be in memory. It might be a bit heavyweight for what you want tho.

Answer 2

I've created an implementation of the LRU cache
https://github.com/mohsenShakiba/LRUCache

Answer 3

Found you answer while googling, also found this:

http://code.google.com/p/csharp-lru-cache/

csharp-lru-cache: LRU cache collection class library

This is a collection class that functions as a least-recently-used cache. It implements ICollection<T>, but also exposes three other members:

• Capacity, the maximum number of items the cache can contain. Once the collection is at capacity, adding a new item to the cache will cause the least recently used item to be discarded. If the Capacity is set to 0 at construction, the cache will not automatically discard items.
• Oldest, the oldest (i.e. least recently used) item in the collection.
• DiscardingOldestItem, an event raised when the cache is about to discard its oldest item. This is an extremely simple implementation. While its Add and Remove methods are thread-safe, it shouldn't be used in heavy multithreading environments because the entire collection is locked during those methods.

Answer 4

This a very simple an fast implementation we developed for a web site we own.

We try to improve the code as much as possible but keeping it thread safe. I think the code is very simple and clear, but if you need some explanation or a guide related to how to use it, don't hesitate to ask.

namespace LRUCache
{
    public class LRUCache<K,V>
    {
        private int capacity;
        private Dictionary<K, LinkedListNode<LRUCacheItem<K, V>>> cacheMap = new Dictionary<K, LinkedListNode<LRUCacheItem<K, V>>>();
        private LinkedList<LRUCacheItem<K, V>> lruList = new LinkedList<LRUCacheItem<K, V>>();

        public LRUCache(int capacity)
        {
            this.capacity = capacity;
        }

        [MethodImpl(MethodImplOptions.Synchronized)]
        public V get(K key)
        {
            LinkedListNode<LRUCacheItem<K, V>> node;
            if (cacheMap.TryGetValue(key, out node))
            {
                V value = node.Value.value;
                lruList.Remove(node);
                lruList.AddLast(node);
                return value;
            }
            return default(V);
        }

        [MethodImpl(MethodImplOptions.Synchronized)]
        public void add(K key, V val)
        {
            if (cacheMap.Count >= capacity)
            {
                RemoveFirst();
            }

            LRUCacheItem<K, V> cacheItem = new LRUCacheItem<K, V>(key, val);
            LinkedListNode<LRUCacheItem<K, V>> node = new LinkedListNode<LRUCacheItem<K, V>>(cacheItem);
            lruList.AddLast(node);
            cacheMap.Add(key, node);
        }

        private void RemoveFirst()
        {
            // Remove from LRUPriority
            LinkedListNode<LRUCacheItem<K,V>> node = lruList.First;
            lruList.RemoveFirst();

            // Remove from cache
            cacheMap.Remove(node.Value.key);
        }
    }

    class LRUCacheItem<K,V>
    {
        public LRUCacheItem(K k, V v)
        {
            key = k;
            value = v;
        }
        public K key;
        public V value;
    }
}