MruCache.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / cdf / src / System.Runtime.DurableInstancing / System / Runtime / MruCache.cs / 1305376 / MruCache.cs
                        
                        
                            //------------------------------------------------------------ 
// Copyright (c) Microsoft Corporation.  All rights reserved.
//-----------------------------------------------------------
namespace System.Runtime
{ 
    using System.Collections.Generic;
 
    class MruCache 
        where TKey : class
        where TValue : class 
    {
        LinkedList mruList;
        Dictionary items;
        int lowWatermark; 
        int highWatermark;
        CacheEntry mruEntry; 
 
        public MruCache(int watermark)
            : this(watermark * 4 / 5, watermark) 
        {
        }

        // 
        // The cache will grow until the high watermark. At which point, the least recently used items
        // will be purge until the cache's size is reduced to low watermark 
        // 
        public MruCache(int lowWatermark, int highWatermark)
            : this(lowWatermark, highWatermark, null) 
        {
        }

        public MruCache(int lowWatermark, int highWatermark, IEqualityComparer comparer) 
        {
            Fx.Assert(lowWatermark < highWatermark, ""); 
            Fx.Assert(lowWatermark >= 0, ""); 

            this.lowWatermark = lowWatermark; 
            this.highWatermark = highWatermark;
            this.mruList = new LinkedList();
            if (comparer == null)
            { 
                this.items = new Dictionary();
            } 
            else 
            {
                this.items = new Dictionary(comparer); 
            }
        }

        public void Add(TKey key, TValue value) 
        {
            Fx.Assert(null != key, ""); 
 
            // if anything goes wrong (duplicate entry, etc) we should
            // clear our caches so that we don't get out of [....] 
            bool success = false;
            try
            {
                if (this.items.Count == this.highWatermark) 
                {
                    // If the cache is full, purge enough LRU items to shrink the 
                    // cache down to the low watermark 
                    int countToPurge = this.highWatermark - this.lowWatermark;
                    for (int i = 0; i < countToPurge; i++) 
                    {
                        TKey keyRemove = this.mruList.Last.Value;
                        this.mruList.RemoveLast();
                        TValue item = this.items[keyRemove].value; 
                        this.items.Remove(keyRemove);
                        OnSingleItemRemoved(item); 
                    } 
                }
                // Add  the new entry to the cache and make it the MRU element 
                CacheEntry entry;
                entry.node = this.mruList.AddFirst(key);
                entry.value = value;
                this.items.Add(key, entry); 
                this.mruEntry = entry;
                success = true; 
            } 
            finally
            { 
                if (!success)
                {
                    this.Clear();
                } 
            }
        } 
 
        public void Clear()
        { 
            this.mruList.Clear();
            this.items.Clear();
            this.mruEntry.value = null;
            this.mruEntry.node = null; 
        }
 
        public bool Remove(TKey key) 
        {
            Fx.Assert(null != key, ""); 

            CacheEntry entry;
            if (this.items.TryGetValue(key, out entry))
            { 
                this.items.Remove(key);
                OnSingleItemRemoved(entry.value); 
                this.mruList.Remove(entry.node); 
                if (object.ReferenceEquals(this.mruEntry.node, entry.node))
                { 
                    this.mruEntry.value = null;
                    this.mruEntry.node = null;
                }
                return true; 
            }
 
            return false; 
        }
 
        protected virtual void OnSingleItemRemoved(TValue item)
        {
        }
 
        //
        // If found, make the entry most recently used 
        // 
        public bool TryGetValue(TKey key, out TValue value)
        { 
            // first check our MRU item
            if (this.mruEntry.node != null && key != null && key.Equals(this.mruEntry.node.Value))
            {
                value = this.mruEntry.value; 
                return true;
            } 
 
            CacheEntry entry;
 
            bool found = this.items.TryGetValue(key, out entry);
            value = entry.value;

            // Move the node to the head of the MRU list if it's not already there 
            if (found && this.mruList.Count > 1
                && !object.ReferenceEquals(this.mruList.First, entry.node)) 
            { 
                this.mruList.Remove(entry.node);
                this.mruList.AddFirst(entry.node); 
                this.mruEntry = entry;
            }

            return found; 
        }
 
        struct CacheEntry 
        {
            internal TValue value; 
            internal LinkedListNode node;
        }
    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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MruCache.cs source code in C# .NET

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