Merge remote-tracking branch 'os/master'

1 files changed, 1870 insertions, 0 deletions

diff --git a/OpenSim/Framework/CnmMemoryCache.cs b/OpenSim/Framework/CnmMemoryCache.cs
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+/*
+ * Copyright (c) Contributors, http://opensimulator.org/
+ * See CONTRIBUTORS.TXT for a full list of copyright holders.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *     * Neither the name of the OpenSimulator Project nor the
+ *       names of its contributors may be used to endorse or promote products
+ *       derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Diagnostics;
+
+namespace OpenSim.Framework
+{
+    /// <summary>
+    /// Cenome memory based cache to store key/value pairs (elements) limited time and/or limited size.
+    /// </summary>
+    /// <typeparam name="TKey">
+    /// The type of keys in the cache. 
+    /// </typeparam>
+    /// <typeparam name="TValue">
+    /// The type of values in the dictionary. 
+    /// </typeparam>
+    /// <remarks>
+    /// <para>
+    /// Cenome memory cache stores elements to hash table generations. When new element is being added to cache, and new size would exceed 
+    /// maximal allowed size or maximal amount of allowed element count, then elements in oldest generation are deleted. Last access time
+    /// is also tracked in generation level - thus it is possible that some elements are staying in cache far beyond their expiration time.
+    /// If elements in older generations are accessed through <see cref="TryGetValue"/> method, they are moved to newest generation.
+    /// </para>
+    /// </remarks>
+    public class CnmMemoryCache<TKey, TValue> : ICnmCache<TKey, TValue>
+    {
+        /// <summary>
+        /// Default maximal count.
+        /// </summary>
+        /// <seealso cref="MaxCount"/>
+        public const int DefaultMaxCount = 4096;
+
+        /// <summary>
+        /// Default maximal size.
+        /// </summary>
+        /// <remarks>
+        /// <para>
+        /// 128MB = 128 * 1024^2 = 134 217 728 bytes.
+        /// </para>
+        /// </remarks>
+        /// <seealso cref="MaxSize"/>
+        public const long DefaultMaxSize = 134217728;
+
+        /// <summary>
+        /// How many operations between time checks.
+        /// </summary>
+        private const int DefaultOperationsBetweenTimeChecks = 40;
+
+        /// <summary>
+        /// Default expiration time.
+        /// </summary>
+        /// <remarks>
+        /// <para>
+        /// 30 minutes.
+        /// </para>
+        /// </remarks>
+        public static readonly TimeSpan DefaultExpirationTime = TimeSpan.FromMinutes(30.0);
+
+        /// <summary>
+        /// Minimal allowed expiration time.
+        /// </summary>
+        /// <remarks>
+        /// <para>
+        /// 5 minutes.
+        /// </para>
+        /// </remarks>
+        public static readonly TimeSpan MinExpirationTime = TimeSpan.FromSeconds(10.0);
+
+        /// <summary>
+        /// Comparer used to compare element keys.
+        /// </summary>
+        /// <remarks>
+        /// Comparer is initialized by constructor.
+        /// </remarks>
+        /// <seealso cref="CnmMemoryCache{TKey,TValue}"/>
+        public readonly IEqualityComparer<TKey> Comparer;
+
+        /// <summary>
+        /// Expiration time.
+        /// </summary>
+        private TimeSpan m_expirationTime = DefaultExpirationTime;
+
+        /// <summary>
+        /// Generation bucket count.
+        /// </summary>
+        private int m_generationBucketCount;
+
+        /// <summary>
+        /// Generation entry count.
+        /// </summary>
+        private int m_generationElementCount;
+
+        /// <summary>
+        /// Generation max size.
+        /// </summary>
+        private long m_generationMaxSize;
+
+        /// <summary>
+        /// Maximal allowed count of elements.
+        /// </summary>
+        private int m_maxCount;
+
+        /// <summary>
+        /// Maximal allowed total size of elements.
+        /// </summary>
+        private long m_maxElementSize;
+
+        /// <summary>
+        /// Maximal size.
+        /// </summary>
+        private long m_maxSize;
+
+        /// <summary>
+        /// New generation.
+        /// </summary>
+        private IGeneration m_newGeneration;
+
+        /// <summary>
+        /// Old generation.
+        /// </summary>
+        private IGeneration m_oldGeneration;
+
+        /// <summary>
+        /// Operations between time check.
+        /// </summary>
+        private int m_operationsBetweenTimeChecks = DefaultOperationsBetweenTimeChecks;
+
+        /// <summary>
+        /// Synchronization root object, should always be private and exists always
+        /// </summary>
+        private readonly object m_syncRoot = new object();
+
+        /// <summary>
+        /// Version of cache.
+        /// </summary>
+        /// <remarks>
+        /// <para>
+        /// Updated every time when cache has been changed (element removed, expired, added, replaced).
+        /// </para>
+        /// </remarks>
+        private int m_version;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="CnmMemoryCache{TKey,TValue}"/> class.
+        /// </summary>
+        public CnmMemoryCache()
+            : this(DefaultMaxSize)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="CnmMemoryCache{TKey,TValue}"/> class. 
+        /// </summary>
+        /// <param name="maximalSize">
+        /// Maximal cache size.
+        /// </param>
+        public CnmMemoryCache(long maximalSize)
+            : this(maximalSize, DefaultMaxCount)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="CnmMemoryCache{TKey,TValue}"/> class.
+        /// </summary>
+        /// <param name="maximalSize">
+        /// Maximal cache size.
+        /// </param>
+        /// <param name="maximalCount">
+        /// Maximal element count.
+        /// </param>
+        public CnmMemoryCache(long maximalSize, int maximalCount)
+            : this(maximalSize, maximalCount, DefaultExpirationTime)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="CnmMemoryCache{TKey,TValue}"/> class. 
+        /// </summary>
+        /// <param name="maximalSize">
+        /// Maximal cache size.
+        /// </param>
+        /// <param name="maximalCount">
+        /// Maximal element count.
+        /// </param>
+        /// <param name="expirationTime">
+        /// Elements expiration time.
+        /// </param>
+        public CnmMemoryCache(long maximalSize, int maximalCount, TimeSpan expirationTime)
+            : this(maximalSize, maximalCount, expirationTime, EqualityComparer<TKey>.Default)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="CnmMemoryCache{TKey,TValue}"/> class. 
+        /// </summary>
+        /// <param name="maximalSize">
+        /// Maximal cache size.
+        /// </param>
+        /// <param name="maximalCount">
+        /// Maximal element count.
+        /// </param>
+        /// <param name="expirationTime">
+        /// Elements expiration time.
+        /// </param>
+        /// <param name="comparer">
+        /// Comparer used for comparing elements.
+        /// </param>
+        /// <exception cref="ArgumentNullException">
+        /// <see cref="comparer"/>is <see langword="null"/> reference.
+        /// </exception>
+        public CnmMemoryCache(long maximalSize,
+            int maximalCount,
+            TimeSpan expirationTime,
+            IEqualityComparer<TKey> comparer)
+        {
+            if (comparer == null)
+                throw new ArgumentNullException("comparer");
+
+            if (expirationTime < MinExpirationTime)
+                expirationTime = MinExpirationTime;
+            if (maximalCount < 8)
+                maximalCount = 8;
+            if (maximalSize < 8)
+                maximalSize = 8;
+            if (maximalCount > maximalSize)
+                maximalCount = (int) maximalSize;
+
+            Comparer = comparer;
+            m_expirationTime = expirationTime;
+            m_maxSize = maximalSize;
+            m_maxCount = maximalCount;
+
+            Initialize();
+        }
+
+        /// <summary>
+        /// Add element to new generation.
+        /// </summary>
+        /// <param name="bucketIndex">
+        /// The bucket index.
+        /// </param>
+        /// <param name="key">
+        /// The element's key.
+        /// </param>
+        /// <param name="value">
+        /// The element's value.
+        /// </param>
+        /// <param name="size">
+        /// The element's size.
+        /// </param>
+        protected virtual void AddToNewGeneration(int bucketIndex, TKey key, TValue value, long size)
+        {
+            // Add to newest generation
+            if (!m_newGeneration.Set(bucketIndex, key, value, size))
+            {
+                // Failed to add new generation
+                RecycleGenerations();
+                m_newGeneration.Set(bucketIndex, key, value, size);
+            }
+
+            m_version++;
+        }
+
+        /// <summary>
+        /// <para>
+        /// Get keys bucket index.
+        /// </para>
+        /// </summary>
+        /// <param name="key">
+        /// <para>
+        /// Key which bucket index is being retrieved.
+        /// </para>
+        /// </param>
+        /// <returns>
+        /// <para>
+        /// Bucket index.
+        /// </para>
+        /// </returns>
+        /// <remarks>
+        /// <para>
+        /// Method uses <see cref="Comparer"/> to calculate <see cref="key"/> hash code.
+        /// </para>
+        /// <para>
+        /// Bucket index is remainder when element key's hash value is divided by bucket count.
+        /// </para>
+        /// <para>
+        /// For example: key's hash is 72, bucket count is 5, element's bucket index is 72 % 5 = 2.
+        /// </para>
+        /// </remarks>
+        protected virtual int GetBucketIndex(TKey key)
+        {
+            return (Comparer.GetHashCode(key) & 0x7FFFFFFF) % m_generationBucketCount;
+        }
+
+        /// <summary>
+        /// Purge generation from the cache.
+        /// </summary>
+        /// <param name="generation">
+        /// The generation that is purged.
+        /// </param>
+        protected virtual void PurgeGeneration(IGeneration generation)
+        {
+            generation.Clear();
+            m_version++;
+        }
+
+        /// <summary>
+        /// check expired.
+        /// </summary>
+        private void CheckExpired()
+        {
+            // Do this only one in every m_operationsBetweenTimeChecks 
+            // Fetching time is using several millisecons - it is better not to do all time.
+            m_operationsBetweenTimeChecks--;
+            if (m_operationsBetweenTimeChecks <= 0)
+                PurgeExpired();
+        }
+
+        /// <summary>
+        /// Initialize cache.
+        /// </summary>
+        private void Initialize()
+        {
+            m_version++;
+
+            m_generationMaxSize = MaxSize / 2;
+            MaxElementSize = MaxSize / 8;
+            m_generationElementCount = MaxCount / 2;
+
+            // Buckets need to be prime number to get better spread of hash values
+            m_generationBucketCount = PrimeNumberHelper.GetPrime(m_generationElementCount);
+
+            m_newGeneration = new HashGeneration(this);
+            m_oldGeneration = new HashGeneration(this);
+            m_oldGeneration.MakeOld();
+        }
+
+        /// <summary>
+        /// Recycle generations.
+        /// </summary>
+        private void RecycleGenerations()
+        {
+            // Rotate old generation to new generation, new generation to old generation
+            IGeneration temp = m_newGeneration;
+            m_newGeneration = m_oldGeneration;
+            m_newGeneration.Clear();
+            m_oldGeneration = temp;
+            m_oldGeneration.MakeOld();
+        }
+
+        #region Nested type: Enumerator
+
+        /// <summary>
+        /// Key and value pair enumerator.
+        /// </summary>
+        private class Enumerator : IEnumerator<KeyValuePair<TKey, TValue>>
+        {
+            /// <summary>
+            /// Current enumerator.
+            /// </summary>
+            private int m_currentEnumerator = -1;
+
+            /// <summary>
+            /// Enumerators to different generations.
+            /// </summary>
+            private readonly IEnumerator<KeyValuePair<TKey, TValue>>[] m_generationEnumerators =
+                new IEnumerator<KeyValuePair<TKey, TValue>>[2];
+
+            /// <summary>
+            /// Initializes a new instance of the <see cref="Enumerator"/> class. 
+            /// </summary>
+            /// <param name="cache">
+            /// The cache.
+            /// </param>
+            public Enumerator(CnmMemoryCache<TKey, TValue> cache)
+            {
+                m_generationEnumerators[ 0 ] = cache.m_newGeneration.GetEnumerator();
+                m_generationEnumerators[ 1 ] = cache.m_oldGeneration.GetEnumerator();
+            }
+
+            #region IEnumerator<KeyValuePair<TKey,TValue>> Members
+
+            /// <summary>
+            /// Gets the element in the collection at the current position of the enumerator.
+            /// </summary>
+            /// <returns>
+            /// The element in the collection at the current position of the enumerator.
+            /// </returns>
+            /// <exception cref="InvalidOperationException">
+            /// The enumerator has reach end of collection or <see cref="MoveNext"/> is not called.
+            /// </exception>
+            public KeyValuePair<TKey, TValue> Current
+            {
+                get
+                {
+                    if (m_currentEnumerator == -1 || m_currentEnumerator >= m_generationEnumerators.Length)
+                        throw new InvalidOperationException();
+
+                    return m_generationEnumerators[ m_currentEnumerator ].Current;
+                }
+            }
+
+            /// <summary>
+            /// Gets the current element in the collection.
+            /// </summary>
+            /// <returns>
+            /// The current element in the collection.
+            /// </returns>
+            /// <exception cref="T:System.InvalidOperationException">
+            /// The enumerator is positioned before the first element of the collection or after the last element.
+            /// </exception><filterpriority>2</filterpriority>
+            object IEnumerator.Current
+            {
+                get { return Current; }
+            }
+
+            /// <summary>
+            /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
+            /// </summary>
+            /// <filterpriority>2</filterpriority>
+            public void Dispose()
+            {
+            }
+
+            /// <summary>
+            /// Advances the enumerator to the next element of the collection.
+            /// </summary>
+            /// <returns>
+            /// <see langword="true"/>if the enumerator was successfully advanced to the next element; <see langword="false"/> if the enumerator has passed the end of the collection.
+            /// </returns>
+            /// <exception cref="T:System.InvalidOperationException">
+            /// The collection was modified after the enumerator was created. 
+            /// </exception>
+            /// <filterpriority>2</filterpriority>
+            public bool MoveNext()
+            {
+                if (m_currentEnumerator == -1)
+                    m_currentEnumerator = 0;
+
+                while (m_currentEnumerator < m_generationEnumerators.Length)
+                {
+                    if (m_generationEnumerators[ m_currentEnumerator ].MoveNext())
+                        return true;
+
+                    m_currentEnumerator++;
+                }
+
+                return false;
+            }
+
+            /// <summary>
+            /// Sets the enumerator to its initial position, which is before the first element in the collection.
+            /// </summary>
+            /// <exception cref="T:System.InvalidOperationException">
+            /// The collection was modified after the enumerator was created. 
+            /// </exception>
+            /// <filterpriority>2</filterpriority>
+            public void Reset()
+            {
+                foreach (IEnumerator<KeyValuePair<TKey, TValue>> enumerator in m_generationEnumerators)
+                {
+                    enumerator.Reset();
+                }
+
+                m_currentEnumerator = -1;
+            }
+
+            #endregion
+        }
+
+        #endregion
+
+        #region Nested type: HashGeneration
+
+        /// <summary>
+        /// Hash generation class
+        /// </summary>
+        /// <remarks>
+        /// <para>
+        /// Current implementation is based to separated chaining with move-to-front heuristics. Hash generations have fixed
+        /// amount of buckets and it is never rehashed.
+        /// </para>
+        /// <para>
+        /// Read more about hash tables from <a href="http://en.wikipedia.org/wiki/Hash_table">Wiki article</a>.
+        /// </para>
+        /// </remarks>
+        /// <seealso href="http://en.wikipedia.org/wiki/Hash_table"/>
+        private class HashGeneration : IGeneration
+        {
+            /// <summary>
+            /// Value indicating whether generation was accessed since last time check.
+            /// </summary>
+            private bool m_accessedSinceLastTimeCheck;
+
+            /// <summary>
+            /// Index of first element's in element chain.
+            /// </summary>
+            /// <value>
+            /// -1 if there is no element in bucket; otherwise first element's index in the element chain.
+            /// </value>
+            /// <remarks>
+            /// Bucket index is remainder when element key's hash value is divided by bucket count.
+            /// For example: key's hash is 72, bucket count is 5, element's bucket index is 72 % 5 = 2.
+            /// </remarks>
+            private readonly int[] m_buckets;
+
+            /// <summary>
+            /// Cache object.
+            /// </summary>
+            private readonly CnmMemoryCache<TKey, TValue> m_cache;
+
+            /// <summary>
+            /// Generation's element array.
+            /// </summary>
+            /// <seealso cref="Element"/>
+            private readonly Element[] m_elements;
+
+            /// <summary>
+            /// Generation's expiration time.
+            /// </summary>
+            private DateTime m_expirationTime1;
+
+            /// <summary>
+            /// Index to first free element. 
+            /// </summary>
+            private int m_firstFreeElement;
+
+            /// <summary>
+            /// Free element count.
+            /// </summary>
+            /// <remarks>
+            /// When generation is cleared or constructed, this is NOT set to element count.
+            /// This is only tracking elements that are removed and are currently free.
+            /// </remarks>
+            private int m_freeCount;
+
+            /// <summary>
+            /// Is this generation "new generation".
+            /// </summary>
+            private bool m_newGeneration;
+
+            /// <summary>
+            /// Next unused entry.
+            /// </summary>
+            private int m_nextUnusedElement;
+
+            /// <summary>
+            /// Size of data stored to generation.
+            /// </summary>
+            private long m_size;
+
+            /// <summary>
+            /// Initializes a new instance of the <see cref="HashGeneration"/> class.
+            /// </summary>
+            /// <param name="cache">
+            /// The cache.
+            /// </param>
+            public HashGeneration(CnmMemoryCache<TKey, TValue> cache)
+            {
+                m_cache = cache;
+                m_elements = new Element[m_cache.m_generationElementCount];
+                m_buckets = new int[m_cache.m_generationBucketCount];
+                Clear();
+            }
+
+            /// <summary>
+            /// Find element's index
+            /// </summary>
+            /// <param name="bucketIndex">
+            /// The element's bucket index.
+            /// </param>
+            /// <param name="key">
+            /// The element's key.
+            /// </param>
+            /// <param name="moveToFront">
+            /// Move element to front of elements.
+            /// </param>
+            /// <param name="previousIndex">
+            /// The previous element's index.
+            /// </param>
+            /// <returns>
+            /// Element's index, if found from the generation; -1 otherwise (if element is not found the generation).
+            /// </returns>
+            private int FindElementIndex(int bucketIndex, TKey key, bool moveToFront, out int previousIndex)
+            {
+                previousIndex = -1;
+                int elementIndex = m_buckets[ bucketIndex ];
+                while (elementIndex >= 0)
+                {
+                    if (m_cache.Comparer.Equals(key, m_elements[ elementIndex ].Key))
+                    {
+                        // Found match
+                        if (moveToFront && previousIndex >= 0)
+                        {
+                            // Move entry to front
+                            m_elements[ previousIndex ].Next = m_elements[ elementIndex ].Next;
+                            m_elements[ elementIndex ].Next = m_buckets[ bucketIndex ];
+                            m_buckets[ bucketIndex ] = elementIndex;
+                            previousIndex = 0;
+                        }
+
+                        return elementIndex;
+                    }
+
+                    previousIndex = elementIndex;
+                    elementIndex = m_elements[ elementIndex ].Next;
+                }
+
+                return -1;
+            }
+
+            /// <summary>
+            /// Remove element front the generation.
+            /// </summary>
+            /// <param name="bucketIndex">
+            /// The bucket index.
+            /// </param>
+            /// <param name="entryIndex">
+            /// The element index.
+            /// </param>
+            /// <param name="previousIndex">
+            /// The element's previous index.
+            /// </param>
+            private void RemoveElement(int bucketIndex, int entryIndex, int previousIndex)
+            {
+                if (previousIndex >= 0)
+                    m_elements[ previousIndex ].Next = m_elements[ entryIndex ].Next;
+                else
+                    m_buckets[ bucketIndex ] = m_elements[ entryIndex ].Next;
+
+                Size -= m_elements[ entryIndex ].Size;
+                m_elements[ entryIndex ].Value = default(TValue);
+                m_elements[ entryIndex ].Key = default(TKey);
+
+                // Add element to free elements list
+                m_elements[ entryIndex ].Next = m_firstFreeElement;
+                m_firstFreeElement = entryIndex;
+                m_freeCount++;
+            }
+
+            #region Nested type: Element
+
+            /// <summary>
+            /// Element that stores key, next element in chain, size and value.
+            /// </summary>
+            private struct Element
+            {
+                /// <summary>
+                /// Element's key.
+                /// </summary>
+                public TKey Key;
+
+                /// <summary>
+                /// Next element in chain.
+                /// </summary>
+                /// <remarks>
+                /// When element have value (something is stored to it), this is index of 
+                /// next element with same bucket index. When element is free, this 
+                /// is index of next element in free element's list.
+                /// </remarks>
+                public int Next;
+
+                /// <summary>
+                /// Size of element.
+                /// </summary>
+                /// <value>
+                /// 0 if element is free; otherwise larger than 0.
+                /// </value>
+                public long Size;
+
+                /// <summary>
+                /// Element's value. 
+                /// </summary>
+                /// <remarks>
+                /// It is possible that this value is <see langword="null"/> even when element
+                /// have value - element's value is then <see langword="null"/> reference.
+                /// </remarks>
+                public TValue Value;
+
+                /// <summary>
+                /// Gets a value indicating whether element is free or have value.
+                /// </summary>
+                /// <value>
+                /// <see langword="true"/> when element is free; otherwise <see langword="false"/>.
+                /// </value>
+                public bool IsFree
+                {
+                    get { return Size == 0; }
+                }
+            }
+
+            #endregion
+
+            #region Nested type: Enumerator
+
+            /// <summary>
+            /// Key value pair enumerator for <see cref="HashGeneration"/> object.
+            /// </summary>
+            private class Enumerator : IEnumerator<KeyValuePair<TKey, TValue>>
+            {
+                /// <summary>
+                /// Current element.
+                /// </summary>
+                private KeyValuePair<TKey, TValue> m_current;
+
+                /// <summary>
+                /// Current index.
+                /// </summary>
+                private int m_currentIndex;
+
+                /// <summary>
+                /// Generation that is being enumerated.
+                /// </summary>
+                private readonly HashGeneration m_generation;
+
+                /// <summary>
+                /// Cache version.
+                /// </summary>
+                /// <remarks>
+                /// When cache is change, version number is changed.
+                /// </remarks>
+                /// <seealso cref="CnmMemoryCache{TKey,TValue}.m_version"/>
+                private readonly int m_version;
+
+                /// <summary>
+                /// Initializes a new instance of the <see cref="Enumerator"/> class.
+                /// </summary>
+                /// <param name="generation">
+                /// The generation.
+                /// </param>
+                public Enumerator(HashGeneration generation)
+                {
+                    m_generation = generation;
+                    m_version = m_generation.m_cache.m_version;
+                }
+
+                #region IEnumerator<KeyValuePair<TKey,TValue>> Members
+
+                /// <summary>
+                /// Gets the element in the collection at the current position of the enumerator.
+                /// </summary>
+                /// <returns>
+                /// The element in the collection at the current position of the enumerator.
+                /// </returns>
+                /// <exception cref="InvalidOperationException">
+                /// The enumerator has reach end of collection or <see cref="MoveNext"/> is not called.
+                /// </exception>
+                public KeyValuePair<TKey, TValue> Current
+                {
+                    get
+                    {
+                        if (m_currentIndex == 0 || m_currentIndex >= m_generation.Count)
+                            throw new InvalidOperationException();
+
+                        return m_current;
+                    }
+                }
+
+                /// <summary>
+                /// Gets the current element in the collection.
+                /// </summary>
+                /// <returns>
+                /// The current element in the collection.
+                /// </returns>
+                /// <exception cref="InvalidOperationException">
+                /// The enumerator is positioned before the first element of the collection or after the last element.
+                /// </exception><filterpriority>2</filterpriority>
+                object IEnumerator.Current
+                {
+                    get { return Current; }
+                }
+
+                /// <summary>
+                /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
+                /// </summary>
+                /// <filterpriority>2</filterpriority>
+                public void Dispose()
+                {
+                }
+
+                /// <summary>
+                /// Advances the enumerator to the next element of the collection.
+                /// </summary>
+                /// <returns>
+                /// true if the enumerator was successfully advanced to the next element; false if the enumerator has passed the end of the collection.
+                /// </returns>
+                /// <exception cref="InvalidOperationException">
+                /// The collection was modified after the enumerator was created. 
+                /// </exception>
+                public bool MoveNext()
+                {
+                    if (m_version != m_generation.m_cache.m_version)
+                        throw new InvalidOperationException();
+
+                    while (m_currentIndex < m_generation.Count)
+                    {
+                        if (m_generation.m_elements[ m_currentIndex ].IsFree)
+                        {
+                            m_currentIndex++;
+                            continue;
+                        }
+
+                        m_current = new KeyValuePair<TKey, TValue>(m_generation.m_elements[ m_currentIndex ].Key,
+                            m_generation.m_elements[ m_currentIndex ].Value);
+                        m_currentIndex++;
+                        return true;
+                    }
+
+                    m_current = new KeyValuePair<TKey, TValue>();
+                    return false;
+                }
+
+                /// <summary>
+                /// Sets the enumerator to its initial position, which is before the first element in the collection.
+                /// </summary>
+                /// <exception cref="InvalidOperationException">
+                /// The collection was modified after the enumerator was created. 
+                /// </exception>
+                /// <filterpriority>2</filterpriority>
+                public void Reset()
+                {
+                    if (m_version != m_generation.m_cache.m_version)
+                        throw new InvalidOperationException();
+
+                    m_currentIndex = 0;
+                }
+
+                #endregion
+            }
+
+            #endregion
+
+            #region IGeneration Members
+
+            /// <summary>
+            /// Gets or sets a value indicating whether generation was accessed since last time check.
+            /// </summary>
+            public bool AccessedSinceLastTimeCheck
+            {
+                get { return m_accessedSinceLastTimeCheck; }
+
+                set { m_accessedSinceLastTimeCheck = value; }
+            }
+
+            /// <summary>
+            /// Gets element count in generation.
+            /// </summary>
+            public int Count
+            {
+                get { return m_nextUnusedElement - m_freeCount; }
+            }
+
+            /// <summary>
+            /// Gets or sets generation's expiration time.
+            /// </summary>
+            public DateTime ExpirationTime
+            {
+                get { return m_expirationTime1; }
+
+                set { m_expirationTime1 = value; }
+            }
+
+            /// <summary>
+            /// Gets or sets size of data stored to generation.
+            /// </summary>
+            public long Size
+            {
+                get { return m_size; }
+
+                private set { m_size = value; }
+            }
+
+            /// <summary>
+            /// Clear all elements from the generation and make generation new again.
+            /// </summary>
+            /// <remarks>
+            /// When generation is new, it is allowed to add new elements to it and
+            /// <see cref="IGeneration.TryGetValue"/>doesn't remove elements from it.
+            /// </remarks>
+            /// <seealso cref="IGeneration.MakeOld"/>
+            public void Clear()
+            {
+                for (int i = m_buckets.Length - 1 ; i >= 0 ; i--)
+                {
+                    m_buckets[ i ] = -1;
+                }
+
+                Array.Clear(m_elements, 0, m_elements.Length);
+                Size = 0;
+                m_firstFreeElement = -1;
+                m_freeCount = 0;
+                m_nextUnusedElement = 0;
+                m_newGeneration = true;
+                ExpirationTime = DateTime.MaxValue;
+            }
+
+            /// <summary>
+            /// Determines whether the <see cref="IGeneration"/> contains an element with the specific key.
+            /// </summary>
+            /// <param name="bucketIndex">
+            /// The bucket index for the <see cref="key"/> to locate in <see cref="IGeneration"/>.
+            /// </param>
+            /// <param name="key">
+            /// The key to locate in the <see cref="IGeneration"/>.
+            /// </param>
+            /// <returns>
+            /// <see langword="true"/>if the <see cref="IGeneration"/> contains an element with the <see cref="key"/>; 
+            /// otherwise <see langword="false"/>.
+            /// </returns>
+            public bool Contains(int bucketIndex, TKey key)
+            {
+                int previousIndex;
+                if (FindElementIndex(bucketIndex, key, true, out previousIndex) == -1)
+                    return false;
+
+                AccessedSinceLastTimeCheck = true;
+                return true;
+            }
+
+            /// <summary>
+            /// Returns an enumerator that iterates through the elements stored <see cref="HashGeneration"/>.
+            /// </summary>
+            /// <returns>
+            /// A <see cref="IEnumerator"/> that can be used to iterate through the <see cref="HashGeneration"/>.
+            /// </returns>
+            /// <filterpriority>1</filterpriority>
+            public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
+            {
+                return new Enumerator(this);
+            }
+
+            /// <summary>
+            /// Make from generation old generation.
+            /// </summary>
+            /// <remarks>
+            /// When generation is old, <see cref="IGeneration.TryGetValue"/> hit removes element from the generation.
+            /// </remarks>
+            /// <seealso cref="IGeneration.Clear"/>
+            public void MakeOld()
+            {
+                m_newGeneration = false;
+            }
+
+            /// <summary>
+            /// Remove element associated with the key from the generation.
+            /// </summary>
+            /// <param name="bucketIndex">
+            /// The element's bucket index.
+            /// </param>
+            /// <param name="key">
+            /// The element's key.
+            /// </param>
+            /// <returns>
+            /// <see langword="true"/>, if remove was successful; otherwise <see langword="false"/>.
+            /// </returns>
+            public bool Remove(int bucketIndex, TKey key)
+            {
+                int previousIndex;
+                int entryIndex = FindElementIndex(bucketIndex, key, false, out previousIndex);
+                if (entryIndex != -1)
+                {
+                    RemoveElement(bucketIndex, entryIndex, previousIndex);
+                    AccessedSinceLastTimeCheck = true;
+                    return true;
+                }
+
+                return false;
+            }
+
+            /// <summary>
+            /// Set or add element to generation.
+            /// </summary>
+            /// <param name="bucketIndex">
+            /// The element's bucket index.
+            /// </param>
+            /// <param name="key">
+            /// The element's key.
+            /// </param>
+            /// <param name="value">
+            /// The element's value.
+            /// </param>
+            /// <param name="size">
+            /// The element's size.
+            /// </param>
+            /// <returns>
+            /// <see langword="true"/>, if setting or adding was successful; otherwise <see langword="false"/>.
+            /// </returns>
+            /// <remarks>
+            /// <para>
+            /// If element was already existing in generation and new element size fits to collection limits, 
+            /// then it's value is replaced with new one and size information is updated. If element didn't
+            /// exists in generation before, then generation must have empty space for a new element and
+            /// size must fit generation's limits, before element is added to generation.
+            /// </para>
+            /// </remarks>
+            public bool Set(int bucketIndex, TKey key, TValue value, long size)
+            {
+                Debug.Assert(m_newGeneration, "It is possible to insert new elements only to newest generation.");
+                Debug.Assert(size > 0, "New element size should be more than 0.");
+
+                int previousIndex;
+                int elementIndex = FindElementIndex(bucketIndex, key, true, out previousIndex);
+                if (elementIndex == -1)
+                {
+                    // New key
+                    if (Size + size > m_cache.m_generationMaxSize ||
+                        (m_nextUnusedElement == m_cache.m_generationElementCount && m_freeCount == 0))
+                    {
+                        // Generation is full
+                        return false;
+                    }
+
+                    // Increase size of generation
+                    Size += size;
+
+                    // Get first free entry and update free entry list
+                    if (m_firstFreeElement != -1)
+                    {
+                        // There was entry that was removed
+                        elementIndex = m_firstFreeElement;
+                        m_firstFreeElement = m_elements[ elementIndex ].Next;
+                        m_freeCount--;
+                    }
+                    else
+                    {
+                        // No entries removed so far - just take a last one
+                        elementIndex = m_nextUnusedElement;
+                        m_nextUnusedElement++;
+                    }
+
+                    Debug.Assert(m_elements[ elementIndex ].IsFree, "Allocated element is not free.");
+
+                    // Move new entry to front
+                    m_elements[ elementIndex ].Next = m_buckets[ bucketIndex ];
+                    m_buckets[ bucketIndex ] = elementIndex;
+
+                    // Set key and update count
+                    m_elements[ elementIndex ].Key = key;
+                }
+                else
+                {
+                    // Existing key
+                    if (Size - m_elements[ elementIndex ].Size + size > m_cache.m_generationMaxSize)
+                    {
+                        // Generation is full
+                        // Remove existing element, because generation is going to be recycled to 
+                        // old generation and element is stored to new generation
+                        RemoveElement(bucketIndex, elementIndex, previousIndex);
+                        return false;
+                    }
+
+                    // Update generation's size
+                    Size = Size - m_elements[ elementIndex ].Size + size;
+                }
+
+                // Finally set value and size
+                m_elements[ elementIndex ].Value = value;
+                m_elements[ elementIndex ].Size = size;
+
+                // Success - key was inserterted to generation
+                AccessedSinceLastTimeCheck = true;
+                return true;
+            }
+
+            /// <summary>
+            /// Try to get element associated with key.
+            /// </summary>
+            /// <param name="bucketIndex">
+            /// The element's bucket index.
+            /// </param>
+            /// <param name="key">
+            /// The element's key.
+            /// </param>
+            /// <param name="value">
+            /// The element's value.
+            /// </param>
+            /// <param name="size">
+            /// The element's size.
+            /// </param>
+            /// <returns>
+            /// <see langword="true"/>, if element was successful retrieved; otherwise <see langword="false"/>.
+            /// </returns>
+            /// <remarks>
+            /// <para>
+            /// If element is not found from generation then <paramref name="value"/> and <paramref name="size"/>
+            /// are set to default value (default(TValue) and 0). 
+            /// </para>
+            /// </remarks>
+            public bool TryGetValue(int bucketIndex, TKey key, out TValue value, out long size)
+            {
+                // Find entry index, 
+                int previousIndex;
+                int elementIndex = FindElementIndex(bucketIndex, key, m_newGeneration, out previousIndex);
+                if (elementIndex == -1)
+                {
+                    value = default(TValue);
+                    size = 0;
+                    return false;
+                }
+
+                value = m_elements[ elementIndex ].Value;
+                size = m_elements[ elementIndex ].Size;
+
+                if (!m_newGeneration)
+                {
+                    // Old generation - remove element, because it is moved to new generation
+                    RemoveElement(bucketIndex, elementIndex, previousIndex);
+                }
+
+                AccessedSinceLastTimeCheck = true;
+                return true;
+            }
+
+            /// <summary>
+            /// Returns an enumerator that iterates through a collection.
+            /// </summary>
+            /// <returns>
+            /// An <see cref="T:System.Collections.IEnumerator"/> object that can be used to iterate through the collection.
+            /// </returns>
+            /// <filterpriority>2</filterpriority>
+            IEnumerator IEnumerable.GetEnumerator()
+            {
+                return GetEnumerator();
+            }
+
+            #endregion
+        }
+
+        #endregion
+
+        #region Nested type: IGeneration
+
+        /// <summary>
+        /// Cache element generation interface
+        /// </summary>
+        /// <remarks>
+        /// <para>
+        /// Generation can hold limited count of elements and limited size of data.
+        /// </para>
+        /// <para>
+        /// There are two kind generations: "new generation" and "old generation(s)". All new elements
+        /// are added to "new generation". 
+        /// </para>
+        /// </remarks>
+        protected interface IGeneration : IEnumerable<KeyValuePair<TKey, TValue>>
+        {
+            /// <summary>
+            /// Gets or sets a value indicating whether generation was accessed since last time check.
+            /// </summary>
+            bool AccessedSinceLastTimeCheck { get; set; }
+
+            /// <summary>
+            /// Gets element count in generation.
+            /// </summary>
+            int Count { get; }
+
+            /// <summary>
+            /// Gets or sets generation's expiration time.
+            /// </summary>
+            DateTime ExpirationTime { get; set; }
+
+            /// <summary>
+            /// Gets size of data stored to generation.
+            /// </summary>
+            long Size { get; }
+
+            /// <summary>
+            /// Clear all elements from the generation and make generation new again.
+            /// </summary>
+            /// <remarks>
+            /// When generation is new, it is allowed to add new elements to it and
+            /// <see cref="TryGetValue"/>doesn't remove elements from it.
+            /// </remarks>
+            /// <seealso cref="MakeOld"/>
+            void Clear();
+
+            /// <summary>
+            /// Determines whether the <see cref="IGeneration"/> contains an element with the specific key.
+            /// </summary>
+            /// <param name="bucketIndex">
+            /// The bucket index for the <see cref="key"/> to locate in <see cref="IGeneration"/>.
+            /// </param>
+            /// <param name="key">
+            /// The key to locate in the <see cref="IGeneration"/>.
+            /// </param>
+            /// <returns>
+            /// <see langword="true"/>if the <see cref="IGeneration"/> contains an element with the <see cref="key"/>; 
+            /// otherwise <see langword="false"/>.
+            /// </returns>
+            bool Contains(int bucketIndex, TKey key);
+
+            /// <summary>
+            /// Make from generation old generation.
+            /// </summary>
+            /// <remarks>
+            /// When generation is old, <see cref="TryGetValue"/> hit removes element from the generation.
+            /// </remarks>
+            /// <seealso cref="Clear"/>
+            void MakeOld();
+
+            /// <summary>
+            /// Remove element associated with the key from the generation.
+            /// </summary>
+            /// <param name="bucketIndex">
+            /// The element's bucket index.
+            /// </param>
+            /// <param name="key">
+            /// The element's key.
+            /// </param>
+            /// <returns>
+            /// <see langword="true"/>, if remove was successful; otherwise <see langword="false"/>.
+            /// </returns>
+            bool Remove(int bucketIndex, TKey key);
+
+            /// <summary>
+            /// Set or add element to generation.
+            /// </summary>
+            /// <param name="bucketIndex">
+            /// The element's bucket index.
+            /// </param>
+            /// <param name="key">
+            /// The element's key.
+            /// </param>
+            /// <param name="value">
+            /// The element's value.
+            /// </param>
+            /// <param name="size">
+            /// The element's size.
+            /// </param>
+            /// <returns>
+            /// <see langword="true"/>, if setting or adding was successful; otherwise <see langword="false"/>.
+            /// </returns>
+            /// <remarks>
+            /// <para>
+            /// If element was already existing in generation and new element size fits to collection limits, 
+            /// then it's value is replaced with new one and size information is updated. If element didn't
+            /// exists in generation before, then generation must have empty space for a new element and
+            /// size must fit generation's limits, before element is added to generation.
+            /// </para>
+            /// </remarks>
+            bool Set(int bucketIndex, TKey key, TValue value, long size);
+
+            /// <summary>
+            /// Try to get element associated with key.
+            /// </summary>
+            /// <param name="bucketIndex">
+            /// The element's bucket index.
+            /// </param>
+            /// <param name="key">
+            /// The element's key.
+            /// </param>
+            /// <param name="value">
+            /// The element's value.
+            /// </param>
+            /// <param name="size">
+            /// The element's size.
+            /// </param>
+            /// <returns>
+            /// <see langword="true"/>, if element was successful retrieved; otherwise <see langword="false"/>.
+            /// </returns>
+            /// <remarks>
+            /// <para>
+            /// If element is not found from generation then <paramref name="value"/> and <paramref name="size"/>
+            /// are set to default value (default(TValue) and 0). 
+            /// </para>
+            /// </remarks>
+            bool TryGetValue(int bucketIndex, TKey key, out TValue value, out long size);
+        }
+
+        #endregion
+
+        #region ICnmCache<TKey,TValue> Members
+
+        /// <summary>
+        /// Gets current count of elements stored to <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </summary>
+        /// <remarks>
+        /// <para>
+        /// When adding an new element to <see cref="ICnmCache{TKey,TValue}"/> that is limiting element count, 
+        /// <see cref="ICnmCache{TKey,TValue}"/> will remove less recently used elements until it can fit an new element. 
+        /// </para>
+        /// </remarks>
+        /// <seealso cref="ICnmCache{TKey,TValue}.MaxCount"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsCountLimited"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsSizeLimited"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsTimeLimited"/>
+        public int Count
+        {
+            get { return m_newGeneration.Count + m_oldGeneration.Count; }
+        }
+
+        /// <summary>
+        /// Gets or sets elements expiration time.
+        /// </summary>
+        /// <value>
+        /// Elements expiration time.
+        /// </value>
+        /// <remarks>
+        /// <para>
+        /// When element has been stored in <see cref="ICnmCache{TKey,TValue}"/> longer than <see cref="ICnmCache{TKey,TValue}.ExpirationTime"/> 
+        /// and it is not accessed through <see cref="ICnmCache{TKey,TValue}.TryGetValue"/> method or element's value is 
+        /// not replaced by <see cref="ICnmCache{TKey,TValue}.Set"/> method, then it is automatically removed from the 
+        /// <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </para>
+        /// <para>
+        /// It is possible that <see cref="ICnmCache{TKey,TValue}"/> implementation removes element before it's expiration time, 
+        /// because total size or count of elements stored to cache is larger than <see cref="ICnmCache{TKey,TValue}.MaxSize"/> or <see cref="ICnmCache{TKey,TValue}.MaxCount"/>.
+        /// </para>
+        /// <para>
+        /// It is also possible that element stays in cache longer than <see cref="ICnmCache{TKey,TValue}.ExpirationTime"/>.
+        /// </para>
+        /// <para>
+        /// Calling <see cref="ICnmCache{TKey,TValue}.PurgeExpired"/> try to remove all elements that are expired.
+        /// </para>
+        /// <para>
+        /// To disable time limit in cache, set <see cref="ICnmCache{TKey,TValue}.ExpirationTime"/> to <see cref="DateTime.MaxValue"/>.
+        /// </para>
+        /// </remarks>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsTimeLimited"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsCountLimited"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsSizeLimited"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.PurgeExpired"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Count"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.MaxCount"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.MaxSize"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Size"/>
+        public TimeSpan ExpirationTime
+        {
+            get { return m_expirationTime; }
+
+            set
+            {
+                if (value < MinExpirationTime)
+                    value = MinExpirationTime;
+
+                if (m_expirationTime == value)
+                    return;
+
+                m_newGeneration.ExpirationTime = (m_newGeneration.ExpirationTime - m_expirationTime) + value;
+                m_oldGeneration.ExpirationTime = (m_oldGeneration.ExpirationTime - m_expirationTime) + value;
+                m_expirationTime = value;
+
+                PurgeExpired();
+            }
+        }
+
+        /// <summary>
+        /// Gets a value indicating whether <see cref="ICnmCache{TKey,TValue}"/> is limiting count of elements.
+        /// </summary>
+        /// <value>
+        /// <see langword="true"/> if the <see cref="ICnmCache{TKey,TValue}"/> count of elements is limited; 
+        /// otherwise, <see langword="false"/>. 
+        /// </value>
+        /// <remarks>
+        /// <para>
+        /// When adding an new element to <see cref="ICnmCache{TKey,TValue}"/> that is limiting element count, 
+        /// <see cref="ICnmCache{TKey,TValue}"/> will remove less recently used elements until it can fit an new element. 
+        /// </para>
+        /// </remarks>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Count"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.MaxCount"/> 
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsSizeLimited"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsTimeLimited"/>
+        public bool IsCountLimited
+        {
+            get { return true; }
+        }
+
+        /// <summary>
+        /// Gets a value indicating whether <see cref="ICnmCache{TKey,TValue}"/> is limiting size of elements.
+        /// </summary>
+        /// <value>
+        /// <see langword="true"/> if the <see cref="ICnmCache{TKey,TValue}"/> total size of elements is limited; 
+        /// otherwise, <see langword="false"/>. 
+        /// </value>
+        /// <remarks>
+        /// <para>
+        /// When adding an new element to <see cref="ICnmCache{TKey,TValue}"/> that is limiting total size of elements, 
+        /// <see cref="ICnmCache{TKey,TValue}"/> will remove less recently used elements until it can fit an new element. 
+        /// </para>
+        /// </remarks>
+        /// <seealso cref="ICnmCache{TKey,TValue}.MaxElementSize"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Size"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.MaxSize"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsCountLimited"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsTimeLimited"/>
+        public bool IsSizeLimited
+        {
+            get { return true; }
+        }
+
+        /// <summary>
+        /// Gets a value indicating whether or not access to the <see cref="ICnmCache{TKey,TValue}"/> is synchronized (thread safe).
+        /// </summary>
+        /// <value>
+        /// <see langword="true"/> if access to the <see cref="ICnmCache{TKey,TValue}"/> is synchronized (thread safe); 
+        /// otherwise, <see langword="false"/>. 
+        /// </value>
+        /// <remarks>
+        /// <para>
+        /// To get synchronized (thread safe) access to <see cref="ICnmCache{TKey,TValue}"/> object, use 
+        /// <see cref="CnmSynchronizedCache{TKey,TValue}.Synchronized"/> in <see cref="CnmSynchronizedCache{TKey,TValue}"/> class
+        /// to retrieve synchronized wrapper for <see cref="ICnmCache{TKey,TValue}"/> object.
+        /// </para>
+        /// </remarks>
+        /// <seealso cref="ICnmCache{TKey,TValue}.SyncRoot"/>
+        /// <seealso cref="CnmSynchronizedCache{TKey,TValue}"/>
+        public bool IsSynchronized
+        {
+            get { return false; }
+        }
+
+        /// <summary>
+        /// Gets a value indicating whether elements stored to <see cref="ICnmCache{TKey,TValue}"/> have limited inactivity time.
+        /// </summary>
+        /// <value>
+        /// <see langword="true"/> if the <see cref="ICnmCache{TKey,TValue}"/> has a fixed total size of elements; 
+        /// otherwise, <see langword="false"/>. 
+        /// </value>
+        /// <remarks>
+        /// If <see cref="ICnmCache{TKey,TValue}"/> have limited inactivity time and element is not accessed through <see cref="ICnmCache{TKey,TValue}.Set"/>
+        /// or <see cref="ICnmCache{TKey,TValue}.TryGetValue"/> methods in <see cref="ICnmCache{TKey,TValue}.ExpirationTime"/> , then element is automatically removed from 
+        /// the cache. Depending on implementation of the <see cref="ICnmCache{TKey,TValue}"/>, some of the elements may 
+        /// stay longer in cache.
+        /// </remarks>
+        /// <seealso cref="ICnmCache{TKey,TValue}.ExpirationTime"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.PurgeExpired"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsCountLimited"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsSizeLimited"/>
+        public bool IsTimeLimited
+        {
+            get { return ExpirationTime != TimeSpan.MaxValue; }
+        }
+
+        /// <summary>
+        /// Gets or sets maximal allowed count of elements that can be stored to <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </summary>
+        /// <value>
+        /// <see cref="int.MaxValue"/>, if <see cref="ICnmCache{TKey,TValue}"/> is not limited by count of elements; 
+        /// otherwise maximal allowed count of elements.
+        /// </value>
+        /// <remarks>
+        /// <para>
+        /// When adding an new element to <see cref="ICnmCache{TKey,TValue}"/> that is limiting element count, 
+        /// <see cref="ICnmCache{TKey,TValue}"/> will remove less recently used elements until it can fit an new element. 
+        /// </para>
+        /// </remarks>
+        public int MaxCount
+        {
+            get { return m_maxCount; }
+
+            set
+            {
+                if (value < 8)
+                    value = 8;
+                if (m_maxCount == value)
+                    return;
+
+                m_maxCount = value;
+                Initialize();
+            }
+        }
+
+        /// <summary>
+        /// <para>Gets maximal allowed element size.</para>
+        /// </summary>
+        /// <value>
+        /// Maximal allowed element size.
+        /// </value>
+        /// <remarks>
+        /// <para>
+        /// If element's size is larger than <see cref="ICnmCache{TKey,TValue}.MaxElementSize"/>, then element is 
+        /// not added to the <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </para>
+        /// </remarks>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Set"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsSizeLimited"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Size"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.MaxSize"/>
+        public long MaxElementSize
+        {
+            get { return m_maxElementSize; }
+
+            private set { m_maxElementSize = value; }
+        }
+
+        /// <summary>
+        /// Gets or sets maximal allowed total size for elements stored to <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </summary>
+        /// <value>
+        /// Maximal allowed total size for elements stored to <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </value>
+        /// <remarks>
+        /// <para>
+        /// Normally size is total bytes used by elements in the cache. But it can be any other suitable unit of measure.
+        /// </para>
+        /// <para>
+        /// When adding an new element to <see cref="ICnmCache{TKey,TValue}"/> that is limiting total size of elements, 
+        /// <see cref="ICnmCache{TKey,TValue}"/> will remove less recently used elements until it can fit an new element. 
+        /// </para>
+        /// </remarks>
+        /// <seealso cref="ICnmCache{TKey,TValue}.MaxElementSize"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsSizeLimited"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Size"/>
+        public long MaxSize
+        {
+            get { return m_maxSize; }
+
+            set
+            {
+                if (value < 8)
+                    value = 8;
+                if (m_maxSize == value)
+                    return;
+
+                m_maxSize = value;
+                Initialize();
+            }
+        }
+
+        /// <summary>
+        /// Gets total size of elements stored to <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </summary>
+        /// <value>
+        /// Total size of elements stored to <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </value>
+        /// <remarks>
+        /// <para>
+        /// Normally bytes, but can be any suitable unit of measure.
+        /// </para>
+        /// <para>
+        /// Element's size is given when element is added or replaced by <see cref="ICnmCache{TKey,TValue}.Set"/> method. 
+        /// </para>
+        /// <para>
+        /// When adding an new element to <see cref="ICnmCache{TKey,TValue}"/> that is limiting total size of elements, 
+        /// <see cref="ICnmCache{TKey,TValue}"/> will remove less recently used elements until it can fit an new element. 
+        /// </para>
+        /// </remarks>
+        /// <seealso cref="ICnmCache{TKey,TValue}.MaxElementSize"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsSizeLimited"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.MaxSize"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsCountLimited"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.ExpirationTime"/>
+        public long Size
+        {
+            get { return m_newGeneration.Size + m_oldGeneration.Size; }
+        }
+
+        /// <summary>
+        /// Gets an object that can be used to synchronize access to the <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </summary>
+        /// <value>
+        /// An object that can be used to synchronize access to the <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </value>
+        /// <remarks>
+        /// <para>
+        /// To get synchronized (thread safe) access to <see cref="ICnmCache{TKey,TValue}"/>, use <see cref="CnmSynchronizedCache{TKey,TValue}"/> 
+        /// method <see cref="CnmSynchronizedCache{TKey,TValue}.Synchronized"/> to retrieve synchronized wrapper interface to 
+        /// <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </para>
+        /// </remarks>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsSynchronized"/>
+        /// <seealso cref="CnmSynchronizedCache{TKey,TValue}"/>
+        public object SyncRoot
+        {
+            get { return m_syncRoot; }
+        }
+
+        /// <summary>
+        /// Removes all elements from the <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </summary>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Set"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Remove"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.RemoveRange"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.TryGetValue"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.PurgeExpired"/>
+        public void Clear()
+        {
+            m_newGeneration.Clear();
+            m_oldGeneration.Clear();
+            m_oldGeneration.MakeOld();
+            m_version++;
+        }
+
+        /// <summary>
+        /// Returns an enumerator that iterates through the elements stored to <see cref="CnmMemoryCache{TKey,TValue}"/>.
+        /// </summary>
+        /// <returns>
+        /// A <see cref="IEnumerator{T}"/> that can be used to iterate through the collection.
+        /// </returns>
+        /// <filterpriority>1</filterpriority>
+        public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
+        {
+            return new Enumerator(this);
+        }
+
+        /// <summary>
+        /// Purge expired elements from the <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </summary>
+        /// <remarks>
+        /// <para>
+        /// Element becomes expired when last access time to it has been longer time than <see cref="ICnmCache{TKey,TValue}.ExpirationTime"/>.
+        /// </para>
+        /// <para>
+        /// Depending on <see cref="ICnmCache{TKey,TValue}"/> implementation, some of expired elements
+        /// may stay longer than <see cref="ICnmCache{TKey,TValue}.ExpirationTime"/> in the cache.
+        /// </para>
+        /// </remarks>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsTimeLimited"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.ExpirationTime"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Set"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Remove"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.RemoveRange"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.TryGetValue"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Clear"/>
+        public void PurgeExpired()
+        {
+            m_operationsBetweenTimeChecks = DefaultOperationsBetweenTimeChecks;
+
+            if (!IsTimeLimited)
+                return;
+
+            DateTime now = DateTime.Now;
+            if (m_newGeneration.AccessedSinceLastTimeCheck)
+            {
+                // New generation has been accessed since last check
+                // Update it's expiration time.
+                m_newGeneration.ExpirationTime = now + ExpirationTime;
+                m_newGeneration.AccessedSinceLastTimeCheck = false;
+            }
+            else if (m_newGeneration.ExpirationTime < now)
+            {
+                // New generation has been expired.
+                // --> also old generation must be expired.
+                PurgeGeneration(m_newGeneration);
+                PurgeGeneration(m_oldGeneration);
+                return;
+            }
+
+            if (m_oldGeneration.ExpirationTime < now)
+                PurgeGeneration(m_oldGeneration);
+        }
+
+        /// <summary>
+        /// Removes element associated with <paramref name="key"/> from the <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </summary>
+        /// <param name="key">
+        /// The key that is associated with element to remove from the <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </param>
+        /// <exception cref="ArgumentNullException">
+        /// <paramref name="key"/>is <see langword="null"/>.
+        /// </exception>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Set"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.RemoveRange"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.TryGetValue"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Clear"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.PurgeExpired"/>
+        public void Remove(TKey key)
+        {
+            if (key == null)
+                throw new ArgumentNullException("key");
+
+            int bucketIndex = GetBucketIndex(key);
+            if (!m_newGeneration.Remove(bucketIndex, key))
+            {
+                if (!m_oldGeneration.Remove(bucketIndex, key))
+                {
+                    CheckExpired();
+                    return;
+                }
+            }
+
+            CheckExpired();
+            m_version++;
+        }
+
+        /// <summary>
+        /// Removes elements that are associated with one of <paramref name="keys"/> from the <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </summary>
+        /// <param name="keys">
+        /// The keys that are associated with elements to remove from the <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </param>
+        /// <exception cref="ArgumentNullException">
+        /// <paramref name="keys"/>is <see langword="null"/>.
+        /// </exception>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Set"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Remove"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.TryGetValue"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Clear"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.PurgeExpired"/>
+        public void RemoveRange(IEnumerable<TKey> keys)
+        {
+            if (keys == null)
+                throw new ArgumentNullException("keys");
+
+            foreach (TKey key in keys)
+            {
+                if (key == null)
+                    continue;
+
+                int bucketIndex = GetBucketIndex(key);
+                if (!m_newGeneration.Remove(bucketIndex, key))
+                    m_oldGeneration.Remove(bucketIndex, key);
+            }
+
+            CheckExpired();
+            m_version++;
+        }
+
+        /// <summary>
+        /// Add or replace an element with the provided <paramref name="key"/>, <paramref name="value"/> and <paramref name="size"/> to 
+        /// <see cref="ICnmCache{TKey,TValue}"/>.
+        /// </summary>
+        /// <param name="key">
+        /// The object used as the key of the element. Can't be <see langword="null"/> reference.
+        /// </param>
+        /// <param name="value">
+        /// The object used as the value of the element to add or replace. <see langword="null"/> is allowed.
+        /// </param>
+        /// <param name="size">
+        /// The element's size. Normally bytes, but can be any suitable unit of measure.
+        /// </param>
+        /// <returns>
+        /// <see langword="true"/>if element has been added successfully to the <see cref="ICnmCache{TKey,TValue}"/>; 
+        /// otherwise <see langword="false"/>.
+        /// </returns>
+        /// <exception cref="ArgumentNullException">
+        /// <paramref name="key"/>is <see langword="null"/>.
+        /// </exception>
+        /// <exception cref="ArgumentOutOfRangeException">
+        /// The element's <paramref name="size"/> is less than 0.
+        /// </exception>
+        /// <remarks>
+        /// <para>
+        /// If element's <paramref name="size"/> is larger than <see cref="ICnmCache{TKey,TValue}.MaxElementSize"/>, then element is 
+        /// not added to the <see cref="ICnmCache{TKey,TValue}"/>, however - possible older element is 
+        /// removed from the <see cref="ICnmCache{TKey,TValue}"/>. 
+        /// </para>
+        /// <para>
+        /// When adding an new element to <see cref="ICnmCache{TKey,TValue}"/> that is limiting total size of elements, 
+        /// <see cref="ICnmCache{TKey,TValue}"/>will remove less recently used elements until it can fit an new element. 
+        /// </para>
+        /// <para>
+        /// When adding an new element to <see cref="ICnmCache{TKey,TValue}"/> that is limiting element count, 
+        /// <see cref="ICnmCache{TKey,TValue}"/>will remove less recently used elements until it can fit an new element. 
+        /// </para>
+        /// </remarks>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsSizeLimited"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.IsCountLimited"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Remove"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.RemoveRange"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.TryGetValue"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Clear"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.PurgeExpired"/>
+        public bool Set(TKey key, TValue value, long size)
+        {
+            if (key == null)
+                throw new ArgumentNullException("key");
+
+            if (size < 0)
+                throw new ArgumentOutOfRangeException("size", size, "Value's size can't be less than 0.");
+
+            if (size > MaxElementSize)
+            {
+                // Entry size is too big to fit cache - ignore it
+                Remove(key);
+                return false;
+            }
+
+            if (size == 0)
+                size = 1;
+
+            int bucketIndex = GetBucketIndex(key);
+            m_oldGeneration.Remove(bucketIndex, key);
+            AddToNewGeneration(bucketIndex, key, value, size);
+            CheckExpired();
+
+            return true;
+        }
+
+        /// <summary>
+        /// Gets the <paramref name="value"/> associated with the specified <paramref name="key"/>.
+        /// </summary>
+        /// <returns>
+        /// <see langword="true"/>if the <see cref="ICnmCache{TKey,TValue}"/> contains an element with 
+        /// the specified key; otherwise, <see langword="false"/>.
+        /// </returns>
+        /// <param name="key">
+        /// The key whose <paramref name="value"/> to get.
+        /// </param>
+        /// <param name="value">
+        /// When this method returns, the value associated with the specified <paramref name="key"/>, 
+        /// if the <paramref name="key"/> is found; otherwise, the 
+        /// default value for the type of the <paramref name="value"/> parameter. This parameter is passed uninitialized.
+        /// </param>
+        /// <exception cref="ArgumentNullException">
+        /// <paramref name="key"/>is <see langword="null"/>.
+        /// </exception>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Set"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Remove"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.RemoveRange"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.Clear"/>
+        /// <seealso cref="ICnmCache{TKey,TValue}.PurgeExpired"/>
+        public bool TryGetValue(TKey key, out TValue value)
+        {
+            if (key == null)
+                throw new ArgumentNullException("key");
+
+            int bucketIndex = GetBucketIndex(key);
+            long size;
+            if (m_newGeneration.TryGetValue(bucketIndex, key, out value, out size))
+            {
+                CheckExpired();
+                return true;
+            }
+
+            if (m_oldGeneration.TryGetValue(bucketIndex, key, out value, out size))
+            {
+                // Move element to new generation
+                AddToNewGeneration(bucketIndex, key, value, size);
+                CheckExpired();
+                return true;
+            }
+
+            CheckExpired();
+            return false;
+        }
+
+        /// <summary>
+        /// Returns an enumerator that iterates through a collection.
+        /// </summary>
+        /// <returns>
+        /// An <see cref="T:System.Collections.IEnumerator"/> object that can be used to iterate through the collection.
+        /// </returns>
+        /// <filterpriority>2</filterpriority>
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return GetEnumerator();
+        }
+
+        #endregion
+    }
+}