TimeBoundedCache.cs source code in C# .NET

                        Code:
                         / WCF / WCF / 3.5.30729.1 / untmp / Orcas / SP / ndp / cdf / src / WCF / ServiceModel / System / ServiceModel / Security / TimeBoundedCache.cs / 1 / TimeBoundedCache.cs
                        
                        
                            //------------------------------------------------------------------------------ 
// Copyright (c) Microsoft Corporation.  All rights reserved.
//-----------------------------------------------------------------------------

namespace System.ServiceModel.Security 
{
    using System; 
    using System.ServiceModel; 
    using System.Collections;
    using System.Collections.Generic; 
    using System.Runtime.InteropServices;
    using System.Threading;
    using System.Diagnostics;
    using System.ServiceModel.Channels; 

    ///  
    /// NOTE: this class does minimum argument checking as it is all internal 
    /// 
    internal class TimeBoundedCache 
    {
        static WaitCallback purgeCallback;
        ReaderWriterLock cacheLock;
        Hashtable entries; 
        // if there are less than lowWaterMark entries, no purging is done
        int lowWaterMark; 
        int maxCacheItems; 
        DateTime nextPurgeTimeUtc;
        TimeSpan purgeInterval; 
        PurgingMode purgingMode;
        IOThreadTimer purgingTimer;
        bool doRemoveNotification;
 
        protected TimeBoundedCache(int lowWaterMark, int maxCacheItems, IEqualityComparer keyComparer, PurgingMode purgingMode, TimeSpan purgeInterval, bool doRemoveNotification)
        { 
            this.entries = new Hashtable(keyComparer); 
            this.cacheLock = new ReaderWriterLock();
            this.lowWaterMark = lowWaterMark; 
            this.maxCacheItems = maxCacheItems;
            this.purgingMode = purgingMode;
            this.purgeInterval = purgeInterval;
            this.doRemoveNotification = doRemoveNotification; 
            this.nextPurgeTimeUtc = DateTime.UtcNow.Add(this.purgeInterval);
        } 
 
        public int Count
        { 
            get
            {
                return this.entries.Count;
            } 
        }
 
        static WaitCallback PurgeCallback 
        {
            get 
            {
                if (purgeCallback == null)
                {
                    purgeCallback = new WaitCallback(PurgeCallbackStatic); 
                }
                return purgeCallback; 
            } 
        }
 
        protected int Capacity
        {
            get
            { 
                return this.maxCacheItems;
            } 
        } 

        protected Hashtable Entries 
        {
            get
            {
                return this.entries; 
            }
        } 
 
        protected ReaderWriterLock CacheLock
        { 
            get
            {
                return this.cacheLock;
            } 
        }
 
        protected bool TryAddItem(object key, object item, DateTime expirationTime, bool replaceExistingEntry) 
        {
            return this.TryAddItem(key, new ExpirableItem(item, expirationTime), replaceExistingEntry); 
        }

        void CancelTimerIfNeeded()
        { 
            if (this.Count == 0 && this.purgingTimer != null)
            { 
                this.purgingTimer.Cancel(); 
                this.purgingTimer = null;
            } 
        }

        void StartTimerIfNeeded()
        { 
            if (this.purgingMode != PurgingMode.TimerBasedPurge)
            { 
                return; 
            }
            if (this.purgingTimer == null) 
            {
                this.purgingTimer = new IOThreadTimer(PurgeCallback, this, false);
                this.purgingTimer.Set(this.purgeInterval);
            } 
        }
 
        protected bool TryAddItem(object key, IExpirableItem item, bool replaceExistingEntry) 
        {
            bool lockHeld = false; 
            try
            {
                try { }
                finally 
                {
                    this.cacheLock.AcquireWriterLock(-1); 
                    lockHeld = true; 
                }
                PurgeIfNeeded(); 
                EnforceQuota();
                IExpirableItem currentItem = this.entries[key] as IExpirableItem;
                if (currentItem == null || IsExpired(currentItem))
                { 
                    this.entries[key] = item;
                } 
                else if (!replaceExistingEntry) 
                {
                    return false; 
                }
                else
                {
                    this.entries[key] = item; 
                }
                if (currentItem != null && doRemoveNotification) 
                { 
                    this.OnRemove(ExtractItem(currentItem));
                } 
                StartTimerIfNeeded();
                return true;
            }
            finally 
            {
                if (lockHeld) 
                { 
                    this.cacheLock.ReleaseWriterLock();
                } 
            }
        }

        protected bool TryReplaceItem(object key, object item, DateTime expirationTime) 
        {
            bool lockHeld = false; 
            try 
            {
                try { } 
                finally
                {
                    this.cacheLock.AcquireWriterLock(-1);
                    lockHeld = true; 
                }
                PurgeIfNeeded(); 
                EnforceQuota(); 
                IExpirableItem currentItem = this.entries[key] as IExpirableItem;
                if (currentItem == null || IsExpired(currentItem)) 
                {
                    return false;
                }
                else 
                {
                    this.entries[key] = new ExpirableItem(item, expirationTime); 
                    if (currentItem != null && doRemoveNotification) 
                    {
                        this.OnRemove(ExtractItem(currentItem)); 
                    }
                    StartTimerIfNeeded();
                    return true;
                } 
            }
            finally 
            { 
                if (lockHeld)
                { 
                    this.cacheLock.ReleaseWriterLock();
                }
            }
        } 

        protected void ClearItems() 
        { 
            bool lockHeld = false;
            try 
            {
                try { }
                finally
                { 
                    this.cacheLock.AcquireWriterLock(-1);
                    lockHeld = true; 
                } 

                int count = this.entries.Count; 
                if (doRemoveNotification)
                {
                    foreach (IExpirableItem item in this.entries.Values)
                    { 
                        OnRemove(ExtractItem(item));
                    } 
                } 
                this.entries.Clear();
                CancelTimerIfNeeded(); 
            }
            finally
            {
                if (lockHeld) 
                {
                    this.cacheLock.ReleaseWriterLock(); 
                } 
            }
        } 

        protected object GetItem(object key)
        {
            bool lockHeld = false; 
            try
            { 
                try { } 
                finally
                { 
                    this.cacheLock.AcquireReaderLock(-1);
                    lockHeld = true;
                }
                IExpirableItem item = this.entries[key] as IExpirableItem; 
                if (item == null)
                { 
                    return null; 
                }
                else if (IsExpired(item)) 
                {
                    // this is a stale item
                    return null;
                } 
                else
                { 
                    return ExtractItem(item); 
                }
            } 
            finally
            {
                if (lockHeld)
                { 
                    this.cacheLock.ReleaseReaderLock();
                } 
            } 
        }
 
        protected virtual ArrayList OnQuotaReached(Hashtable cacheTable)
        {
            this.ThrowQuotaReachedException();
            return null; 
        }
 
        protected virtual void OnRemove(object item) 
        {
        } 

        protected bool TryRemoveItem(object key)
        {
            bool lockHeld = false; 
            try
            { 
                try { } 
                finally
                { 
                    this.cacheLock.AcquireWriterLock(-1);
                    lockHeld = true;
                }
                PurgeIfNeeded(); 
                IExpirableItem currentItem = this.entries[key] as IExpirableItem;
                bool result = (currentItem != null) && !IsExpired(currentItem); 
                if (currentItem != null) 
                {
                    this.entries.Remove(key); 
                    if (doRemoveNotification)
                    {
                        this.OnRemove(ExtractItem(currentItem));
                    } 
                    CancelTimerIfNeeded();
                } 
                return result; 
            }
            finally 
            {
                if (lockHeld)
                {
                    this.cacheLock.ReleaseWriterLock(); 
                }
            } 
        } 

 
        void EnforceQuota()
        {
            if (!(this.cacheLock.IsWriterLockHeld == true))
            { 
                // we failfast here because if we don't have the lock we could corrupt the cache
                DiagnosticUtility.DebugAssert("Cache write lock is not held."); 
                DiagnosticUtility.FailFast("Cache write lock is not held."); 
            }
            if (this.Count >= this.maxCacheItems) 
            {
                ArrayList keysToBeRemoved;
                keysToBeRemoved = this.OnQuotaReached(this.entries);
                if (keysToBeRemoved != null) 
                {
                    for (int i = 0; i < keysToBeRemoved.Count; ++i) 
                    { 
                        this.entries.Remove(keysToBeRemoved[i]);
                    } 

                }
                CancelTimerIfNeeded();
                if (this.Count >= this.maxCacheItems) 
                {
                    this.ThrowQuotaReachedException(); 
                } 
            }
        } 

        protected object ExtractItem(IExpirableItem val)
        {
            ExpirableItem wrapper = (val as ExpirableItem); 
            if (wrapper != null)
            { 
                return wrapper.Item; 
            }
            else 
            {
                return val;
            }
        } 

        bool IsExpired(IExpirableItem item) 
        { 
            DiagnosticUtility.DebugAssert(item.ExpirationTime == DateTime.MaxValue || item.ExpirationTime.Kind == DateTimeKind.Utc, "");
            return (item.ExpirationTime <= DateTime.UtcNow); 
        }

        bool ShouldPurge()
        { 
            if (this.Count >= this.maxCacheItems)
            { 
                return true; 
            }
            else if (this.purgingMode == PurgingMode.AccessBasedPurge && DateTime.UtcNow > this.nextPurgeTimeUtc && this.Count > this.lowWaterMark) 
            {
                return true;
            }
            else 
            {
                return false; 
            } 
        }
 
        void PurgeIfNeeded()
        {
            if (!(this.cacheLock.IsWriterLockHeld == true))
            { 
                // we failfast here because if we don't have the lock we could corrupt the cache
                DiagnosticUtility.DebugAssert("Cache write lock is not held."); 
                DiagnosticUtility.FailFast("Cache write lock is not held."); 
            }
            if (ShouldPurge()) 
            {
                PurgeStaleItems();
            }
        } 

        ///  
        /// This method must be called from within a writer lock 
        /// 
        void PurgeStaleItems() 
        {
            if (!(this.cacheLock.IsWriterLockHeld == true))
            {
                // we failfast here because if we don't have the lock we could corrupt the cache 
                DiagnosticUtility.DebugAssert("Cache write lock is not held.");
                DiagnosticUtility.FailFast("Cache write lock is not held."); 
            } 
            ArrayList expiredItems = new ArrayList();
            foreach (object key in this.entries.Keys) 
            {
                IExpirableItem item = this.entries[key] as IExpirableItem;
                if (IsExpired(item))
                { 
                    // this is a stale item. Remove!
                    this.OnRemove(ExtractItem(item)); 
                    expiredItems.Add(key); 
                }
            } 
            for (int i = 0; i < expiredItems.Count; ++i)
            {
                this.entries.Remove(expiredItems[i]);
            } 
            CancelTimerIfNeeded();
            this.nextPurgeTimeUtc = DateTime.UtcNow.Add(this.purgeInterval); 
        } 

        void ThrowQuotaReachedException() 
        {
            string message = SR.GetString(SR.CacheQuotaReached, this.maxCacheItems);
            Exception inner = new QuotaExceededException(message);
            throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(new CommunicationException(message, inner)); 
        }
 
        static void PurgeCallbackStatic(object state) 
        {
            TimeBoundedCache self = (TimeBoundedCache)state; 

            bool lockHeld = false;
            try
            { 
                try { }
                finally 
                { 
                    self.cacheLock.AcquireWriterLock(-1);
                    lockHeld = true; 
                }

                if (self.purgingTimer == null)
                { 
                    return;
                } 
                self.PurgeStaleItems(); 
                if (self.Count > 0 && self.purgingTimer != null)
                { 
                    self.purgingTimer.Set(self.purgeInterval);
                }
            }
            finally 
            {
                if (lockHeld) 
                { 
                    self.cacheLock.ReleaseWriterLock();
                } 
            }
        }

        internal interface IExpirableItem 
        {
            DateTime ExpirationTime { get; } 
        } 

        internal class ExpirableItemComparer : IComparer 
        {
            static ExpirableItemComparer instance;

            public static ExpirableItemComparer Default 
            {
                get 
                { 
                    if (instance == null)
                    { 
                        instance = new ExpirableItemComparer();
                    }
                    return instance;
                } 
            }
 
            // positive, if item1 will expire before item2. 
            public int Compare(IExpirableItem item1, IExpirableItem item2)
            { 
                if (ReferenceEquals(item1, item2))
                {
                    return 0;
                } 
                DiagnosticUtility.DebugAssert(item1.ExpirationTime.Kind == item2.ExpirationTime.Kind, "");
                if (item1.ExpirationTime < item2.ExpirationTime) 
                { 
                    return 1;
                } 
                else if (item1.ExpirationTime > item2.ExpirationTime)
                {
                    return -1;
                } 
                else
                { 
                    return 0; 
                }
            } 
        }

        internal sealed class ExpirableItem : IExpirableItem
        { 
            DateTime expirationTime;
            object item; 
 
            public ExpirableItem(object item, DateTime expirationTime)
            { 
                this.item = item;
                DiagnosticUtility.DebugAssert( expirationTime == DateTime.MaxValue || expirationTime.Kind == DateTimeKind.Utc, "");
                this.expirationTime = expirationTime;
            } 

            public DateTime ExpirationTime { get { return this.expirationTime; } } 
            public object Item { get { return this.item; } } 
        }
    } 

    enum PurgingMode
    {
        TimerBasedPurge, 
        AccessBasedPurge
    } 
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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TimeBoundedCache.cs source code in C# .NET

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