WeakEventTable.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Base / MS / Internal / WeakEventTable.cs / 1305600 / WeakEventTable.cs
                        
                        
                            //---------------------------------------------------------------------------- 
//
// 
//    Copyright (C) Microsoft Corporation.  All rights reserved.
//  
//
// Description: Storage for the "weak event listener" pattern. 
//              See WeakEventManager.cs for an overview. 
//
//--------------------------------------------------------------------------- 

using System;
using System.Diagnostics;           // Debug
using System.Collections;           // Hashtable 
using System.Collections.Specialized; // HybridDictionary
using System.Runtime.CompilerServices;  // RuntimeHelpers 
using System.Security;              // [SecurityCritical,SecurityTreatAsSafe] 
using System.Threading;             // [ThreadStatic]
using System.Windows;               // WeakEventManager 
using System.Windows.Threading;     // DispatcherObject
using MS.Utility;                   // FrugalList

namespace MS.Internal 
{
    ///  
    /// This class manages the correspondence between event types and 
    /// event managers, in support of the "weak event listener" pattern.
    /// It also stores data on behalf of the managers;  a manager can store 
    /// data of its own choosing, indexed by the pair (manager, source).
    /// 
    internal class WeakEventTable : DispatcherObject
    { 
        #region Constructors
 
        // 
        //  Constructors
        // 

        /// 
        /// Create a new instance of WeakEventTable.
        ///  
        /// 
        ///     Critical: This code calls into Link demanded methods 
        ///         (AppDomain.DomainUnload and AppDomain.ProcessExit) to attach handlers 
        ///     TreatAsSafe: This code does not take any parameter or return state.
        ///     It simply attaches private call back. 
        /// 
        [SecurityCritical,SecurityTreatAsSafe]
        private WeakEventTable()
        { 
            WeakEventTableShutDownListener listener = new WeakEventTableShutDownListener(this);
        } 
 
        #endregion Constructors
 
        #region Internal Properties

        //
        //  Internal Properties 
        //
 
        ///  
        /// Return the WeakEventTable for the current thread
        ///  
        internal static WeakEventTable CurrentWeakEventTable
        {
            get
            { 
                // _currentTable is [ThreadStatic], so there's one per thread
                if (_currentTable == null) 
                { 
                    _currentTable = new WeakEventTable();
                } 

                return _currentTable;
            }
        } 

        ///  
        /// Take a read-lock on the table, and return the IDisposable. 
        /// Queries to the table should occur within a
        /// "using (Table.ReadLock) { ... }" clause, except for queries 
        /// that are already within a write lock.
        /// 
        internal IDisposable ReadLock
        { 
            get { return _lock.ReadLock; }
        } 
 
        /// 
        /// Take a write-lock on the table, and return the IDisposable. 
        /// All modifications to the table should occur within a
        /// "using (Table.WriteLock) { ... }" clause.
        /// 
        internal IDisposable WriteLock 
        {
            get { return _lock.WriteLock; } 
        } 

        ///  
        /// Get or set the manager instance for the given type.
        /// 
        internal WeakEventManager this[Type managerType]
        { 
            get { return (WeakEventManager)_managerTable[managerType]; }
            set { _managerTable[managerType] = value; } 
        } 

        ///  
        /// Get or set the data stored by the given manager for the given source.
        /// 
        internal object this[WeakEventManager manager, object source]
        { 
            get
            { 
                EventKey key = new EventKey(manager, source); 
                object result = _dataTable[key];
                return result; 
            }

            set
            { 
                EventKey key = new EventKey(manager, source, true);
                _dataTable[key] = value; 
            } 
        }
 
        /// 
        /// Indicates whether cleanup is enabled.
        /// 
        ///  
        /// Normally cleanup is always enabled, but a perf test environment might
        /// want to disable cleanup so that it doesn't interfere with the real 
        /// perf measurements. 
        /// 
        internal bool IsCleanupEnabled 
        {
            get { return _cleanupEnabled; }
            set { _cleanupEnabled = value; }
        } 

        #endregion Internal Properties 
 
        #region Internal Methods
 
        //
        //  Internal Methods
        //
 
        /// 
        /// Remove the data for the given manager and source. 
        ///  
        internal void Remove(WeakEventManager manager, object source)
        { 
            EventKey key = new EventKey(manager, source);
            _dataTable.Remove(key);
        }
 
        /// 
        /// Schedule a cleanup pass.  This can be called from any thread. 
        ///  
        internal void ScheduleCleanup()
        { 
            // only the first request after a previous cleanup should schedule real work
            if (Interlocked.Increment(ref _cleanupRequests) == 1)
            {
                Dispatcher.BeginInvoke(DispatcherPriority.ContextIdle, new DispatcherOperationCallback(CleanupOperation), null); 
            }
        } 
 
        /// 
        /// Perform a cleanup pass. 
        /// 
        internal static bool Cleanup()
        {
            return CurrentWeakEventTable.Purge(false); 
        }
 
        #endregion Internal Methods 

        #region Private Methods 

        //
        //  Private Methods
        // 

        // run a cleanup pass 
        private object CleanupOperation(object arg) 
        {
            // allow new requests, even if cleanup is disabled 
            Interlocked.Exchange(ref _cleanupRequests, 0);

            if (IsCleanupEnabled)
            { 
                Purge(false);
            } 
 
            return null;
        } 

        // remove dead entries.  When purgeAll is true, remove all entries.
        private bool Purge(bool purgeAll)
        { 
            bool foundDirt = false;
 
            using (this.WriteLock) 
            {
                // copy the keys into a separate array, so that later on 
                // we can change the table while iterating over the keys
                ICollection ic = _dataTable.Keys;
                EventKey[] keys = new EventKey[ic.Count];
                ic.CopyTo(keys, 0); 

                for (int i=keys.Length-1; i>=0; --i) 
                { 
                    object source = keys[i].Source;
                    foundDirt |= keys[i].Manager.PurgeInternal(source, _dataTable[keys[i]], purgeAll); 

                    // if source has been GC'd, remove its data
                    if (!purgeAll && source == null)
                    { 
                        _dataTable.Remove(keys[i]);
                    } 
                } 

                if (purgeAll) 
                {
                    _managerTable.Clear();
                    _dataTable.Clear();
                } 
            }
 
            return foundDirt; 
        }
 

        // do the final cleanup when the Dispatcher or AppDomain is shut down
        private void OnShutDown()
        { 
            Purge(true);
 
            // remove the table from thread storage 
            _currentTable = null;
        } 

        #endregion Private Methods

        #region Private Fields 

        // 
        //  Private Fields 
        //
 
        private Hashtable _managerTable = new Hashtable();  // maps manager type -> instance
        private Hashtable _dataTable = new Hashtable();     // maps EventKey -> data

        ReaderWriterLockWrapper     _lock = new ReaderWriterLockWrapper(); 
        private int                 _cleanupRequests;
        private bool                _cleanupEnabled = true; 
 
        [ThreadStatic]
        private static WeakEventTable   _currentTable;  // one table per thread 

        #endregion Private Fields

        #region WeakEventTableShutDownListener 

        private sealed class WeakEventTableShutDownListener : ShutDownListener 
        { 
            /// 
            ///     Critical: accesses AppDomain.DomainUnload event 
            ///     TreatAsSafe: This code does not take any parameter or return state.
            ///                  It simply attaches private callbacks.
            /// 
            [SecurityCritical,SecurityTreatAsSafe] 
            public WeakEventTableShutDownListener(WeakEventTable target) : base(target)
            { 
            } 

            internal override void OnShutDown(object target, object sender, EventArgs e) 
            {
                WeakEventTable table = (WeakEventTable)target;
                table.OnShutDown();
            } 
        }
 
        #endregion WeakEventTableShutDownListener 

        #region Table Keys 

        // the key for the data table:  
        private struct EventKey
        { 
            internal EventKey(WeakEventManager manager, object source, bool useWeakRef)
            { 
                _manager = manager; 
                _source = new WeakReference(source);
                _hashcode = unchecked(manager.GetHashCode() + RuntimeHelpers.GetHashCode(source)); 
            }

            internal EventKey(WeakEventManager manager, object source)
            { 
                _manager = manager;
                _source = source; 
                _hashcode = unchecked(manager.GetHashCode() + RuntimeHelpers.GetHashCode(source)); 
            }
 
            internal object Source
            {
                get { return ((WeakReference)_source).Target; }
            } 

            internal WeakEventManager Manager 
            { 
                get { return _manager; }
            } 

            public override int GetHashCode()
            {
#if DEBUG 
                WeakReference wr = _source as WeakReference;
                object source = (wr != null) ? wr.Target : _source; 
                if (source != null) 
                {
                    int hashcode = unchecked(_manager.GetHashCode() + RuntimeHelpers.GetHashCode(source)); 
                    Debug.Assert(hashcode == _hashcode, "hashcodes disagree");
                }
#endif
 
                return _hashcode;
            } 
 
            public override bool Equals(object o)
            { 
                if (o is EventKey)
                {
                    WeakReference wr;
                    EventKey ek = (EventKey)o; 

                    if (_manager != ek._manager || _hashcode != ek._hashcode) 
                        return false; 

                    wr = this._source as WeakReference; 
                    object s1 = (wr != null) ? wr.Target : this._source;
                    wr = ek._source as WeakReference;
                    object s2 = (wr != null) ? wr.Target : ek._source;
 
                    if (s1!=null && s2!=null)
                        return (s1 == s2); 
                    else 
                        return (_source == ek._source);
                } 
                else
                {
                    return false;
                } 
            }
 
            public static bool operator==(EventKey key1, EventKey key2) 
            {
                return key1.Equals(key2); 
            }

            public static bool operator!=(EventKey key1, EventKey key2)
            { 
                return !key1.Equals(key2);
            } 
 
            WeakEventManager _manager;
            object _source;             // lookup: direct ref;  In table: WeakRef 
            int _hashcode;              // cached, in case source is GC'd
        }

        #endregion Table Keys 
    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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