Code:
/ DotNET / DotNET / 8.0 / untmp / WIN_WINDOWS / lh_tools_devdiv_wpf / Windows / wcp / Shared / MS / Internal / WeakReferenceList.cs / 1 / WeakReferenceList.cs
using System; using System.Collections; using System.Diagnostics; #if WINDOWS_BASE using MS.Internal.WindowsBase; #elif PRESENTATION_CORE using MS.Internal.PresentationCore; #elif PRESENTATIONFRAMEWORK using MS.Internal.PresentationFramework; #elif DRT using MS.Internal.Drt; #else #error Attempt to use FriendAccessAllowedAttribute from an unknown assembly. using MS.Internal.YourAssemblyName; #endif namespace MS.Internal { ////// This is a Cached ThreadSafe ArrayList of WeakReferences. /// - When the "List" property is requested a readonly reference to the /// list is returned and a reference to the readonly list is cached. /// - If the "List" is requested again, the same cached reference is returned. /// - When the list is modified, if a readonly reference is present in the /// cache then the list is copied before it is modified and the readonly list is /// released from the cache. /// [FriendAccessAllowed] internal class WeakReferenceList : CopyOnWriteList, IEnumerable { public WeakReferenceList():base(null) { } public WeakReferenceList(object syncRoot):base(syncRoot) { } public WeakReferenceListEnumerator GetEnumerator() { return new WeakReferenceListEnumerator(List); } IEnumerator IEnumerable.GetEnumerator() { return GetEnumerator(); } ////// Add a weak reference to the List. /// Returns true if successfully added. /// Returns false if object is already on the list. /// public override bool Add(object obj) { Debug.Assert(null!=obj, "WeakReferenceList.Add() should not be passed null."); lock(base.SyncRoot) { int index = FindWeakReference(obj); // If the object is already on the list then // we are done. (return false) if(index >= 0) return false; return base.Internal_Add(new WeakReference(obj)); } } ////// Remove a weak reference to the List. /// Returns true if successfully added. /// Returns false if object is already on the list. /// public override bool Remove(object obj) { Debug.Assert(null!=obj, "WeakReferenceList.Remove() should not be passed null."); lock(base.SyncRoot) { int index = FindWeakReference(obj); // If the object is not on the list then // we are done. (return false) if(index < 0) return false; return base.RemoveAt(index); } } ////// Insert a weak reference into the List. /// Returns true if successfully inserted. /// Returns false if object is already on the list. /// public bool Insert(int index, object obj) { Debug.Assert(null!=obj, "WeakReferenceList.Add() should not be passed null."); lock(base.SyncRoot) { int existingIndex = FindWeakReference(obj); // If the object is already on the list then // we are done. (return false) if(existingIndex >= 0) return false; return base.Internal_Insert(index, new WeakReference(obj)); } } ////// Find an object on the List. /// Also cleans up dead weakreferences. /// private int FindWeakReference(object obj) { // syncRoot Lock MUST be held by the caller. // Search the LiveList looking for the object, also remove any // dead references.we find. These two operations are combinded // to prevent having to walk the list twice. // // We use the "LiveList" to avoid snapping a Clone everytime we // Change something. // To do this correctly you need to understand how the base class // virtualizes the Copy On Write. ArrayList list = base.LiveList; int foundItem = -1; for(int i = 0; i < list.Count; i++) { WeakReference weakRef = (WeakReference) list[i]; if(weakRef.IsAlive) { if(obj == weakRef.Target) foundItem = i; } else { // Removing dead refs should not invalidate "foundItem" above. // Call the base RemoveAt to preserve the Copy on Write // virtualization. ie. list.RemoveAt(i) would be WRONG! // The RemoveAt call might Clone the LiveList (the first // time only) so we should get a new reference to it. base.RemoveAt(i); list = base.LiveList; // Also the ArrayList will copy-up to fill the Removed element // so back up and do the same index again. i -= 1; } } return foundItem; } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007. // Copyright (c) Microsoft Corporation. All rights reserved.
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