Code:
/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Base / System / Windows / DependentList.cs / 1305600 / DependentList.cs
using System; using MS.Utility; using MS.Internal; namespace System.Windows { // // The list of Dependents that depend on a Source[ID] // // Steps are taken to guard against list corruption due to re-entrancy when // the Invalidation callbacks call Add / Remove. But multi-treaded // access is not expected and so locks are not used. // internal class DependentList: MS.Utility.FrugalObjectList{ static int _skipper=0; public void Add(DependencyObject d, DependencyProperty dp, Expression expr) { // don't clean up every time. This will midigate the O(N) nature of Add(). // Which would cause building a list to have O(N^2). yuck! // Clean the list less often the longer it gets. if(0 == ++_skipper%(1+ (base.Count/4))) CleanUpDeadWeakReferences(true); Dependent dep = new Dependent(d, dp, expr); base.Add(dep); } public void Remove(DependencyObject d, DependencyProperty dp, Expression expr) { Dependent dep = new Dependent(d, dp, expr); base.Remove(dep); } public bool IsEmpty { get { if(0 == base.Count) return true; CleanUpDeadWeakReferences(false); return 0 == base.Count; } } public void InvalidateDependents(DependencyObject source, DependencyPropertyChangedEventArgs sourceArgs) { // Take a snapshot of the list to protect against re-entrancy via Add / Remove. Dependent[] snapList = base.ToArray(); for(int i=0; i = 0; i--) { if(!snapList[i].IsValid()) { base.RemoveAt(i); } else { if(!doAll) return; } } } } internal struct Dependent { private DependencyProperty _DP; private WeakReference _wrDO; private WeakReference _wrEX; public bool IsValid() { // Expression is never null (could Assert that but throw is fine) if(!_wrEX.IsAlive) return false; // It is OK to be null but if it isn't, then the target mustn't be dead. if(null != _wrDO && !_wrDO.IsAlive) return false; return true; } public Dependent(DependencyObject o, DependencyProperty p, Expression e) { _wrEX = (null == e) ? null : new WeakReference(e); _DP = p; _wrDO = (null == o) ? null : new WeakReference(o); } public DependencyObject DO { get { if(null == _wrDO) return null; else return (DependencyObject)_wrDO.Target; } } public DependencyProperty DP { get { return _DP; } } public Expression Expr { get { if(null == _wrEX) return null; else return (Expression)_wrEX.Target; } } override public bool Equals(object o) { if(! (o is Dependent)) return false; Dependent d = (Dependent)o; // Not equal to Dead values. // This is assuming that at least one of the compared items is live. // This assumtion comes from knowing that Equal is used by FrugalList.Remove() // and if you look at DependentList.Remove()'s arguments, it can only // be passed strong references. // Therefore: Items being removed (thus compared here) will not be dead. if(!IsValid() || !d.IsValid()) return false; if(_wrEX.Target != d._wrEX.Target) return false; if(_DP != d._DP) return false; // if they are both non-null then the Targets must match. if(null != _wrDO && null != d._wrDO) { if(_wrDO.Target != d._wrDO.Target) return false; } // but only one is non-null then they are not equal else if(null != _wrDO || null != d._wrDO) return false; return true; } public static bool operator== (Dependent first, Dependent second) { return first.Equals(second); } public static bool operator!= (Dependent first, Dependent second) { return !(first.Equals(second)); } // We don't expect to need this function. [Required when overriding Equals()] // Write a good HashCode anyway (if not a fast one) override public int GetHashCode() { int hashCode; Expression ex = (Expression)_wrEX.Target; hashCode = (null == ex) ? 0 : ex.GetHashCode(); if(null != _wrDO) { DependencyObject DO = (DependencyObject)_wrDO.Target; hashCode += (null == DO) ? 0 : DO.GetHashCode(); } hashCode += (null == _DP) ? 0 : _DP.GetHashCode(); return hashCode; } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007. // Copyright (c) Microsoft Corporation. All rights reserved.
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