TextElementCollectionHelper.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Framework / System / Windows / Documents / TextElementCollectionHelper.cs / 1305600 / TextElementCollectionHelper.cs
                        
                        
                            //---------------------------------------------------------------------------- 
//
// Copyright (C) Microsoft Corporation.  All rights reserved.
//
// Description: Static methods for all TextElementCollection instances. 
//
//--------------------------------------------------------------------------- 
 
namespace System.Windows.Documents
{ 
    // This class maintains a static list of "clean" TextElementCollection
    // instances.  Clean in this sense means guarantee not to have been
    // modified in a way that could invalidate their _indexCache members.
    // 
    // The cache is a simple list of WeakReferences to collections.
    // The size of the list limits the number of collections 
    // that can be used to modify content simultaneously with good IList 
    // performance.  The scenario we're concerned about is the parser,
    // which will allocate one collection for each scoping TextElement 
    // in a document: hello world
    // requires a minimum cache size of 3 to keep load times O(n).
    internal static class TextElementCollectionHelper
    { 
        //-------------------------------------------------------------------
        // 
        //  Internal Methods 
        //
        //------------------------------------------------------------------- 

        #region Internal Methods

        // Invalidates any collection tracking parent's children. 
        // Called by the TextContainer.
        internal static void MarkDirty(DependencyObject parent) 
        { 
            if (parent == null)
            { 
                return;
            }

            lock (_cleanParentList) 
            {
                for (int i = 0; i < _cleanParentList.Length; i++) 
                { 
                    if (_cleanParentList[i] != null)
                    { 
                        ParentCollectionPair pair = (ParentCollectionPair)_cleanParentList[i].Target;

                        if (pair == null || pair.Parent == parent)
                        { 
                            _cleanParentList[i] = null;
                        } 
                    } 
                }
            } 
        }

        // Tags a parent/collection as synchronized.
        // Since we use a most-recently-used algorithm, it's useful 
        // to call this any time a collection is touched, even if it is
        // only read. 
        internal static void MarkClean(DependencyObject parent, object collection) 
        {
            lock (_cleanParentList) 
            {
                int firstFreeIndex;
                int index = GetCleanParentIndex(parent, collection, out firstFreeIndex);
 
                if (index == -1)
                { 
                    index = firstFreeIndex >= 0 ? firstFreeIndex : _cleanParentList.Length - 1; 
                    _cleanParentList[index] = new WeakReference(new ParentCollectionPair(parent, collection));
                } 

                TouchCleanParent(index);
            }
        } 

        // Returns true if the parent/collection pair are clean. 
        // Since we use a most-recently-used algorithm, it's useful 
        // to call this any time a collection is touched, even if it is
        // only read. 
        internal static bool IsCleanParent(DependencyObject parent, object collection)
        {
            int index = -1;
 
            lock (_cleanParentList)
            { 
                int firstFreeIndex; 
                index = GetCleanParentIndex(parent, collection, out firstFreeIndex);
 
                if (index >= 0)
                {
                    TouchCleanParent(index);
                } 
            }
 
            return (index >= 0); 
        }
 
        #endregion Internal Methods

        //--------------------------------------------------------------------
        // 
        //  Private Methods
        // 
        //------------------------------------------------------------------- 

        #region Private Methods 

        // Moves an entry to the top of the most-recently-used list.
        // Caller must hold a lock on _cleanParentList!
        private static void TouchCleanParent(int index) 
        {
            WeakReference parentReference = _cleanParentList[index]; 
            // Shift preceding parents down, dropping the last parent. 
            Array.Copy(_cleanParentList, 0, _cleanParentList, 1, index);
            // Put the mru parent at the head. 
            _cleanParentList[0] = parentReference;
        }

        // Returns the index of an entry in the list, or -1 if not present. 
        // Caller must hold a lock on _cleanParentList!
        private static int GetCleanParentIndex(DependencyObject parent, object collection, out int firstFreeIndex) 
        { 
            int index = -1;
 
            firstFreeIndex = -1;

            for (int i = 0; i < _cleanParentList.Length; i++)
            { 
                if (_cleanParentList[i] == null)
                { 
                    if (firstFreeIndex == -1) 
                    {
                        firstFreeIndex = i; 
                    }
                }
                else
                { 
                    ParentCollectionPair pair = (ParentCollectionPair)_cleanParentList[i].Target;
 
                    if (pair == null) 
                    {
                        // WeakReference is dead, remove it. 
                        _cleanParentList[i] = null;
                        if (firstFreeIndex == -1)
                        {
                            firstFreeIndex = i; 
                        }
                    } 
                    else if (pair.Parent == parent && pair.Collection == collection) 
                    {
                        // Found a match.  Keep going to clean up any dead WeakReferences 
                        // or set firstFreeIndex.
                        index = i;
                    }
                } 
            }
 
            return index; 
        }
 
        #endregion Private Methods

        //--------------------------------------------------------------------
        // 
        //  Private Types
        // 
        //-------------------------------------------------------------------- 

        #region Private Types 

        // A parent/collection entry.
        private class ParentCollectionPair
        { 
            internal ParentCollectionPair(DependencyObject parent, object collection)
            { 
                _parent = parent; 
                _collection = collection;
            } 

            internal DependencyObject Parent { get { return _parent; } }

            internal object Collection { get { return _collection; } } 

            private readonly DependencyObject _parent; 
 
            private readonly object _collection;
        } 

        #endregion Private Types

        //------------------------------------------------------------------- 
        //
        //  Private Fields 
        // 
        //--------------------------------------------------------------------
 
        #region Private Fields

        // Static list of clean parent/collection pairs.
        private static readonly WeakReference []_cleanParentList = new WeakReference[10]; 

        #endregion Private Fields 
    } 
}

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

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