TypefaceMetricsCache.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / DotNET / DotNET / 8.0 / untmp / WIN_WINDOWS / lh_tools_devdiv_wpf / Windows / wcp / Core / MS / Internal / FontCache / TypefaceMetricsCache.cs / 1 / TypefaceMetricsCache.cs
                        

                        
                            //---------------------------------------------------------------------------- 
//
// Copyright (c) Microsoft Corporation.  All rights reserved.
//
// Description: TypefaceMetricsCache 
//
//  History:    5-25-2005 [....], Created. 
// 
//---------------------------------------------------------------------------
 
using System;
using System.Collections;
using System.Security;
using System.Text; 
using System.Windows;
using System.Windows.Media; 
using System.Windows.Threading; 

using MS.Internal.FontFace; 
using MS.Internal.Shaping;

namespace MS.Internal.FontCache
{ 
    /// 
    /// TypefaceMetricsCache caches managed objects related to a Font's realization. It caches the 3 kinds of 
    /// key-value pairs currently: 
    /// o Friendly name        - canonical name
    /// o FontFamilyIdentifier - First IFontFamily 
    /// o Typeface             - CachedTypeface
    ///
    /// The cache lives in managed space to save working set by allowing multiple instances of FontFamily
    /// and Typeface to share the same IFontFamily and ITypefaceMetrics object. 
    /// For example: in MSNBAML, there are 342 typeface objects and they are canonicalized to only 5
    /// ITypefaceMetrics. 
    /// 
    /// When cache is full, a new instance of the hashtable will be created and the old one will be discarded.
    /// Hence, it is important that the cached object do not keep a pointer to the hashtable to ensure obsolete cached 
    /// values are properly GC'ed.
    /// 
    internal static class TypefaceMetricsCache
    { 
        /// 
        /// Readonly lookup from the cache. 
        ///  
        internal static object ReadonlyLookup(object key)
        { 
            return _hashTable[key];
        }

        ///  
        /// The method adds values into the cache. It uses lock to synchronize access.
        ///  
        internal static void Add(object key, object value) 
        {
            // Hashtable allows for one writer and multiple reader at the same time. So we don't have 
            // read-write confict. In heavy threading environment, the worst is adding
            // the same value more than once.
            lock(_lock)
            { 
                if (_hashTable.Count >= MaxCacheCapacity)
                { 
                    // when cache is full, we just renew the cache. 
                    _hashTable = new Hashtable(MaxCacheCapacity);
                } 

                _hashTable[key] = value;
            }
        } 

        private static Hashtable _hashTable = new Hashtable(MaxCacheCapacity); 
        private static object _lock         = new object(); 
        private const int MaxCacheCapacity  = 64;   // Maximum cache capacity
    } 
}

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

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