BaseHashHelper.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Base / MS / Internal / BaseHashHelper.cs / 1305600 / BaseHashHelper.cs
                        

                        
                            //---------------------------------------------------------------------------- 
//
// 
//    Copyright (C) 2003 by Microsoft Corporation.  All rights reserved.
//  
//
// 
// Description: Static class to help work around hashing-related bugs. 
//
//--------------------------------------------------------------------------- 

using System;
using System.Reflection;                // Assembly
using System.Collections.Specialized;   // HybridDictionary 
using MS.Internal.WindowsBase;          // [FriendAccessAllowed]
 
namespace MS.Internal 
{
    [FriendAccessAllowed]   // defined in Base, used in Core and Framework 
    internal static class BaseHashHelper
    {
        static BaseHashHelper()
        { 
            // register bad types from WindowsBase
            MS.Internal.Hashing.WindowsBase.HashHelper.Initialize(); 
        } 

        [FriendAccessAllowed]   // defined in Base, used in Core and Framework 
        internal static void RegisterTypes(Assembly assembly, Type[] types)
        {
            HybridDictionary dictionary = DictionaryFromList(types);
 
            lock(_table)
            { 
                _table[assembly] = dictionary; 
            }
        } 

        // Some types don't have reliable hash codes - the hashcode can change
        // during the lifetime of an object of that type.  Such an object cannot
        // be used as the key of a hashtable or dictionary.  This is where we 
        // detect such objects, so the caller can find some other way to cope.
        [FriendAccessAllowed]   // defined in Base, used in Core and Framework 
        internal static bool HasReliableHashCode(object item) 
        {
            // null doesn't actually have a hashcode at all.  This method can be 
            // called with a representative item from a collection - if the
            // representative is null, we'll be pessimistic and assume the
            // items in the collection should not be hashed.
            if (item == null) 
                return false;
 
            Type type = item.GetType(); 
            Assembly assembly = type.Assembly;
            HybridDictionary dictionary; 

            lock(_table)
            {
                dictionary = (HybridDictionary)_table[assembly]; 
            }
 
            if (dictionary == null) 
            {
                dictionary = new HybridDictionary(); 

                lock(_table)
                {
                    _table[assembly] = dictionary; 
                }
            } 
 
            return !dictionary.Contains(type);
        } 

        // populate a dictionary from the given list
        private static HybridDictionary DictionaryFromList(Type[] types)
        { 
            HybridDictionary dictionary = new HybridDictionary(types.Length);
            for (int i=0; i

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