BaseHashHelper.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 / Base / MS / Internal / BaseHashHelper.cs / 2 / 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) 
            {
                // if we don't have an entry for the object's assembly, 
                // see if we know something about the assembly
                /* no external types on the `blacklist any more
                if (type.Namespace == "System.Data" && IsSystemData(assembly))
                { 
                    dictionary = TypesForSystemData();
                } 
                else 
                */
                { 
                    // if we don't know anything about the assembly, give it an
                    // empty dictionary.  This makes future lookups fast.  We just
                    // have to hope that every type in the assembly has reliable
                    // hashcodes. 
                    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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