Code:
/ FX-1434 / FX-1434 / 1.0 / untmp / whidbey / REDBITS / ndp / fx / src / CompMod / System / Collections / Specialized / HybridDictionary.cs / 1 / HybridDictionary.cs
//------------------------------------------------------------------------------ //// Copyright (c) Microsoft Corporation. All rights reserved. // //----------------------------------------------------------------------------- namespace System.Collections.Specialized { using System.Collections; using System.Globalization; ////// [Serializable] public class HybridDictionary: IDictionary { // These numbers have been carefully tested to be optimal. Please don't change them // without doing thorough performance testing. private const int CutoverPoint = 9; private const int InitialHashtableSize = 13; private const int FixedSizeCutoverPoint = 6; // Instance variables. This keeps the HybridDictionary very light-weight when empty private ListDictionary list; private Hashtable hashtable; private bool caseInsensitive; ////// This data structure implements IDictionary first using a linked list /// (ListDictionary) and then switching over to use Hashtable when large. This is recommended /// for cases where the number of elements in a dictionary is unknown and might be small. /// /// It also has a single boolean parameter to allow case-sensitivity that is not affected by /// ambient culture and has been optimized for looking up case-insensitive symbols /// ////// public HybridDictionary() { } ///[To be supplied.] ////// public HybridDictionary(int initialSize) : this(initialSize, false) { } ///[To be supplied.] ////// public HybridDictionary(bool caseInsensitive) { this.caseInsensitive = caseInsensitive; } ///[To be supplied.] ////// public HybridDictionary(int initialSize, bool caseInsensitive) { this.caseInsensitive = caseInsensitive; if (initialSize >= FixedSizeCutoverPoint) { if (caseInsensitive) { hashtable = new Hashtable(initialSize, StringComparer.OrdinalIgnoreCase); } else { hashtable = new Hashtable(initialSize); } } } ///[To be supplied.] ////// public object this[object key] { get { //[To be supplied.] ///// Hashtable supports multiple read, one writer thread safety. // Although we never made the same guarantee for HybridDictionary, // it is still nice to do the same thing here since we have recommended // HybridDictioary as replacement for Hashtable. // // ListDictionary cachedList = list; if (hashtable != null) { return hashtable[key]; } else if (cachedList != null) { return cachedList[key]; } else { //// cachedList can be null in too cases: // (1) The dictionary is empty, we will return null in this case // (2) There is writer which is doing ChangeOver. However in that case // we should see the change to hashtable as well. // So it should work just fine. // // if (key == null) { throw new ArgumentNullException("key", SR.GetString(SR.ArgumentNull_Key)); } return null; } } set { if (hashtable != null) { hashtable[key] = value; } else if (list != null) { if (list.Count >= CutoverPoint - 1) { ChangeOver(); hashtable[key] = value; } else { list[key] = value; } } else { list = new ListDictionary(caseInsensitive ? StringComparer.OrdinalIgnoreCase : null); list[key] = value; } } } private ListDictionary List { get { if (list == null) { list = new ListDictionary(caseInsensitive ? StringComparer.OrdinalIgnoreCase : null); } return list; } } private void ChangeOver() { IDictionaryEnumerator en = list.GetEnumerator(); Hashtable newTable; if (caseInsensitive) { newTable = new Hashtable(InitialHashtableSize, StringComparer.OrdinalIgnoreCase); } else { newTable = new Hashtable(InitialHashtableSize); } while (en.MoveNext()) { newTable.Add(en.Key, en.Value); } //// Keep the order of writing to hashtable and list. // We assume we will see the change in hashtable if list is set to null in // this method in another reader thread. // hashtable = newTable; list = null; } ////// public int Count { get { ListDictionary cachedList = list; if (hashtable != null) { return hashtable.Count; } else if (cachedList != null) { return cachedList.Count; } else { return 0; } } } ///[To be supplied.] ////// public ICollection Keys { get { if (hashtable != null) { return hashtable.Keys; } else { return List.Keys; } } } ///[To be supplied.] ////// public bool IsReadOnly { get { return false; } } ///[To be supplied.] ////// public bool IsFixedSize { get { return false; } } ///[To be supplied.] ////// public bool IsSynchronized { get { return false; } } ///[To be supplied.] ////// public object SyncRoot { get { return this; } } ///[To be supplied.] ////// public ICollection Values { get { if (hashtable != null) { return hashtable.Values; } else { return List.Values; } } } ///[To be supplied.] ////// public void Add(object key, object value) { if (hashtable != null) { hashtable.Add(key, value); } else { if (list == null) { list = new ListDictionary(caseInsensitive ? StringComparer.OrdinalIgnoreCase : null); list.Add(key, value); } else { if (list.Count + 1 >= CutoverPoint) { ChangeOver(); hashtable.Add(key, value); } else { list.Add(key, value); } } } } ///[To be supplied.] ////// public void Clear() { if(hashtable != null) { Hashtable cachedHashtable = hashtable; hashtable = null; cachedHashtable.Clear(); } if( list != null) { ListDictionary cachedList = list; list = null; cachedList.Clear(); } } ///[To be supplied.] ////// public bool Contains(object key) { ListDictionary cachedList = list; if (hashtable != null) { return hashtable.Contains(key); } else if (cachedList != null) { return cachedList.Contains(key); } else { if (key == null) { throw new ArgumentNullException("key", SR.GetString(SR.ArgumentNull_Key)); } return false; } } ///[To be supplied.] ////// public void CopyTo(Array array, int index) { if (hashtable != null) { hashtable.CopyTo(array, index); } else { List.CopyTo(array, index); } } ///[To be supplied.] ////// public IDictionaryEnumerator GetEnumerator() { if (hashtable != null) { return hashtable.GetEnumerator(); } if (list == null) { list = new ListDictionary(caseInsensitive ? StringComparer.OrdinalIgnoreCase : null); } return list.GetEnumerator(); } ///[To be supplied.] ////// IEnumerator IEnumerable.GetEnumerator() { if (hashtable != null) { return hashtable.GetEnumerator(); } if (list == null) { list = new ListDictionary(caseInsensitive ? StringComparer.OrdinalIgnoreCase : null); } return list.GetEnumerator(); } ///[To be supplied.] ////// public void Remove(object key) { if (hashtable != null) { hashtable.Remove(key); } else if (list != null){ list.Remove(key); } else { if (key == null) { throw new ArgumentNullException("key", SR.GetString(SR.ArgumentNull_Key)); } } } } }[To be supplied.] ///
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