Code:
/ DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / fx / src / Data / System / Data / ProviderBase / DbReferenceCollection.cs / 2 / DbReferenceCollection.cs
//------------------------------------------------------------------------------ //// Copyright (c) Microsoft Corporation. All rights reserved. // //[....] //[....] //----------------------------------------------------------------------------- namespace System.Data.ProviderBase { using System; using System.Collections; using System.Diagnostics; internal abstract class DbReferenceCollection { #if ORACLE abstract public void Add(object value, int tag); abstract public void Notify(int message); abstract public void Remove(object value); #else private struct CollectionEntry { private int _tag; // information about the reference private WeakReference _weak; // the reference itself. public bool HasTarget { get { Debug.Assert((0 != _tag && null != _weak) || (null == _weak || !_weak.IsAlive), "0 tag with Target"); return ((0 != _tag) && null != _weak && _weak.IsAlive); } } public bool InUse { get { return (null != _weak); } } public int Tag { get { return _tag; } set { _tag = value; } } public object Target { get { if (0 != _tag) { return _weak.Target; } Debug.Assert(!_weak.IsAlive, "0 tag with Target"); return null; } set { if (null == _weak) { _weak = new WeakReference(value, false); } else { _weak.Target = value; } } } } private CollectionEntry[] _items; protected DbReferenceCollection() { _items = new CollectionEntry[5]; } abstract public void Add(object value, int tag); protected void AddItem(object value, int tag) { Debug.Assert(null != value && 0 != tag, "AddItem with null value or 0 tag"); CollectionEntry[] items = _items; for (int i = 0; i < items.Length; ++i) { if (!items[i].HasTarget) { items[i].Target = value; items[i].Tag = tag; Debug.Assert(items[i].HasTarget, "missing expected target"); return; } } int newlength = ((5 == items.Length) ? 15 : (items.Length + 15)); CollectionEntry[] jtems = new CollectionEntry[newlength]; for (int i = 0; i < items.Length; ++i) { jtems[i] = items[i]; } jtems[items.Length].Target = value; jtems[items.Length].Tag = tag; Debug.Assert(jtems[items.Length].HasTarget, "missing expected target"); _items = jtems; } internal IEnumerable Filter(int tag) { return new DbFilteredReferenceCollection (_items, tag); } public void Notify(int message) { CollectionEntry[] items = _items; for (int index = 0; index < items.Length; ++index) { if (items[index].InUse) { object value = items[index].Target; // checks tag & gets target if (null != value) { Debug.Assert(items[index].HasTarget, "missing expected target"); if (!NotifyItem(message, items[index].Tag, value)) { items[index].Tag = 0; items[index].Target = null; Debug.Assert(!items[index].HasTarget, "has unexpected target"); } } // else (0 == Tag) or !IsAlive } else { Debug.Assert(!items[index].HasTarget, "has unexpected target"); break; // we're done as soon as we find the first null in the list } } } abstract protected bool NotifyItem(int message, int tag, object value); public void Purge() { CollectionEntry[] items = _items; #if DEBUG for(int i = 0; i < items.Length; ++i) { Debug.Assert(!items[i].HasTarget, "unexpected target during purge"); } #endif if (100 < items.Length) { _items = new CollectionEntry[5]; // revert back to 5 items if we're really big... } } abstract public void Remove(object value); protected void RemoveItem(object value) { Debug.Assert(null != value, "RemoveItem with null"); CollectionEntry[] items = _items; for (int index = 0; index < items.Length; ++index) { if (items[index].InUse) { if (value == items[index].Target) { // checks tag & gets target items[index].Tag = 0; items[index].Target = null; Debug.Assert(!items[index].HasTarget, "has unexpected target"); break; } // else (0 == Tag) or !IsAlive or (value != Target) } else { break; // we're done as soon as we find the first null in the list } } } private struct DbFilteredReferenceCollection : IEnumerable { private readonly DbReferenceCollection.CollectionEntry[] _items; private readonly int _filterTag; internal DbFilteredReferenceCollection(DbReferenceCollection.CollectionEntry[] items, int filterTag) { _items = items; _filterTag = filterTag; } IEnumerator IEnumerable.GetEnumerator() { return new DbFilteredReferenceCollectionedEnumerator(_items, _filterTag); } private struct DbFilteredReferenceCollectionedEnumerator : IEnumerator { private readonly DbReferenceCollection.CollectionEntry[] _items; private readonly int _filterTag; private int _current; internal DbFilteredReferenceCollectionedEnumerator(DbReferenceCollection.CollectionEntry[] items, int filterTag) { _items = items; _filterTag = filterTag; _current = -1; } object IEnumerator.Current { get { return _items[_current].Target; } } bool IEnumerator.MoveNext() { while (++_current < _items.Length) { if (_items[_current].InUse) { if (_items[_current].Tag == _filterTag) { return true; } } else { break; } } return false; } void IEnumerator.Reset() { _current = -1; } } } #endif } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007. // Copyright (c) Microsoft Corporation. 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