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/* ****************************************************************************
*
* Copyright (c) Microsoft Corporation.
*
* This source code is subject to terms and conditions of the Microsoft Public License. A
* copy of the license can be found in the License.html file at the root of this distribution. If
* you cannot locate the Microsoft Public License, please send an email to
* dlr@microsoft.com. By using this source code in any fashion, you are agreeing to be bound
* by the terms of the Microsoft Public License.
*
* You must not remove this notice, or any other, from this software.
*
*
* ***************************************************************************/
using System;
using System.Collections.Generic;
namespace Microsoft.Scripting.Utils {
/// <summary>
/// Simple class for tracking a list of items and enumerating over them.
/// The items are stored in weak references; if the objects are collected,
/// they will not be seen when enumerating.
/// </summary>
/// <typeparam name="T">The type of the collection element.</typeparam>
internal sealed class WeakCollection<T> : IEnumerable<T> where T : class {
private const int DefaultCapacity = 4; // default capacity of List<T>
private WeakReference[] _items = new WeakReference[DefaultCapacity];
private int _size;
public void Add(T t) {
EnsureCapacity(_size + 1);
_items[_size++] = new WeakReference(t);
}
private void EnsureCapacity(int size) {
if (size > _items.Length) {
// Clear out dead entires first; we might not have to resize it
Compact();
if (size > _items.Length) {
// Need to expand the list
int newSize = _items.Length * 2;
if (newSize < size) {
newSize = size;
}
var newList = new WeakReference[newSize];
_items.CopyTo(newList, 0);
_items = newList;
}
}
}
private void Compact() {
int newSize = 0;
for (int i = 0; i < _size; i++) {
if (_items[i].IsAlive) {
if (newSize < i) {
_items[newSize] = _items[i];
}
newSize++;
}
}
for (int i = newSize; i < _size; i++) {
_items[i] = null;
}
_size = newSize;
}
public IEnumerator<T> GetEnumerator() {
for (int i = 0; i < _size; i++) {
T light = (T)_items[i].Target;
if (light != null) {
yield return light;
}
}
}
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
return GetEnumerator();
}
}
}
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