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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.Collections.Generic;
using System.Threading;
using Microsoft.Contracts;
namespace Microsoft.Scripting.Utils {
/// <summary>
/// List optimized for few writes and multiple reads. It provides thread-safe read and write access.
/// Iteration is not thread-safe by default, but GetCopyForRead allows for iteration
/// without taking a lock.
/// </summary>
public class CopyOnWriteList<T> : IList<T> {
List<T> _list = new List<T>();
List<T> GetNewListForWrite() {
List<T> oldList = _list;
List<T> newList = new List<T>(oldList.Count + 1);
newList.AddRange(oldList);
return newList;
}
/// <summary>
/// Gets a copy of the contents of the list. The copy will not change even if the original
/// CopyOnWriteList object is modified. This method should be used to iterate the list in
/// a thread-safe way if no lock is taken. Iterating on the original list is not guaranteed
/// to be thread-safe.
/// </summary>
/// <returns>The returned copy should not be modified by the caller.</returns>
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1024:UsePropertiesWhereAppropriate")] // TODO: fix
public List<T> GetCopyForRead() {
// Just return the underlying list
return _list;
}
#region IList<T> Members
public int IndexOf(T item) {
return _list.IndexOf(item);
}
public void Insert(int index, T item) {
List<T> oldList, replacedList;
do {
oldList = _list;
List<T> newList = GetNewListForWrite();
newList.Insert(index, item);
replacedList = Interlocked.CompareExchange(ref _list, newList, oldList);
} while (replacedList != oldList);
}
public void RemoveAt(int index) {
List<T> oldList, replacedList;
do {
oldList = _list;
List<T> newList = GetNewListForWrite();
newList.RemoveAt(index);
replacedList = Interlocked.CompareExchange(ref _list, newList, oldList);
} while (replacedList != oldList);
}
public T this[int index] {
get {
return _list[index];
}
set {
List<T> oldList, replacedList;
do {
oldList = _list;
List<T> newList = GetNewListForWrite();
newList[index] = value;
replacedList = Interlocked.CompareExchange(ref _list, newList, oldList);
} while (replacedList != oldList);
}
}
#endregion
#region ICollection<T> Members
public void Add(T item) {
List<T> oldList, replacedList;
do {
oldList = _list;
List<T> newList = GetNewListForWrite();
newList.Add(item);
replacedList = Interlocked.CompareExchange(ref _list, newList, oldList);
} while (replacedList != oldList);
}
public void Clear() {
_list = new List<T>();
}
[Confined]
public bool Contains(T item) {
return _list.Contains(item);
}
public void CopyTo(T[] array, int arrayIndex) {
_list.CopyTo(array, arrayIndex);
}
public int Count {
get { return _list.Count; }
}
public bool IsReadOnly {
get { return false; }
}
public bool Remove(T item) {
List<T> oldList, replacedList;
bool ret;
do {
oldList = _list;
List<T> newList = GetNewListForWrite();
ret = newList.Remove(item);
replacedList = Interlocked.CompareExchange(ref _list, newList, oldList);
} while (replacedList != oldList);
return ret;
}
#endregion
#region IEnumerable<T> Members
[Pure]
public IEnumerator<T> GetEnumerator() {
return _list.GetEnumerator();
}
#endregion
#region IEnumerable Members
[Pure]
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
return ((System.Collections.IEnumerable)_list).GetEnumerator();
}
#endregion
}
}
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