corrade-vassal – Rev 1
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/*
* Copyright (c) 2006-2014, openmetaverse.org
* All rights reserved.
*
* - Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* - Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
* - Neither the name of the openmetaverse.org nor the names
* of its contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
using System;
using System.Threading;
namespace OpenMetaverse
{
/// <summary>
/// A thread-safe lockless queue that supports multiple readers and
/// multiple writers
/// </summary>
public sealed class LocklessQueue<T>
{
/// <summary>
/// Provides a node container for data in a singly linked list
/// </summary>
private sealed class SingleLinkNode
{
/// <summary>Pointer to the next node in list</summary>
public SingleLinkNode Next;
/// <summary>The data contained by the node</summary>
public T Item;
/// <summary>
/// Constructor
/// </summary>
public SingleLinkNode() { }
/// <summary>
/// Constructor
/// </summary>
public SingleLinkNode(T item)
{
this.Item = item;
}
}
/// <summary>Queue head</summary>
SingleLinkNode head;
/// <summary>Queue tail</summary>
SingleLinkNode tail;
/// <summary>Queue item count</summary>
int count;
/// <summary>Gets the current number of items in the queue. Since this
/// is a lockless collection this value should be treated as a close
/// estimate</summary>
public int Count { get { return count; } }
/// <summary>
/// Constructor
/// </summary>
public LocklessQueue()
{
count = 0;
head = tail = new SingleLinkNode();
}
/// <summary>
/// Enqueue an item
/// </summary>
/// <param name="item">Item to enqeue</param>
public void Enqueue(T item)
{
SingleLinkNode newNode = new SingleLinkNode { Item = item };
while (true)
{
SingleLinkNode oldTail = tail;
SingleLinkNode oldTailNext = oldTail.Next;
if (tail == oldTail)
{
if (oldTailNext != null)
{
CAS(ref tail, oldTail, oldTailNext);
}
else if (CAS(ref tail.Next, null, newNode))
{
CAS(ref tail, oldTail, newNode);
Interlocked.Increment(ref count);
return;
}
}
}
}
/// <summary>
/// Try to dequeue an item
/// </summary>
/// <param name="item">Dequeued item if the dequeue was successful</param>
/// <returns>True if an item was successfully deqeued, otherwise false</returns>
public bool TryDequeue(out T item)
{
while (true)
{
SingleLinkNode oldHead = head;
SingleLinkNode oldHeadNext = oldHead.Next;
if (oldHead == head)
{
if (oldHeadNext == null)
{
item = default(T);
count = 0;
return false;
}
if (CAS(ref head, oldHead, oldHeadNext))
{
item = oldHeadNext.Item;
Interlocked.Decrement(ref count);
return true;
}
}
}
}
private static bool CAS(ref SingleLinkNode location, SingleLinkNode comparand, SingleLinkNode newValue)
{
return
(object)comparand ==
(object)Interlocked.CompareExchange<SingleLinkNode>(ref location, newValue, comparand);
}
}
}
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