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/*
* Copyright (c) 2009, 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 OpenSim.Framework
{
public class LocklessQueue<T>
{
private sealed class SingleLinkNode
{
public SingleLinkNode Next;
public T Item;
}
SingleLinkNode head;
SingleLinkNode tail;
int count;
public virtual int Count { get { return count; } }
public LocklessQueue()
{
Init();
}
public void Enqueue(T item)
{
SingleLinkNode oldTail = null;
SingleLinkNode oldTailNext;
SingleLinkNode newNode = new SingleLinkNode();
newNode.Item = item;
bool newNodeWasAdded = false;
while (!newNodeWasAdded)
{
oldTail = tail;
oldTailNext = oldTail.Next;
if (tail == oldTail)
{
if (oldTailNext == null)
newNodeWasAdded = CAS(ref tail.Next, null, newNode);
else
CAS(ref tail, oldTail, oldTailNext);
}
}
CAS(ref tail, oldTail, newNode);
Interlocked.Increment(ref count);
}
public virtual bool Dequeue(out T item)
{
item = default(T);
SingleLinkNode oldHead = null;
bool haveAdvancedHead = false;
while (!haveAdvancedHead)
{
oldHead = head;
SingleLinkNode oldTail = tail;
SingleLinkNode oldHeadNext = oldHead.Next;
if (oldHead == head)
{
if (oldHead == oldTail)
{
if (oldHeadNext == null)
{
count = 0;
return false;
}
CAS(ref tail, oldTail, oldHeadNext);
}
else
{
item = oldHeadNext.Item;
haveAdvancedHead = CAS(ref head, oldHead, oldHeadNext);
if (haveAdvancedHead)
{
oldHeadNext.Item = default(T);
oldHead.Next = null;
}
}
}
}
Interlocked.Decrement(ref count);
return true;
}
public void Clear()
{
// ugly
T item;
while(Dequeue(out item));
Init();
}
private void Init()
{
count = 0;
head = tail = new SingleLinkNode();
}
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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