/// <summary>
/// Adds an object to the end of the queue.
/// </summary>
/// <param name="item">the object to add to the queue</param>
public void Enqueue(T item)
{
SingleLinkNode <T> oldTail = null;
SingleLinkNode <T> oldTailNext;
var newNode = new SingleLinkNode <T> {
Item = item
};
bool newNodeWasAdded = false;
while (!newNodeWasAdded)
{
oldTail = _tail;
oldTailNext = oldTail.Next;
if (_tail == oldTail)
{
if (oldTailNext == null)
{
newNodeWasAdded =
Interlocked.CompareExchange <SingleLinkNode <T> >(ref _tail.Next, newNode, null) == null;
}
else
{
Interlocked.CompareExchange <SingleLinkNode <T> >(ref _tail, oldTailNext, oldTail);
}
}
}
Interlocked.CompareExchange <SingleLinkNode <T> >(ref _tail, newNode, oldTail);
Interlocked.Increment(ref _count);
}
/// <summary>
/// Returns an enumerator that iterates through the queue.
/// </summary>
/// <returns>an enumerator for the queue</returns>
public IEnumerator <T> GetEnumerator()
{
SingleLinkNode <T> currentNode = _head;
do
{
if (currentNode.Item == null)
{
yield break;
}
else
{
yield return(currentNode.Item);
}
}while ((currentNode = currentNode.Next) != null);
yield break;
}
/// <summary>
/// Clears the queue.
/// </summary>
/// <remarks>This method is not thread-safe.</remarks>
public void Clear()
{
SingleLinkNode <T> tempNode;
SingleLinkNode <T> currentNode = _head;
while (currentNode != null)
{
tempNode = currentNode;
currentNode = currentNode.Next;
tempNode.Item = default(T);
tempNode.Next = null;
}
_head = new SingleLinkNode <T>();
_tail = _head;
_count = 0;
}
/// <summary>
/// Removes and returns the object at the beginning of the queue.
/// </summary>
/// <param name="item">
/// when the method returns, contains the object removed from the beginning of the queue,
/// if the queue is not empty; otherwise it is the default value for the element type
/// </param>
/// <returns>
/// true if an object from removed from the beginning of the queue;
/// false if the queue is empty
/// </returns>
public bool TryDequeue(out T item)
{
item = default(T);
SingleLinkNode <T> oldHead = null;
bool haveAdvancedHead = false;
while (!haveAdvancedHead)
{
oldHead = _head;
SingleLinkNode <T> oldTail = _tail;
SingleLinkNode <T> oldHeadNext = oldHead.Next;
if (oldHead == _head)
{
if (oldHead == oldTail)
{
if (oldHeadNext == null)
{
return(false);
}
Interlocked.CompareExchange <SingleLinkNode <T> >(ref _tail, oldHeadNext, oldTail);
}
else
{
item = oldHeadNext.Item;
haveAdvancedHead =
Interlocked.CompareExchange <SingleLinkNode <T> >(ref _head, oldHeadNext, oldHead) == oldHead;
}
}
}
Interlocked.Decrement(ref _count);
return(true);
}
/// <summary>
/// Default constructor.
/// </summary>
public LockfreeQueue()
{
_head = new SingleLinkNode <T>();
_tail = _head;
}