/// <summary>
/// Returns the first actual (non-header) node on list.
/// </summary>
/// <returns>First node.</returns>
Node <T> First()
{
for (; ;)
{
Node <T> h = _head;
Node <T> t = _tail;
Node <T> first = h.Next;
if (h == _head)
{
if (h == t)
{
if (first == null)
{
return(null);
}
else
{
ThreadingUtils.CompareAndSwap(ref _tail, t, first);
}
}
else
{
if (first.Item != null)
{
return(first);
}
else // remove deleted node and continue
{
ThreadingUtils.CompareAndSwap(ref _head, h, first);
}
}
}
}
}
/// <summary>
/// Inserts the specified element at the tail of this queue.
/// </summary>
/// <param name="item">The item to insert in the queue.</param>
public void Enqueue(T item)
{
Node <T> oldTail = null;
Node <T> oldTailNext;
Node <T> newNode = new Node <T>(item);
bool newNodeWasAdded = false;
while (!newNodeWasAdded)
{
oldTail = _tail;
oldTailNext = oldTail.Next;
if (_tail == oldTail)
{
if (oldTailNext == null)
{
newNodeWasAdded = ThreadingUtils.CompareAndSwap(ref _tail.Next, null, newNode);
}
else
{
ThreadingUtils.CompareAndSwap(ref _tail, oldTail, oldTailNext);
}
}
}
ThreadingUtils.CompareAndSwap(ref _tail, oldTail, newNode);
}
/// <summary>
/// Removes an item from the queue.
/// </summary>
/// <param name="item">The dequeued item.</param>
/// <returns>
/// The dequeued item, or the default value for the element type if the queue was empty.
/// </returns>
public bool Dequeue(out T item)
{
item = default(T);
Node <T> oldHead = null;
bool haveAdvancedHead = false;
while (!haveAdvancedHead)
{
oldHead = _head;
Node <T> oldTail = _tail;
Node <T> oldHeadNext = oldHead.Next;
if (oldHead == _head)
{
if (oldHead == oldTail)
{
if (oldHeadNext == null)
{
return(false);
}
ThreadingUtils.CompareAndSwap(ref _tail, oldTail, oldHeadNext);
}
else
{
item = oldHeadNext.Item;
haveAdvancedHead = ThreadingUtils.CompareAndSwap(ref _head, oldHead, oldHeadNext);
}
}
}
return(true);
}