protected MpscLinkedQueueNode <T> GetAndSetTailRef(MpscLinkedQueueNode <T> value)
{
#pragma warning disable 420
return(Interlocked.Exchange(ref this.tailRef, value));
#pragma warning restore 420
}
public IEnumerator <T> GetEnumerator()
{
MpscLinkedQueueNode <T> node = this.PeekNode();
while (node != null)
{
yield return(node.Value);
node = node.Next;
}
}
/// <summary>
/// Returns the node right next to the head, which contains the first element of this queue.
/// </summary>
MpscLinkedQueueNode <T> PeekNode()
{
MpscLinkedQueueNode <T> head = this.HeadRef;
MpscLinkedQueueNode <T> next = head.Next;
if (next == null && head != this.TailRef)
{
// if tail != head this is not going to change until consumer makes progress
// we can avoid reading the head and just spin on next until it shows up
//
// See https://github.com/akka/akka/pull/15596
do
{
next = head.Next;
}while (next == null);
}
return(next);
}
public T Dequeue()
{
MpscLinkedQueueNode <T> next = this.PeekNode();
if (next == null)
{
return(null);
}
// next becomes a new head.
MpscLinkedQueueNode <T> oldHead = this.HeadRef;
// todo: research storestore vs loadstore barriers
// See: http://robsjava.blogspot.com/2013/06/a-faster-volatile.html
// See: http://psy-lob-saw.blogspot.com/2012/12/atomiclazyset-is-performance-win-for.html
this.HeadRef = next;
// Break the linkage between the old head and the new head.
oldHead.Unlink();
return(next.ClearMaybe());
}
public bool Enqueue(T value)
{
Contract.Requires(value != null);
MpscLinkedQueueNode <T> newTail;
var node = value as MpscLinkedQueueNode <T>;
if (node != null)
{
newTail = node;
newTail.Next = null;
}
else
{
newTail = new DefaultNode(value);
}
MpscLinkedQueueNode <T> oldTail = this.GetAndSetTailRef(newTail);
oldTail.Next = newTail;
return(true);
}
public T Peek()
{
MpscLinkedQueueNode <T> next = this.PeekNode();
return(next == null ? null : next.Value);
}