/// <summary>
/// Lock free poll using ordered loads/stores. As class name suggests, access is limited to a single thread.
/// </summary>
/// <param name="item">The dequeued item.</param>
/// <returns><c>true</c> if an item was retrieved, otherwise <c>false</c>.</returns>
/// <seealso cref="IQueue{T}.TryDequeue"/>
public override bool TryDequeue(out T item)
{
long consumerIndex = this.ConsumerIndex; // LoadLoad
long offset = this.CalcElementOffset(consumerIndex);
// Copy field to avoid re-reading after volatile load
T[] buffer = this.Buffer;
// If we can't see the next available element we can't poll
T e = RefArrayAccessUtil.LvElement(buffer, offset); // LoadLoad
if (null == e)
{
// NOTE: Queue may not actually be empty in the case of a producer (P1) being interrupted after
// winning the CAS on offer but before storing the element in the queue. Other producers may go on
// to fill up the queue after this element.
if (consumerIndex != this.ProducerIndex)
{
do
{
e = RefArrayAccessUtil.LvElement(buffer, offset);
} while (e == null);
}
else
{
item = default(T);
return(false);
}
}
RefArrayAccessUtil.SpElement(buffer, offset, default(T));
this.ConsumerIndex = consumerIndex + 1; // StoreStore
item = e;
return(true);
}
/// <summary> /// A plain store (no ordering/fences) of an element to a given offset. /// </summary> /// <param name="offset">Computed via <see cref="CalcElementOffset"/>.</param> /// <param name="e">A kitty.</param> protected void SpElement(long offset, T e) => RefArrayAccessUtil.SpElement(this.Buffer, offset, e);