/// {@inheritDoc} /// <p /> /// IMPLEMENTATION NOTES: /// <br /> /// Lock free peek using ordered loads. As class name suggests access is limited to a single thread. /// @see java.util.Queue#poll() public override bool TryPeek(out T item) { // Copy field to avoid re-reading after volatile load T[] buffer = this.Buffer; long consumerIndex = this.ConsumerIndex; // LoadLoad long offset = this.CalcElementOffset(consumerIndex); T e = RefArrayAccessUtil.LvElement(buffer, offset); 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); } } item = e; return(true); }
/// A volatile load (load + LoadLoad barrier) of an element from a given offset. /// @param offset computed via {@link ConcurrentCircularArrayQueue#calcElementOffset(long)} /// @return the element at the offset protected T LvElement(long offset) => RefArrayAccessUtil.LvElement(this.Buffer, offset);