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/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.jctools.queues;

/**
 * This is a weakened version of the MPSC algorithm as presented
 *  on
 * 1024 Cores by D. Vyukov. The original has been adapted to Java and it's quirks with regards to memory
 * model and layout:
 * 
 * Use inheritance to ensure no false sharing occurs between producer/consumer node reference fields.
 * 
As this is an SPSC we have no need for XCHG, an ordered store is enough.
 * 
 * The queue is initialized with a stub node which is set to both the producer and consumer node references.
 * From this point follow the notes on offer/poll.
 *
 * @param 
 * @author nitsanw
 */
public class SpscLinkedQueue extends BaseLinkedQueue
{

    public SpscLinkedQueue()
    {
        LinkedQueueNode node = newNode();
        spProducerNode(node);
        spConsumerNode(node);
        node.soNext(null); // this ensures correct construction: StoreStore
    }

    /**
     * {@inheritDoc} 

     * 
     * IMPLEMENTATION NOTES:

     * Offer is allowed from a SINGLE thread.

     * Offer allocates a new node (holding the offered value) and:
     * 

     * Sets the new node as the producerNode
     * 
Sets that node as the lastProducerNode.next
     * 
     * From this follows that producerNode.next is always null and for all other nodes node.next is not null.
     *
     * @see MessagePassingQueue#offer(Object)
     * @see java.util.Queue#offer(java.lang.Object)
     */
    @Override
    public boolean offer(final E e)
    {
        if (null == e)
        {
            throw new NullPointerException();
        }
        final LinkedQueueNode nextNode = newNode(e);
        LinkedQueueNode oldNode = lpProducerNode();
        soProducerNode(nextNode);
        // Should a producer thread get interrupted here the chain WILL be broken until that thread is resumed
        // and completes the store in prev.next. This is a "bubble".
        // Inverting the order here will break the `isEmpty` invariant, and will require matching adjustments elsewhere.
        oldNode.soNext(nextNode);
        return true;
    }

    @Override
    public int fill(Supplier s)
    {
        return MessagePassingQueueUtil.fillUnbounded(this, s);
    }

    @Override
    public int fill(Supplier s, int limit)
    {
        if (null == s)
            throw new IllegalArgumentException("supplier is null");
        if (limit < 0)
            throw new IllegalArgumentException("limit is negative:" + limit);
        if (limit == 0)
            return 0;

        LinkedQueueNode tail = newNode(s.get());
        final LinkedQueueNode head = tail;
        for (int i = 1; i < limit; i++)
        {
            final LinkedQueueNode temp = newNode(s.get());
            // spNext : soProducerNode ensures correct construction
            tail.spNext(temp);
            tail = temp;
        }
        final LinkedQueueNode oldPNode = lpProducerNode();
        soProducerNode(tail);
        // same bubble as offer, and for the same reasons.
        oldPNode.soNext(head);
        return limit;
    }

    @Override
    public void fill(Supplier s, WaitStrategy wait, ExitCondition exit)
    {
        MessagePassingQueueUtil.fill(this, s, wait, exit);
    }
}