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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;

import org.jctools.queues.IndexedQueueSizeUtil.IndexedQueue;
import org.jctools.util.Pow2;

import java.util.AbstractQueue;
import java.util.Iterator;
import java.util.NoSuchElementException;

import static org.jctools.util.UnsafeRefArrayAccess.*;

abstract class ConcurrentCircularArrayQueueL0Pad extends AbstractQueue
{
    byte b000,b001,b002,b003,b004,b005,b006,b007;//  8b
    byte b010,b011,b012,b013,b014,b015,b016,b017;// 16b
    byte b020,b021,b022,b023,b024,b025,b026,b027;// 24b
    byte b030,b031,b032,b033,b034,b035,b036,b037;// 32b
    byte b040,b041,b042,b043,b044,b045,b046,b047;// 40b
    byte b050,b051,b052,b053,b054,b055,b056,b057;// 48b
    byte b060,b061,b062,b063,b064,b065,b066,b067;// 56b
    byte b070,b071,b072,b073,b074,b075,b076,b077;// 64b
    byte b100,b101,b102,b103,b104,b105,b106,b107;// 72b
    byte b110,b111,b112,b113,b114,b115,b116,b117;// 80b
    byte b120,b121,b122,b123,b124,b125,b126,b127;// 88b
    byte b130,b131,b132,b133,b134,b135,b136,b137;// 96b
    byte b140,b141,b142,b143,b144,b145,b146,b147;//104b
    byte b150,b151,b152,b153,b154,b155,b156,b157;//112b
    byte b160,b161,b162,b163,b164,b165,b166,b167;//120b
    byte b170,b171,b172,b173,b174,b175,b176,b177;//128b
}

/**
 * Common functionality for array backed queues. The class is pre-padded and the array is padded on either side to help
 * with False Sharing prevention. It is expected that subclasses handle post padding.
 */
abstract class ConcurrentCircularArrayQueue extends ConcurrentCircularArrayQueueL0Pad
    implements MessagePassingQueue, IndexedQueue, QueueProgressIndicators, SupportsIterator
{
    protected final long mask;
    protected final E[] buffer;

    ConcurrentCircularArrayQueue(int capacity)
    {
        int actualCapacity = Pow2.roundToPowerOfTwo(capacity);
        mask = actualCapacity - 1;
        buffer = allocateRefArray(actualCapacity);
    }

    @Override
    public int size()
    {
        return IndexedQueueSizeUtil.size(this, IndexedQueueSizeUtil.PLAIN_DIVISOR);
    }

    @Override
    public boolean isEmpty()
    {
        return IndexedQueueSizeUtil.isEmpty(this);
    }

    @Override
    public String toString()
    {
        return this.getClass().getName();
    }

    @Override
    public void clear()
    {
        while (poll() != null)
        {
            // if you stare into the void
        }
    }

    @Override
    public int capacity()
    {
        return (int) (mask + 1);
    }

    @Override
    public long currentProducerIndex()
    {
        return lvProducerIndex();
    }

    @Override
    public long currentConsumerIndex()
    {
        return lvConsumerIndex();
    }

    /**
     * Get an iterator for this queue. This method is thread safe.
     * 
     * The iterator provides a best-effort snapshot of the elements in the queue.
     * The returned iterator is not guaranteed to return elements in queue order,
     * and races with the consumer thread may cause gaps in the sequence of returned elements.
     * Like {link #relaxedPoll}, the iterator may not immediately return newly inserted elements.
     *
     * @return The iterator.
     */
    @Override
    public Iterator iterator() {
        final long cIndex = lvConsumerIndex();
        final long pIndex = lvProducerIndex();

        return new WeakIterator(cIndex, pIndex, mask, buffer);
    }

    private static class WeakIterator implements Iterator {
        private final long pIndex;
        private final long mask;
        private final E[] buffer;
        private long nextIndex;
        private E nextElement;

        WeakIterator(long cIndex, long pIndex, long mask, E[] buffer) {
            this.nextIndex = cIndex;
            this.pIndex = pIndex;
            this.mask = mask;
            this.buffer = buffer;
            nextElement = getNext();
        }

        @Override
        public void remove() {
            throw new UnsupportedOperationException("remove");
        }

        @Override
        public boolean hasNext() {
            return nextElement != null;
        }

        @Override
        public E next() {
            final E e = nextElement;
            if (e == null)
                throw new NoSuchElementException();
            nextElement = getNext();
            return e;
        }

        private E getNext() {
            while (nextIndex < pIndex) {
                long offset = calcCircularRefElementOffset(nextIndex++, mask);
                E e = lvRefElement(buffer, offset);
                if (e != null) {
                    return e;
                }
            }
            return null;
        }
    }
}