EDIT

/**

* Copyright (C) 2019 EDIT

* European Distributed Institute of Taxonomy

* http://www.e-taxonomy.eu

*

* The contents of this file are subject to the Mozilla Public License Version 1.1

* See LICENSE.TXT at the top of this package for the full license terms.

*/

package eu.etaxonomy.cdm.common.concurrent;

import java.util.LinkedList;

import java.util.List;

import org.apache.logging.log4j.LogManager;

import org.apache.logging.log4j.Logger;

/**

 * Concurrent queue. Example taken from

 * {@link

 * https://stackoverflow.com/questions/33195290/producer-consumer-model-using-javasynchronized-but-always-run-the-same-thread

 * } for Producer-Consumer pattern.

 *

 * @author a.mueller

 * @since 26.08.2019

 */

public class ConcurrentQueue<T> {

    private static final Logger logger = LogManager.getLogger(ConcurrentQueue.class);

    private int capacity;

    private List<T> queue = new LinkedList<>();

    public ConcurrentQueue(int capacity) {

        this.capacity = capacity;

    }

    public synchronized void enqueue(T item) throws InterruptedException {

        while (queue.size() == this.capacity) {

            wait();

        }

//            System.out.println("Thread " + Thread.currentThread().getName() +

//                               " producing " + item);

        queue.add(item);

        printSize();

        if (queue.size() >= 1) {

            notifyAll();

        }

    }

    public synchronized T dequeue() throws InterruptedException {

        T item;

        while (queue.size() == 0) {

            wait();

        }

        item = queue.remove(0);

        printSize();

//            System.out.println("Thread " + Thread.currentThread().getName() +

//                               " consuming " + item);

        if (queue.size() == (capacity - 1)) {

            notifyAll();

        }

        return item;

    }

    /**

     *

     */

    private void printSize() {

        logger.warn("size:" + queue.size());

    }

}