Java Component Examples

LockFreePriorityQueue Example

/*
* Copyright (c) 2008 IBM Corporation
*
* 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.amino.examples;

/*   The Priority Queue is a queue contains elements with priority.
*   This example show the main interfaces of LockFreePriorityQueue.
*   Including : offer(), peek(), poll(), iterator(), size(), isEmpty()
*
*   The QueueAdder class will add items of String from "1" to "ELEMENT_NUM".
*   The QueueRemover class will remove no more than ELEMENT_NUM items.
*   The main thread will wait for all the threads in pool to finish.
*   2009/05/22
*/

import java.util.AbstractQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.Iterator;

import org.amino.ds.lockfree.LockFreePriorityQueue;

public class PriorityQueueExample {

    public static final int ELEMENT_NUM = 100;
    private static final int TASKS_NUM = 4;

    public static void main(String[] argvs) {

        ExecutorService exec = Executors.newFixedThreadPool(TASKS_NUM);

        final AbstractQueue<String> queueStr = new LockFreePriorityQueue<String>();

        for (int i = 0; i < TASKS_NUM; ++i) {
            exec.submit(new QueueAdder(queueStr));
            if (i%2 == 0)exec.submit(new QueueRemover(queueStr));
        }

        exec.shutdown();

        // Wait until all the threads in pool to finish.
        try {
            while(!exec.awaitTermination(600, TimeUnit.SECONDS));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        // If the Queue is empty now, the program will exit.
        if (queueStr.isEmpty())
        {
            System.out.println("The queue is empty, so I will exit!");
            System.exit(1);
        }

        // The poll() will delete minimum.
        String min = queueStr.poll();
        System.out.println("polled :" +min);

        // Print all the elements in Queue.
        for (String str : queueStr)
            System.out.println(str);

        System.out.println("Queue size before clearing: "+ queueStr.size());
        queueStr.clear();
        System.out.println("Queue size after clearing: "+ queueStr.size());
    }
}

/*
*  The QueueAdder class will add elements to the given Queue.
*/
class QueueAdder implements Runnable {
    AbstractQueue<String> taskQ;
    private int count = 0;

    public QueueAdder(AbstractQueue<String> taskQueue)
    {
        taskQ = taskQueue;
    }

    public void run(){
        while (count < PriorityQueueExample.ELEMENT_NUM)
        {
            if (taskQ.add(Integer.toString(count++)))
                System.out.println(Thread.currentThread()+ " Offered:" + count);
        }
        Thread.yield();
    }
}

/*
*  The QueueRemover class will remove the existed elements from the given Queue.
*/
class QueueRemover implements Runnable {
    AbstractQueue<String> taskQ;

    public QueueRemover(AbstractQueue<String> taskQueue)
    {
        taskQ = taskQueue;
    }

    public void run(){
        int times = 0;

        while (times < PriorityQueueExample.ELEMENT_NUM)
        {
            String toRemove = taskQ.remove();
            System.out.println(Thread.currentThread()+ " Removed:" + toRemove);
            times++;
        }
        Thread.yield();
    }
}
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