Java高并发BlockingQueue重要的实现类二

DelayQueue

> DelayQueue是一个无界阻塞队列，只有在延迟期满时才能从中提取元素。该队列的头部是延迟期满后保存时间最长的Delayed元素。 > 存放到DelayDeque的元素必须继承Delayed接口。Delayed接口使对象成为延迟对象，它使存放在DelayQueue类中的对象具有了激活日期，该接口强制执行下列两个方法：

CompareTo(Delayed o)：Delayed接口继承了Comparable接口，因此有了这个方法
getDelay(TimeUnit unit):这个方法返回到激活日期的剩余时间，时间单位由单位参数指定

DelayQueue使用场景

关闭空闲链接。服务器中,有很多客户端链接,空闲一段时间后需要关闭。
缓存超过了缓存时间,就需要从缓存中移除。

DelayQueue超时订单处理案例

package com.rumenz.learn.delayqueue;

import java.util.concurrent.Delayed;
import java.util.concurrent.TimeUnit;

//DelayQueue里面的元素必须实现Delayed

public class Item<t> implements Delayed {

    private Long expireTime;
    private T data;

    public Item(Long expireTime, T data) {
        this.expireTime = expireTime+System.currentTimeMillis();
        this.data = data;
    }

    @Override
    public long getDelay(TimeUnit unit) {
        long d = unit.convert(this.expireTime - System.currentTimeMillis(),unit);
        return d;
    }

    @Override
    public int compareTo(Delayed o) {
        long d=getDelay(TimeUnit.MILLISECONDS)-o.getDelay(TimeUnit.MILLISECONDS);
        if(d==0){
            return 0;
        }
        return d&gt;0?1:-1;
    }

    public Long getExpireTime() {
        return expireTime;
    }

    public void setExpireTime(Long expireTime) {
        this.expireTime = expireTime;
    }

    public T getData() {
        return data;
    }

    public void setData(T data) {
        this.data = data;
    }
}


// 订单实体类
package com.rumenz.learn.delayqueue;
public class OrderItem {
    private Double orderAmount;
    private String orderNo;
    //0未支付 1支付了
    private Integer orderStatus;

    public OrderItem(Double orderAmount, String orderNo, Integer orderStatus) {
        this.orderAmount = orderAmount;
        this.orderNo = orderNo;
        this.orderStatus = orderStatus;
    }

    public Double getOrderAmount() {
        return orderAmount;
    }

    public void setOrderAmount(Double orderAmount) {
        this.orderAmount = orderAmount;
    }

    public String getOrderNo() {
        return orderNo;
    }

    public void setOrderNo(String orderNo) {
        this.orderNo = orderNo;
    }

    public Integer getOrderStatus() {
        return orderStatus;
    }

    public void setOrderStatus(Integer orderStatus) {
        this.orderStatus = orderStatus;
    }
}

//

package com.rumenz.learn.delayqueue;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Iterator;
import java.util.Map;
import java.util.Random;
import java.util.concurrent.*;


public class DelayQueueExample {
    //3个线程 1个线程下单 1个线程支付  1个线程关闭超时订单  订单支付超时时间为10s
    public static void main(String[] args) {

        ExecutorService executorService = Executors.newFixedThreadPool(3);
        DelayQueue<item<orderitem>&gt; delayeds = new DelayQueue&lt;&gt;();
        ConcurrentMap<string, orderitem> map = new ConcurrentHashMap&lt;&gt;();

        //下单线程
        executorService.execute(()-&gt;{
            SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

            Integer orderNo=100;
            while (true){
                try{
                    Thread.sleep(3000);
                    Integer amount = new Random().nextInt(1000);
                    OrderItem orderItem=new OrderItem(amount.doubleValue(), String.valueOf(orderNo), 0);
                    Item<orderitem> item=new Item&lt;&gt;(10*1000L,orderItem);
                    Date date=new Date();
                    date.setTime(item.getExpireTime());

                    System.out.println("=======================下单==========================");

                    System.out.println("生成订单时间:"+simpleDateFormat.format(new Date()));
                    System.out.println("订单编号:"+orderNo);
                    System.out.println("订单金额:"+orderItem.getOrderAmount());
                    System.out.println("支付过期时间:"+simpleDateFormat.format(date));
                    System.out.println("========================下单=========================");


                    map.put(String.valueOf(orderNo),orderItem);
                    orderNo++;
                    delayeds.offer(item);


                }catch (Exception e){
                    e.printStackTrace();
                }

            }

        });
        //支付线程
        executorService.execute(()-&gt;{
            while (true){
                try {
                    //随机等待 再支付
                    Thread.sleep(new Random().nextInt(15)*1000);
                    String orderNo="";
                    Iterator<map.entry<string, orderitem>&gt; iterator = map.entrySet().iterator();
                    if(iterator.hasNext()){
                        OrderItem orderItem = iterator.next().getValue();
                        orderItem.setOrderStatus(1);
                        orderNo=orderItem.getOrderNo();
                        System.out.println("-----------------------支付订单-----------------------");
                        System.out.println("订单支付"+orderNo);
                        System.out.println("支付金额"+orderItem.getOrderAmount());
                        System.out.println("-----------------------支付订单-----------------------");
                    }
                    map.remove(orderNo);

                }catch (Exception e){
                    e.printStackTrace();
                }
            }

        });
        //关系过期的订单
        executorService.execute(()-&gt;{
            SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            while (true){
                try{
                    Item<orderitem> item = delayeds.take();
                    OrderItem data = item.getData();
                    Date date=new Date();
                    date.setTime(item.getExpireTime());
                    if(data.getOrderStatus()==0){
                        System.out.println("########################过期订单########################");
                        System.out.println("订单编号:"+data.getOrderNo());
                        System.out.println("订单金额:"+data.getOrderAmount());
                        System.out.println("订单到期支付时间:"+simpleDateFormat.format(date));
                        System.out.println("########################过期订单########################");
                    }


                    map.remove(data.getOrderNo());
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        });
        executorService.shutdown();
    }
}

SynchronousQueue

> 它是一个特殊的队列交做同步队列,特点是当一个线程往队列里写一个元素,写入操作不会理解返回,需要等待另外一个线程来将这个元素拿走。同理,当一个读线程做读操作的时候,同样需要一个相匹配写线程的写操作。这里的Synchronous指的就是读写线程需要同步,一个读线程匹配一个写线程,同理一个写线程匹配一个读线程。

> 不像ArrayBlockingQueue、LinkedBlockingDeque之类的阻塞队列依赖AQS实现并发操作，SynchronousQueue直接使用CAS实现线程的安全访问。

> 较少使用到 SynchronousQueue 这个类，不过它在线程池的实现类 ScheduledThreadPoolExecutor 中得到了应用。

public class SynchronousQueue<e> extends AbstractQueue<e>
    implements BlockingQueue<e>, java.io.Serializable {
    //内部栈
    static final class TransferStack<e> extends Transferer<e> {}
    //内部队列
    static final class TransferQueue<e> extends Transferer<e> {}
    public SynchronousQueue() {this(false);}
    public SynchronousQueue(boolean fair) {
        transferer = fair ? 
                 new TransferQueue<e>() : new TransferStack<e>();
    }
}

`SynchronousQueue`代码演示

package com.rumenz.learn.synchronousqueue;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.TimeUnit;

public class SynchronousQueueExample {
    public static void main(String[] args) {
        SynchronousQueue<string> queue = new SynchronousQueue&lt;&gt;();
        ExecutorService executorService = Executors.newFixedThreadPool(2);
        executorService.execute(()-&gt;{
          try {
              System.out.println(Thread.currentThread().getName()+"put 1");
              queue.put("1");
              System.out.println(Thread.currentThread().getName()+"put 2");
              queue.put("2");
              System.out.println(Thread.currentThread().getName()+"put 3");
              queue.put("3");
              System.out.println(Thread.currentThread().getName()+"put 4");
              queue.put("4");

          }catch (Exception e){
              e.printStackTrace();
          }

        });
        executorService.execute(()-&gt;{
            try{
              TimeUnit.SECONDS.sleep(1);
              System.out.println("获取数据:"+queue.take());

              TimeUnit.SECONDS.sleep(1);
              System.out.println("获取数据:"+queue.take());

              TimeUnit.SECONDS.sleep(1);
              System.out.println("获取数据:"+queue.take());


              TimeUnit.SECONDS.sleep(1);
              System.out.println("获取数据:"+queue.take());

            }catch (Exception e){
                e.printStackTrace();
            }

        });
        executorService.shutdown();
    }

}

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