Java高并发BlockingQueue重要的实现类二

入门小站 2021-01-23 21:43:58
java 并发 blockingqueue 实现 重要


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>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>> delayeds = new DelayQueue<>();
ConcurrentMap<String, OrderItem> map = new ConcurrentHashMap<>();
//下单线程
executorService.execute(()->{
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<>(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(()->{
while (true){
try {
//随机等待 再支付
Thread.sleep(new Random().nextInt(15)*1000);
String orderNo="";
Iterator<Map.Entry<String, OrderItem>> 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(()->{
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ArrayBlockingQueueLinkedBlockingDeque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<>();
ExecutorService executorService = Executors.newFixedThreadPool(2);
executorService.execute(()->{
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(()->{
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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