Java high concurrency BlockingQueue important implementation class II

Entry station 2021-01-23 21:44:17
java high concurrency blockingqueue important


DelayQueue

DelayQueue It's an unbounded blocking queue , You can only extract elements from it when the delay expires . The head of the queue is the longest stored after the delay expires Delayed Elements .
Store in DelayDeque The elements of must inherit Delayed Interface .Delayed Interfaces make objects deferred objects , It makes storage in DelayQueue Objects in the class have activation dates , The interface enforces the following two methods :
  • CompareTo(Delayed o):Delayed Interface inherited Comparable Interface , So with this method
  • getDelay(TimeUnit unit): This method returns to the remaining time of the activation date , The time unit is specified by the unit parameter

DelayQueue Use scenarios

  • Close idle Links . Server , There are a lot of client Links , It needs to be shut down after being idle for a while .
  • The cache has exceeded the cache time , You need to remove it from the cache .

DelayQueue Overtime order processing cases

package com.rumenz.learn.delayqueue;
import java.util.concurrent.Delayed;
import java.util.concurrent.TimeUnit;
//DelayQueue The elements in it have to implement 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;
}
}
// Order entity class
package com.rumenz.learn.delayqueue;
public class OrderItem {
private Double orderAmount;
private String orderNo;
//0 Did not pay 1 Paid
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 Threads 1 A thread orders 1 Thread payment 1 Thread close timeout order The order payment timeout is 10s
public static void main(String[] args) {
ExecutorService executorService = Executors.newFixedThreadPool(3);
DelayQueue<Item<OrderItem>> delayeds = new DelayQueue<>();
ConcurrentMap<String, OrderItem> map = new ConcurrentHashMap<>();
// Single thread
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("======================= Place an order ==========================");
System.out.println(" Order generation time :"+simpleDateFormat.format(new Date()));
System.out.println(" The order no. :"+orderNo);
System.out.println(" Order amount :"+orderItem.getOrderAmount());
System.out.println(" Payment expiration time :"+simpleDateFormat.format(date));
System.out.println("======================== Place an order =========================");
map.put(String.valueOf(orderNo),orderItem);
orderNo++;
delayeds.offer(item);
}catch (Exception e){
e.printStackTrace();
}
}
});
// Payment thread
executorService.execute(()->{
while (true){
try {
// Wait at random Pay again
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("----------------------- Payment order -----------------------");
System.out.println(" Order payment "+orderNo);
System.out.println(" Pay the amount "+orderItem.getOrderAmount());
System.out.println("----------------------- Payment order -----------------------");
}
map.remove(orderNo);
}catch (Exception e){
e.printStackTrace();
}
}
});
// Relationship expired orders
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("######################## Overdue orders ########################");
System.out.println(" The order no. :"+data.getOrderNo());
System.out.println(" Order amount :"+data.getOrderAmount());
System.out.println(" Order due time :"+simpleDateFormat.format(date));
System.out.println("######################## Overdue orders ########################");
}
map.remove(data.getOrderNo());
}catch (Exception e){
e.printStackTrace();
}
}
});
executorService.shutdown();
}
}

SynchronousQueue

It's a special queue that is used as a synchronization queue , The feature is that when a thread writes an element to the queue , The write operation does not understand the return , You need to wait for another thread to take this element away . Empathy , When a read thread does a read operation , You also need a write operation that matches the write thread . there Synchronous It means that the read and write threads need to be synchronized , A read thread matches a write thread , Similarly, a write thread matches a read thread .

Unlike ArrayBlockingQueueLinkedBlockingDeque And so on AQS Implement concurrent operations ,SynchronousQueue Use it directly CAS Secure access to threads .

Less used to SynchronousQueue This class , However, it is the implementation class of the thread pool ScheduledThreadPoolExecutor It has been applied to .

public class SynchronousQueue<E> extends AbstractQueue<E>
implements BlockingQueue<E>, java.io.Serializable {
// Internal stack
static final class TransferStack<E> extends Transferer<E> {}
// Internal queues
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 Code demonstration

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(" get data :"+queue.take());
TimeUnit.SECONDS.sleep(1);
System.out.println(" get data :"+queue.take());
TimeUnit.SECONDS.sleep(1);
System.out.println(" get data :"+queue.take());
TimeUnit.SECONDS.sleep(1);
System.out.println(" get data :"+queue.take());
}catch (Exception e){
e.printStackTrace();
}
});
executorService.shutdown();
}
}

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