DelayQueue 试用

简述：

《Java编程思想》第四版 P726 ~ P727

DelayQueue, 是一个无界的BlockingQueue, 用于放置实现了Delay接口的对象，其中的对象只能在器到期时才能从队列中取走。这种队列是有序的，即对头对象的延迟到期时间最长。如果没有任何延迟到期，那么就不会有任何头元素

代码：

DelayedTask.java

package com.anialy.test.concurrency.delayqueue;

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

public class DelayedTask implements Runnable, Delayed {

	private static int counter = 0;
	
	private final int id = counter++;
	
	private int delta;
	
	private long trigger;
	
	protected static List<DelayedTask> sequence = 
			new ArrayList<DelayedTask>();
	
	public DelayedTask(int delayInMilliseconds){
		delta = delayInMilliseconds;
		// 设置触发的延时时间
		trigger = System.nanoTime() 
				+ TimeUnit.NANOSECONDS.convert(delta, TimeUnit.MILLISECONDS);
		sequence.add(this);
	}
	
	public int compareTo(Delayed arg) {
		DelayedTask that = (DelayedTask)arg;
		if(trigger < that.trigger)
			return -1;
		if(trigger > that.trigger)
			return 1;
		return 0;
	}

	public long getDelay(TimeUnit unit) {
		return unit.convert(trigger - System.nanoTime(), TimeUnit.NANOSECONDS);
	}

	public void run() {
		System.out.printf(this + " \n");
	}

	@Override
	public String toString() {
		return String.format("[%1$-4d]", delta)
				+ " Task " + id;
	}

	public String summary() {
		return "(" + id + ":" + delta + ")";
	}
	
}

DelayedTaskConsumer.java

package com.anialy.test.concurrency.delayqueue;

import java.util.concurrent.DelayQueue;

public class DelayedTaskConsumer implements Runnable {

	private DelayQueue<DelayedTask> q;
	
	public DelayedTaskConsumer(DelayQueue<DelayedTask> q){
		this.q = q;
	}
	
	public void run() {
		try {
			while(!Thread.interrupted()){
				q.take().run();
			}
		} catch (InterruptedException e) {
			// Acceptable way to exit
		}
		
		System.out.println("Finished DelayedTaskConsumer");
		
	}
}

最后一个关闭executorService的线程

EndSentinel.java

package com.anialy.test.concurrency.delayqueue;

import java.util.concurrent.ExecutorService;

public class EndSentinel extends DelayedTask {
	
	private ExecutorService exec;
	
	public EndSentinel(int delay, ExecutorService e){
		super(delay);
		exec = e;
	}
	
	@Override
	public void run() {
		for(DelayedTask pt : sequence){
			System.out.printf(pt.summary() + " \n");
		}
		System.out.printf("\n" + this + " Calling shutdownNow()\n");
		exec.shutdownNow();
	}
	
}

DelayQueueDemo.java

package com.anialy.test.concurrency.delayqueue;

import java.util.Random;
import java.util.concurrent.DelayQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class DelayQueueDemo {
	public static void main(String[] args) {
		Random rand = new Random(47);
		
		ExecutorService exec = Executors.newCachedThreadPool();
		DelayQueue<DelayedTask> queue = new DelayQueue<DelayedTask>();
		
		for(int i=0; i<20; i++){
			queue.put(new DelayedTask(rand.nextInt(5000)));
		}
		queue.add(new EndSentinel(5000, exec));
		
		exec.execute(new DelayedTaskConsumer(queue));
	}
}

输出：

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