Thinking in Java学习笔记 DelayQueue和Delayed接口

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本文介绍了一个基于Java的延迟任务处理机制。通过实现Delayed接口并利用DelayQueue，可以按指定延迟执行任务。静态类EndSentinel用于标记所有任务完成，并通过ExecutorService.shutdownNow()停止线程池。

DelayedTask线程要实现Delayed接口的getDelay()和compareTo()方法，放入DelayQueue队列后，通过take()方法取出时，可根据compareTo方法制定的顺序来优先取出线程执行

静态类EndSentinel负责遍历所有的线程，其设置的trigger最大，最后被执行时调用ExecutorService.shutdownNow()，来结束线程的执行

package com.test.concurrent;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.DelayQueue;
import java.util.concurrent.Delayed;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class DelayedQueueDemo {

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

}

class DelayedTask implements Delayed, Runnable{
	private static int counter=0;
	private final int id=counter++;
	private final int delta;
	private final long trigger;
	protected static List<DelayedTask> sequence=new ArrayList<DelayedTask>();
	public DelayedTask(int delayInMilliseconds){
		delta=delayInMilliseconds;
		trigger=System.nanoTime()+java.util.concurrent.TimeUnit.NANOSECONDS.convert(delta,java.util.concurrent.TimeUnit.MILLISECONDS);
		sequence.add(this);
	}
	@Override
	public int compareTo(Delayed o) {
		// TODO Auto-generated method stub
		DelayedTask that=(DelayedTask)o;
		if(this.trigger>that.trigger)
			return 1;
		if(this.trigger<that.trigger)
			return -1;
		return 0;
	}

	@Override
	public void run() {
		// TODO Auto-generated method stub
		System.out.println(this+"  is running");
	}
	public String toString(){
		return "  Task:"+id+" delta:"+delta;
	}
	public String summary(){
		return " id:"+id+"  delta:"+delta;
	}

	@Override
	public long getDelay(TimeUnit unit) {
		// TODO Auto-generated method stub
		return unit.convert(trigger-System.nanoTime(), java.util.concurrent.TimeUnit.NANOSECONDS);
	}
	public static class EndSentinel extends DelayedTask{
		private ExecutorService exec;
		public EndSentinel(int delayInMilliseconds,ExecutorService exec) {
			super(delayInMilliseconds);
			this.exec=exec;
		}
		public void run(){
			for(DelayedTask dt:sequence){
				System.out.println(dt.summary()+"  ");
			}
			System.out.print(' ');
			System.out.println(this+" Calling ShutdownNow()");
			exec.shutdownNow();
		}
	}
}
class DelayedTaskConsumer implements Runnable{
	private DelayQueue<DelayedTask> dq;
	public DelayedTaskConsumer(DelayQueue<DelayedTask> q){
		dq=q;
	}
	@Override
	public void run(){
		try {
			while(!Thread.interrupted()){
				dq.take().run();
			}
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		System.out.println("finished delayedtask consume!!!!!");
	}
}