ScheduledExecutorService的一些错误理解的地方

前言：

       关于这个延时线程池，我相信大部分人还是理解的不够深。包括我自己。大部分任务，如果开一个延时线程池，里面有四个线程。那么并发过来，会不会没有线程可用，因为之前的线程都在延时中。这种理解是错误的。我们用代码来证明。

正文：

     WorldManager

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

public class WorldManager {
	private static final WorldManager worldManager = new WorldManager();
	public static WorldManager getInstance() {
		return worldManager;
	}
	private ScheduledExecutorService aiSheduled = Executors.newScheduledThreadPool(4, new ThreadFactory() {
		
		AtomicInteger index = new AtomicInteger();

		@Override
		public Thread newThread(Runnable r) {
			return new Thread(r, "AI_TASK_"
					+ index.incrementAndGet());
		}
	});
	
	public ScheduledFuture<?> scheduledAi(Runnable task, long delay, TimeUnit unit) {
		return aiSheduled.schedule(task, delay, unit);
	}
}
​

TestSchedule

import java.util.Random;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


public class TestSchedule {
	private static final Logger LOG = LoggerFactory.getLogger(TestSchedule.class);
	private   ScheduledFuture<?> aiShedule;

	public ScheduledFuture<?> getAiShedule() {
		return aiShedule;
	}
	
		private class TestEvent implements Runnable{
			private Integer pid;
			public TestEvent(Integer _pid){
				this.pid = _pid;
			}
			@Override
			public void run() {
				try {
					LOG.info("------------------------------------------------"+pid);
					Random random = new Random(System.currentTimeMillis());
					int delay = random.nextInt(20) + 1;
					aiShedule = WorldManager.getInstance().scheduledAi(new TestEvent(pid), delay, TimeUnit.SECONDS);
					//LOG.info(aiShedule.hashCode()+"");
				} catch (NumberFormatException e) {
					LOG.error(e.getMessage(), e);
				} 
			}
			
		}
		public void ready(Integer i){
			LOG.info("======================================="+i);
			//worldManager.getInstance是一个线程池，里面总共有四个线程
			aiShedule = WorldManager.getInstance().scheduledAi(new TestEvent(i), 5, TimeUnit.SECONDS);
			//LOG.info(aiShedule.hashCode()+"");
		}
		public static void main(String[] args) {
			for(int i =1 ;i <=100;i++){
				new TestSchedule().ready(i);
			}
		}
}
​

从上面的测试结果看出一个结论：延时和线程没关，延时其实是放在线程池底层构造的一个延时队列中的，这个队列放的是延时任务。线程池，只负责从对列中取出任务来执行。延时也不会占用线程