多线程07-线程池

1. 概念

    线程池主要是通过Executors这个类来创建 返回的是ExecutorService对象 

2.固定大小线程池

    例子：创建固定线程数目为3的线程池

package org.lkl.thead.foo.threadpool;

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

/**
 * 
 * Function : 线程池
 * @author : Liaokailin 
 * CreateDate : 2014-6-18
 * version : 1.0
 */
public class ExecutorThreadPool {
    public static void main(String[] args) {
        /**
         * 创建固定大小的线程池  
         */
        ExecutorService threadPool = Executors.newFixedThreadPool(3) ;
        for(int i=1 ;i<=10 ;i++){
            final int taskid = i ;
            threadPool.execute(new Runnable() {
                @Override
                public void run() {
                    for(int j=1 ;j<=2 ;j++){
                        try {
                            Thread.sleep(20) ;
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        
                        System.out.println("["+Thread.currentThread().getName()+" ]is loop of  "+j+" for task of "+taskid);
                        
                      }
                }    
            }) ;
        }
    }
}

     运行结果如下：

[pool-1-thread-1 ]is loop of  1 for task of 1
[pool-1-thread-3 ]is loop of  1 for task of 3
[pool-1-thread-2 ]is loop of  1 for task of 2
[pool-1-thread-2 ]is loop of  2 for task of 2
[pool-1-thread-1 ]is loop of  2 for task of 1
[pool-1-thread-3 ]is loop of  2 for task of 3
[pool-1-thread-2 ]is loop of  1 for task of 4
[pool-1-thread-1 ]is loop of  1 for task of 5
[pool-1-thread-3 ]is loop of  1 for task of 6
[pool-1-thread-2 ]is loop of  2 for task of 4
[pool-1-thread-1 ]is loop of  2 for task of 5
[pool-1-thread-3 ]is loop of  2 for task of 6
[pool-1-thread-1 ]is loop of  1 for task of 7
[pool-1-thread-2 ]is loop of  1 for task of 8
[pool-1-thread-3 ]is loop of  1 for task of 9
[pool-1-thread-1 ]is loop of  2 for task of 7
[pool-1-thread-2 ]is loop of  2 for task of 8
[pool-1-thread-3 ]is loop of  2 for task of 9
[pool-1-thread-1 ]is loop of  1 for task of 10
[pool-1-thread-1 ]is loop of  2 for task of 10

    固定的线程池数目为3，那么始终只会有三个线程在运行，只有等到该三个线程的任务完成以后才会去执行其他的任务

 3. 缓冲池

    

ExecutorService threadPool = Executors.newCachedThreadPool() ;

运行结果：

[pool-1-thread-2 ]is loop of  1 for task of 2
[pool-1-thread-1 ]is loop of  1 for task of 1
[pool-1-thread-3 ]is loop of  1 for task of 3
[pool-1-thread-5 ]is loop of  1 for task of 5
[pool-1-thread-4 ]is loop of  1 for task of 4
[pool-1-thread-7 ]is loop of  1 for task of 7
[pool-1-thread-6 ]is loop of  1 for task of 6
[pool-1-thread-10 ]is loop of  1 for task of 10
[pool-1-thread-8 ]is loop of  1 for task of 8
[pool-1-thread-9 ]is loop of  1 for task of 9
[pool-1-thread-1 ]is loop of  2 for task of 1
[pool-1-thread-2 ]is loop of  2 for task of 2
[pool-1-thread-3 ]is loop of  2 for task of 3
[pool-1-thread-5 ]is loop of  2 for task of 5
[pool-1-thread-4 ]is loop of  2 for task of 4
[pool-1-thread-7 ]is loop of  2 for task of 7
[pool-1-thread-6 ]is loop of  2 for task of 6
[pool-1-thread-9 ]is loop of  2 for task of 9
[pool-1-thread-10 ]is loop of  2 for task of 10
[pool-1-thread-8 ]is loop of  2 for task of 8

　　缓冲池会按照jvm的调度来分配若干个线程来执行当前需要完成的任务 ，上面的例子有是个线程任务要执行，那么自动分配了10个线程来完成

4.单一的线程池

    

ExecutorService threadPool = Executors.newSingleThreadExecutor() ;

   运行结果：

[pool-1-thread-1 ]is loop of  1 for task of 1
[pool-1-thread-1 ]is loop of  2 for task of 1
[pool-1-thread-1 ]is loop of  1 for task of 2
[pool-1-thread-1 ]is loop of  2 for task of 2
[pool-1-thread-1 ]is loop of  1 for task of 3
[pool-1-thread-1 ]is loop of  2 for task of 3
[pool-1-thread-1 ]is loop of  1 for task of 4
[pool-1-thread-1 ]is loop of  2 for task of 4
[pool-1-thread-1 ]is loop of  1 for task of 5
[pool-1-thread-1 ]is loop of  2 for task of 5
[pool-1-thread-1 ]is loop of  1 for task of 6
[pool-1-thread-1 ]is loop of  2 for task of 6
[pool-1-thread-1 ]is loop of  1 for task of 7
[pool-1-thread-1 ]is loop of  2 for task of 7
[pool-1-thread-1 ]is loop of  1 for task of 8
[pool-1-thread-1 ]is loop of  2 for task of 8
[pool-1-thread-1 ]is loop of  1 for task of 9
[pool-1-thread-1 ]is loop of  2 for task of 9
[pool-1-thread-1 ]is loop of  1 for task of 10
[pool-1-thread-1 ]is loop of  2 for task of 10

　　　　只会有一个线程来执行当前的任务　

5. shutdown 和shutdownNow

     ExecutorService对象中有两个方法 一个是shutdown   一个是shutdownNow   看如下代码：

　　

package org.lkl.thead.foo.threadpool;

import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * 
 * Function : 线程池
 * @author : Liaokailin 
 * CreateDate : 2014-6-18
 * version : 1.0
 */
public class ExecutorThreadPool {
    public static void main(String[] args) {
        ExecutorService threadPool = Executors.newFixedThreadPool(3) ;
        for(int i=1 ;i<=10 ;i++){
            final int taskid = i ;
            threadPool.execute(new Runnable() {
                @Override
                public void run() {
                    for(int j=1 ;j<=2 ;j++){
                        try {
                     //    Thread.sleep(20) ;
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                        
                        System.out.println("["+Thread.currentThread().getName()+" ]is loop of  "+j+" for task of "+taskid);
                        
                      }
                }    
            }) ;
        }
        
        List<Runnable> list = threadPool.shutdownNow() ;
    
        System.out.println("-----");
        for(Runnable r :list){
            //System.out.println(r.run());
            r.run() ;
        }
        System.out.println("-------------");
        
       
    }
}

　　　   执行的结果：

[pool-1-thread-2 ]is loop of  1 for task of 2
[pool-1-thread-1 ]is loop of  1 for task of 1
[pool-1-thread-1 ]is loop of  2 for task of 1
[pool-1-thread-2 ]is loop of  2 for task of 2
-----
[pool-1-thread-3 ]is loop of  1 for task of 3
[pool-1-thread-3 ]is loop of  2 for task of 3
[main ]is loop of  1 for task of 4
[main ]is loop of  2 for task of 4
[main ]is loop of  1 for task of 5
[main ]is loop of  2 for task of 5
[main ]is loop of  1 for task of 6
[main ]is loop of  2 for task of 6
[main ]is loop of  1 for task of 7
[main ]is loop of  2 for task of 7
[main ]is loop of  1 for task of 8
[main ]is loop of  2 for task of 8
[main ]is loop of  1 for task of 9
[main ]is loop of  2 for task of 9
[main ]is loop of  1 for task of 10
[main ]is loop of  2 for task of 10
-------------

       threadPool.shutdown() 表示结束当前的线程池  但是在线程池中的任务还会允许继续运行完成，但是不会接收新的任务,方法返回void

       threadPool.shutdownNow() 表示立即结束当前的线程池，不管线程池中是否还存在没有完成的任务，返回一个List<Runnable> 表示线程池中没有运行完的任务

6. 通过线程池启动定时器

ScheduledExecutorService scheduledService = Executors.newScheduledThreadPool(3) ;
        //两秒后执行
        scheduledService.schedule(new Runnable() {
            
            @Override
            public void run() {
                System.out.println("hello");
            }
        }, 2, TimeUnit.SECONDS) ;
        
        //两秒后执行  以后每隔3秒执行一次
        scheduledService.scheduleAtFixedRate(new Runnable() {
            
            @Override
            public void run() {
                System.out.println("world");
            }
        }, 2, 3, TimeUnit.SECONDS) ;