欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页

JAVA进阶----ThreadPoolExecutor机制 博客分类: JAVA进阶java-多线程框架 javaExecutors并发线程池ThreadPoolExecutor 

程序员文章站 2024-03-12 10:51:50
...
ThreadPoolExecutor机制
一、概述
1、ThreadPoolExecutor作为java.util.concurrent包对外提供基础实现,以内部线程池的形式对外提供管理任务执行,线程调度,线程池管理等等服务;
2、Executors方法提供的线程服务,都是通过参数设置来实现不同的线程池机制。
3、先来了解其线程池管理的机制,有助于正确使用,避免错误使用导致严重故障。同时可以根据自己的需求实现自己的线程池


二、核心构造方法讲解
下面是ThreadPoolExecutor最核心的构造方法
public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              ThreadFactory threadFactory,
                              RejectedExecutionHandler handler) {
        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }

构造方法参数讲解
参数名 作用
corePoolSize 核心线程池大小
maximumPoolSize 最大线程池大小
keepAliveTime 线程池中超过corePoolSize数目的空闲线程最大存活时间;可以allowCoreThreadTimeOut(true)使得核心线程有效时间
TimeUnit keepAliveTime时间单位
workQueue 阻塞任务队列
threadFactory 新建线程工厂
RejectedExecutionHandler 当提交任务数超过maxmumPoolSize+workQueue之和时,任务会交给RejectedExecutionHandler来处理


重点讲解:
其中比较容易让人误解的是:corePoolSize,maximumPoolSize,workQueue之间关系。

1.当线程池小于corePoolSize时,新提交任务将创建一个新线程执行任务,即使此时线程池中存在空闲线程。
2.当线程池达到corePoolSize时,新提交任务将被放入workQueue中,等待线程池中任务调度执行
3.当workQueue已满,且maximumPoolSize>corePoolSize时,新提交任务会创建新线程执行任务
4.当提交任务数超过maximumPoolSize时,新提交任务由RejectedExecutionHandler处理
5.当线程池中超过corePoolSize线程,空闲时间达到keepAliveTime时,关闭空闲线程
6.当设置allowCoreThreadTimeOut(true)时,线程池中corePoolSize线程空闲时间达到keepAliveTime也将关闭


线程管理机制图示:
JAVA进阶----ThreadPoolExecutor机制
            
    
    博客分类: JAVA进阶java-多线程框架 javaExecutors并发线程池ThreadPoolExecutor 

三、Executors提供的线程池配置方案

1、构造一个固定线程数目的线程池,配置的corePoolSize与maximumPoolSize大小相同,同时使用了一个*LinkedBlockingQueue存放阻塞任务,因此多余的任务将存在再阻塞队列,不会由RejectedExecutionHandler处理
public static ExecutorService newFixedThreadPool(int nThreads) {
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>());
    }

2、构造一个缓冲功能的线程池,配置corePoolSize=0,maximumPoolSize=Integer.MAX_VALUE,keepAliveTime=60s,以及一个无容量的阻塞队列 SynchronousQueue,因此任务提交之后,将会创建新的线程执行;线程空闲超过60s将会销毁
public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>());
    }

3、构造一个只支持一个线程的线程池,配置corePoolSize=maximumPoolSize=1,*阻塞队列LinkedBlockingQueue;保证任务由一个线程串行执行
public static ExecutorService newSingleThreadExecutor() {
        return new FinalizableDelegatedExecutorService
            (new ThreadPoolExecutor(1, 1,
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue<Runnable>()));
    }

4、构造有定时功能的线程池,配置corePoolSize,*延迟阻塞队列DelayedWorkQueue;有意思的是:maximumPoolSize=Integer.MAX_VALUE,由于DelayedWorkQueue是*队列,所以这个值是没有意义的
public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
        return new ScheduledThreadPoolExecutor(corePoolSize);
    }

public static ScheduledExecutorService newScheduledThreadPool(
            int corePoolSize, ThreadFactory threadFactory) {
        return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);
    }

public ScheduledThreadPoolExecutor(int corePoolSize,
                             ThreadFactory threadFactory) {
        super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
              new DelayedWorkQueue(), threadFactory);
    }


四、定制属于自己的非阻塞线程池
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.RejectedExecutionHandler;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;


public class CustomThreadPoolExecutor {

	
	private ThreadPoolExecutor pool = null;
	
	
	/**
	 * 线程池初始化方法
	 * 
	 * corePoolSize 核心线程池大小----10
	 * maximumPoolSize 最大线程池大小----30
	 * keepAliveTime 线程池中超过corePoolSize数目的空闲线程最大存活时间----30+单位TimeUnit
	 * TimeUnit keepAliveTime时间单位----TimeUnit.MINUTES
	 * workQueue 阻塞队列----new ArrayBlockingQueue<Runnable>(10)====10容量的阻塞队列
	 * threadFactory 新建线程工厂----new CustomThreadFactory()====定制的线程工厂
	 * rejectedExecutionHandler 当提交任务数超过maxmumPoolSize+workQueue之和时,
	 * 							即当提交第41个任务时(前面线程都没有执行完,此测试方法中用sleep(100)),
	 * 						          任务会交给RejectedExecutionHandler来处理
	 */
	public void init() {
		pool = new ThreadPoolExecutor(
				10,
				30,
				30,
				TimeUnit.MINUTES,
				new ArrayBlockingQueue<Runnable>(10),
				new CustomThreadFactory(),
				new CustomRejectedExecutionHandler());
	}

	
	public void destory() {
		if(pool != null) {
			pool.shutdownNow();
		}
	}
	
	
	public ExecutorService getCustomThreadPoolExecutor() {
		return this.pool;
	}
	
	private class CustomThreadFactory implements ThreadFactory {

		private AtomicInteger count = new AtomicInteger(0);
		
		@Override
		public Thread newThread(Runnable r) {
			Thread t = new Thread(r);
			String threadName = CustomThreadPoolExecutor.class.getSimpleName() + count.addAndGet(1);
			System.out.println(threadName);
			t.setName(threadName);
			return t;
		}
	}
	
	
	private class CustomRejectedExecutionHandler implements RejectedExecutionHandler {

		@Override
		public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
			// 记录异常
			// 报警处理等
			System.out.println("error.............");
		}
	}
	
	
	
	// 测试构造的线程池
	public static void main(String[] args) {
		CustomThreadPoolExecutor exec = new CustomThreadPoolExecutor();
		// 1.初始化
		exec.init();
		
		ExecutorService pool = exec.getCustomThreadPoolExecutor();
		for(int i=1; i<100; i++) {
			System.out.println("提交第" + i + "个任务!");
			pool.execute(new Runnable() {
				@Override
				public void run() {
					try {
						Thread.sleep(3000);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
					System.out.println("running=====");
				}
			});
		}
		
		
		
		// 2.销毁----此处不能销毁,因为任务没有提交执行完,如果销毁线程池,任务也就无法执行了
		// exec.destory();
		
		try {
			Thread.sleep(10000);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}

方法中建立一个核心线程数为30个,缓冲队列有10个的线程池。每个线程任务,执行时会先睡眠3秒,保证提交10任务时,线程数目被占用完,再提交30任务时,阻塞队列被占用完,,这样提交第41个任务是,会交给CustomRejectedExecutionHandler 异常处理类来处理。

提交任务的代码如下:
public void execute(Runnable command) {
        if (command == null)
            throw new NullPointerException();
        /*
         * Proceed in 3 steps:
         *
         * 1. If fewer than corePoolSize threads are running, try to
         * start a new thread with the given command as its first
         * task.  The call to addWorker atomically checks runState and
         * workerCount, and so prevents false alarms that would add
         * threads when it shouldn't, by returning false.
         *
         * 2. If a task can be successfully queued, then we still need
         * to double-check whether we should have added a thread
         * (because existing ones died since last checking) or that
         * the pool shut down since entry into this method. So we
         * recheck state and if necessary roll back the enqueuing if
         * stopped, or start a new thread if there are none.
         *
         * 3. If we cannot queue task, then we try to add a new
         * thread.  If it fails, we know we are shut down or saturated
         * and so reject the task.
         */
        int c = ctl.get();
        if (workerCountOf(c) < corePoolSize) {
            if (addWorker(command, true))
                return;
            c = ctl.get();
        }
        if (isRunning(c) && workQueue.offer(command)) {
            int recheck = ctl.get();
            if (! isRunning(recheck) && remove(command))
                reject(command);
            else if (workerCountOf(recheck) == 0)
                addWorker(null, false);
        }
        else if (!addWorker(command, false))
            reject(command);
    }

注意:41以后提交的任务就不能正常处理了,因为,execute中提交到任务队列是用的offer方法,如上面代码,这个方法是非阻塞的,所以就会交给CustomRejectedExecutionHandler 来处理,所以对于大数据量的任务来说,这种线程池,如果不设置队列长度会OOM,设置队列长度,会有任务得不到处理,接下来我们构建一个阻塞的自定义线程池

五、定制属于自己的阻塞线程池
package com.tongbanjie.trade.test.commons;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.RejectedExecutionHandler;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

public class CustomThreadPoolExecutor {  
	  
      
    private ThreadPoolExecutor pool = null;  
      
      
    /** 
     * 线程池初始化方法 
     *  
     * corePoolSize 核心线程池大小----1 
     * maximumPoolSize 最大线程池大小----3 
     * keepAliveTime 线程池中超过corePoolSize数目的空闲线程最大存活时间----30+单位TimeUnit 
     * TimeUnit keepAliveTime时间单位----TimeUnit.MINUTES 
     * workQueue 阻塞队列----new ArrayBlockingQueue<Runnable>(5)====5容量的阻塞队列 
     * threadFactory 新建线程工厂----new CustomThreadFactory()====定制的线程工厂 
     * rejectedExecutionHandler 当提交任务数超过maxmumPoolSize+workQueue之和时, 
     *                          即当提交第41个任务时(前面线程都没有执行完,此测试方法中用sleep(100)), 
     *                                任务会交给RejectedExecutionHandler来处理 
     */  
    public void init() {  
        pool = new ThreadPoolExecutor(  
                1,  
                3,  
                30,  
                TimeUnit.MINUTES,  
                new ArrayBlockingQueue<Runnable>(5),  
                new CustomThreadFactory(),  
                new CustomRejectedExecutionHandler());  
    }  
  
      
    public void destory() {  
        if(pool != null) {  
            pool.shutdownNow();  
        }  
    }  
      
      
    public ExecutorService getCustomThreadPoolExecutor() {  
        return this.pool;  
    }  
      
    private class CustomThreadFactory implements ThreadFactory {  
  
        private AtomicInteger count = new AtomicInteger(0);  
          
        @Override  
        public Thread newThread(Runnable r) {  
            Thread t = new Thread(r);  
            String threadName = CustomThreadPoolExecutor.class.getSimpleName() + count.addAndGet(1);  
            System.out.println(threadName);  
            t.setName(threadName);  
            return t;  
        }  
    }  
      
      
    private class CustomRejectedExecutionHandler implements RejectedExecutionHandler {  
  
        @Override  
        public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {  
        	try {
                                // 核心改造点,由blockingqueue的offer改成put阻塞方法
				executor.getQueue().put(r);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
        }  
    }  
      
      
      
    // 测试构造的线程池  
    public static void main(String[] args) {  
    	
        CustomThreadPoolExecutor exec = new CustomThreadPoolExecutor();  
        // 1.初始化  
        exec.init();  
          
        ExecutorService pool = exec.getCustomThreadPoolExecutor();  
        for(int i=1; i<100; i++) {  
            System.out.println("提交第" + i + "个任务!");  
            pool.execute(new Runnable() {  
                @Override  
                public void run() {  
                    try {  
                    	System.out.println(">>>task is running====="); 
                        TimeUnit.SECONDS.sleep(10);
                    } catch (InterruptedException e) {  
                        e.printStackTrace();  
                    }  
                }  
            });  
        }  
          
          
        // 2.销毁----此处不能销毁,因为任务没有提交执行完,如果销毁线程池,任务也就无法执行了  
        // exec.destory();  
          
        try {  
            Thread.sleep(10000);  
        } catch (InterruptedException e) {  
            e.printStackTrace();  
        }  
    }  
}  


解释:当提交任务被拒绝时,进入拒绝机制,我们实现拒绝方法,把任务重新用阻塞提交方法put提交,实现阻塞提交任务功能,防止队列过大,OOM,提交被拒绝方法在下面

   
public void execute(Runnable command) {
        if (command == null)
            throw new NullPointerException();

        int c = ctl.get();
        if (workerCountOf(c) < corePoolSize) {
            if (addWorker(command, true))
                return;
            c = ctl.get();
        }
        if (isRunning(c) && workQueue.offer(command)) {
            int recheck = ctl.get();
            if (! isRunning(recheck) && remove(command))
                reject(command);
            else if (workerCountOf(recheck) == 0)
                addWorker(null, false);
        }
        else if (!addWorker(command, false))
            // 进入拒绝机制, 我们把runnable任务拿出来,重新用阻塞操作put,来实现提交阻塞功能
            reject(command);
    }



总结:
1、用ThreadPoolExecutor自定义线程池,看线程是的用途,如果任务量不大,可以用*队列,如果任务量非常大,要用有界队列,防止OOM
2、如果任务量很大,还要求每个任务都处理成功,要对提交的任务进行阻塞提交,重写拒绝机制,改为阻塞提交。保证不抛弃一个任务
3、最大线程数一般设为2N+1最好,N是CPU核数
4、核心线程数,看应用,如果是任务,一天跑一次,设置为0,合适,因为跑完就停掉了,如果是常用线程池,看任务量,是保留一个核心还是几个核心线程数
5、如果要获取任务执行结果,用CompletionService,但是注意,获取任务的结果的要重新开一个线程获取,如果在主线程获取,就要等任务都提交后才获取,就会阻塞大量任务结果,队列过大OOM,所以最好异步开个线程获取结果
  • JAVA进阶----ThreadPoolExecutor机制
            
    
    博客分类: JAVA进阶java-多线程框架 javaExecutors并发线程池ThreadPoolExecutor 
  • 大小: 33.1 KB