003-多线程-JUC线程池-几种特殊的ThreadPoolExecutor【newFixedThreadPool、newCachedThreadPool、newSingleThreadExecutor、newScheduledThreadPool】

一、概述

  在java doc中,并不提倡我们直接使用ThreadPoolExecutor,而是使用Executors类中提供的几个静态方法来创建线程池:

  以下方法是Executors下的静态方法,Executors中所定义的 Executor、ExecutorService、ScheduledExecutorService、ThreadFactory 和 Callable 类的工厂和实用方法。

  Executors只是一个工厂类,它所有的方法返回的都是ThreadPoolExecutorScheduledThreadPoolExecutor这两个类的实例。一共可以创建四种线程池。

1.1、基础类

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.TimeUnit;

public class TestThread implements Runnable {
    // 线程私有属性,创建线程时创建
    private Integer num = 0;

    public TestThread(Integer num) {
        this.num = num;
    }

    @Override
    public void run() {
        SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
        System.out.println("thread:" + Thread.currentThread().getName() + ",time:" + sdf1.format(new Date()) + ",num:" + num);
        try {
            //使线程睡眠,模拟线程阻塞情况
            TimeUnit.SECONDS.sleep(3);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("task "+num+"执行完毕");
    }
}

0、使用ThreadPoolExecutor 创建使用

    public static void testThreadPoolExecutor() {
        ThreadPoolExecutor executor = new ThreadPoolExecutor(5, 10, 200, TimeUnit.MILLISECONDS,
                new ArrayBlockingQueue<Runnable>(5));
        for (int i = 0; i < 15; i++) {
            TestThread myTask = new TestThread(i);
            executor.execute(myTask);
            System.out.println("线程池中线程数目:" + executor.getPoolSize() + ",队列中等待执行的任务数目:" +
                    executor.getQueue().size() + ",已执行玩别的任务数目:" + executor.getCompletedTaskCount());
        }
        executor.shutdown();
    }

输出:

/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/bin/java "-javaagent:/Applications/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=54880:/Applications/IntelliJ IDEA.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath /Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_172.jdk/Contents/Home/lib/tools.jar:/Users/lihongxu6/IdeaProjects/java-data-structure-algorithm/data-005-jdkstruct/target/classes:/Users/lihongxu6/.m2/repository/junit/junit/4.11/junit-4.11.jar com.github.bjlhx15.datastructure.algorithm.thread.ThreadPoolDemo2
线程池中线程数目:1,队列中等待执行的任务数目:0,已执行完的任务数目:0
线程池中线程数目:2,队列中等待执行的任务数目:0,已执行完的任务数目:0
线程池中线程数目:3,队列中等待执行的任务数目:0,已执行完的任务数目:0
线程池中线程数目:4,队列中等待执行的任务数目:0,已执行完的任务数目:0
线程池中线程数目:5,队列中等待执行的任务数目:0,已执行完的任务数目:0
线程池中线程数目:5,队列中等待执行的任务数目:1,已执行完的任务数目:0
线程池中线程数目:5,队列中等待执行的任务数目:2,已执行完的任务数目:0
线程池中线程数目:5,队列中等待执行的任务数目:3,已执行完的任务数目:0
线程池中线程数目:5,队列中等待执行的任务数目:4,已执行完的任务数目:0
线程池中线程数目:5,队列中等待执行的任务数目:5,已执行完的任务数目:0
线程池中线程数目:6,队列中等待执行的任务数目:5,已执行完的任务数目:0
线程池中线程数目:7,队列中等待执行的任务数目:5,已执行完的任务数目:0
线程池中线程数目:8,队列中等待执行的任务数目:5,已执行完的任务数目:0
线程池中线程数目:9,队列中等待执行的任务数目:5,已执行完的任务数目:0
线程池中线程数目:10,队列中等待执行的任务数目:5,已执行完的任务数目:0
thread:pool-1-thread-6,time:2019-06-19 06:10:53,num:10
thread:pool-1-thread-2,time:2019-06-19 06:10:53,num:1
thread:pool-1-thread-7,time:2019-06-19 06:10:53,num:11
thread:pool-1-thread-5,time:2019-06-19 06:10:53,num:4
thread:pool-1-thread-9,time:2019-06-19 06:10:53,num:13
thread:pool-1-thread-8,time:2019-06-19 06:10:53,num:12
thread:pool-1-thread-4,time:2019-06-19 06:10:53,num:3
thread:pool-1-thread-10,time:2019-06-19 06:10:53,num:14
thread:pool-1-thread-1,time:2019-06-19 06:10:53,num:0
thread:pool-1-thread-3,time:2019-06-19 06:10:53,num:2
task 11执行完毕
task 14执行完毕
task 12执行完毕
task 0执行完毕
task 2执行完毕
task 3执行完毕
task 13执行完毕
task 1执行完毕
task 10执行完毕
task 4执行完毕
thread:pool-1-thread-3,time:2019-06-19 06:10:56,num:9
thread:pool-1-thread-1,time:2019-06-19 06:10:56,num:8
thread:pool-1-thread-10,time:2019-06-19 06:10:56,num:7
thread:pool-1-thread-8,time:2019-06-19 06:10:56,num:6
thread:pool-1-thread-7,time:2019-06-19 06:10:56,num:5
task 8执行完毕
task 5执行完毕
task 7执行完毕
task 9执行完毕
task 6执行完毕

Process finished with exit code 0
View Code

1.2、线程池的submit和execute方法区别

1、接收的参数不一样

2、submit有返回值,而execute没有

3、submit方便Exception处理
意思就是如果你在你的task里会抛出checked或者unchecked exception,
而你又希望外面的调用者能够感知这些exception并做出及时的处理,那么就需要用到submit,通过捕获Future.get抛出的异常。

1.3、用法统一说明

理解:001-多线程-基础-进程线程、线程状态、优先级、用户线程和守护线程

  java中线程分为两种类型:用户线程和守护线程。通过Thread.setDaemon(false)设置为用户线程;通过Thread.setDaemon(true)设置为守护线程。如果不设置此属性,默认为用户线程
  用户线程和守护线程的区别:【用户线程存活程序存活,其他则结束

故创建后会等待结果

注意点一、单元测试,如果不加Thread.sleep(3000)会直接退出,或者没有Future get 也会直接退出

  用户线程为什么直接退出?

  单元测试核心类:TestRunner

public class TestRunner extends BaseTestRunner {
    private ResultPrinter fPrinter;
    public static final int SUCCESS_EXIT = 0;
    public static final int FAILURE_EXIT = 1;
    public static final int EXCEPTION_EXIT = 2;
    //……
    public static void main(String[] args) {
        TestRunner aTestRunner = new TestRunner();
        try {
            TestResult r = aTestRunner.start(args);
            if (!r.wasSuccessful()) {
                System.exit(1);
            }
            System.exit(0);
        } catch (Exception var3) {
            System.err.println(var3.getMessage());
            System.exit(2);
        }
    }

  查看TestResult

    /**
     * Returns whether the entire test was successful or not.
     * 返回整个测试是否成功。
     */
    public synchronized boolean wasSuccessful() {
        return failureCount() == 0 && errorCount() == 0;
    }

  可以看到:当aTestRunner调用start方法后不会去等待子线程执行完毕在关闭主线程,而是直接调用TestResult.wasSuccessful()方法,而这个方法始终返回的是false,所以主线程接下来就会执行System.exit,这个放回会结束当前运行的jvm虚拟机,所以使用junit测试多线程方法的结果异常就正常了;

  想要正常输出的话可以让主线程不要结束,等待子线程全部运行结束后在结束主线程,输出结果就会正常。

  使用:1、Thread.sleep(2000);或者 2、future.get()阻塞 或者 3、直接使用main方法测试

注意点二、方法内调用多线程方法,方法结束,多线程不结束

web中Controller请求

    //容器主线程持续运行,程序会立即返回,然后后台默默执行开启的线程
    @RequestMapping(value = "/poolSubmit", method = RequestMethod.GET)
    @ResponseBody
    public Object poolSubmit() {
        for (int i = 0; i < 10; i++) {
            fixedThreadPool.execute(() -> {
                try {
                    Thread.sleep(2000);
                    System.out.println(new Date());
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            });
        }
        fixedThreadPool.shutdown();
        return "ok";
    }

  上述可能拿不到结果,如果需要结果,推荐使用submit带返回Future的get阻塞方式,如下

    //容器主线程 持续运行,程序阻塞
    @RequestMapping(value = "/poolSubmitGet", method = RequestMethod.GET)
    @ResponseBody
    public Object poolSubmitGet() {
        List<Future<String>> futureList = new ArrayList<>();
        for (int i = 0; i < 15; i++) {
            Future<String> submit = fixedThreadPool.submit(() -> {
                try {
                    System.out.println("======-----------------------------" + new Date());
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                return "ok:" + new Date();
            });
            futureList.add(submit);
        }

        for (Future<String> future : futureList) {
            try {
                System.out.println(future.get() + "ok");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return "ok";
    }
View Code

  相当于:便于理解web请求

    public static void main(String[] args) {
        System.out.println(getTest());
        //程序立即打印 Ok
        //同时 都是用户线程 会等方法中的全部线程执行完毕后退出
    }
    public static String getTest(){
        ExecutorService fixedThreadPool = Executors.newFixedThreadPool(5);
        for (int i = 0; i < 10; i++) {
            fixedThreadPool.submit(()->{
                try {

                    Thread.sleep(2000);
                    System.out.println(new Date()+":"+Thread.currentThread().getName()
                            +";守护线程:"+Thread.currentThread().isDaemon());
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            });
        }
        fixedThreadPool.shutdown();
        return "ok";
    }

 二、内置工具类库

2.1、newFixedThreadPool  //创建固定容量大小的缓冲池

  构造一个固定线程数目的线程池,配置的corePoolSize与maximumPoolSize大小相同,同时使用了一个无界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 ,容易OOM

public static ExecutorService newFixedThreadPool(int nThreads) {  
    return new ThreadPoolExecutor(nThreads, nThreads,  
                                  0L, TimeUnit.MILLISECONDS,  
                                  new LinkedBlockingQueue<Runnable>());  
} 
  示例:
    public static void main(String[] args) {
        ExecutorService fixedThreadPool = Executors.newFixedThreadPool(5);
        for (int i = 0; i < 50; i++) {
            fixedThreadPool.submit(new TestThread((i + 1)));
        }
        fixedThreadPool.shutdown();
    } 

2、newCachedThreadPool //创建一个缓冲池,缓冲池容量大小为Integer.MAX_VALUE,空闲60s销毁

  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>());  
}   

  newCachedThreadPool比较适合没有固定大小并且比较快速就能完成的小任务,没必要维持一个Pool,这比直接new Thread来处理的好处是能在60秒内重用已创建的线程。
  其他类型的ThreadPool看看构建参数再结合上面所说的特性就大致知道它的特性。该线程池不会对线程数目加以限制,完全依赖于JVM能创建线程的数量,可能引起内存不足。

  newCachedThreadPool将corePoolSize设置为0,将maximumPoolSize设置为Integer.MAX_VALUE,使用的SynchronousQueue,也就是说来了任务就创建线程运行,当线程空闲超过60秒,就销毁线程。

    public static void main(String[] args) {
        ExecutorService cachedThreadPool = Executors.newCachedThreadPool();
        for (int i = 0; i < 50; i++) {
            cachedThreadPool.submit(new TestThread((i + 1)));
        }
        cachedThreadPool.shutdown();
    }

3、newSingleThreadExecutor //创建容量为1的缓冲池

  构造一个只支持一个线程的线程池,配置corePoolSize=maximumPoolSize=1,无界阻塞队列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>()));
    }

  newSingleThreadExecutor返回以个包含单线程的Executor,将多个任务交给此Exector时,这个线程处理完一个任务后接着处理下一个任务,若该线程出现异常,将会有一个新的线程来替代。它只会用唯一的工作线程来执行任务,保证所有任务按照指定顺序(FIFO, LIFO, 优先级)执行。

  newSingleThreadExecutor将corePoolSize和maximumPoolSize都设置为1,也使用的LinkedBlockingQueue;

  从它们的具体实现来看,它们实际上也是调用了ThreadPoolExecutor,只不过参数都已配置好了。

  实际中,如果Executors提供的三个静态方法能满足要求,就尽量使用它提供的三个方法,因为自己去手动配置ThreadPoolExecutor的参数有点麻烦,要根据实际任务的类型和数量来进行配置。

  另外,如果ThreadPoolExecutor达不到要求,可以自己继承ThreadPoolExecutor类进行重写。

    public static void main(String[] args) {
        ExecutorService singleThreadPool = Executors.newSingleThreadExecutor();
        for (int i = 0; i < 50; i++) {
            singleThreadPool.submit(new TestThread((i + 1)));
        }
        singleThreadPool.shutdown();
    }

4、newScheduledThreadPool

可调度线程池

造有定时功能的线程池,配置corePoolSize,无界延迟阻塞队列DelayedWorkQueue;有意思的是:maximumPoolSize=Integer.MAX_VALUE,由于DelayedWorkQueue是无界队列,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);  
    } 

 

实例

    public static void main(String[] args) {
        ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5);
        //定时
//        scheduledThreadPool.schedule(new Runnable() {
//            @Override
//            public void run() {
//                SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
//                System.out.println("thread:" + Thread.currentThread().getName() + ",time:" + sdf1.format(new Date()));
//            }
//        }, 3, TimeUnit.SECONDS);

        //循环周期执行
        scheduledThreadPool.scheduleAtFixedRate(new Runnable() {
            @Override
            public void run() {
                System.out.println("delay 1 seconds, and excute every 3 seconds");
            }
        }, 1, 3, TimeUnit.SECONDS);
    }

 

posted @ 2019-06-19 18:13  bjlhx15  阅读(405)  评论(0编辑  收藏  举报
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