Java多线程技术11——ThreadPoolExecutor类的使用2

1 isShutdown()方法

? ? ? ? public boolean??isShutdown()方法的作用是判断线程池是否已经关闭

public class Run1 {
    public static void main(String[] args) {
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                try {
                    System.out.println("开始: " + Thread.currentThread().getName());
                    Thread.sleep(1000);
                    System.out.println("结束: " + Thread.currentThread().getName());
                }catch (InterruptedException e){
                    e.printStackTrace();
                }
            }
        };
        ThreadPoolExecutor pool = new ThreadPoolExecutor(2,2,Integer.MAX_VALUE, TimeUnit.SECONDS,new LinkedBlockingDeque<>());
        pool.execute(runnable);
        System.out.println("A = " + pool.isShutdown());
        pool.shutdown();
        System.out.println("B = " + pool.isShutdown());
    }
}

? ? ? ? 由运行结果可知，只要调用了shutdown()方法，isShutdown()方法的返回值就是true。

2? isTerminating()和isTerminated()方法

? ? ? ? public boolean?isTerminating()方法：如果此执行程序处于在shutdown或shutdownNow之后且正在终止但尚未完全终止的过程中，也就是还有任务在执行，则返回true。此方法可以比喻成门是否正在关闭。

? ? ? public boolean?isTerminated()方法：如果关闭后所有任务都已完成，则返回true。此方法可以比喻成门是否已经关闭。

? ? ? ? shutdown或shutdownNow方法的功能是发出一个关闭线程池的命令，isShutdown方法用于判断关闭线程池的命令发出或未发出。??isTerminating方法用于判断线程池是否正在关闭中，isTerminated方法判断线程池是否已经关闭了。

public class MyRunnable implements Runnable{
    @Override
    public void run() {
        try {
            System.out.println(Thread.currentThread().getName()+"begin: "+ Utils.data(System.currentTimeMillis()));
            Thread.sleep(2000);
            System.out.println(Thread.currentThread().getName()+"end: "+ Utils.data(System.currentTimeMillis()));
        }catch (InterruptedException e){
            e.printStackTrace();
        }

    }
}

public class Test {
    public static void main(String[] args) throws InterruptedException {
        MyRunnable runnable = new MyRunnable();
        ThreadPoolExecutor pool = new ThreadPoolExecutor(2,99999,99999, TimeUnit.SECONDS,new LinkedBlockingDeque<>());
        pool.execute(runnable);
        pool.execute(runnable);
        pool.execute(runnable);
        pool.execute(runnable);
        System.out.println(pool.isTerminating() + " " + pool.isTerminated());
        pool.shutdown();
        Thread.sleep(1000);
        System.out.println(pool.isTerminating() + " " + pool.isTerminated());
        Thread.sleep(1000);
        System.out.println(pool.isTerminating() + " " + pool.isTerminated());
        Thread.sleep(1000);
        System.out.println(pool.isTerminating() + " " + pool.isTerminated());
        Thread.sleep(1000);
        System.out.println(pool.isTerminating() + " " + pool.isTerminated());
        Thread.sleep(1000);
        System.out.println(pool.isTerminating() + " " + pool.isTerminated());
    }
}

3? awaitTermination(long timeout, TimeUnit unit)

?????????public boolean awaitTermination(long timeout, TimeUnit unit)方法：查看在指定的时间内，线程池是否已经终止工作，也就是“最多”等待多少时间后去判断线程池是否已经终止工作。如果在指定的时间之内，线程池销毁会导致该方法不再阻塞，而超过timeout时间也会导致该方法不再阻塞。此方法的使用需要shutdown()方法的配合。

public class MyRunnable1 implements Runnable{
    @Override
    public void run() {
        try {
            System.out.println(Thread.currentThread().getName() + " " + Utils.data(System.currentTimeMillis()));
            Thread.sleep(4000);
            System.out.println(Thread.currentThread().getName() + " " + Utils.data(System.currentTimeMillis()));
        }catch (InterruptedException e){
            e.printStackTrace();
        }
    }
}

public class Test1 {
    public static void main(String[] args) throws InterruptedException {
        MyRunnable1 runnable1 = new MyRunnable1();
        ThreadPoolExecutor pool = new ThreadPoolExecutor(2,99999,9999L, TimeUnit.SECONDS,new LinkedBlockingQueue<>());
        pool.execute(runnable1);
        System.out.println("main开始：" + Utils.data(System.currentTimeMillis()));
        System.out.println(pool.awaitTermination(10,TimeUnit.SECONDS));
        System.out.println("main结束：" + Utils.data(System.currentTimeMillis()));
    }
}

? ? ? ? 从控制台可以看出，main开始到main结束需要10秒，因为main线程并未销毁，所以?awaitTermination方法需要阻塞10秒。打印false的原因是未对线程池执行shutdown方法。如果对线程池执行shutdown方法，在运行时间上会有什么效果呢？

public class Test2 {
    public static void main(String[] args) throws InterruptedException {
        MyRunnable1 runnable1 = new MyRunnable1();
        ThreadPoolExecutor pool = new ThreadPoolExecutor(2,99999,9999L, TimeUnit.SECONDS,new LinkedBlockingQueue<>());
        pool.execute(runnable1);
        pool.shutdown();
        System.out.println("main开始：" + Utils.data(System.currentTimeMillis()));
        System.out.println(pool.awaitTermination(10,TimeUnit.SECONDS));
        System.out.println("main结束：" + Utils.data(System.currentTimeMillis()));
    }
}

? ? ? ? 可以看出，main开始和mian结束之间耗时4秒，因为4秒后线程池销毁了，导致?awaitTermination方法取消阻塞。

4 set/getRejectedExceptionHandler()方法

????????public void setRejectedExecutionHandler(RejectedExecutionHandler handler)和

????????public RejectedExecutionHandler getRejectedExecutionHandler()方法的作用是可以处理任务被拒绝执行时的行为。

public class MyRunnable1 implements Runnable{
    private String username;

    public MyRunnable1(String username) {
        this.username = username;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    @Override
    public void run() {
        try {
            System.out.println(Thread.currentThread().getName()+ "开始时间 =  " + Utils.data(System.currentTimeMillis()));
            Thread.sleep(4000);
            System.out.println(Thread.currentThread().getName()+ "结束时间 =  " + Utils.data(System.currentTimeMillis()));
        }catch (InterruptedException e){
            e.printStackTrace();
        }
    }
}

public class Run1 {
    public static void main(String[] args) {
        MyRunnable1 myRunnable1 = new MyRunnable1("a1");
        MyRunnable1 myRunnable2 = new MyRunnable1("a2");
        MyRunnable1 myRunnable3 = new MyRunnable1("a3");
        MyRunnable1 myRunnable4 = new MyRunnable1("a4");
        ThreadPoolExecutor pool = new ThreadPoolExecutor(2,3,999L, TimeUnit.SECONDS,new SynchronousQueue<>());
        pool.execute(myRunnable1);
        pool.execute(myRunnable2);
        pool.execute(myRunnable3);
        pool.execute(myRunnable4);
    }
}

? ? ? ? 控制台打印的信息说明? MyRunnable1 myRunnable4 = new MyRunnable1("a4");任务被拒绝执行，在出现这样的异常时可以自定义拒绝执行任务的行为。创建MyRejectedExecutionHandler.java类。

public class MyRejectedExecutionHandler implements RejectedExecutionHandler {
    @Override
    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
        System.out.println(((MyRunnable1) r).getUsername() + "被拒绝执行");
    }
}

public class Run2 {
    public static void main(String[] args) {
        MyRunnable1 myRunnable1 = new MyRunnable1("a1");
        MyRunnable1 myRunnable2 = new MyRunnable1("a2");
        MyRunnable1 myRunnable3 = new MyRunnable1("a3");
        MyRunnable1 myRunnable4 = new MyRunnable1("a4");
        ThreadPoolExecutor pool = new ThreadPoolExecutor(2,3,999L, TimeUnit.SECONDS,new SynchronousQueue<>());
        pool.setRejectedExecutionHandler(new MyRejectedExecutionHandler());
        pool.execute(myRunnable1);
        pool.execute(myRunnable2);
        pool.execute(myRunnable3);
        pool.execute(myRunnable4);
        pool.shutdown();
    }
}

5 allowsCoreThreadTimeOut()和allowCoreThreadTimeOut(bool)方法

????????allowsCoreThreadTimeOut(true)可使核心池中的空闲线程具有超时销毁的特性。其中，public boolean allowsCoreThreadTimeOut() 方法的作用是判断是否具有这个特性。

public void allowCoreThreadTimeOut(boolean value)方法的作用是设置是否有这个特性。

public class MyRunnable implements Runnable{
    @Override
    public void run() {
        System.out.println(Thread.currentThread() + "开始：" + Utils.data(System.currentTimeMillis()));
        System.out.println(Thread.currentThread() + "结束：" + Utils.data(System.currentTimeMillis()));
    }
}

public class Run1 {
    public static void main(String[] args) throws InterruptedException {
        ThreadPoolExecutor pool = new ThreadPoolExecutor(4,5,5, TimeUnit.SECONDS,new SynchronousQueue<>());
        System.out.println(pool.allowsCoreThreadTimeOut());
        for (int i = 0; i < 4; i++) {
            MyRunnable myRunnable = new MyRunnable();
            pool.execute(myRunnable);
        }
        Thread.sleep(8000);
        System.out.println(pool.getPoolSize());
    }
}

创建Run2.java类

public class Run2 {
    public static void main(String[] args) throws InterruptedException {
        ThreadPoolExecutor pool = new ThreadPoolExecutor(4,5,5, TimeUnit.SECONDS,new SynchronousQueue<>());
        pool.allowCoreThreadTimeOut(true);
        System.out.println(pool.allowsCoreThreadTimeOut());
        for (int i = 0; i < 4; i++) {
            MyRunnable myRunnable = new MyRunnable();
            pool.execute(myRunnable);
        }
        Thread.sleep(8000);
        System.out.println(pool.getPoolSize());
    }
}

?

6?prestartCoreThread()和prestartAllCoreThreads()方法

? ? ? ? 在实例化ThreadPoolExecutor类后，线程池并没有核心线程，除非执行execute()方法，但是在不执行execute()方法时也可以通过执行prestartCoreThread()和prestartAllCoreThreads()方法来创建核心线程。

????????public boolean prestartCoreThread()方法的作用是每调用一次就创建一个核心线程并使它变成启动状态，返回值类型为boolean，代表是否创建成功。

????????public int prestartAllCoreThreads()方法的作用是同时启动全部核心线程，返回值是启动核心线程的数量。

public class Run1 {
    public static void main(String[] args) {
        ThreadPoolExecutor pools = new ThreadPoolExecutor(4,8,5, TimeUnit.SECONDS,new LinkedBlockingQueue<>());
        System.out.println("线程池中的线程数a= " + pools.getPoolSize());
        System.out.println("Z1 = " + pools.prestartCoreThread());
        System.out.println("线程池中的线程数a= " + pools.getPoolSize());
        System.out.println("Z2 = " + pools.prestartCoreThread());
        System.out.println("线程池中的线程数a= " + pools.getPoolSize());
        System.out.println("Z3 = " + pools.prestartCoreThread());
        System.out.println("线程池中的线程数a= " + pools.getPoolSize());
        System.out.println("Z4 = " + pools.prestartCoreThread());
        System.out.println("线程池中的线程数a= " + pools.getPoolSize());
        System.out.println("Z5 = " + pools.prestartCoreThread());
        System.out.println("线程池中的线程数a= " + pools.getPoolSize());
        System.out.println("Z6 = " + pools.prestartCoreThread());
    }
}

????????????????

? ? ? ? 最后连续打印了2个false代表核心池中的线程数量已经到了最大值，是4。不能再创建新的核心池中的线程了。

? ? ? ? 创建Run2.java类。

public class Run2 {
    public static void main(String[] args) {
        ThreadPoolExecutor pools = new ThreadPoolExecutor(4,8,5, TimeUnit.SECONDS,new LinkedBlockingQueue<>());
        System.out.println("线程池中的线程数a= " + pools.getPoolSize());
        System.out.println("Z1 = " + pools.prestartAllCoreThreads());
        System.out.println("线程池中的线程数a= " + pools.getPoolSize());
        System.out.println();
        System.out.println("Z2 = " + pools.prestartAllCoreThreads());
        System.out.println("线程池中的线程数a= " + pools.getPoolSize());

    }
}

?

? ? ? ? 打印信息Z2 = 0,说明核心池中的线程已满，不需要创建新的核心池中的线程。?