停止线程池的正确方法

shutdown()方法仅仅是关闭线程池的队列入口

package threadpool;

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

/**
 * 描述：     演示关闭线程池
 */
public class ShutDown {

    public static void main(String[] args) throws InterruptedException {
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        for (int i = 0; i < 100; i++) {
            executorService.execute(new ShutDownTask());
        }
        Thread.sleep(1500);

        System.out.println("演示关闭队列入口之后不再允许提交任务到队列");
        System.out.println("关闭线程池之前isShutdown的值：" + executorService.isShutdown());
        executorService.shutdown();
        System.out.println("关闭线程池之后isShutdown的值：" + executorService.isShutdown());
        executorService.execute(new ShutDownTask());
    }
}

class ShutDownTask implements Runnable {
    @Override
    public void run() {
        try {
            Thread.sleep(500);
            System.out.println(Thread.currentThread().getName());
        } catch (InterruptedException e) {
            System.out.println(Thread.currentThread().getName() + "被中断了");
        }
    }
}

1、shutdown()代表关闭线程池队列入口，那么isShutdown()判断的就是线程池队列入口有没关闭。
2、线程池队列入口关闭之后还继续往线程池添加任务则会抛出RejectedExecutionException异常。

isTerminated()是判断线程池是否停止

停止：线程池队列入口关闭且线程池中任务都执行完毕

package threadpool;

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

/**
 * 描述：     演示关闭线程池
 */
public class ShutDown {

    public static void main(String[] args) throws InterruptedException {
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        for (int i = 0; i < 100; i++) {
            executorService.execute(new ShutDownTask());
        }
        Thread.sleep(1500);

        System.out.println("演示主线程等待10s之后，看线程池的isTerminated的值");
        executorService.shutdown();// 需要注意，线程池不调用shutdown方法是不能关闭的，那么isTerminated一直是false，且该程序也不能关闭
        Thread.sleep(10000);
        System.out.println("线程等待10s之后isTerminated的值：" + executorService.isTerminated());
    }
}

class ShutDownTask implements Runnable {
    @Override
    public void run() {
        try {
            Thread.sleep(500);
            System.out.println(Thread.currentThread().getName());
        } catch (InterruptedException e) {
            System.out.println(Thread.currentThread().getName() + "被中断了");
        }
    }
}

执行结果

1、如果没有关闭线程池队列入口，那么线程池isTerminated永远为false，不管线程池中任务是否都执行完毕

awaitTermination等待一段时间，检查线程池isTerminated()

package threadpool;

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

/**
 * 描述：     演示关闭线程池
 */
public class ShutDown {

    public static void main(String[] args) throws InterruptedException {
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        for (int i = 0; i < 100; i++) {
            executorService.execute(new ShutDownTask());
        }
        Thread.sleep(1500);

        System.out.println("演示线程池等待n秒之后");
        executorService.shutdown();// 需要注意，线程池不调用shutdown方法是不能关闭的，也就是awaitTermination无论等待多久都是false，且该程序也不能关闭
        boolean b = executorService.awaitTermination(7L, TimeUnit.SECONDS);
        System.out.println("线程池等待n秒之后,awaitTermination返回的值" + b) ;
    }
}

class ShutDownTask implements Runnable {
    @Override
    public void run() {
        try {
            Thread.sleep(500);
            System.out.println(Thread.currentThread().getName());
        } catch (InterruptedException e) {
            System.out.println(Thread.currentThread().getName() + "被中断了");
        }
    }
}

执行结果

1、既然是判断线程池是否停止，那么同第二个例子一样，在执行awaitTermination方法之前需要执行shutdown()方法。

shutdownNow()方法会中断正在执行的线程，并且关闭队列入口和将队列中的任务返回

package threadpool;

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

/**
 * 描述：     演示关闭线程池
 */
public class ShutDown {

    public static void main(String[] args) throws InterruptedException {
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        for (int i = 0; i < 100; i++) {
            executorService.execute(new ShutDownTask());
        }
        Thread.sleep(1500);

        System.out.println("演示shutdownNow()方法会中断正在执行的线程，并且将队列中的任务返回");
        List runnableList = executorService.shutdownNow();
        System.out.println(runnableList);
        System.out.println("shutdownNow之后线程池isShutdown的值" + executorService.isShutdown());
        System.out.println("shutdownNow之后线程池isTerminated的值" + executorService.isTerminated());
    }
}

class ShutDownTask implements Runnable {
    @Override
    public void run() {
        try {
            Thread.sleep(500);
            System.out.println(Thread.currentThread().getName());
        } catch (InterruptedException e) {
            System.out.println(Thread.currentThread().getName() + "被中断了");
        }
    }
}

执行结果

1、shutdownNow()方法既关闭线程池队列入口，还”强迫“线程池中任务立刻完成（即中断）。