java多线程-线程的停止【interrupt】

java多线程-线程的停止

线程停止的原理

使用interrupt来通知，而不是强制

java提供了interrrupt让一个线程来通知另一个线程停止

如果想中断一个线程，但是那个线程不想去中断，那就无能为力，我们没有强制去中断线程的手段，因为线程停止前需要做一定的收尾工作

所以正确停止线程，是如何用interrupt来通知那个线程，以及被停止的线程如何进行配合

如何正确停止线程

在普通情况下停止线程

代码展示

• 调用interrupt没有作用
• 下面这段代码，执行interrupt之后，线程并没有被中断
• 因为被执行的线程并没有相应中断的方式

public class stopThreadWithoutSleep  implements Runnable{

    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(new stopThreadWithoutSleep());
        thread.start();
        Thread.sleep(1000);
        thread.interrupt();
    }

    @Override
    public void run() {
        int num = 0;
        while(num <= Integer.MAX_VALUE / 2) {
            if (num % 10000 == 0) {
                System.out.println(num + "是10000的倍数");
            }
            num++;
        }
        System.out.println("结束");
    }
}

/*
由于太长，只展示结尾部分的结果 
1073710000是10000的倍数
1073720000是10000的倍数
1073730000是10000的倍数
1073740000是10000的倍数
结束
* */

• 被执行线程加上相应中断的操作之后
• 结果可知，被执行线程相应一秒之后就结束了

public class stopThreadWithoutSleep  implements Runnable{

    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(new stopThreadWithoutSleep());
        thread.start();
        Thread.sleep(1000);
        thread.interrupt();
    }

    @Override
    public void run() {
        int num = 0;
        while(!Thread.currentThread().isInterrupted() && num <= Integer.MAX_VALUE / 2) {
            if (num % 10000 == 0) {
                System.out.println(num + "是10000的倍数");
            }
            num++;
        }
        System.out.println("结束");
    }
}

/*
由于太长，只展示结尾部分的结果
587830000是10000的倍数
587840000是10000的倍数
587850000是10000的倍数
587860000是10000的倍数
结束
* */

在阻塞情况下停止线程

代码展示

• 中断之后，抛出异常
• 线程在sleep的过程中，会catch到InterruptedException这个异常，从而相应中断

public class stopThreadWithSleep {

    public static void main(String[] args) {
        Runnable runnable = () -> {
            int num = 0;
            while (num <= 300 && !Thread.currentThread().isInterrupted()) {
                if (num % 100 == 0) {
                    System.out.println(num + "是100的倍数");
                }
                num++;
            }
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        };
        Thread thread = new Thread(runnable);
        thread.start();
        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        thread.interrupt();
    }
}

/*
* 0是100的倍数
100是100的倍数
200是100的倍数
300是100的倍数
java.lang.InterruptedException: sleep interrupted
   at java.lang.Thread.sleep(Native Method)
   at com.jx.JavaTest.stopThread.stopThreadWithSleep.lambda$main$0(stopThreadWithSleep.java:15)
   at java.lang.Thread.run(Thread.java:748)
* */

线程在每次迭代后都阻塞

代码展示

• 即使不在while判断是否中断，sleep也能中断异常

public class stopThreadWithSleepEveryLoop {

    public static void main(String[] args) {
        Runnable runnable = () -> {
            int num = 0;
            try {
                while (num <= 10000) {
                    if (num % 100 == 0) {
                        System.out.println(num + "是100的倍数");
                    }
                    num++;

                    Thread.sleep(10);
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        };
        
        Thread thread = new Thread(runnable);
        thread.start();
        try {
            Thread.sleep(5000);
        } catch (
                InterruptedException e) {
            e.printStackTrace();
        }
        thread.interrupt();
    }
}

/*
* 0是100的倍数
100是100的倍数
200是100的倍数
300是100的倍数
java.lang.InterruptedException: sleep interrupted
   at java.lang.Thread.sleep(Native Method)
   at com.jx.JavaTest.stopThread.stopThreadWithSleepEveryLoop.lambda$main$0(stopThreadWithSleepEveryLoop.java:15)
   at java.lang.Thread.run(Thread.java:748)

Process finished with exit code 0

* 
* */

• 当catch写到while内，则不能正常中断

public class CantInterrupt {

    public static void main(String[] args) {
        Runnable runnable = () -> {
            int num = 0;
            while (num <= 10000) {
                if (num % 100 == 0) {
                    System.out.println(num + "是100的倍数");
                }
                num ++;
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };
        Thread thread = new Thread(runnable);
        thread.start();
        try {
            Thread.sleep(5000);
        } catch (
                InterruptedException e) {
            e.printStackTrace();
        }
        thread.interrupt();
    }
}

/*
* 0是100的倍数
100是100的倍数
200是100的倍数
300是100的倍数
java.lang.InterruptedException: sleep interrupted
   at java.lang.Thread.sleep(Native Method)
   at com.jx.JavaTest.stopThread.CantInterrupt.lambda$main$0(CantInterrupt.java:14)
   at java.lang.Thread.run(Thread.java:748)
400是100的倍数
500是100的倍数
600是100的倍数
700是100的倍数
800是100的倍数
900是100的倍数

Process finished with exit code -1

* */

• 即使在while的判断条件中，加上检测中断的机制，也不能正常中断
• 因为java的sleep函数，一旦相应中断，就会将中断的标志位删除

public class CantInterrupt {

    public static void main(String[] args) {
        Runnable runnable = () -> {
            int num = 0;
            while (num <= 10000 && !Thread.currentThread().isInterrupted()) {
                if (num % 100 == 0) {
                    System.out.println(num + "是100的倍数");
                }
                num++;
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };
        Thread thread = new Thread(runnable);
        thread.start();
        try {
            Thread.sleep(5000);
        } catch (
                InterruptedException e) {
            e.printStackTrace();
        }
        thread.interrupt();
    }
}

/*
0是100的倍数
100是100的倍数
200是100的倍数
300是100的倍数
java.lang.InterruptedException: sleep interrupted
   at java.lang.Thread.sleep(Native Method)
   at com.jx.JavaTest.stopThread.CantInterrupt.lambda$main$0(CantInterrupt.java:14)
   at java.lang.Thread.run(Thread.java:748)
400是100的倍数
500是100的倍数

Process finished with exit code -1


* */

停止线程的最佳实践

• 在方法签名中抛出异常，在run方法中强制进行try catch

public class StopThreadInProd implements Runnable{

    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(new StopThreadInProd());
        thread.start();
        Thread.sleep(1000);
        thread.interrupt();
    }

    @Override
    public void run() {
        while (true) {
            System.out.println("start");
            try {
                throwInMethod();
            } catch (InterruptedException e) {
                System.out.println("保存日志/关闭程序");
                e.printStackTrace();
            }
        }
    }

    private void throwInMethod() throws InterruptedException {
            Thread.sleep(2000);
    }
}

/*
* start
保存日志/关闭程序
start
java.lang.InterruptedException: sleep interrupted
   at java.lang.Thread.sleep(Native Method)
   at com.jx.JavaTest.stopThread.StopThreadInProd.throwInMethod(StopThreadInProd.java:26)
   at com.jx.JavaTest.stopThread.StopThreadInProd.run(StopThreadInProd.java:17)
   at java.lang.Thread.run(Thread.java:748)
start
start

Process finished with exit code -1

* 
* */

• 在catch语句中调用Thread.currentThread().interrupt恢复中断状态
• 结果：抛出异常，程序结束

public class StopThreadInProd2 implements Runnable{

    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(new StopThreadInProd2());
        thread.start();
        Thread.sleep(1000);
        thread.interrupt();
    }

    @Override
    public void run() {
        while (true) {
            if (Thread.currentThread().isInterrupted()) {
                System.out.println("Interrupt");
                break;
            }
            reInterrupt();
        }
    }

    private void reInterrupt() {
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            e.printStackTrace();
        }
    }
}

/*
java.lang.InterruptedException: sleep interrupted
   at java.lang.Thread.sleep(Native Method)
   at com.jx.JavaTest.stopThread.StopThreadInProd2.reInterrupt(StopThreadInProd2.java:25)
   at com.jx.JavaTest.stopThread.StopThreadInProd2.run(StopThreadInProd2.java:19)
   at java.lang.Thread.run(Thread.java:748)
Interrupt
*
* */

• 依照上面的代码，如果方法没有没有重新抛出异常
• 结果：程序抛出异常，但是程序没有停止运行

public class StopThreadInProd2 implements Runnable{

    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(new StopThreadInProd2());
        thread.start();
        Thread.sleep(1000);
        thread.interrupt();
    }

    @Override
    public void run() {
        while (true) {
            if (Thread.currentThread().isInterrupted()) {
                System.out.println("Interrupt");
                break;
            }
            reInterrupt();
        }
    }

    private void reInterrupt() {
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
//            Thread.currentThread().interrupt();
            e.printStackTrace();
        }
    }
}

/*
java.lang.InterruptedException: sleep interrupted
   at java.lang.Thread.sleep(Native Method)
   at com.jx.JavaTest.stopThread.StopThreadInProd2.reInterrupt(StopThreadInProd2.java:25)
   at com.jx.JavaTest.stopThread.StopThreadInProd2.run(StopThreadInProd2.java:19)
   at java.lang.Thread.run(Thread.java:748)
*
* */

错误停止的方法

被弃用的stop,suspend和resume方法

• 使用stop停止线程，会导致线程运行一半突然停止，没办法完成最基本的操作，会造成脏数据
• 下面这段代码的结果会造成一个连队只有部分人领取到了装备
• stop是不安全的，会直接停止监视器
• suspend和resume不会破坏对象，但是会让线程挂起，不释放锁，容易造成死锁

public class StopThread implements Runnable{


    @Override
    public void run() {
        // 模拟指挥军队,一共五个连队,每个连队一百人
        // 以连队为单位发放武器
        for (int i = 0; i < 5; i++) {
            System.out.println("连队" + i + "领取武器");
            for (int j = 0; j < 10; j++) {
                System.out.println(j);
                try {
                    Thread.sleep(50);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            System.out.println("连队" + i + "领取完毕");
        }
    }

    public static void main(String[] args) {
        Thread thread = new Thread(new StopThread());
        thread.start();
        try {
            thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        thread.stop();
    }
}

/*
* 连队0领取武器
0
1
2
3
4
5
6
7
8
9
连队0领取完毕
连队1领取武器
0
1
2
3
4
5

Process finished with exit code 0

* */

用volatile设置boolean标记位

• 下面这段代码，通过改变标志位的值会成功终止线程

public class Volatile implements Runnable {

    private volatile boolean canceled = false;

    @Override
    public void run() {
        int num = 0;
        try {
            while (num <= 10000 && !canceled) {
                if (num % 100 == 0) {
                    System.out.println(num + " 是100的倍数");
                }
                num++;

                Thread.sleep(1);
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        Volatile v = new Volatile();
        Thread thread = new Thread(v);
        thread.start();
        Thread.sleep(1000);
        v.canceled = true;
    }

}

/*
*0 是100的倍数
100 是100的倍数
200 是100的倍数
300 是100的倍数
400 是100的倍数
500 是100的倍数
600 是100的倍数

Process finished with exit code 0

* 
* */

• 当陷入阻塞的时候，是无法停止线程的
• 下面这段代码的运行结果，并没有打印生产者停止运行，说明根本没有执行生产者的finally那部分代码
• 同时程序也没停止
• 原因见生产者代码 while循环中的注释

// 模拟生产者和消费者
public class cantStop {

    public static void main(String[] args) throws InterruptedException {

        // 阻塞队列
        // 满了之后,放不进去
        // 空的时候取数据,也会堵塞
        ArrayBlockingQueue storage = new ArrayBlockingQueue(10);
        Producer producer = new Producer(storage);

        Thread producerThread = new Thread(producer);

        producerThread.start();
        Thread.sleep(1000);

        Consumer consumer = new Consumer(storage);
        while (consumer.needMore()) {
            System.out.println(consumer.storage.take() + "被消费");
            Thread.sleep(100);
        }
        System.out.println("消费者不需要更多数据");

        // 消费者不需要数据,让生产者停下来
        producer.canceled = true;

    }

}

// 生产者
class Producer implements Runnable {

    public volatile boolean canceled = false;

    BlockingQueue storage;

    public Producer(BlockingQueue storage) {
        this.storage = storage;
    }

    @Override
    public void run() {
        int num = 0;
        try {
            while (num <= 10000 && !canceled) {
                if (num % 100 == 0) {
                    // 当堵塞队列满了之后，会堵塞在这里，而这段代码没有判断机制
                    storage.put(num);
                    System.out.println("num" + "生产");
                }
                num++;
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            System.out.println("生产者停止运行");
        }
    }
}

// 消费者
class Consumer {
    BlockingQueue storage;

    public Consumer(BlockingQueue storage) {
        this.storage = storage;
    }

    public boolean needMore() {
        if (Math.random() > 0.9) {
            return false;
        }
        return true;
    }
}

/*
* num生产
num生产
num生产
num生产
num生产
num生产
num生产
num生产
num生产
num生产
0被消费
num生产
消费者不需要更多数据

* 
* */

• 将上面代码用interrupt进行中断
• 程序成功停止

public class finxed {

    public static void main(String[] args) throws InterruptedException {

        finxed finxed = new finxed();

        // 阻塞队列
        // 满了之后,放不进去
        // 空的时候取数据,也会堵塞
        ArrayBlockingQueue storage = new ArrayBlockingQueue(10);
        Producer producer = finxed.new Producer(storage);

        Thread producerThread = new Thread(producer);

        producerThread.start();
        Thread.sleep(1000);

        Consumer consumer = finxed.new Consumer(storage);
        while (consumer.needMore()) {
            System.out.println(consumer.storage.take() + "被消费");
            Thread.sleep(100);
        }
        System.out.println("消费者不需要更多数据");

        // 消费者不需要数据,让生产者停下来
        producerThread.interrupt();

    }

    class Producer implements Runnable {

        public volatile boolean canceled = false;

        BlockingQueue storage;

        public Producer(BlockingQueue storage) {
            this.storage = storage;
        }

        @Override
        public void run() {
            int num = 0;
            try {
                while (num <= 10000 && !Thread.currentThread().isInterrupted()) {
                    if (num % 100 == 0) {
                        storage.put(num);
                        System.out.println("num" + "生产");
                    }
                    num++;
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                System.out.println("生产者停止运行");
            }
        }
    }

    class Consumer {
        BlockingQueue storage;

        public Consumer(BlockingQueue storage) {
            this.storage = storage;
        }

        public boolean needMore() {
            if (Math.random() > 0.9) {
                return false;
            }
            return true;
        }
    }

}

/*
* 2100被消费
num生产
2200被消费
num生产
2300被消费
num生产
消费者不需要更多数据
生产者停止运行
java.lang.InterruptedException
   at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.reportInterruptAfterWait(AbstractQueuedSynchronizer.java:2014)
   at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2048)
   at java.util.concurrent.ArrayBlockingQueue.put(ArrayBlockingQueue.java:353)
   at com.jx.JavaTest.stopThread.volatiledmo.finxed$Producer.run(finxed.java:51)
   at java.lang.Thread.run(Thread.java:748)

Process finished with exit code 0

* 
* */

interrupt源码查看

• 这段代码做的都是一些判断，真正执行中断的代码时interrupt0
• interrupt0是native代码

public void interrupt() {
    if (this != Thread.currentThread())
        checkAccess();

    synchronized (blockerLock) {
        Interruptible b = blocker;
        if (b != null) {
            interrupt0();           // Just to set the interrupt flag
            b.interrupt(this);
            return;
        }
    }
    interrupt0();
}

private native void interrupt0();

interrupt相关函数练习

• isInterrupted获取中断标志，获取的是前面的线程
• interrupted获取中断标志并重置，只关心执行的线程，所以下面代码执行的是main线程

public class InterruptedTest {

    public static void main(String[] args) throws InterruptedException {

        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {

                }
            }
        });

        thread.start();

        thread.interrupt();
        // 获取中断标志
        System.out.println(thread.isInterrupted()); // true
        // 获取中断标志并重置
        System.out.println(thread.interrupted()); //false
        System.out.println(Thread.interrupted()); // false
        System.out.println(thread.isInterrupted()); //true
        thread.join();
        System.out.println("over");

    }
}