Java线程的停止实现原理详解

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2023-07-26
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标签   Java多线程
目录
  • 线程停止的原理
  • 如何正确停止线程
  • 在普通情况下停止线程
  • 在阻塞情况下停止线程
  • 线程在每次迭代后都阻塞
  • 停止线程的最佳实践
  • 错误停止的方法
  • 被弃用的stop,suspend和resume方法
  • 用volatile设置boolean标记位
  • interrupt源码查看
  • interrupt相关函数练习

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();
        thread.interrupt();
    }
    @Override
    public void run() {
        int num =;
        while(num <= Integer.MAX_VALUE /) {
            if (num % == 0) {
                System.out.println(num + "是的倍数");
            }
            num++;
        }
        System.out.println("结束");
    }
}
/*
由于太长，只展示结尾部分的结果是10000的倍数
是10000的倍数
是10000的倍数
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();
        thread.interrupt();
    }
    @Override
    public void run() {
        int num =;
        while(!Thread.currentThread().isInterrupted() && num <= Integer.MAX_VALUE /) {
            if (num % == 0) {
                System.out.println(num + "是的倍数");
            }
            num++;
        }
        System.out.println("结束");
    }
}
/*
由于太长，只展示结尾部分的结果是10000的倍数
是10000的倍数
是10000的倍数
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 =;
            while (num <= && !Thread.currentThread().isInterrupted()) {
                if (num % == 0) {
                    System.out.println(num + "是的倍数");
                }
                num++;
            }
            try {
                Thread.sleep();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        };
        Thread thread = new Thread(runnable);
        thread.start();
        try {
            Thread.sleep();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        thread.interrupt();
    }
}
/*
*是100的倍数
是100的倍数
是100的倍数
是100的倍数
java.lang.InterruptedException: sleep interrupted
   at java.lang.Thread.sleep(Native Method)
   at com.jx.JavaTest.stopThread.stopThreadWithSleep.lambda$main$(stopThreadWithSleep.java:15)
   at java.lang.Thread.run(Thread.java:)
* */

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 =;
            try {
                while (num <=) {
                    if (num % == 0) {
                        System.out.println(num + "是的倍数");
                    }
                    num++;
                    Thread.sleep();
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        };
        Thread thread = new Thread(runnable);
        thread.start();
        try {
            Thread.sleep();
        } catch (
                InterruptedException e) {
            e.printStackTrace();
        }
        thread.interrupt();
    }
}
/*
*是100的倍数
是100的倍数
是100的倍数
是100的倍数
java.lang.InterruptedException: sleep interrupted
   at java.lang.Thread.sleep(Native Method)
   at com.jx.JavaTest.stopThread.stopThreadWithSleepEveryLoop.lambda$main$(stopThreadWithSleepEveryLoop.java:15)
   at java.lang.Thread.run(Thread.java:)
Process finished with exit code
* 
* */

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 =;
            while (num <=) {
                if (num % == 0) {
                    System.out.println(num + "是的倍数");
                }
                num ++;
                try {
                    Thread.sleep();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };
        Thread thread = new Thread(runnable);
        thread.start();
        try {
            Thread.sleep();
        } catch (
                InterruptedException e) {
            e.printStackTrace();
        }
        thread.interrupt();
    }
}
/*
*是100的倍数
是100的倍数
是100的倍数
是100的倍数
java.lang.InterruptedException: sleep interrupted
   at java.lang.Thread.sleep(Native Method)
   at com.jx.JavaTest.stopThread.CantInterrupt.lambda$main$(CantInterrupt.java:14)
   at java.lang.Thread.run(Thread.java:)
是100的倍数
是100的倍数
是100的倍数
是100的倍数
是100的倍数
是100的倍数
Process finished with exit code -
* */
  • 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 =;
            while (num <= && !Thread.currentThread().isInterrupted()) {
                if (num % == 0) {
                    System.out.println(num + "是的倍数");
                }
                num++;
                try {
                    Thread.sleep();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };
        Thread thread = new Thread(runnable);
        thread.start();
        try {
            Thread.sleep();
        } catch (
                InterruptedException e) {
            e.printStackTrace();
        }
        thread.interrupt();
    }
}
/*是100的倍数
是100的倍数
是100的倍数
是100的倍数
java.lang.InterruptedException: sleep interrupted
   at java.lang.Thread.sleep(Native Method)
   at com.jx.JavaTest.stopThread.CantInterrupt.lambda$main$(CantInterrupt.java:14)
   at java.lang.Thread.run(Thread.java:)
是100的倍数
是100的倍数
Process finished with exit code -
* */

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();
        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();
    }
}
/*
* 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:)
   at com.jx.JavaTest.stopThread.StopThreadInProd.run(StopThreadInProd.java:)
   at java.lang.Thread.run(Thread.java:)
start
start
Process finished with exit code -
* 
* */
  • 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 StopThreadInProd implements Runnable{
    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(new StopThreadInProd());
        thread.start();
        Thread.sleep();
        thread.interrupt();
    }
    @Override
    public void run() {
        while (true) {
            if (Thread.currentThread().isInterrupted()) {
                System.out.println("Interrupt");
                break;
            }
            reInterrupt();
        }
    }
    private void reInterrupt() {
        try {
            Thread.sleep();
        } 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.StopThreadInProd.reInterrupt(StopThreadInProd2.java:25)
   at com.jx.JavaTest.stopThread.StopThreadInProd.run(StopThreadInProd2.java:19)
   at java.lang.Thread.run(Thread.java:)
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 StopThreadInProd implements Runnable{
    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(new StopThreadInProd());
        thread.start();
        Thread.sleep();
        thread.interrupt();
    }
    @Override
    public void run() {
        while (true) {
            if (Thread.currentThread().isInterrupted()) {
                System.out.println("Interrupt");
                break;
            }
            reInterrupt();
        }
    }
    private void reInterrupt() {
        try {
            Thread.sleep();
        } 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.StopThreadInProd.reInterrupt(StopThreadInProd2.java:25)
   at com.jx.JavaTest.stopThread.StopThreadInProd.run(StopThreadInProd2.java:19)
   at java.lang.Thread.run(Thread.java:)
*
* */

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 =; i < 5; i++) {
            System.out.println("连队" + i + "领取武器");
            for (int j =; j < 10; j++) {
                System.out.println(j);
                try {
                    Thread.sleep();
                } 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();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        thread.stop();
    }
}
/*
* 连队领取武器










连队领取完毕
连队领取武器







Process finished with exit code

* */

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 =;
        try {
            while (num <= && !canceled) {
                if (num % == 0) {
                    System.out.println(num + " 是的倍数");
                }
                num++;
                Thread.sleep();
            }
        } 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();
        v.canceled = true;
    }
}
/*
* 是100的倍数
 是100的倍数
 是100的倍数
 是100的倍数
 是100的倍数
 是100的倍数
 是100的倍数
Process finished with exit code
* 
* */
  • 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();
        Producer producer = new Producer(storage);
        Thread producerThread = new Thread(producer);
        producerThread.start();
        Thread.sleep();
        Consumer consumer = new Consumer(storage);
        while (consumer.needMore()) {
            System.out.println(consumer.storage.take() + "被消费");
            Thread.sleep();
        }
        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 =;
        try {
            while (num <= && !canceled) {
                if (num % == 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() >.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();
        Producer producer = finxed.new Producer(storage);
        Thread producerThread = new Thread(producer);
        producerThread.start();
        Thread.sleep();
        Consumer consumer = finxed.new Consumer(storage);
        while (consumer.needMore()) {
            System.out.println(consumer.storage.take() + "被消费");
            Thread.sleep();
        }
        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 =;
            try {
                while (num <= && !Thread.currentThread().isInterrupted()) {
                    if (num % == 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() >.9) {
                return false;
            }
            return true;
        }
    }
}
/*
*被消费
num生产被消费
num生产被消费
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$ConditionObject.reportInterruptAfterWait(AbstractQueuedSynchronizer.java:)
   at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:)
   at java.util.concurrent.ArrayBlockingQueue.put(ArrayBlockingQueue.java:)
   at com.jx.JavaTest.stopThread.volatiledmo.finxed$Producer.run(finxed.java:)
   at java.lang.Thread.run(Thread.java:)
Process finished with exit code
* 
* */

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) {
            interrupt();           // Just to set the interrupt flag
            b.interrupt(this);
            return;
        }
    }
    interrupt();
}
private native void interrupt();

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");
    }
}
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