Java線程的停止實現原理詳解

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線程停止的原理

使用interrupt來通知，而不是強制

java提供瞭interrrupt讓一個線程來通知另一個線程停止

如果想中斷一個線程，但是那個線程不想去中斷，那就無能為力，我們沒有強制去中斷線程的手段，因為線程停止前需要做一定的收尾工作

所以正確停止線程，是如何用interrupt來通知那個線程，以及被停止的線程如何進行配合

如何正確停止線程

在普通情況下停止線程

代碼展示

  • 調用interrupt沒有作用
  • 下面這段代碼，執行interrupt之後，線程並沒有被中斷
  • 因為被執行的線程並沒有相應中斷的方式
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的倍數");
            }
            num++;
        }
        System.out.println("結束");
    }
}
/*
由於太長，隻展示結尾部分的結果 
1073710000是10000的倍數
1073720000是10000的倍數
1073730000是10000的倍數
1073740000是10000的倍數
結束
* */
  • 被執行線程加上相應中斷的操作之後
  • 結果可知，被執行線程相應一秒之後就結束瞭
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的倍數");
            }
            num++;
        }
        System.out.println("結束");
    }
}
/*
由於太長，隻展示結尾部分的結果
587830000是10000的倍數
587840000是10000的倍數
587850000是10000的倍數
587860000是10000的倍數
結束
* */

在阻塞情況下停止線程

代碼展示

  • 中斷之後，拋出異常
  • 線程在sleep的過程中，會catch到InterruptedException這個異常，從而相應中斷
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的倍數");
                }
                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的倍數
100是100的倍數
200是100的倍數
300是100的倍數
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)
* */

線程在每次迭代後都阻塞

  • 代碼展示 即使不在while判斷是否中斷，sleep也能中斷異常
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的倍數");
                    }
                    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的倍數
100是100的倍數
200是100的倍數
300是100的倍數
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
* 
* */

當catch寫到while內，則不能正常中斷

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的倍數");
                }
                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的倍數
100是100的倍數
200是100的倍數
300是100的倍數
java.lang.InterruptedException: sleep interrupted
   at java.lang.Thread.sleep(Native Method)
   at com.jx.JavaTest.stopThread.CantInterrupt.lambda$main$0(CantInterrupt.java:14)
   at java.lang.Thread.run(Thread.java:748)
400是100的倍數
500是100的倍數
600是100的倍數
700是100的倍數
800是100的倍數
900是100的倍數
Process finished with exit code -1
* */
  • 即使在while的判斷條件中，加上檢測中斷的機制，也不能正常中斷
  • 因為java的sleep函數，一旦相應中斷，就會將中斷的標志位刪除
public class CantInterrupt {
    public static void main(String[] args) {
        Runnable runnable = () -> {
            int num = 0;
            while (num <= 10000 && !Thread.currentThread().isInterrupted()) {
                if (num % 100 == 0) {
                    System.out.println(num + "是100的倍數");
                }
                num++;
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };
        Thread thread = new Thread(runnable);
        thread.start();
        try {
            Thread.sleep(5000);
        } catch (
                InterruptedException e) {
            e.printStackTrace();
        }
        thread.interrupt();
    }
}
/*
0是100的倍數
100是100的倍數
200是100的倍數
300是100的倍數
java.lang.InterruptedException: sleep interrupted
   at java.lang.Thread.sleep(Native Method)
   at com.jx.JavaTest.stopThread.CantInterrupt.lambda$main$0(CantInterrupt.java:14)
   at java.lang.Thread.run(Thread.java:748)
400是100的倍數
500是100的倍數
Process finished with exit code -1
* */

停止線程的最佳實踐

  • 在方法簽名中拋出異常，在run方法中強制進行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/關閉程序");
                e.printStackTrace();
            }
        }
    }
    private void throwInMethod() throws InterruptedException {
            Thread.sleep(2000);
    }
}
/*
* start
保存日志/關閉程序
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語句中調用Thread.currentThread().interrupt恢復中斷狀態
  • 結果：拋出異常，程序結束
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
*
* */
  • 依照上面的代碼，如果方法沒有沒有重新拋出異常
  • 結果：程序拋出異常，但是程序沒有停止運行
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)
*
* */

錯誤停止的方法

被棄用的stop,suspend和resume方法

  • 使用stop停止線程，會導致線程運行一半突然停止，沒辦法完成最基本的操作，會造成臟數據
  • 下面這段代碼的結果會造成一個連隊隻有部分人領取到瞭裝備
  • stop是不安全的，會直接停止監視器
  • suspend和resume不會破壞對象，但是會讓線程掛起，不釋放鎖，容易造成死鎖
public class StopThread implements Runnable{
    @Override
    public void run() {
        // 模擬指揮軍隊,一共五個連隊,每個連隊一百人
        // 以連隊為單位發放武器
        for (int i = 0; i < 5; i++) {
            System.out.println("連隊" + i + "領取武器");
            for (int j = 0; j < 10; j++) {
                System.out.println(j);
                try {
                    Thread.sleep(50);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            System.out.println("連隊" + i + "領取完畢");
        }
    }
    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();
    }
}
/*
* 連隊0領取武器
0
1
2
3
4
5
6
7
8
9
連隊0領取完畢
連隊1領取武器
0
1
2
3
4
5

Process finished with exit code 0

* */

用volatile設置boolean標記位

  • 下面這段代碼，通過改變標志位的值會成功終止線程
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的倍數");
                }
                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的倍數
100 是100的倍數
200 是100的倍數
300 是100的倍數
400 是100的倍數
500 是100的倍數
600 是100的倍數
Process finished with exit code 0
* 
* */
  • 當陷入阻塞的時候，是無法停止線程的
  • 下面這段代碼的運行結果，並沒有打印生產者停止運行，說明根本沒有執行生產者的finally那部分代碼
  • 同時程序也沒停止
  • 原因見生產者代碼 while循環中的註釋
// 模擬生產者和消費者
public class cantStop {
    public static void main(String[] args) throws InterruptedException {
        // 阻塞隊列
        // 滿瞭之後,放不進去
        // 空的時候取數據,也會堵塞
        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() + "被消費");
            Thread.sleep(100);
        }
        System.out.println("消費者不需要更多數據");
        // 消費者不需要數據,讓生產者停下來
        producer.canceled = true;
    }
}
// 生產者
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) {
                    // 當堵塞隊列滿瞭之後，會堵塞在這裡，而這段代碼沒有判斷機制
                    storage.put(num);
                    System.out.println("num" + "生產");
                }
                num++;
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            System.out.println("生產者停止運行");
        }
    }
}
// 消費者
class Consumer {
    BlockingQueue storage;
    public Consumer(BlockingQueue storage) {
        this.storage = storage;
    }
    public boolean needMore() {
        if (Math.random() > 0.9) {
            return false;
        }
        return true;
    }
}
/*
* num生產
num生產
num生產
num生產
num生產
num生產
num生產
num生產
num生產
num生產
0被消費
num生產
消費者不需要更多數據

* 
* */
  • 將上面代碼用interrupt進行中斷
  • 程序成功停止
public class finxed {
    public static void main(String[] args) throws InterruptedException {
        finxed finxed = new finxed();
        // 阻塞隊列
        // 滿瞭之後,放不進去
        // 空的時候取數據,也會堵塞
        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() + "被消費");
            Thread.sleep(100);
        }
        System.out.println("消費者不需要更多數據");
        // 消費者不需要數據,讓生產者停下來
        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" + "生產");
                    }
                    num++;
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                System.out.println("生產者停止運行");
            }
        }
    }
    class Consumer {
        BlockingQueue storage;
        public Consumer(BlockingQueue storage) {
            this.storage = storage;
        }
        public boolean needMore() {
            if (Math.random() > 0.9) {
                return false;
            }
            return true;
        }
    }
}
/*
* 2100被消費
num生產
2200被消費
num生產
2300被消費
num生產
消費者不需要更多數據
生產者停止運行
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源碼查看

  • 這段代碼做的都是一些判斷，真正執行中斷的代碼時interrupt0
  • interrupt0是native代碼
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相關函數練習

  • isInterrupted獲取中斷標志，獲取的是前面的線程
  • interrupted獲取中斷標志並重置，隻關心執行的線程，所以下面代碼執行的是main線程
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();
        // 獲取中斷標志
        System.out.println(thread.isInterrupted()); // true
        // 獲取中斷標志並重置
        System.out.println(thread.interrupted()); //false
        System.out.println(Thread.interrupted()); // false
        System.out.println(thread.isInterrupted()); //true
        thread.join();
        System.out.println("over");
    }
}

到此這篇關於Java線程的停止實現原理詳解的文章就介紹到這瞭,更多相關Java線程的停止內容請搜索WalkonNet以前的文章或繼續瀏覽下面的相關文章希望大傢以後多多支持WalkonNet！

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