如何停止一个正在运行的线程?

淡淡的烟草味﹌ 2023-05-22 06:37 30阅读 0赞

如何停止一个正在运行的线程? 这个一个面试常问的问题, 我们有两种办法, 分别是stop()和interrupt(), 但stop()太过于暴力, 无法保证线程业务的原子性, 且已过期, 不推荐使用.

**使用stop()来停止线程**

stop()方法让线程立即停止运行, 这种暴力停止可能会破坏线程业务的原子性, 如下所示:

static class MyThread extends Thread {
    	@Override
    	public void run() {
    		while (true) {
    			System.out.println("线程开始执行...");
    			System.out.println("业务步骤1");
    			try {
    				Thread.sleep(3000);
    			} catch (InterruptedException e) {
    				e.printStackTrace();
    			}
    			System.out.println("业务步骤2");
    			System.out.println("线程执行完毕...");
    		}
    	}
    }
    
    public static void main(String[] args) {
    	MyThread thread = new MyThread();
    	thread.start();
    
    	try {
    		Thread.sleep(2000);
    		thread.stop();
    	} catch (InterruptedException e) {
    		e.printStackTrace();
    	}
    }

执行结果为:

线程开始执行...
    业务步骤1

**使用interrupt() + return来停止线程**

线程调用interrupt()会生成一个中断标记, 在线程逻辑中通过isInterrupted()判断是否存在中断标记, 存在则return.

static class MyThread extends Thread {
    	@Override
    	public void run() {
    		for (int i = 0; i < 500000; i++) {
    			if (this.isInterrupted()) {
    				System.out.println("线程终止, 停止for循环.");
    				return;
    			}
    			System.out.println("i=" + (i + 1));
    		}
    	}
    }
    
    public static void main(String[] args) {
    	MyThread thread = new MyThread();
    	thread.start();
    
    	try {
    		Thread.sleep(200);
    		thread.interrupt();
    	} catch (InterruptedException e) {
    		e.printStackTrace();
    	}
    }

结果:  
…  
i=38319  
i=38320  
i=38321  
线程终止, 停止for循环.

**使用interrupt() + InterruptedException来停止线程**

线程调用interrupt()会生成一个中断标记, 在线程逻辑中通过isInterrupted()判断是否存在中断标记, 存在则抛出一个InterruptedException, 同时捕获它.

static class MyThread extends Thread {
    	@Override
    	public void run() {
    		try {
    			for (int i = 0; i < 100000; i++) {
    				if (this.isInterrupted()) {
    					System.out.println("线程终止, 停止for循环.");
    					throw new InterruptedException();
    				}
    				System.out.println("i=" + (i + 1));
    			}
    		} catch (InterruptedException e) {
    			System.out.println("MyThread抛出InterruptedException.");
    			e.printStackTrace();
    		}
    	}
    }
    
    public static void main(String[] args) {
    	MyThread thread = new MyThread();
    	thread.start();
    
    	try {
    		Thread.sleep(200);
    		thread.interrupt();
    	} catch (InterruptedException e) {
    		e.printStackTrace();
    	}
    }

结果:

i=34901
    i=34902
    i=34903
    线程终止, 停止for循环.
    MyThread抛出InterruptedException.
    java.lang.InterruptedException
    	at org.tyshawn.thread.ThreadTest$MyThread.run(ThreadTest.java:27)

**interrupt()遇到sleep(), join()和wait()会抛出一个InterruptedException**

当线程是阻塞状态时, 这时调用interrupt()方法会抛出一个InterruptedException.

static class MyThread extends Thread {
    	@Override
    	public void run() {
    		try {
    			System.out.println("线程开始执行");
    			Thread.sleep(300);
    			//this.join();
    			//this.wait();
    			System.out.println("线程执行完毕");
    		} catch (InterruptedException e) {
    			System.out.println("MyThread抛出InterruptedException.");
    			e.printStackTrace();
    		}
    	}
    }
    
    public static void main(String[] args) {
    	MyThread thread = new MyThread();
    	thread.start();
    
    	try {
    		Thread.sleep(200);
    		thread.interrupt();
    	} catch (InterruptedException e) {
    		e.printStackTrace();
    	}
    }

结果:

线程开始执行
    java.lang.InterruptedException: sleep interrupted
    	at java.lang.Thread.sleep(Native Method)
    	at org.tyshawn.thread.ThreadTest$MyThread.run(ThreadTest.java:56)
    MyThread抛出InterruptedException.