java 如何优雅的停止一个线程

写过多线程的童鞋，可能都会遇到一个问题，那就是线程如何优雅的停止！这里主要介绍两个办法：标志位和 thread.isInterrupted

1.通过标志位来终止线程

private static class Runner implements Runnable{
        private long i;
        private (volatile) boolean running =true;
        @Override
        public void run() {
            System.out.println("current Thread Name:"+Thread.currentThread().getName());
            while (running ){
                i++;
                try {
                    TimeUnit.SECONDS.sleep(10);
                } catch (InterruptedException e) {
                }
            }
            System.out.println("Count i= "+i);
            System.out.println("current Thread Name:"+Thread.currentThread().getName());
            
        }
        public void cancel(){
            running =false;
            System.out.println("running=false");
        }
    }

此程序会在 running=false 之后，继续等待 10s ,通过标识位并不能阻止 sleep wait 等继续执行。
所以此方法不是特别优雅

2.通过 Thread.currentThread().isInterrupted() 来判断

public class Shutdoown {
    public static void main(String[] args) {
        Runner one = new Runner();
        Thread countThread = new Thread(one, "CountThread");
        countThread.start();
        try {
            //保证线程已启动
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
        }
        countThread.interrupt();
    }
    
    private static class Runner implements Runnable {
        private long i;
        private volatile boolean running = true;
        
        @Override
        public void run() {
            System.out.println("current Thread Name start:" + Thread.currentThread().getName());
            while (!Thread.currentThread().isInterrupted()) {
                System.out.println("=== " + Thread.currentThread().isInterrupted());
                i++;
                try {
                    TimeUnit.SECONDS.sleep(5);
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                    System.out.println("error=== " + e);
                }
            }
            System.out.println("Count i= " + i);
            System.out.println("current Thread Name stop:" + Thread.currentThread().getName());
            
        }
    }

thread 被中断之后，就可以无视 sleep wait 等方法，马上停止，乍一看，还是蛮优雅的，推荐使用。

可如果我把 sleep 换乘 while(true)会怎么样？

通过 Thread.currentThread().isInterrupted() 来判断-while(true) 版本

public class Shutdoown {
    public static void main(String[] args) {
        Runner one = new Runner();
        Thread countThread = new Thread(one, "CountThread");
        countThread.start();
        try {
            //保证线程已启动
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
        }
        countThread.interrupt();
    }
    
    private static class Runner implements Runnable {
        private long i;
        private volatile boolean running = true;
        
        @Override
        public void run() {
            System.out.println("current Thread Name start:" + Thread.currentThread().getName());
            while (!Thread.currentThread().isInterrupted()) {
                System.out.println("=== " + Thread.currentThread().isInterrupted());
                i++;
                while(true){
                }
            }
            System.out.println("Count i= " + i);
            System.out.println("current Thread Name stop:" + Thread.currentThread().getName());
            
        }
    }

不要意思，除非主动 kill，不然线程永远停止不了。

总结：
显然，通过 Thread.currentThread().isInterrupted() 来停止线程，显然要比标示位优雅一些，但要防止条件判断永远无法生效。

最后编辑于：2020.01.08 11:20:44