Java Thread 安全退出

package com.pc.screenproject;

public class Test {

    private static boolean isStop = false;

    /**
     * 自定义退出标识isStop
     * Before : isStop=false
     * After : isStop=true
     */
    private static void test0() {
        isStop = false;
        Thread t = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("测试自定义退出标识isStop用法");
                System.out.println("Before : isStop=" + isStop);
                while (!isStop) {
                    try {
                        Thread.sleep(100);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                System.out.println("After : isStop=" + isStop);
            }
        });
        t.start();

        try {
            Thread.sleep(500);
            isStop = true;
            t.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    /**
     * 非阻塞状态下
     * Thread.currentThread().isInterrupted() ： 获取中断标志位，调用不会清空中断标志位；
     * 运行结果
     * Before : false
     * After : true
     */
    private static void test1() {
        Thread t = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("测试非阻塞状态下isInterrupted用法");
                System.out.println("Before : " + Thread.currentThread().isInterrupted());
                while (!Thread.currentThread().isInterrupted()) {
                    ;
                }
                System.out.println("After : " + Thread.currentThread().isInterrupted());
            }
        });
        t.start();

        try {
            Thread.sleep(500);
            t.interrupt();
            t.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    /**
     * 非阻塞状态下
     * Thread.interrupted() ： 获取中断标志位，调用一次就立即清空中断标志位；
     * 运行结果
     * Before : false
     * After : false
     */
    private static void test2() {
        Thread t = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("测试非阻塞状态下interrupted用法");
                System.out.println("Before : " + Thread.currentThread().isInterrupted());
                while (!Thread.interrupted()) {
                    ;
                }
                System.out.println("After : " + Thread.currentThread().isInterrupted());
            }
        });
        t.start();
        try {
            Thread.sleep(500);
            t.interrupt();
            t.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    /**
     * 阻塞状态下
     * sleep() ： 抛出InterruptedException后中断标志位被清除，所以循环无法退出。标准做法是
     *      1. 再次调用interrupt恢复中断；
     *      2. 直接break退出；
     * 运行结果
     * Before : false
     * After : false
     */
    private static void test3() {
        Thread t = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("测试sleep阻塞状态下中断用法");
                System.out.println("Before : " + Thread.currentThread().isInterrupted());
                while (!Thread.interrupted()) {
                    try {
                        Thread.sleep(100);
                    } catch (InterruptedException e) {
                        Thread.currentThread().interrupt();
//                        break;
                    }
                }
                System.out.println("After : " + Thread.currentThread().isInterrupted());
            }
        });
        t.start();
        try {
            Thread.sleep(500);
            t.interrupt();
            t.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        test0();
        test1();
        test2();
        test3();
    }
}

线程安全退出总结：

1. 自定义停止标识；如test0()
2. 通过interrupt()函数，这里分为两种情况：
   • 非阻塞情况，则通过Thread.interrupted()或者Thread.currentThread().isInterrupted()
   • 阻塞情况，一般会抛出InterruptedException异常，则需要在 try...catch再次执行Thread.currentThread().interrupt()或者break，否则循环无法退出。
3. InterruptedException异常会清除中断标识位，此时通过Thread.interrupted()或者Thread.currentThread().isInterrupted()查看则都为false；
4. 捕获到InterruptedException异常之后，需要通过Thread.currentThread().interrupt()再次设置一下中断标识位，才能保证中断标识位正常；
5. Thread.interrupted()和Thread.currentThread().isInterrupted()的区别在于，Thread.currentThread().isInterrupted()不改变中断标识位，而Thread.interrupted()调用之后会重置中断标识位。