死锁排查

死锁案例

import java.util.concurrent.TimeUnit;

@Slf4j
public class Demo {

    public static void main(String[] args) throws InterruptedException {
        Object a = new Object();
        Object b = new Object();

        new Thread(() -> {
            synchronized (a) {
                log.info("获取到A");
                try {
                    TimeUnit.SECONDS.sleep(2);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }

                synchronized (b) {
                    log.info("获取到b");
                }
            }
        }).start();

        new Thread(() -> {
            synchronized (b) {
                log.info("获取到B");
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }

                synchronized (a) {
                    log.info("获取到A");
                }
            }
        }).start();

    }
}

jstack

1. jps 查看所有进程id

2. jstack
   jstack 6952

活锁

解决办法就是将时间错开

@Slf4j
public class Demo {

    static volatile int count = 10;

    public static void main(String[] args) throws InterruptedException {

        new Thread(() -> {
            while (count < 20) {
                count++;
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
                log.info("{}", count);
            }
        }, "t1").start();

        new Thread(() -> {
            while (count > 0) {
                count--;
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
                log.info("{}", count);
            }
        }, "t2").start();


    }
}