死锁

什么是死锁

两个或两个以上的线程在执行过程中，因为争夺资源而造成一种相互等待的现象

死锁的原因

系统资源不足
线程运行推进的顺序不合理
资源分配不当

手写死锁

package com.hz.xhf;

public class HoldLockThread implements Runnable {

    private String lockA;
    private String lockB;

    public HoldLockThread(String lockA, String lockB) {
        this.lockA = lockA;
        this.lockB = lockB;
    }

    @Override
    public void run() {
        synchronized (lockA){
            System.out.println(Thread.currentThread().getName() + "拿到" + lockA + "锁，尝试获取" + lockB + "锁");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            synchronized (lockB){
                System.out.println(Thread.currentThread().getName() + "拿到" + lockB + "锁，尝试获取" + lockA + "锁");
            }
        }
    }
}

package com.hz.xhf;

public class DeadLockTest {
    public static void main(String[] args) {
        String lockA = "lockA";
        String lockB = "lockB";

        new Thread(new HoldLockThread(lockA, lockB), "ThreadA").start();
        new Thread(new HoldLockThread(lockB, lockA), "ThreadB").start();
    }
}

解决死锁方法

jps -l 定位进程号
jstack XXX 查错