java 死锁简单分析

1. 看一段代码关于死锁的

public class DeadLockDemo2 {

    public static void main(String[] args) throws InterruptedException {
        // 这里是创建了三个对象资源，这些资源被传入到了三个线程中，开启线程之后就会调用这三个资源的相关方法
        Object obj1 = new Object();
        Object obj2 = new Object();
        Object obj3 = new Object();
        // 这里
        Thread t1 = new Thread(new SyncThread(obj1, obj2), "t1");
        Thread t2 = new Thread(new SyncThread(obj2, obj1), "t2");

        t1.start();
        Thread.sleep(500);
        t2.start();
    }

}

// 定义一个线程对象
class SyncThread implements Runnable {
    private Object obj1;
    private Object obj2;

    public SyncThread(Object o1, Object o2) {
        this.obj1 = o1;
        this.obj2 = o2;
    }

    @Override
    public void run() {
        String name = Thread.currentThread().getName();
        System.out.println(name + " acquiring lock on " + obj1);
        // 两个锁对象，这了有一个线程进入之后就持有了obj1，那么另一个线程因为obj1被持有了，那么就
        // 不会持有obj1，而会进入到obj2，那么线程1因为此时持有了obj1，而obj2却被另一个线程持有，那么
        // 现在的线程1就没办法获取到obj2，就会一直处于等待状态，而线程2也是处于等待
        synchronized (obj1) {
            System.out.println(name + " acquired lock on " + obj1);
            work(1);
            System.out.println(name + " acquiring lock on " + obj2);
            // 这里obj2被互斥
            synchronized (obj2) {
                System.out.println(name + " acquired lock on " + obj2);
                work(2);
            }
            System.out.println(name + " released lock on " + obj2);
        }
        System.out.println(name + " released lock on " + obj1);
        System.out.println(name + " finished execution.");
    }

    private void work(int i) {
        try {
            String name = Thread.currentThread().getName();
            if (i == 1) {
                System.out.println(name + " working sleep " + i + " # " + this.obj1);
            } else {
                System.out.println(name + " working sleep " + i + " # " + this.obj2);
            }
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

通过两次的互斥，并且对不同对象进行互斥，然后两个线程持有这两个对象进行操作，就死锁了