java学习笔记 死锁

Posted 2020-08-04

在锁对象期间，会产生一个问题就是死锁，双方都在等在对方释放资源

范例：

public class Test {
    public static void main(String[] args) throws Exception {
        MyThread mt1 = new MyThread();
        MyThread mt2 = new MyThread();
        mt1.flag = 1;
        mt2.flag = 2;
        Thread t1 = new Thread(mt1);
        Thread t2 = new Thread(mt2);        
        t1.start();
        t2.start();  
    }
}

class MyThread implements Runnable {
    static Object ob1 = new Object();//注意是static
    static Object ob2 = new Object();//注意是static
    int flag = 0;
  
    public void run() {
        if (flag == 1) {
            System.out.println("flag = 1");
            synchronized (ob1) {
                try {
                    Thread.sleep(1000);    
                }    catch (InterruptedException e) {
                    System.out.println("休眠中断");    
                }
                synchronized (ob2) {
                    System.out.println("1");    
                }
            }    
        }
        if (flag == 2) {
            System.out.println("flag = 2");
            synchronized (ob2) {
                try {
                    Thread.sleep(1000);    
                }    catch (InterruptedException e) {
                    System.out.println("休眠中断");    
                }
                synchronized (ob1) {
                    System.out.println("2");    
                }
            }            
        }    
    }
}