死锁

化妆的例子

两个女生同时要化妆，需要用口红和镜子：

• 当女孩1拿到口红时，1秒后需要拿到镜子，才能解除对口红的锁（即：同步块中嵌套类一个同步块）

• 同一时间下女孩2拿到镜子，2秒后需要拿到口红才能解除对镜子的锁

• 因此两方僵持住了，形成了死锁

package test2;


public class DeadLock {
    public static void main(String[] args) {

        Makeup g1=new Makeup(0,"girl1");
        Makeup g2=new Makeup(1,"gilr2");

        g1.start();
        g2.start();
    }
}

//口红
class LipStick{

}

//镜子
class Mirror{

}

//化妆
class Makeup extends Thread{

    //需要的资源只有一个，用static保证只有一份

    static  LipStick lipStick=new LipStick();
    static  Mirror mirror=new Mirror();

    int choice;
    String girlName;

     Makeup(int choice,String girlName){
        this.choice=choice;
        this.girlName=girlName;
    }

    @Override
    public void run() {
        try {
            makeup();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private void makeup() throws InterruptedException {
        if(this.choice==0){
            synchronized (lipStick){

                System.out.println(this.girlName+"获得口红的锁");
                sleep(1000);

                synchronized (mirror){
                    System.out.println(this.girlName+"获得镜子的锁");
                }
            }
        }else{

            synchronized (mirror){

                System.out.println(this.girlName+"获得镜子的锁");
                sleep(2000);

                synchronized (lipStick){
                    System.out.println(this.girlName+"获得口红的锁");
                }

        }

    }
}

}

修改代码，使其不会死锁：把嵌套的代码块分离

    private void makeup() throws InterruptedException {
        if(this.choice==0){
            synchronized (lipStick){

                System.out.println(this.girlName+"获得口红的锁");
                sleep(1000);

            }
            synchronized (mirror){
                System.out.println(this.girlName+"获得镜子的锁");
            }
        }else{

            synchronized (mirror){

                System.out.println(this.girlName+"获得镜子的锁");
                sleep(2000);

            }
            synchronized (lipStick){
                System.out.println(this.girlName+"获得口红的锁");
            }

             }
}