化妝的例子

兩個女生同時要化妝，需要用口紅和鏡子：

• 當女孩1拿到口紅時，1秒後需要拿到鏡子，才能解除對口紅的鎖（即：同步塊中巢狀類一個同步塊）

• 同一時間下女孩2拿到鏡子，2秒後需要拿到口紅才能解除對鏡子的鎖

• 因此兩方僵持住了，形成了死鎖

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();
    }
}

//口紅
class LipStick{

}

//鏡子
class Mirror{

}

//化妝
class Makeup extends Thread{

    //需要的資源只有一個，用static保證只有一份

    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+"獲得口紅的鎖");
                sleep(1000);

                synchronized (mirror){
                    System.out.println(this.girlName+"獲得鏡子的鎖");
                }
            }
        }else{

            synchronized (mirror){

                System.out.println(this.girlName+"獲得鏡子的鎖");
                sleep(2000);

                synchronized (lipStick){
                    System.out.println(this.girlName+"獲得口紅的鎖");
                }

        }

    }
}

}
 

修改程式碼，使其不會死鎖：把巢狀的程式碼塊分離

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

                System.out.println(this.girlName+"獲得口紅的鎖");
                sleep(1000);

            }
            synchronized (mirror){
                System.out.println(this.girlName+"獲得鏡子的鎖");
            }
        }else{

            synchronized (mirror){

                System.out.println(this.girlName+"獲得鏡子的鎖");
                sleep(2000);

            }
            synchronized (lipStick){
                System.out.println(this.girlName+"獲得口紅的鎖");
            }

             }
}