线程死锁

产生死锁的四个必要条件：

1. 互斥条件：一个资源每次只能被一个进程使用
2. 请求与保持条件：一个进程因请求资源而阻塞时，对已经获得的资源保持不放
3. 不剥夺条件：进程已经获得的资源，在未使用完之前不进行强行剥夺
4. 循环等待条件：若干进程之间形成一种头尾相接的循环等待资源关系

只要想办法破坏四个必要条件中的任意一个或多个，就能避免死锁发送

package thread;

import javax.swing.plaf.synth.SynthCheckBoxMenuItemUI;

/**
 * @author scy
 * @create 2021-03-27 14:39
 */

//死锁：多个线程互相抱着对方需要的资源，然后形成僵持
public class DeadLock {
    public static void main(String[] args) {
        Makeup g1 = new Makeup(0,"g1");
        Makeup g2 = new Makeup(1,"g2");

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

//口红
class Lipstick{

}
//镜子
class Mirror{

}

class Makeup extends Thread{

    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() {
        //化妆
        try {
            makeup();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    //写个方法：化妆，互相持有对方的锁，就是需要拿到对方的资源
    private void makeup() throws InterruptedException{
        if(choice == 0){
            synchronized (lipstick){//获得口红的锁
                System.out.println(this.girlName + "获得口红的锁");
                Thread.sleep(1000);
                synchronized (mirror){//获得镜子的锁
                    System.out.println(this.girlName+"活得镜子的锁");
                }
            }

        }else{
            synchronized (mirror){//获得镜子的锁
                System.out.println(this.girlName+"获得镜子的锁");
                Thread.sleep(1000);
                synchronized (lipstick){//获得口红的锁
                    System.out.println(this.girlName+"获得口红的锁");
                }
            }

        }
    }
}

输出结果：

破坏其必要条件：

package thread;

import javax.swing.plaf.synth.SynthCheckBoxMenuItemUI;

/**
 * @author scy
 * @create 2021-03-27 14:39
 */

//死锁：多个线程互相抱着对方需要的资源，然后形成僵持
public class DeadLock {
    public static void main(String[] args) {
        Makeup g1 = new Makeup(0,"g1");
        Makeup g2 = new Makeup(1,"g2");

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

//口红
class Lipstick{

}
//镜子
class Mirror{

}

class Makeup extends Thread{

    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() {
        //化妆
        try {
            makeup();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    //写个方法：化妆，互相持有对方的锁，就是需要拿到对方的资源
    private void makeup() throws InterruptedException{
        if(choice == 0){
            synchronized (lipstick){//获得口红的锁
                System.out.println(this.girlName + "获得口红的锁");
                Thread.sleep(1000);
            }
            synchronized (mirror){//获得镜子的锁
                System.out.println(this.girlName+"活得镜子的锁");
            }

        }else{
            synchronized (mirror){//获得镜子的锁
                System.out.println(this.girlName+"获得镜子的锁");
                Thread.sleep(1000);
            }
            synchronized (lipstick){//获得口红的锁
                System.out.println(this.girlName+"获得口红的锁");
            }

        }
    }
}

输出结果：

线程死锁

原文：https://www.cnblogs.com/helloMargaret/p/14585907.html