Java篇——多线程（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，对已获得的资源保持不放。
3.不剥夺条件：进程已获得的资源，在末使用完之前，不能强行剥夺。
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。

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产生死锁例子

线程A拿到了资源A需要获取资源B，线程B拿到了资源B需要获取资源A，当两个线程都在等待资源时，就出现死锁现象。

package Thread_test;

public class DeadLock {
    public static void main(String[] args) {
        MakeUp girl1 = new MakeUp(0, "灰姑娘");
        MakeUp girl2 = new MakeUp(1, "白雪公主");
        girl1.start();
        girl2.start();
    }
}

class Lipstick {
    //口红
}

class Mirror {
    //镜子
}

class MakeUp extends Thread {
    static Lipstick lipstick = new Lipstick();
    static Mirror mirror = new Mirror();
    int choice;
    String getName;

    MakeUp(int choice, String getName) {
        this.choice = choice;
        this.getName = getName;
    }

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

    public void makeup() throws InterruptedException {
        if (choice == 0) {
            synchronized (lipstick) {
                System.out.println(this.getName + "获得口红的锁");
                Thread.sleep(1000);
                synchronized (mirror) {
                    System.out.println(this.getName + "获得镜子的锁");
                }
            }

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

        }


    }
}

修改之后（解除上述第二个条件）

package Thread_test;

public class DeadLock {
    public static void main(String[] args) {
        MakeUp girl1 = new MakeUp(0, "灰姑娘");
        MakeUp girl2 = new MakeUp(1, "白雪公主");
        girl1.start();
        girl2.start();
    }
}

class Lipstick {
    //口红
}

class Mirror {
    //镜子
}

class MakeUp extends Thread {
    static Lipstick lipstick = new Lipstick();
    static Mirror mirror = new Mirror();
    int choice;
    String getName;

    MakeUp(int choice, String getName) {
        this.choice = choice;
        this.getName = getName;
    }

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

    public void makeup() throws InterruptedException {
        if (choice == 0) {
            synchronized (lipstick) {
                System.out.println(this.getName + "获得口红的锁");
                Thread.sleep(1000);
            }
            synchronized (mirror) {
                System.out.println(this.getName + "获得镜子的锁");
            }

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

本文地址：https://blog.csdn.net/weixin_47016497/article/details/107596216