【笔记】单线程执行设计模式，有一个门，始终只能一个人通过

末蓝、 2022-03-07 00:45 140阅读 0赞

![在这里插入图片描述][20190315202316354.png]

Gate：共享资源  
User：多个  
Clinet：创建Gate和Person

多个人通过门时，只能一个一个的通过。

1.Gate

/**
     * SharedResource
     */
    public class Gate {
        private int counter = 0;
        private String name = "Nobody";
        private String address = "Nowhere";
    
        /**
         * 临界值
         *
         * @param name
         * @param address
         */
        public synchronized void pass(String name, String address) {
            this.counter++;
            /*race*/
            this.name = name;
            this.address = address;
            verify();
        }
    
        private void verify() {
            if (this.name.charAt(0) != this.address.charAt(0)) {
                System.out.println("*******BROKEN********" + toString());
            }
        }
    
        public synchronized String toString() {
            return "No." + counter + ":" + name + "," + address;
        }
    }

2.user

public class User extends Thread {
    
        private final String myName;
    
        private final String myAddress;
    
        private final Gate gate;
    
        public User(String myName, String myAddress, Gate gate) {
            this.myName = myName;
            this.myAddress = myAddress;
            this.gate = gate;
        }
    
        @Override
        public void run() {
            System.out.println(myName + " BEGIN");
            while (true) {
                this.gate.pass(myName, myAddress);
            }
        }
    }

3.client

public class Client {
        public static void main(String[] args) {
            Gate gate = new Gate();
            User bj = new User("Baobao", "Beijing", gate);
            User sh = new User("ShangLao", "ShangHai", gate);
            User gz = new User("GuangLao", "GuangZhou", gate);
    
            bj.start();
            sh.start();
            gz.start();
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80Mjg2ODYzOA_size_16_color_FFFFFF_t_70]  
这里会涉及到线程安全的问题，打个比方：  
线程 bj：执行到 private void verify() 时，然后让出cpu执行权，线程sh开始执行，修改了myName值，然后线程sh让出cpu执行权，线程 bj继续执行，最终导出 this.name.charAt(0) != this.address.charAt(0)。

[20190315202316354.png]: /images/20220307/8343321ee09144118c30cfa35064814a.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80Mjg2ODYzOA_size_16_color_FFFFFF_t_70]: /images/20220307/d9546d1af4624ed68bed7dcb99dbfe99.png