线程三大不安全案例&同步方法及同步块

线程三大不安全案例&同步方法及同步块

线程三大不安全案例

买票

package com.deng.syn;

//不安全的买票
//线程不安全，有负数
public class UnsafeBuyTicket {
    public static void main(String[] args) {
        BuyTicket station = new BuyTicket();

        new Thread(station, "我").start();
        new Thread(station, "你").start();
        new Thread(station, "黄牛党").start();
    }
}

class BuyTicket implements Runnable {
    //票
    private int ticketNums = 10;
    boolean flag = true;//外部停止方式

    @Override
    public void run() {
        //买票
        while (flag) {
            try {
                buy();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

    }

    private void buy() throws InterruptedException {
        //判断是否有票
        if (ticketNums <= 0) {
            flag = false;
            return;
        }
        //模拟延时
        Thread.sleep(200);

        //买票
        System.out.println(Thread.currentThread().getName() + "拿到" + ticketNums--);

    }
}

银行取钱

package com.deng.syn;

//不安全的取钱
//两个人去银行取钱，账户
public class UnsafeBank {
    public static void main(String[] args) {
        //账户
        Account account = new Account(100, "结婚基金");

        Drawing you = new Drawing(account, 50, "You");
        Drawing me = new Drawing(account, 100, "Me");

        you.start();
        me.start();


    }
}

//账户
class Account {
    int money;//余额
    String name;//卡名

    public Account(int money, String name) {
        this.money = money;
        this.name = name;
    }
}

//银行:模拟取款
class Drawing extends Thread {
    Account account;//账户
    //取了多少钱
    int drawingMoney;
    //现在手里有多少钱
    int nowMoney;

    public Drawing(Account account, int drawingMoney, String name) {
        super(name);
        this.account = account;
        this.drawingMoney = drawingMoney;

    }

    //取钱
    @Override
    public void run() {
        //判断有没有钱
        if (account.money - drawingMoney < 0) {
            System.out.println(Thread.currentThread().getName() + "钱不够，取不了");
            return;
        }

        //sleep放大问题的发生性
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //卡内余额 = 余额-你取的钱
        account.money = account.money - drawingMoney;
        //你手里的钱
        nowMoney = nowMoney + drawingMoney;

        System.out.println(account.name + "余额为：" + account.money);
        //Thread.currentThread().getName()=this.getName();
        System.out.println(this.getName() + "手里的钱：" + nowMoney);
    }
}

集合

package com.deng.syn;

import java.util.ArrayList;
import java.util.List;

public class UnsafeList {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        for (int i = 0; i < 10000; i++) {
            new Thread(()->{
                list.add((Thread.currentThread().getName()));
            }).start();
        }
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(list.size());
    }
}

同步方法及同步块

• 同步方法

  public synchronized void method(int args){}
  

• 同步块

  synchronized(obj){}
  

补充：JUC

package com.deng.syn;

import java.util.concurrent.CopyOnWriteArrayList;

//测试JUC安全类型的集合
public class TestJUC {
    public static void main(String[] args) {
        CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<String>();
        for (int i = 0; i < 10000; i++) {
            new Thread(() -> {
                list.add(Thread.currentThread().getName());
            }).start();
        }
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(list.size());
    }
}