线程同步-synchronized版

三大不安全案例及解决办法

买票

不安全代码

// 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,"苦逼的我").start();
        new Thread(station,"牛逼的你们").start();
        new Thread(station,"可恶的黄牛党").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(100);
        // 买票
        System.out.println(Thread.currentThread().getName() + "拿到" + ticketNums--);
    }
}

安全代码

// 安全的买票
public class UnsafeBuyTicket {

    public static void main(String[] args) {
        BuyTicket station = new BuyTicket();

        new Thread(station,"苦逼的我").start();
        new Thread(station,"牛逼的你们").start();
        new Thread(station,"可恶的黄牛党").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();
            }
        }
    }

    // synchronized 同步方法,锁的是this
    private synchronized void buy() throws InterruptedException {
        // 判断是否有票
        if (ticketNums <= 0) {
            flag = false;
            return;
        }
        // 模拟延时
        Thread.sleep(100);
        // 买票
        System.out.println(Thread.currentThread().getName() + "拿到" + ticketNums--);

    }
}

取钱

不安全代码

// 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 girlFriend = new Drawing(account, 100, "girlFriend");
        Drawing you = new Drawing(account, 50, "你");

        you.start();
        girlFriend.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可以放大问题的发生性
        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);
    }
}

安全代码

// 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 girlFriend = new Drawing(account, 100, "girlFriend");
        Drawing you = new Drawing(account, 50, "你");

        you.start();
        girlFriend.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
    // synchronized 默认锁的是this
    @Override
    public void run() {
        // 锁对象就是变化的量,需要增删改的对象
        synchronized (account) {
            // 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可以放大问题的发生性
            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

不安全代码

// 线程不安全的集合
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(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(list.size());
    }
}

安全代码

// 线程安全的集合
public class UnsafeList {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        for (int i = 0; i < 10000; i++) {
            new Thread(() -> {
                synchronized (list) {
                    list.add(Thread.currentThread().getName());
                }
            }).start();
        }

        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(list.size());
    }
}