多线程的同步方法

Posted 2020-12-13 zouzhang

多线程的同步方法

1.买票的例子

通过synchronized锁住保证线程的安全

//买票
public class SafeBuyTicket {
    public static void main(String[] args) {
        BuyTicket sation=new BuyTicket();
        new Thread(sation,"买票的第一位").start();
        new Thread(sation,"买票的第二位").start();
        new Thread(sation,"买票的第三位").start();
    }
}

class BuyTicket implements Runnable{
    private int ticketNums=10;
    boolean flag=true;
    //线程关闭的标志位置
    @Override
    public void run() {
        while (flag){
            try {
                buy();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    private synchronized void buy() throws InterruptedException {
        //锁的是this
        if (ticketNums<=0){
            flag=false;
            return;
        }
//            模拟延迟
//            Thread.sleep(200);
        System.out.println(Thread.currentThread().getName()+"拿到"+ticketNums--);
    }
}

---

2.去银行取钱

用synchronized块锁住account（卡）

//两个不安全的取钱
public class SafeBank {
    public static void main(String[] args) {
        Account account=new Account(10000,"备用金");
        Drawing you=new Drawing(account,50,"你");
        Drawing girlFriend=new Drawing(account,100,"女朋友");
        you.start();
        girlFriend.start();
    }
}
//账户
class Account{
    int money;
    String name;

    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
    int drawingMoney;//收了多少钱
    int nowMoney;//现在还剩多少钱

    public Drawing(Account account,int drawingMoney,String name) {
        super(name);
        this.account=account;
        this.drawingMoney=drawingMoney;
    }
    @Override
    public void run() {
//        默认锁的是this，这个程序中是bank；
//        但是需要锁account，锁bank并没用
        synchronized (account){
            if (account.money-drawingMoney<0){
                System.out.println(Thread.currentThread().getName()+"钱不够");
                return;
            }
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            account.money=account.money-drawingMoney;
            nowMoney=nowMoney+drawingMoney;
            System.out.println(account.name+"余额为："+account.money);
            System.out.println(this.getName()+"手里的钱:"+nowMoney);
        }
    }
}

---

3.list

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

public class UnsafeList {
    public static void main(String[] args) {
        List<String> list=new ArrayList<String>();
        for (int i = 0; i < 100000; i++) {
            new Thread(()->{
                //将list锁住就可以了
                synchronized (list) {
                    list.add(Thread.currentThread().getName());
                }
            }).start();
        }
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(list.size());
    }
}

---

参考自up主：狂神说Java