三大不安全案例
package top.ltyzqhh.thread.study;
//不安全的买票
//线程不安全有负数
public class syn {
public static void main(String[] args) {
BuyTicket buyTicket = new BuyTicket();
new Thread(buyTicket,"我").start();
new Thread(buyTicket,"小明").start();
new Thread(buyTicket,"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 {
if (ticketNums<=0)
{
flag=false;
return;
}
//模拟延时
Thread.sleep(100);
//买票
System.out.println(Thread.currentThread().getName()+"拿到"+ticketNums--);
}
}
//不安全的取钱
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,"你");
Drawing girlFriend = new Drawing(account,100,"girlFriend");
you.start();
girlFriend.start();
}
}
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;
//现在收里有多少钱
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() {
//synchronized 同步块 锁的对象是变化的两,需要增删改的对象
synchronized (account){
//判读有没有钱
if(account.money-drawingMoney<0){
System.out.println(Thread.currentThread().getName()+"钱不够了");
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);
}
}
}
package top.ltyzqhh.thread.study;
import java.util.ArrayList;
import java.util.List;
//线程不安全的集合
public class UnsafeList {
public static void main(String[] args) {
List<String> list = new ArrayList<String>();
for (int i = 0; i < 10000; i++) {
new Thread(()->{
synchronized (list){
list.add(Thread.currentThread().getName());
}
}).start();
}
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(list.size());
}
}
运行结果
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