day014synchronized

Java 中的锁机制 程序安全
synchronized

多线程

• 多条道路解决单条道路无法满足的需求场景
• 线程之间并行由CPU随机处理
• io包下载网路图片 FileUtile.copyUrlToFile(URL,name)
• Runnable run 方法执行
• Callable call方法 创建ExciuitorServe 服务， submit 进去实例，接收返回值，shutdownnow关闭
• 代理模式
• 对象本身执行自己的事情，写字， 代理类在真实对象做的事基础上还要做自己的事，真实对象，和代理对象同时实现同一个接口需要
• lambda 一个接口只有一个方法时，实现它和这个方法只需要()->代替
• lambda 表达式演变 接口实现类》》静态内部类》》局部类》》匿名内部类》》（）-> 表达式，函数式编程简化无用代码
• new Thread 线程新生 thread .start 线程就绪 运行 sleep wait 阻塞状态 由CPU随机分配调用 dead 线程结束，线程结束后不能重新start
• thread.getState NEW RUNNABLE TIMED_WITING TERMINATED
• thread .setPriority优先级 不一定优先级高的先执行
• thread.setDaemon(true) 守护线程 跟随同进程内的用户线程结束而结束

线程同步

synchronized synchronized

同步锁

package thread.syn;

/**
 * @ Author     ：wwwzhqwww
 * @ Date       ：Created in 18:19 2021/1/16
 * @ Description：线程不安全的买车票
 * @ Modified By：
 * @Version: $version$
 */
public class UnsafeTicket {
    public static void main(String[] args) {
        Buyticket buyticket = new Buyticket();
        new Thread(buyticket,"wwwww").start();
        new Thread(buyticket,"ttttttttttt").start();
        new Thread(buyticket,"gggg").start();
    }


}
class Buyticket implements Runnable{



    int ticketNum = 10;//一百张票
    boolean flag = true;

    @Override
    public void run() {
        while (flag){
            buy();
        }
    }

    private synchronized void buy(){//同步锁 买票不会出错
        if(ticketNum <= 0){
            flag = false;
            return;
        }
        System.out.println(Thread.currentThread().getName()+"买到了第"+ticketNum+"张票");
        ticketNum--;
        try {//休眠放大场景不安全问题
            Thread.sleep(10);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

package thread.syn;

/**
 * @ Author     ：wwwzhqwww
 * @ Date       ：Created in 19:04 2021/1/16
 * @ Description：
 * @ Modified By：
 * @Version: $version$
 */
public class UnsafeBack {
    public static void main(String[] args) {
        Account account =new Account(100,"marryMoney");
        Drawing me = new Drawing(account,20,"我");
        Drawing girl = new Drawing(account,100,"女朋友");
        me.start();
        girl.start();
    }
}
class Account{
    int money;//余额
    String name;//卡名

    public Account(int money, String name) {
        this.money = money;
        this.name = name;
    }
}
class Drawing extends Thread{
    Account account;
    int drawingMoney;
    int handMoney;

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

    @Override
    public void run() {
        super.run();
        synchronized(account){//同步锁块，默认锁的是this Drawing  此处应锁住account变化的属性
            if(account.money - drawingMoney < 0){
                System.out.println("money is less 无法取出那么多");
                return;
            }
            try {//模拟延时同时取钱
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            account.money -= drawingMoney;//账户的钱
            handMoney += drawingMoney;//手里的钱
            System.out.println("账户余额："+account.money);
            System.out.println(this.getName()+"手里的钱数："+handMoney);
        }

    }
}