线程同步

1. 什么是线程同步

同一个对象被多个线程同时操作--->并发
买火车票的例子
实现线程同步：队列+锁（synchronized）
缺陷：损失性能

2. 同步方法及同步块

3. 案例：两个人取钱,使用同步块

//两个人去银行取钱
public class UnsafeBank {
    public static void main(String[] args) {
        Account account = new Account(100,"结婚基金");
        Drawing you = new Drawing(account,50,"你");
        Drawing gilrFriend = new Drawing(account,80,"gilrFriend");

        you.start();
        gilrFriend.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;//取了多少钱
    int nowMoney;//现在手里多少钱

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

    }

    //取钱
    @Override
    public void run() {

        //同步块
        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;
            }

            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            //卡内余额=余额-你取的钱
            account.money = account.money - drawingMoney;
            System.out.println(Thread.currentThread().getName()+"取走了"+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);
        }
    }
}

4. 生产者消费者问题

4.1 问题分析

4.2 管程法

//测试：生产者消费者模型-->利用缓冲区解决：管程法

//生产者，消费者，产品，缓冲区

public class TestPC {
    public static void main(String[] args) {
        SynContainer container = new SynContainer();
        new Productor(container).start();
        new Consumer(container).start();
    }
}

//生产者
class Productor extends Thread {
    SynContainer container;

    public Productor(SynContainer container) {
        this.container = container;
    }

    @Override
    public void run() {
        for (int i = 1; i <= 100; i++) {
            container.push(new Chicken(i));
            System.out.println("生成了第" + i + "只鸡");
        }
    }
}

//消费者
class Consumer extends Thread {
    SynContainer container;

    public Consumer(SynContainer container) {
        this.container = container;
    }

    @Override
    public void run() {
        for (int i = 1; i <= 100; i++) {
            System.out.println("消费了第-->" + container.pop().id + "只鸡");
        }
    }
}

//产品
class Chicken {
    int id;

    public Chicken(int id) {
        this.id = id;
    }
}

//缓冲区
class SynContainer {

    //需要容器大小
    Chicken[] chickens = new Chicken[10];
    int count = 0;

    //生产者放入产品
    public synchronized void push(Chicken chicken) {
        //如果容器满了，就需要等待消费者消费
        while (count == chickens.length) {
            //通知消费者消费
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        //如果没有满，就需要放入产品
        chickens[count] = chicken;
        count++;

        //可以通知消费者消费了
        this.notifyAll();
    }

    //消费者消费
    public synchronized Chicken pop() {
        //如果没有产品
        while (count == 0) {
            //等待生产者生成，消费者等待
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        //可以消费
        count--;
        Chicken chicken = chickens[count];

        //吃完了，通知生产者生成
        this.notifyAll();

        return chicken;
    }
}

4.2 信号灯法-->flag

public class TestPC2 {
    public static void main(String[] args) {
        TV tv = new TV();
        new Player(tv).start();
        new Watcher(tv).start();
    }
}

//生产者-->演员
class Player extends Thread{
    TV tv;
    public Player(TV tv){
        this.tv = tv;
    }

    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            if (i % 2 == 0){
                this.tv.play("这就是街舞");
            }
            else {
                this.tv.play("广告时间");
            }
        }
    }
}

//消费者-->观众
class Watcher extends Thread{
    TV tv;
    public Watcher(TV tv){
        this.tv = tv;
    }

    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            this.tv.watch();
        }
    }
}

//产品-->节目
class TV{
    //演员表演，观众等待 T
    //观众观看。演员等待 F
    String show;//节目
    boolean flag = true;

    //表演
    public synchronized void play(String show){
        if (!flag){
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println("演员表演了："+show);
        this.notifyAll();//通知观众观看
        this.show = show;
        this.flag = !this.flag;
    }

    //观看
    public synchronized void watch(){
        if (flag){
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println("观众观看了"+show);
        //通知演员表演
        this.notifyAll();
        this.flag = !this.flag;
    }
}

5. 线程池

//测试线程池
public class TestPool {
    public static void main(String[] args) {
        //1.创建服务，创建线程池
        ExecutorService service = Executors.newFixedThreadPool(5);

        //2.执行
        service.execute(new MyThread());
        service.execute(new MyThread());
        service.execute(new MyThread());
        service.execute(new MyThread());

        //3.关闭链接
        service.shutdownNow();
    }
}

class MyThread implements Runnable{
    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName());
    }
}