线程学习(二)

一、并发

多个线程同时操作一个对象就叫做并发。

线程同步的安全性条件:队列和锁。

 

 

 

例子

public class DeadLock {
    public static void main(String[] args) {
        MakeUp g1 = new MakeUp(0, "白雪公主", "白雪公主");
        MakeUp g2 = new MakeUp(1, "灰姑娘", "灰姑娘");
        g1.start();
        g2.start();
    }
}

//镜子
class Mirror {
}

//口红
class LipStrick {
}

//化妆
class MakeUp extends Thread {
    static Mirror mirror = new Mirror();
    static LipStrick lipStrick = new LipStrick();
    private int choice;
    private String girlName;

    public MakeUp(int choice, String girlName, String name) {
        super(name);
        this.choice = choice;
        this.girlName = girlName;
    }

    @Override
    public void run() {
        try {
            makeup();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public void makeup() throws InterruptedException {
        if (choice == 0) {//先拿口红 再拿镜子
            synchronized (mirror) {
                //Thread.currentThread().getName()==this.getName()
                System.out.println(this.getName() + "拿到了镜子");
                Thread.sleep(1000);
                synchronized (lipStrick) {
                    System.out.println(this.getName() + "拿到了口红");
                }
            }
        } else {
            synchronized (lipStrick) {
                System.out.println(this.getName() + "拿到了口红");
                Thread.sleep(2000);
                synchronized (mirror) {
                    //Thread.currentThread().getName()==this.getName()
                    System.out.println(this.getName() + "拿到了镜子");
                }
            }
        }
    }
}

运行结果：

 

 

 在这个时候就形成了死锁。

 

 

 

所以将上面的代码的makeup方法进行修改

public void makeup() throws InterruptedException {
        if (choice == 0) {//先拿口红 再拿镜子
            synchronized (mirror) {
                //Thread.currentThread().getName()==this.getName()
                System.out.println(this.getName() + "拿到了镜子");
                Thread.sleep(1000);
            }
            synchronized (lipStrick) {
                System.out.println(this.getName() + "拿到了口红");
            }
        } else {
            synchronized (lipStrick) {
                System.out.println(this.getName() + "拿到了口红");
                Thread.sleep(2000);
            }
            synchronized (mirror) {
                //Thread.currentThread().getName()==this.getName()
                System.out.println(this.getName() + "拿到了镜子");
            }
        }
    }

再次运行后的结果

 

 

 

 

 

public class TestLock {
    public static void main(String[] args) {
        BuyTicket buyTicket = new BuyTicket();
        new Thread(buyTicket).start();
        new Thread(buyTicket).start();
        new Thread(buyTicket).start();
    }
}

class BuyTicket implements Runnable {

    private int ticketNum = 10;
    private final ReentrantLock lock = new ReentrantLock();

    @Override
    public void run() {
        while (true) {
            //开启锁
            lock.lock();
            try {
                if (ticketNum > 0) {
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(ticketNum--);
                } else {
                    break;
                }
            } finally {
                //结束锁
                lock.unlock();
            }
        }
    }
}