java线程之Lock锁，三个线程抢票加上lock锁后变成三个线程排队买票

1.三个线程同时抢票导致线程不安全

不安全的代码

//测试Lock锁
public class TestLock {
    public static void main(String[] args) {
        Testlock2 testlock2 = new Testlock2();

        new Thread(testlock2).start();
        new Thread(testlock2).start();
        new Thread(testlock2).start();
    }
}

class Testlock2 implements Runnable {
    int ticketNums = 10;

    //定义lock锁
    private final ReentrantLock lock = new ReentrantLock();

    @Override
    public void run() {
        while (true) {
            if (ticketNums > 0) {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(ticketNums--);
            } else break;
        }
    }
}

三个线程同时访问票，容易出现线程安全问题
运行结果

2.加上Lock锁后

代码

import java.util.concurrent.locks.ReentrantLock;

//测试Lock锁
public class TestLock {
    public static void main(String[] args) {
        Testlock2 testlock2 = new Testlock2();

        new Thread(testlock2).start();
        new Thread(testlock2).start();
        new Thread(testlock2).start();
    }
}

class Testlock2 implements Runnable{
    int ticketNums = 10;

    //定义lock锁
    private final ReentrantLock lock = new ReentrantLock();

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

运行结果

3.Lock锁与synchronized的对比

1. lock是显示锁（手动开启和关闭锁，别忘记关闭锁），synchronized是隐式锁，出了作用域自动释放
2. lock只有代码块锁，synchronized有代码块锁和方法锁
3. 使用lock锁，JVM将花费较少的时间来调度线程（性能更好）

本文地址：https://blog.csdn.net/qq_45895576/article/details/110731986