ReentrantLock可重入锁

可重⼊锁，这个锁可以被线程多次重复进⼊进⾏获取操作。
ReentantLock继承接⼝Lock并实现了接⼝中定义的⽅法，除了能完成synchronized所能完成的所有⼯作 外，还提供了诸如可响应中断锁、可轮询锁请求、定时锁等避免多线程死锁的⽅法。
在并发量较⼩的多线程应⽤程序中，ReentrantLock与synchronized性能相差⽆⼏，但在⾼ 并发量的条件下，synchronized性能会迅速下降⼏⼗倍，⽽ReentrantLock的性能却能依然维持⼀个⽔ 准。
因此我们建议在⾼并发量情况下使⽤ReentrantLock。

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class Counter {
    private final Lock lock = new ReentrantLock();
    private int count = 0;

    public void increment() {
        lock.lock();  // 获取锁
        try {
            count++;
        } finally {
            lock.unlock();  // 释放锁
        }
    }

    public int getCount() {
        return count;
    }
    
    public static void main(String[] args) {
        Counter counter = new Counter();

        // 创建两个线程，模拟并发访问共享资源
        Thread t1 = new Thread(() -> {
            for (int i = 0; i < 1000; i++) {
                counter.increment();
            }
        });

        Thread t2 = new Thread(() -> {
            for (int i = 0; i < 1000; i++) {
                counter.increment();
            }
        });

        t1.start();
        t2.start();

        // 等待两个线程执行完毕
        try {
            t1.join();
            t2.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("Final count is: " + counter.getCount());
    }
}

public class Counter {
    private int count = 0;

    // 使用 synchronized 关键字修饰方法，确保线程安全
    public synchronized void increment() {
        count++;
    }

    public int getCount() {
        return count;
    }

    public static void main(String[] args) {
        Counter counter = new Counter();

        Thread t1 = new Thread(() -> {
            for (int i = 0; i < 1000; i++) {
                counter.increment();
            }
        });

        Thread t2 = new Thread(() -> {
            for (int i = 0; i < 1000; i++) {
                counter.increment();
            }
        });

        t1.start();
        t2.start();

        try {
            t1.join();
            t2.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("Final count is: " + counter.getCount());
    }
}