系列十、ReentrantReadWriteLock

一、概述

ReentrantReadWriteLock是ReadWriteLock的一个子类，具有读锁和写锁的双重功能，通常用于做缓存。

二、案例代码

2.1、ReentrantReadWriteLockCache

/**
 * @Author : 一叶浮萍归大海
 * @Date: 2023/11/20 17:57
 * @Description: 使用ReentrantReadWriteLock实现缓存的功能
 */
public class ReentrantReadWriteLockCache {

    private volatile Map<String, Object> map = new HashMap<>();
    private ReadWriteLock rwLock = new ReentrantReadWriteLock();

    /**
     * 写数据
     * @param key
     * @param value
     */
    public void put(String key, Object value) {
        rwLock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "\t正在写" + key);
            // 线程休眠，单位：毫秒
            try {TimeUnit.MILLISECONDS.sleep(300);} catch (Exception e) {e.printStackTrace();}
            map.put(key, value);
            System.out.println(Thread.currentThread().getName() + "\t写完了" + key);
            System.out.println();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            rwLock.writeLock().unlock();
        }
    }

    /**
     * 读数据
     * @param key
     * @return
     */
    public Object get(String key) {
        rwLock.readLock().lock();
        Object result = null;
        try {
            System.out.println(Thread.currentThread().getName() + "\t正在读" + key);
            // 线程休眠，单位：毫秒
            try {TimeUnit.MILLISECONDS.sleep(300);} catch (Exception e) {e.printStackTrace();}
            result = map.get(key);
            System.out.println(Thread.currentThread().getName() + "\t读完了" + result);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            rwLock.readLock().unlock();
        }

        return result;
    }
}

2.2、ReentrantReadWriteLockMainApp

/**
 * @Author : 一叶浮萍归大海
 * @Date: 2023/11/20 18:00
 * @Description:
 */
public class ReentrantReadWriteLockMainApp {

    public static void main(String[] args) {
        ReentrantReadWriteLockCache cache = new ReentrantReadWriteLockCache();

        for (int i = 1; i <= 5; i++) {
            final int number = i;
            new Thread(() -> {
            	try {
            		cache.put(String.valueOf(number),number);
            	} catch (Exception e) {
            		e.printStackTrace();
            	}
            }, String.valueOf(i)).start();
        }

        for (int i = 1; i <= 5; i++) {
            final int number = i;
            new Thread(() -> {
                try {
                    cache.get(String.valueOf(number));
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }, String.valueOf(i)).start();
        }
    }

}