读写锁案例说明

ReentrantReadWriteLock()
写锁是线程独享，同一时间只能有一个线程操作
读锁是线程共享：同一时间可以有多个线程操作

/**
 * Created by Last on 2020/7/28.
 * 读写锁
 */
public class D {
    public static void main(String[] args) {
        MyCacheLock myCacheLock = new MyCacheLock();
        for (int i = 1; i < 5; i++) {
            final int temp = i;
            new Thread(()->{
                myCacheLock.put(temp+"=","");
            },String.valueOf(i)).start();
        }

        for (int i = 1; i < 5; i++) {
            final int temp = i;
            new Thread(()->{
                myCacheLock.get(temp+"=");
            },String.valueOf(i)).start();
        }
    }
}

class MyCacheLock {
    private volatile Map<String, Object> map = new HashMap<>();

    //普通Lock锁
    private Lock lock = new ReentrantLock();
    //读写锁 也叫独享所和共享锁
    private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();

    public void put(String key, Object obj) {
        //独享写入锁加锁
        readWriteLock.writeLock().lock();
        try {
            System.out.println("写入" + key);
            map.put(key, obj);
            System.out.println(key + "写入完成");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            //独享写入锁解锁
            readWriteLock.writeLock().unlock();
        }
    }

    public void get(String key) {
        //共享读取锁加锁
        readWriteLock.readLock().lock();
        try {
            System.out.println("读取" + key);
            map.get(key);
            System.out.println(key + "读取成功");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            //共享读取锁解锁
            readWriteLock.readLock().unlock();
        }
    }
}