读写锁

ReadWriteLock

/*
独占锁(写锁) 一次只能被一个线程占有
共享锁(读锁) 多个线程可以同时占有
ReadWriteLock
    读-读 可以共存
    读-写 不能共存
    写-写 不能共存
 */
public class ReadWriteLockDemo {
    public static void main(String[] args) {
        MyCacheLock myCache = new MyCacheLock();

        // 写入
        for (int i = 0; i < 5; i++) {
            final int temp = i;
            new Thread(() -> {
                myCache.put(temp + "", temp + "");
            }, String.valueOf(i)).start();
        }

        // 读取
        for (int i = 0; i < 5; i++) {
            final int temp = i;
            new Thread(() -> {
                myCache.get(temp + "");
            }, String.valueOf(i)).start();
        }
    }
}

/*
加锁的自定义缓存
 */
class MyCacheLock{
    private volatile Map<String, Object> map = new HashMap<>();
    // 读写锁:更加细粒度的控制
    private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();


    // 存,写 写入的时候,只希望同时只有一个线程写
    public void put(String key, Object value) {
        readWriteLock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "写入" + key);
            map.put(key, value);
            System.out.println(Thread.currentThread().getName() + "写入OK");
        }finally {
            readWriteLock.writeLock().unlock();
        }
    }

    // 取,读 所有人都可以读!
    public void get(String key) {
        readWriteLock.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "读取" + key);
            Object o = map.get(key);
            System.out.println(Thread.currentThread().getName() + "读取OK");
        } finally {
            readWriteLock.readLock().unlock();
        }
    }
}

/*
自定义缓存
 */
class MyCache{
    private volatile Map<String, Object> map = new HashMap<>();

    // 存, 写
    public void put(String key, Object value) {
        System.out.println(Thread.currentThread().getName() + "写入" + key);
        map.put(key, value);
        System.out.println(Thread.currentThread().getName() + "写入OK");
    }

    // 取, 读
    public void get(String key) {
        System.out.println(Thread.currentThread().getName() + "读取" + key);
        Object o = map.get(key);
        System.out.println(Thread.currentThread().getName() + "读取OK");
    }
}