读写锁

读锁也叫共享锁

写锁也叫独享锁

 

读锁写锁都会造成死锁的问题

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


    public  void put(String key,String value){
        rwLock.writeLock().lock();

        try {

            System.out.println(Thread.currentThread().getName()
                    +"\t 准备写入数据"+key);
                TimeUnit.MILLISECONDS.sleep(200);
            map.put(key, value);
            System.out.println(Thread.currentThread().getName()
                    +"\t 写入数据完成"+key);


        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            rwLock.writeLock().unlock();
        }


    }

    public  void get(String key){
        rwLock.readLock().lock();
        try {

            System.out.println(Thread.currentThread().getName()
                    +"\t 准备读取数据"+key);

                TimeUnit.MILLISECONDS.sleep(200);

            String value = map.get(key);
            System.out.println(Thread.currentThread().getName()
                    +"\t 读取数据完成"+value);

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            rwLock.readLock().unlock();
        }


    }


}




public class ReadWriteLockDemo {

    public static void main(String[] args) throws InterruptedException {

        MyCache myCache = new MyCache();

        for (int i = 1; i <=5 ; i++) {
            String key = String.valueOf(i);
            new Thread(()->{
                myCache.put(key, UUID.randomUUID().toString().substring(0,8));
            },String.valueOf(i)).start();
        }

        TimeUnit.SECONDS.sleep(2);

        for (int i = 1; i <=5 ; i++) {
            String key = String.valueOf(i);
            new Thread(()->{
                myCache.get(key);
            },String.valueOf(i)).start();
        }


    }
}