ReadWriteLock读写锁

ReadWriteLock

翻译：

读取写入锁

解释：

在写入与读取的时候，会被其他线程插队，对于读取线程是不要紧的，但是对于读取线程，就会出现很多的问题
在以前我们可以synchronized ，ReetrentLock锁住
现在使用更加细腻的 ReadWriteLock

用法

不加锁的情况下

public class ReadAndWriteLockTest {

    public static void main(String[] args) {
        MyCache myCache = new MyCache();

        for (int i = 0; i < 5; i++) {
            int finalI = i;
            new Thread(() ->{
                myCache.pushItem(String.valueOf(finalI), finalI);
            },String.valueOf(i)).start();
        }

        for (int i = 0; i < 5; i++) {
            int finalI = i;
            new Thread(() ->{
                myCache.getItem(String.valueOf(finalI));
            },String.valueOf(i)).start();
        }

    }

}
class MyCache{
    private Map<String ,Integer> map = new HashMap<>();

    public void pushItem(String key,Integer value){
        System.out.println(Thread.currentThread().getName() + "准备写入");
        map.put(key,value);
        System.out.println(Thread.currentThread().getName() + "写入成功");
    }

    public void getItem(String key){
        System.out.println(Thread.currentThread().getName() + "准备读取");
        map.get(key);
        System.out.println(Thread.currentThread().getName() + "读取成功");
    }
}

会出现写入的时候，其他线程插队的情况

加入读写锁ReadWriteLock

class MyCache{

    private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
    private Map<String ,Integer> map = new HashMap<>();

    public void pushItem(String key,Integer value){
        readWriteLock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "准备写入");
            map.put(key,value);
            System.out.println(Thread.currentThread().getName() + "写入成功");
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            readWriteLock.writeLock().unlock();
        }
    }

    public void getItem(String key){
        readWriteLock.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "准备读取");
            map.get(key);
            System.out.println(Thread.currentThread().getName() + "读取成功");
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            readWriteLock.readLock().unlock();
        }
    }
}