读写锁---ReentrantReadWriteLock

读写锁---ReentrantReadWriteLock

可重复读写锁：

可以更加细粒度控制读和写的锁情况。

读锁可以多线程一起读，写只能一个一个按顺序写，可以进一步提高代码效率

独占锁即写锁

共享锁即读锁

下面代码可以把注释解开运行下看下效果

package com.example.juc;

import java.util.HashMap;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class TestReadWriteLock {
    public static void main(String[] args) {
//        MyCache myCache = new MyCache();
        MyCacheLock myCache = new MyCacheLock();
        for (int i = 0; i < 6; i++) {
            final int temp = i;
            new Thread(() -> {
                myCache.put(String.valueOf(temp), String.valueOf(temp));
            }, String.valueOf(i)).start();
        }
        for (int i = 0; i < 6; i++) {
            final int temp = i;
            new Thread(() -> {
                myCache.get(String.valueOf(temp));
            }, String.valueOf(i)).start();
        }
    }
}


class MyCacheLock {
    private HashMap map = new HashMap<String, String>();
    private ReadWriteLock lock = new ReentrantReadWriteLock();

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

        try {
            System.out.println("开始获取" + Thread.currentThread().getName());
            map.get(key);
            System.out.println("获取完毕" + Thread.currentThread().getName());
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.readLock().unlock();
        }


    }

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

        try {
            System.out.println("开始写入" + Thread.currentThread().getName());
            map.put(key, value);
            System.out.println("写入完毕" + Thread.currentThread().getName());
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.writeLock().unlock();
        }
    }
}

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

    public void get(String key) {

        System.out.println("开始获取" + Thread.currentThread().getName());
        map.get(key);
        System.out.println("获取完毕" + Thread.currentThread().getName());

    }

    public void put(String key, String value) {
        System.out.println("开始写入" + Thread.currentThread().getName());
        map.put(key, value);
        System.out.println("写入完毕" + Thread.currentThread().getName());
    }
}