读写锁

1、读写锁是啥

读写锁就是对Lock的细化

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.*;

/**
 *
 *  读写锁（也叫独占锁或者共享锁）
 *  写的时候是线程独占的，读的时候是共享的
    写的时候只有一个线程在写不存在插队的情况，读的时候一个线程度，另外的线程可以插进来
 *
 *
 */
public class ReadWriteLockDemo {

    public static void main(String[] args) {

        Mycache mycache = new Mycache();

        for (int i = 1; i <= 5 ; i++) {
            final int t = i;
            new Thread(()->{

                mycache.put(t+"",t+"");
            },String.valueOf(i)).start();
        }


        for (int i = 2; i <= 40 ; i++) {
            final int t = i;
            new Thread(()->{

                mycache.get(t+"");
            },String.valueOf(i)).start();
        }

    }
}

class Mycache{
    private volatile Map hashMap = new HashMap();
    Lock lock = new ReentrantLock();

    ReadWriteLock readWriteLock = new ReentrantReadWriteLock();

    public void put(String key,Object o){
        readWriteLock.writeLock().lock();
        try{
            System.out.println(Thread.currentThread().getName()+"开始写入"+key);
            hashMap.put(key,o);
            System.out.println(Thread.currentThread().getName()+"写入完成"+key);
        }catch (Exception e){

        }finally {
            readWriteLock.writeLock().unlock();
        }

    }


    public void get(String key){
        System.out.println(Thread.currentThread().getName()+"开始读取"+key);
        hashMap.get(key);
        System.out.println(Thread.currentThread().getName()+"读取完成"+key);
    }

}