十四、ReadWriteLock

ReadWriteLock 读写锁又叫排他锁

如果使用互斥锁，一个线程在读，其他线程也不能读也不能写

换成读写锁的时候，读线程是读锁，写线程是写锁，写锁是排他的

在多线程大大提高效率，当一个线程在读的时候，其他线程也可以进来继续读

import java.util.Random;
import java.util.concurrent.atomic.LongAdder;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class T10_TestReadWriteLock {
    static Lock lock = new ReentrantLock();
    private static int value;

    static ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
    static Lock readLock = readWriteLock.readLock();
    static Lock writeLock = readWriteLock.writeLock();

    public static void read(Lock lock) {
        try {
            lock.lock();
            Thread.sleep(1000);
            System.out.println("read over!");
            //模拟读取操作
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    public static void write(Lock lock, int v) {
        try {
            lock.lock();
            Thread.sleep(1000);
            value = v;
            System.out.println("write over!");
            //模拟写操作
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }





    public static void main(String[] args) {
        //Runnable readR = ()-> read(lock);
        Runnable readR = ()-> read(readLock);

        //Runnable writeR = ()->write(lock, new Random().nextInt());
        Runnable writeR = ()->write(writeLock, new Random().nextInt());

        for(int i=0; i<18; i++) new Thread(readR).start();
        for(int i=0; i<2; i++) new Thread(writeR).start();


    }
}

使用ReentrantLock 20s