java多線程（複習-8）ReadWriteLock 讀寫鎖

前言：ReadWriteLock主要提供的是在併發讀寫過程中，可以做到多個線程併發的進行讀操作，而重入鎖並不能達到這個要求

因爲，讀寫操作是會相互阻塞，對於共享資源一次只能時讀，或者是隻能寫，使用該a'pi可以多個線程同時讀，提高效率。

這樣的情況，就會使的ReadWriteLock在讀多寫少的情況下，效率非常高

簡單的實例、

package Java多線程;

import java.util.Random;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class ReadWriteLockDemo {
    public static  Lock reentrantLock = new ReentrantLock();
    //操作的值
    private int value ;

    //讀操作
    public Object handleRead(Lock lock) throws Exception{
        try {
            lock.lock();
            Thread.sleep(1000);
            return value;
        }finally {
            lock.unlock();
        }
    }

    public void handleWrite(Lock lock){
        try{
            lock.lock();
            System.out.println("寫數據開始");
            value = new Random().nextInt(100);//寫入一個隨機值
            System.out.println("線程ID："+Thread.currentThread().getId()+"成功寫入:" + value);
        }finally {
            lock.unlock();
        }
    }

    static class ReadThread implements Runnable{
        private ReadWriteLockDemo readWriteLockDemo;
        private ReentrantReadWriteLock lock;

        public ReadThread(ReadWriteLockDemo readWriteLockDemo,ReentrantReadWriteLock lock){
            this.readWriteLockDemo = readWriteLockDemo;
            this.lock = lock;
        }

        @Override
        public void run() {
            try{
                //System.out.println("線程ID:"+Thread.currentThread().getId()+"讀取的value："+readWriteLockDemo.handleRead(lock.readLock()));
                System.out.println("線程ID:"+Thread.currentThread().getId()+"讀取的value："+readWriteLockDemo.handleRead(reentrantLock));
            }catch (Exception e){
                e.printStackTrace();
            }
        }
    }

    static class WriteThread implements  Runnable{
        private ReadWriteLockDemo readWriteLockDemo;
        private ReentrantReadWriteLock lock;
        public WriteThread(ReadWriteLockDemo readWriteLockDemo,ReentrantReadWriteLock lock){
            this.readWriteLockDemo = readWriteLockDemo;
            this.lock = lock;
        }
        @Override
        public void run() {
            try{
                //readWriteLockDemo.handleWrite(lock.writeLock());//使用讀寫鎖
                readWriteLockDemo.handleWrite(reentrantLock);//使用普通重入鎖
            }catch (Exception e){
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) throws Exception{
        ReadWriteLockDemo readWriteLockDemo = new ReadWriteLockDemo();
        ReentrantReadWriteLock readWriteLock = new ReentrantReadWriteLock();
        //開起兩個寫線程
        for (int i = 0; i <2 ; i++) {
            Thread thread = new Thread(new WriteThread(readWriteLockDemo,readWriteLock));
            thread.start();
        }
        //開啓讀線程
        for (int i = 2; i <20 ; i++) {
            Thread thread = new Thread(new ReadThread(readWriteLockDemo,readWriteLock));
            thread.start();
        }
    }
}

部分截圖，使用讀寫鎖會使讀寫分離，性能提高，，但是使用普通的鎖會使讀寫必須相互阻塞