ReadWriteLock讀寫鎖

ReadWriteLock維護了一對鎖，讀鎖可允許多個讀線程並發使用，寫鎖是獨占的。

下面通過一個簡單的例子來了解ReadWriteLock。

package com.ccfdod.juc;

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

/**
 * 寫寫/讀寫，需要互斥
 * 讀讀，不需要互斥
 */
public class TestReadWriteLock {

    public static void main(String[] args) {
        ReadWriteLockDemo rw = new ReadWriteLockDemo();
        new Thread(new Runnable() {

            @Override
            public void run() {
                rw.set((int) (Math.random() * 101));
            }
            
        }, "Write:").start();
        
        for (int i = 0; i < 100; i++) {
            new Thread(new Runnable() {

                @Override
                public void run() {
                    rw.get();
                }
                
            }, "Read:").start();
        }
    }
}

class ReadWriteLockDemo {
    
    private int number = 0;
    
    private ReadWriteLock lock = new ReentrantReadWriteLock();
    
    //讀
    public void get() {
        lock.readLock().lock();    //上鎖
        try {
            System.out.println(Thread.currentThread().getName() + " : " + number);
        } finally {
            lock.readLock().unlock();    //釋放鎖
        }
    }
    
    //寫
    public void set(int number) {
        lock.writeLock().lock();    //上鎖
        try {
            System.out.println(Thread.currentThread().getName());
            this.number = number;
        } finally {
            lock.writeLock().unlock();    //釋放鎖
        }
    }
}