ReentrantReadWriteLock 讀寫鎖

/**
 * 讀寫鎖ReentrantReadWriteLock
 * 讀寫分離可以有效地減少鎖的競爭
 * 在ReentrantLock中如果給讀線程加鎖，那麼寫線程就需要等待
 * 給寫線程加鎖，那麼讀線程就得等待
 * 這顯然是不合理的，因爲讀操作不會對數據的完整性破壞。
 * 所以在讀的次數遠遠大於寫的次數的時候，使用讀寫鎖子
 * @author beiyaoyao
 */
public class ReadWriteLockDemo {

    private static Lock lock = new ReentrantLock();

    private static ReentrantReadWriteLock reentrantReadWriteLock = new ReentrantReadWriteLock();

    private static Lock readLock = reentrantReadWriteLock.readLock();

    private static Lock writeLock = reentrantReadWriteLock.readLock();

    private int value;

    public Object readMission(Lock lock) throws InterruptedException {

        try {
            //描述讀操作
            lock.lock();
            Thread.sleep(1000);
            return value;
        } finally {
            lock.unlock();
        }

    }

    public void writeMission(Lock lock,int num) throws InterruptedException {
        try {
            //描述寫操作
            lock.lock();
            Thread.sleep(1000);
            value = num;
            System.out.println(value);
        } finally {
            lock.unlock();
        }
    }


    public static void main(String[] args) {


        final  ReadWriteLockDemo  readWriteLockDemo = new ReadWriteLockDemo();
        //讀線程
        Runnable readThread = new Runnable() {

            @Override
            public void run() {
                try {
                    //兩把鎖子交替使用
//                  readWriteLockDemo.readMission(readLock);
                    readWriteLockDemo.readMission(lock);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };      
        //寫線程
        Runnable writeThread = new Runnable() {

            @Override
            public void run() {
                try {
                    //兩把鎖子交替使用
//                  readWriteLockDemo.writeMission(writeLock,new Random().nextInt());
                    readWriteLockDemo.writeMission(lock,new Random().nextInt());
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }


            }
        };      

        //誇張的例子 讀18次
        for(int i = 0  ; i < 18 ; i ++){
            new Thread(readThread).start();
        }
        //寫2次
        for(int i = 0  ; i < 2 ; i ++){
            new Thread(writeThread).start();
        }       


    }

}

如果使用重入鎖，那麼這段程序的執行時間在20秒左右
如果使用讀寫鎖，那麼這段程序的執行時間在2秒左右