你需要實現一個高效的緩存，它允許多個用戶讀，但只允許一個用戶寫，以此來保持它的完整性，你會怎樣去實現它？

Lock讀寫鎖機制可以實現！ 

在Java中Lock接口比synchronized塊的優勢是什么？

 Lock接口最大的優勢是為讀和寫分別提供了鎖。

 

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Random;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;




public class JoinTest2 {    
  
    public static void main(String[] args) {  
        final TheData theData = new TheData();
        for(int i=0;i<4;i++){
            new Thread(new Runnable() {
                @Override
                public void run() {
                    theData.get();
                }
            }).start();
        }
        for(int i=0;i<4;i++){
            new Thread(new Runnable() {
                @Override
                public void run() {
                    theData.put(new Random().nextInt(1000));
                }
            }).start();
        }        
    }  
    

} 

class  TheData{
    private Integer data = 0;
    private ReadWriteLock rwLock = new ReentrantReadWriteLock();
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
    public void get(){
        rwLock.readLock().lock();//讀鎖開啟，讀進程均可進入
        try{//用try finally來防止因異常而造成的死鎖
            System.out.println(Thread.currentThread().getName()+"read lock is ready.."+sdf.format(new Date()));
            Thread.sleep(1000);
            System.out.println(Thread.currentThread().getName()+"read data is"+data);
        }catch (InterruptedException e) {
            e.printStackTrace();
        }finally{
            rwLock.readLock().unlock();//讀鎖解鎖
        }
    }
    
    public void put(Integer data){
        rwLock.writeLock().lock();//寫鎖開啟，這時只有一個寫線程進入
        try{//用try finally來防止因異常而造成的死鎖
            System.out.println(Thread.currentThread().getName()+"write lock is ready.."+sdf.format(new Date()));
            Thread.sleep(1000);
            this.data = data;
            System.out.println(Thread.currentThread().getName()+"write data is"+data);                

        }catch (InterruptedException e) {
            e.printStackTrace();
        }finally{
            rwLock.writeLock().unlock();//寫鎖解鎖
        }
    }
}

運行結果如下：