ReentrantReadWriteLock//讀寫鎖, 只能單執行緒寫，允許多執行緒讀

ReadWriteLock
讀-讀可以共存!
讀-寫不能共存!
寫-寫不能共存!

package Lock;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**  ReentrantReadWriteLock//讀寫鎖, 只能單執行緒寫，允許多執行緒讀
 * @author liu
 */
public class ReadWriteLockA {
    public static void main(String[] args) {
        MyCacheLock myCacheLock = new MyCacheLock();
        for (int i = 1; i <= 5; i++) {
            int finalI = i;
            new Thread(() -> {
                myCacheLock.writer(finalI,finalI);
            }, String.valueOf(i)).start();
        }


        for (int i = 1; i <= 5; i++) {
            int finalI = i;
            new Thread(() -> {
                myCacheLock.read(finalI);
            }, String.valueOf(i)).start();
        }
    }
}

class MyCacheLock {
    private volatile Map<Integer, Object> map = new HashMap<>();
    //讀寫鎖, 只能單執行緒寫，允許多執行緒讀
    private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();

    public void writer(Integer key, Object value) {
        try {
            readWriteLock.writeLock().lock();
            System.out.println(Thread.currentThread().getName() + "寫入" + key);
            map.put(key, value);
            System.out.println(Thread.currentThread().getName() + "寫入OK");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            readWriteLock.writeLock().unlock();
        }
    }

    public void read(Integer key) {
        try {
            readWriteLock.readLock().lock();
            System.out.println(Thread.currentThread().getName() + "讀取" + key);
            map.get(key);
            TimeUnit.SECONDS.sleep(1);
            System.out.println(Thread.currentThread().getName() + "讀取OK");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            readWriteLock.readLock().unlock();
        }
    }
}