ReentrantReadWriteLock读写锁 - ToB企服应用市场:ToB评测及商务社交产业平台

//1.定义资源类
class MyCache {
//volatile关键字，共享的数据，在一个线程修改后，被其他线程访问到
private volatile HashMap<String, Object> hashMap = new HashMap<>();
private ReadWriteLock rwLock = new ReentrantReadWriteLock();
//2.定义操作资源类的方法
public Object get(String key) {
rwLock.readLock().lock();//读锁
Object result = null;
try {
System.out.println(Thread.currentThread().getName() + "正在读取值" + key);
TimeUnit.MILLISECONDS.sleep(300);
result = hashMap.get(key);
System.out.println(Thread.currentThread().getName() + "读取值完成" + key);
} catch (InterruptedException e) {
e.printStackTrace();
}finally {
rwLock.readLock().unlock();
}
return result;
}
public void put(String key, Object value) {
rwLock.writeLock().lock();//写锁
try {
System.out.println(Thread.currentThread().getName() + "正在添加值" + key);
TimeUnit.MILLISECONDS.sleep(300);
hashMap.put(key, value);
System.out.println(Thread.currentThread().getName() + "添加值完成" + key);
} catch (InterruptedException e) {
e.printStackTrace();
}finally {
rwLock.writeLock().unlock();
}
}
}
public class ReadWriteLockDemo {
public static void main(String[] args) {
MyCache cache = new MyCache();
//创建线程，向缓存中添加值
for (int i = 0; i < 5; i++) {
final int num = i;
new Thread(() -> {
cache.put(num + "", num);
}, String.valueOf(i)).start();
}
//创建线程，向缓存中获取值
for (int i = 0; i < 5; i++) {
final int num = i;
new Thread(() -> {
cache.get(num + "");
}, String.valueOf(i)).start();
}
}
}

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/**
* @author 长名06
* @version 1.0
* 读写锁降级演示
*/
public class ReadWriteLockDownLevelDemo {
public static void main(String[] args) {
ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
ReentrantReadWriteLock.WriteLock writeLock = rwLock.writeLock();//写锁
ReentrantReadWriteLock.ReadLock readLock = rwLock.readLock();//读锁
//先读后写，获取读锁后，就获取不到写锁，线程阻塞
//1.获取写锁
writeLock.lock();
System.out.println("获取写锁");
//2.获取读锁
readLock.lock();
System.out.println("获取读锁");
//3.释放写锁
writeLock.unlock();
//4.释放读锁
readLock.unlock();
}
}

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