ReentrantReadWriteLock是否在writeLock锁定时读取？
ReentrantReadWriteLock是否在writeLock锁定时读取？
提问于 2014-04-15 20:13:36
我研究ReentrantReadWriteLock。
我编写了简单的测试代码(我知道使用Thread.sleep()不能保证可预测的结果，但我认为我很幸运：)：
public class RWLock {
private static String val = "old";
private static ReadWriteLock lock = new ReentrantReadWriteLock();
private static long time = System.currentTimeMillis();
public void read() {
try {
lock.readLock().lock();
System.out.println("read " + val +" - "+(System.currentTimeMillis()-time));
Thread.sleep(300);
} catch (InterruptedException e) {
} finally {
lock.readLock().unlock();
}
}
public void write() {
try {
lock.writeLock().lock();
val = "new";
System.out.println("write " + val+" - "+(System.currentTimeMillis()-time));
Thread.sleep(10000);
} catch (InterruptedException e) {
} finally {
lock.writeLock().unlock();
}
}
}
class Tester {
public static void main(String[] args) throws InterruptedException {
new MyThreadRead().start();
Thread.sleep(400);
new MyThreadWrite().start();
}
}
class MyThreadRead extends Thread {
@Override
public void run() {
for (int i = 0; i < 10; i++) {
new RWLock().read();
try {
Thread.sleep(200);
} catch (InterruptedException e) {
}
}
}
}
class MyThreadWrite extends Thread {
@Override
public void run() {
new RWLock().write();
}
}产出：
read old - 0
write new - 401
read new - 10401
read new - 10902
read new - 11402
read new - 11902
read new - 12402
read new - 12902
read new - 13402
read new - 13902
read new - 1440210401 - 401 == 10000
10000是写作的时候了。
正如我所理解的，二读线程不能在写之前完成。因此，写作和二读并行执行。这对我来说是不可预测的行为。
你觉得那个怎么样？
回答 1
Stack Overflow用户
回答已采纳
发布于 2014-04-15 20:40:42
也许你有更多的睡眠()电话比你意识到的多。MyThreadRead#run()和RWLock()#read()中的睡眠调用加起来可达500 ms。下面是发生的事情。
At T=0, the reader thread grabs the read lock and sleeps for 300ms.
At T=300, the reader releases the lock, and then sleeps for another 200ms.
At T=400, the writer grabs the write lock and sleeps for ten seconds,
At T=500, the reader tries to grab the read lock, but it is blocked by the writer.
At T=10400, the writer gives up the lock, and then the reader gets to go round
its loop nine more times.P.S.：将lock()调用移出try/finally语句。例如，
...lock()
try {
...
} finally {
...unlock();
}这样，如果lock()调用抛出一个异常，那么将不会调用unlock()。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/23093581
复制相关文章
相似问题
腾讯云开发者
Copyright © 2013 - 2026 Tencent Cloud. All Rights Reserved. 腾讯云 版权所有
深圳市腾讯计算机系统有限公司 ICP备案/许可证号：粤B2-20090059 
粤公网安备44030502008569号
腾讯云计算（北京）有限责任公司 京ICP证150476号 | 京ICP备11018762号