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Posted to dev@brpc.apache.org by GitBox <gi...@apache.org> on 2020/09/08 04:27:49 UTC

[GitHub] [incubator-brpc] Ailusa0106 opened a new issue #1230: wait_for_butex在加入队列前验证butex锁变量的值可能还是老值而导致进入等待队列而产生永不唤醒

Ailusa0106 opened a new issue #1230:
URL: https://github.com/apache/incubator-brpc/issues/1230


   **Describe the bug (描述bug)**
   thread1 butex_wake释放锁变量移除thread1出队列结束，wait_for_butex获取的锁变量值可能还是老值（未刷新）而导致进入wait而永不唤醒
   
   **To Reproduce (复现方法)**
   使用
   
   **Expected behavior (期望行为)**
   能正常运行
   
   **Versions (各种版本)**
   OS:
   Compiler:
   brpc:
   protobuf:
   
   **Additional context/screenshots (更多上下文/截图)**
   ![image](https://user-images.githubusercontent.com/70932122/92432814-de656c80-f1cd-11ea-943c-fe44d8d72179.png)
   
   


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[GitHub] [incubator-brpc] Ailusa0106 commented on issue #1230: wait_for_butex在加入队列前验证butex锁变量的值可能还是老值而导致进入等待队列而产生永不唤醒

Posted by GitBox <gi...@apache.org>.
Ailusa0106 commented on issue #1230:
URL: https://github.com/apache/incubator-brpc/issues/1230#issuecomment-688672893


   > > 值
   > 
   > butex/futex 的语义本身就不保证能看到最新值， 这里保证的都是"使用姿势正确"的前提下. 1) waiter 能看到最新的只。 or 2) waiter会被waker通过 *utex_wake() 唤醒.
   
   嗯，多谢回复，主要是针对这个正确的姿势，拿bthread_mutex_unlock举例，假设两个thread，thread1解锁，此时锁变量的值去和0交换，交换之后利用butex_wake唤醒队列（但是此时队列为空），如果thread2 wait_for_butex这个时候看不到最新值就会lock（append进入队列），但是已经没有thread能唤醒它了。


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[GitHub] [incubator-brpc] Ailusa0106 commented on issue #1230: wait_for_butex在加入队列前验证butex锁变量的值可能还是老值而导致进入等待队列而产生永不唤醒

Posted by GitBox <gi...@apache.org>.
Ailusa0106 commented on issue #1230:
URL: https://github.com/apache/incubator-brpc/issues/1230#issuecomment-688693930


   > > 嗯，多谢回复，主要是针对这个正确的姿势，拿bthread_mutex_unlock举例，假设两个thread，thread1解锁，此时锁变量的值去和0交换，交换之后利用butex_wake唤醒队列（但是此时队列为空），如果thread2 wait_for_butex这个时候看不到最新值就会lock（append进入队列），但是已经没有thread能唤醒它了。
   > 
   > 这是不可能的，wait一端获取waiter_lock后必然能看到最新值。这类多线程问题的先验知识比较多，解释起来也比较困难，你可能得自己去学习一下了。
   
   好的，多谢戈大神回复


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[GitHub] [incubator-brpc] jamesge commented on issue #1230: wait_for_butex在加入队列前验证butex锁变量的值可能还是老值而导致进入等待队列而产生永不唤醒

Posted by GitBox <gi...@apache.org>.
jamesge commented on issue #1230:
URL: https://github.com/apache/incubator-brpc/issues/1230#issuecomment-688691129


   > 嗯，多谢回复，主要是针对这个正确的姿势，拿bthread_mutex_unlock举例，假设两个thread，thread1解锁，此时锁变量的值去和0交换，交换之后利用butex_wake唤醒队列（但是此时队列为空），如果thread2 wait_for_butex这个时候看不到最新值就会lock（append进入队列），但是已经没有thread能唤醒它了。
   
   这是不可能的，wait一端获取waiter_lock后必然能看到最新值。这类多线程问题的先验知识比较多，解释起来也比较困难，你可能得自己去学习一下了。


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[GitHub] [incubator-brpc] jamesge closed issue #1230: wait_for_butex在加入队列前验证butex锁变量的值可能还是老值而导致进入等待队列而产生永不唤醒

Posted by GitBox <gi...@apache.org>.
jamesge closed issue #1230:
URL: https://github.com/apache/incubator-brpc/issues/1230


   


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[GitHub] [incubator-brpc] chenzhangyi commented on issue #1230: wait_for_butex在加入队列前验证butex锁变量的值可能还是老值而导致进入等待队列而产生永不唤醒

Posted by GitBox <gi...@apache.org>.
chenzhangyi commented on issue #1230:
URL: https://github.com/apache/incubator-brpc/issues/1230#issuecomment-688640358


   请问有复现的case吗？ 还是通过看代码得到的结论


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[GitHub] [incubator-brpc] Ailusa0106 commented on issue #1230: wait_for_butex在加入队列前验证butex锁变量的值可能还是老值而导致进入等待队列而产生永不唤醒

Posted by GitBox <gi...@apache.org>.
Ailusa0106 commented on issue #1230:
URL: https://github.com/apache/incubator-brpc/issues/1230#issuecomment-688651366


   > 请问有复现的case吗？ 还是通过看代码得到的结论
   
   你好，看代码的结论，感觉这块无法完全保证获取的是最新值


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[GitHub] [incubator-brpc] chenzhangyi commented on issue #1230: wait_for_butex在加入队列前验证butex锁变量的值可能还是老值而导致进入等待队列而产生永不唤醒

Posted by GitBox <gi...@apache.org>.
chenzhangyi commented on issue #1230:
URL: https://github.com/apache/incubator-brpc/issues/1230#issuecomment-688665802


   > 值
   
   butex/futex 的语义本身就不保证能看到最新值， 这里保证的都是"使用姿势正确"的前提下. 1) waiter 能看到最新的只。 or 2) waiter会被waker通过 *utex_wake() 唤醒.


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