[GitHub] [rocketmq-client-cpp] legendmaner opened a new issue #362: 可能存在重复消费问题

[GitBox <gi...@apache.org>]

legendmaner opened a new issue #362:
URL: https://github.com/apache/rocketmq-client-cpp/issues/362


   https://github.com/apache/rocketmq-client-cpp/blob/d0f65a191b9e9609939da719d13548898d73f225/src/consumer/DefaultMQPushConsumerImpl.cpp#L799
   
   这里m_PullCallback是复用的，而绑定request是可变的。在多client进程并发重启时候，容易触发某个queue短时间内被Add、Drop然后又Add，就会触发重复消费case：
   1. 线程1: 队列queue1的请求A触发Add mq，绑定cb1，生成 cb1 = getAsyncPullCallBack(A,queue1)
   2. 线程2: 队列queue1的请求A触发Drop mq，然而只是设置了下drop flag，实际清理工作在pull循环里面
   3. 线程3: 队列queue1的请求B触发Add mq，绑定cb1 = getAsyncPullCallBack(B,queue1)，因为cb是复用的，返回了和线程1一样的cb1, 这是cb1绑定是B，所以线程1这时也绑定了B
   4. 线程1: 将cb1加到pull循环工作，原本希望将A加入pull循环结果却将B加入到循环
   5. 线程3: 将cb1加到pull循环工作，将B加入到循环
   6. 这时就2个pull循环在在跑请求B，导致重复消费
   因为cb是复用的而绑定的requst随时有可能被别的request替换掉导致加入pull循环时候导致重复消费；


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[GitHub] [rocketmq-client-cpp] ifplusor commented on issue #362: 可能存在重复消费问题

[GitBox <gi...@apache.org>]

ifplusor commented on issue #362:
URL: https://github.com/apache/rocketmq-client-cpp/issues/362#issuecomment-878831085


   当前复用PullCallback的设计比较差


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