[GitHub] [pulsar] BewareMyPower commented on issue #7168: regex subscription not working for new topics in Python

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

BewareMyPower commented on issue #7168:
URL: https://github.com/apache/pulsar/issues/7168#issuecomment-640269322


   TL;DR It's because there's a deadlock in C++ client. I'll push a PR soon.
   
   Just because C++ stand library doesn't have something like `ConcurrentHashMap`, the current implementation used a `mutex_` to share a `std::map`.
   However, the `mutex_` is also acquired in `receive`, so if you called `receive`, the `mutex_` is acquired and held until a new message was pushed to the internal message queue. Then if the topic discovery timer found new topics, the callback to add new topics also needed to acquire the `mutex_`, which leads to a deadlock.
   
   The deadlock problem is similar to my PR before, see the change of `PartitionedConsumerImpl::receive` in #6732. 


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