[GitHub] [incubator-pekko] jrudolph commented on pull request #408: =str Make use of ConcurrentHashMap instead of List to reduce contention.

["jrudolph (via GitHub)" <gi...@apache.org>]

jrudolph commented on PR #408:
URL: https://github.com/apache/incubator-pekko/pull/408#issuecomment-1674413926

   Yes, this was originally a performance improvement. Regardless of that fact, let's not just merge changes in performance critical code without running benchmarks or discussing arguments why they can be omitted.
   
   It has been a long time since I worked on this / proposed the change (almost 3 years... oh my). I guess in this case, it's fine, it seems after all they ran some benchmarks in Akka to validate it does not introduce obvious performance regressions.
   
   > I'm a bit confused as to the use of `AtomicReference[mutable.Map]` instead of just plain `mutable.Map`.
   
   The comment at its declaration explains it. There's a race condition between scheduling an async callback (i.e. an incoming external event into the stream) and shutting down a stream. The atomic reference makes sure, that we will report feedback to the async callback reliably even if it raced against shutdown (this is basically what this whole feature is about).


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