[PR] [FIX] IMAP execution management [james-project]

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

chibenwa opened a new pull request, #2090:
URL: https://github.com/apache/james-project/pull/2090

   That is my best shot at explaining:
   
   ```
   java.lang.NullPointerException: Cannot invoke "org.apache.james.imap.api.process.SelectedMailbox.existsCount()" because "selected" is null
   ```
   
   CF https://github.com/linagora/james-project/issues/4688 which was mostly fixed incorrectly...
   
   The Netty stack enforce linearisability of operation conducted on the event loop for a single channel, including command decoding.
   
   For command execution, we trigger the processing only reactor. We rely on a linarizer to enforce sequential IMAP execution.
   
   So in theory we do never execute two IMAP commands of a given connection at the same time.
   
   However no mechanism prevents decoding at the same time than command execution - and that is fine - however the channel operations (inactive, idle, parsing failures) MAY interfere with command execution by deciding a logout eventually deselecting the current mailbox and resulting in the NPE.
   
   Lessons learned: always cancel current command execution before deciding to log out!
   
   That, and we were executing blocking code onto the netty event loop which IS BAD.


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Re: [PR] [FIX] IMAP execution management [james-project]

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

Arsnael merged PR #2090:
URL: https://github.com/apache/james-project/pull/2090


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