typelevel / typelevel/fs2

Topic subscribers observe different order of messages on concurrent publishers

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bug
Dominant language
Scala
Stars
2.5k
Forks
636
Avg merge
2d 4h
Merged PRs (30d)
7

Description

Even though the order of messages is non-deterministic for concurrent publishers, all subscribers should receive messages in the same order, as arbitrated by the Topic.

PR with a failing test: https://github.com/typelevel/fs2/pull/3647

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the failing test in PR #3647 and the Topic implementation it exercises. Reproduce the test to observe differing subscriber order, then trace how Topic arbitrates concurrent publishers. Done means all subscribers observe the same arbitrated order and the regression test passes.

Written by the indexing model from the issue text.

Assessment

Tech stack
scala
Domain
stream-processing
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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