typelevel / typelevel/cats

`Eval` thread safety

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Dominant language
Scala
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Description

If we have an Eval like this:

val e = Eval.defer(Eval.always { println("foo") }).memoize

Accessing e.value concurrently from different threads sometimes prints foo twice. I'm not sure if Eval is supposed to be thread safe, but this seems like a bug.

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Research direction

Start by reproducing the reported concurrent accesses to the Eval entry point, especially e.value after Eval.defer(...).memoize. Read the Eval implementation and its existing concurrency-related tests, if present, to determine whether memoization is intended to be thread-safe. Done should establish the expected single-evaluation behavior and document or test the result.

Written by the indexing model from the issue text.

Assessment

Tech stack
scala
Domain
backend
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
35/100

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