[PR] fix(test): pin minimum-runnable=-1 in ForkJoinExecutorConfiguratorSpec auto fixtures [pekko]

["He-Pin (via GitHub)" <gi...@apache.org>]

He-Pin opened a new pull request, #2894:
URL: https://github.com/apache/pekko/pull/2894

   ## Motivation
   
   The nightly build (run [24853126603](https://github.com/apache/pekko/actions/runs/24853126603/job/72758762338)) is red on the JDK 21 / Scala 2.13.x and JDK 25 jobs with two failures in `ForkJoinExecutorConfiguratorSpec`:
   
   ```
   - must keep the legacy value of 1 on JDK < 25 when the default is left untouched *** FAILED ***
     4 was not equal to 1 (ForkJoinExecutorConfiguratorSpec.scala:167)
   - must never drop below 1 even for parallelism = 1 dispatchers *** FAILED ***
   ```
   
   Both come from the same root cause introduced when the spec was added in #2890.
   
   ## Root cause
   
   The two `fj-auto-*` fixtures left `minimum-runnable` unset, expecting the reference.conf default (`-1`, which selects the JDK-aware auto policy). But the nightly workflow pins it via `-D` for JDK 21+ runs ([nightly-builds.yml](https://github.com/apache/pekko/blob/main/.github/workflows/nightly-builds.yml#L160-L162)) for stability:
   
   ```yaml
   if [ "${{ matrix.javaVersion }}" -ge 21 ]; then
     EXTRA_JVM_OPTS="-Dpekko.actor.default-dispatcher.fork-join-executor.minimum-runnable=4 ..."
   fi
   ```
   
   `Dispatchers.config(id)` resolves a dispatcher's config via:
   
   ```
   idConfig(id) → appConfig → nameConfig → defaultDispatcherConfig
   ```
   
   `defaultDispatcherConfig` carries the `pekko.actor.default-dispatcher` values, including any `-D` overrides. So when the spec's `fork-join-executor` block omits `minimum-runnable`, the fallback chain feeds the CI's pinned `4` into `config.getInt("minimum-runnable")` for the auto fixtures, and `resolveMinimumRunnable(4, _, _)` honours it verbatim → `4 != 1`.
   
   ## Modification
   
   Set `minimum-runnable = -1` explicitly in `fj-auto-default-dispatcher` and `fj-auto-small-dispatcher` so the spec always exercises the auto policy regardless of surrounding `-D` pins. The two `fj-explicit-*` fixtures already pin a value and remain unchanged.
   
   ## Result
   
   - Two failing nightly assertions go green again.
   - The CI `-D` pin keeps doing its production-stability job — only the spec is hardened.
   - Tested locally with `sbt actor-tests/testOnly org.apache.pekko.dispatch.ForkJoinExecutorConfiguratorSpec -Dpekko.actor.default-dispatcher.fork-join-executor.minimum-runnable=4` (reproduces the CI environment): all 11 tests pass (1 pending on JDK 25 as designed).


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Re: [PR] fix(test): pin minimum-runnable=-1 in ForkJoinExecutorConfiguratorSpec auto fixtures [pekko]

["He-Pin (via GitHub)" <gi...@apache.org>]

He-Pin merged PR #2894:
URL: https://github.com/apache/pekko/pull/2894


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