8000 testForkedParallel does not behave the same as parallelExecution · Issue #8004 · sbt/sbt · GitHub
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testForkedParallel does not behave the same as parallelExecution #8004

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matthughes opened this issue Jan 10, 2025 · 0 comments
Open

testForkedParallel does not behave the same as parallelExecution #8004

matthughes opened this issue Jan 10, 2025 · 0 comments
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@matthughes
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steps

Configure a project to run its forked tests in parallel:

    fork                          := true,
    testForkedParallel            := true,

problem

When running non-forked tests in parallel the use of concurrent restrictions limits the number of in-flight tests:

concurrentRestrictions := Seq(Tags.limit(Tags.All, 2))

However, when running forked tests, SBT uses the number of cores available to the machine:

See ForkMain.scala

    private ExecutorService executorService(
        final ForkConfiguration config, final ObjectOutputStream os) {
      if (config.isParallel()) {
        final int nbThreads = Runtime.getRuntime().availableProcessors();
        logDebug(os, "Create a test executor with a thread pool of " + nbThreads + " threads.");
        // more options later...
        // TODO we might want to configure the blocking queue with size #proc
        return Executors.newFixedThreadPool(nbThreads);
      } else {
        logDebug(os, "Create a single-thread test executor");
        return Executors.newSingleThreadExecutor();
      }
    }

expectation

testForkedParallel should use the same concurrentRestrictions mechanism to limit the number of in-flight tests OR provide some other setting. (e.g., testForkedParallism := 2).

notes

There is a workaround for this which is configuring the number of cores exposed to the JVM via javaOptions:

    Test / javaOptions ++= 
      // Limit to two test threads
      Seq(
        "-XX:ActiveProcessorCount=2",
      )
@matthughes matthughes added the Bug label Jan 10, 2025
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