Github user MLnick commented on a diff in the pull request: https://github.com/apache/spark/pull/16774#discussion_r110606615 --- Diff: mllib/src/main/scala/org/apache/spark/ml/tuning/ValidatorParams.scala --- @@ -67,6 +71,39 @@ private[ml] trait ValidatorParams extends HasSeed with Params { /** @group getParam */ def getEvaluator: Evaluator = $(evaluator) + /** + * param to control the number of models evaluated in parallel + * Default: 1 + * + * @group param + */ + val numParallelEval: IntParam = new IntParam(this, "numParallelEval", + "max number of models to evaluate in parallel, 1 for serial evaluation", + ParamValidators.gtEq(1)) + + /** @group getParam */ + def getNumParallelEval: Int = $(numParallelEval) + + /** + * Creates a execution service to be used for validation, defaults to a thread-pool with + * size of `numParallelEval` + */ + protected var executorServiceFactory: (Int) => ExecutorService = { + (requestedMaxThreads: Int) => ThreadUtils.newDaemonCachedThreadPool( + s"${this.getClass.getSimpleName}-thread-pool", requestedMaxThreads) + } + + /** + * Sets a function to get an execution service to be used for validation + * + * @param getExecutorService function to get an ExecutorService given a requestedMaxThread size + */ + @Experimental + @InterfaceStability.Unstable + def setExecutorService(getExecutorService: (Int) => ExecutorService): Unit = { --- End diff -- I think I prefer a simpler API: ```scala def setExecutorService(executorService: ExecutorService): Unit = { ``` Not sure the function version will work nicely with Java. I think the idea should be that setting `numParallelEval` will specify the number of threads for the default thread-pool, while a custom one can be set with this method (advanced usage). If set, the custom one will override.
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