OptaPlanner Multithreading: Can I retrieve internally resolved “moveThreadCount” for reproducibility?

OptaPlanner v8.0.0.Final

I want to set my OptaPlanner engine configs’ moveThreadCounts to AUTO, but I need to be able to reproduce runs even if it means I must take the moveThreadCount value from the logs/stdout/whatever (that is the plan).

I see the value is resolved in DefaultSolverFactory::buildSolver line 82:

Integer moveThreadCount_ = new MoveThreadCountResolver().resolveMoveThreadCount(solverConfig.getMoveThreadCount());

This value is then saved to a HeuristicConfigPolicy on line 90 of the same file, but I cannot figure out a way to get the HeuristicConfigPolicy instance, let alone the moveThreadCount.

I could, of course, copy-paste MoveThreadCountResolver::resolveMoveThreadCount, as it is not public but, even if it was public or I did copy-paste, Runtime.getRuntime().availableProcessors() is not guaranteed to return the same result on every call.

Thoughts?

I suppose quick-and-dirty solution is to just manually determine what moveThreadCount (via copy-paste, my own alg., etc.) to use and then do `SolverConfig::setMoveThreadCount’.

Thanks!

Answer

Casting the Solver to DefaultSolver won’t work, because there is no getter for moveThreadCountDescription. Alternatively, going into the CH/LS to detect the Decider implementation is just asking for trouble.

I am less and less recommending people to use AUTO, mainly because currently (in 8.5 and lower) you can have too many threads (8 threads giving worse results than 4 threads due to congestion). That will be fixed in a future version.

So, yes, don’t use AUTO and determine the moveThreadCount yourself based on Runtime.getRuntime().availableProcessors() and pass that along through SolverConfig::setMoveThreadCount.