OptaPlanner threads are not getting released in SpringBoot application

Question

We are using OptaPlanner(8.2.0) library in Spring Boot to solve knapsack problem using construction heuristic algorithm. While running the application we observed that threads created by SolverManager are not getting released even after solving the problem. Because of that, performance of the application starts degrading after some time. Also, solver manager starts responding slowly of the increased thread count.

We also tried with latest version(8.17.0) but issue still persist.

Termination conditions:

<termination>
        <millisecondsSpentLimit>200</millisecondsSpentLimit>
</termination>

optaplanner:
  solver:
    termination:
      best-score-limit: 0hard/*soft

Code:

@Component
@Slf4j
public class SolutionManager {
    private final SolverManager<Solution, String> solutionManager;

    public SolutionManager(SolverManager<Solution, String> solutionManager) {
        this.solutionManager = solutionManager;
    }

    public Solution getSolutionResponse(String solutionId, Solution unsolvedProblem)
            throws InterruptedException, ExecutionException {
        SolverJob<Solution, String> solve = solutionManager.solve(solutionId, unsolvedProblem);
        Solution finalBestSolution = solve.getFinalBestSolution();

        return finalBestSolution;
    }
}

Thread metrics:

Answer 1

I wasn't able to reproduce the problem; after a load represented by solving several datasets in parallel, the number of threads drops back to the same value as before the load started.

The chart you shared doesn't clearly suggest there is a thread leak either; if you take a look at ~12:40 PM and compare it with ~2:00 PM, the number of threads actually did decrease.

Let me also add that the getFinalBestSolution() method actually blocks the calling thread until the solver finishes. If you instead use solve(ProblemId_ problemId, Solution_ problem, Consumer<? super Solution_> finalBestSolutionConsumer), this method returns immediately and the Consumer you provide is called when the solver finishes.

Answer 2

It looks like you might not be using OptaPlanner Spring Boot Starter.

If that's the case, upgrade to a recent version of OptaPlanner and add a dependency to optaplanner-spring-boot-starter. See the docs spring quickstart and the optaplanner-quickstarts repository (in the directory technology) for an example how to use it.