ParallelPiEstimator.java

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.*;

public class ParallelPiEstimator implements PiEstimator {

    @Override
    public double estimatePi(SimulationConfig config) {
        int numThreads = config.getNumThreads();
        int numTasks = config.getNumTasks();
        long totalPoints = config.getTotalPoints();


        long pointsPerTask = totalPoints / numTasks;

        ExecutorService executor = Executors.newFixedThreadPool(numThreads);
        List<Future<Long>> results = new ArrayList<>();

        // Create and submit tasks
        for (int i = 0; i < numTasks; i++) {
            Callable<Long> task = new MonteCarloTask(pointsPerTask);
            results.add(executor.submit(task));
        }

        long totalHits = 0;

        try {
            // Aggregate results
            for (Future<Long> future : results) {
                totalHits += future.get();
            }
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        } finally {
            executor.shutdown();
        }

        return 4.0 * totalHits / (pointsPerTask * numTasks);
    }

    // Inner Callable Task
    private static class MonteCarloTask implements Callable<Long> {
        private final long pointsToSimulate;

        public MonteCarloTask(long pointsToSimulate) {
            this.pointsToSimulate = pointsToSimulate;
        }

        @Override
        public Long call() {
            long hits = 0;
            ThreadLocalRandom random = ThreadLocalRandom.current();

            for (long i = 0; i < pointsToSimulate; i++) {
                double x = random.nextDouble();
                double y = random.nextDouble();

                if ((x * x) + (y * y) <= 1.0) {
                    hits++;
                }
            }
            return hits;
        }
    }
}