Артем

• Скачайте в другую директорию Play! версии: 1.2.7 (возможно у Вас какие нет каких-то библиотек )
  
• Создайте голый проект и настройте его по документации
  

def index(client: String, /* other params*/) = Action {....}

import java.util.concurrent.*;

class CMatrix {

    private double det = 0;

    int availableProcessors = Runtime.getRuntime().availableProcessors();
    ExecutorService executorService = Executors.newFixedThreadPool(availableProcessors);

    public void callback(Double[][] A, int N, Double[][] m, int j1) throws InterruptedException {
        det += Math.pow(-1.0, 1.0 + j1 + 1.0) * A[0][j1] * determinant(m, N - 1, false);
    }

    /**
     * 
     * @param A
     * @param N
     * @param isMain - if true then shutdown and await all threads
     * return
     * @throws InterruptedException
     */
    public double determinant(Double A[][], int N, boolean isMain) throws InterruptedException {
        //todo: if N=0
        if (N == 1) {
            det = A[0][0];
        } else if (N == 2) {
            det = A[0][0] * A[1][1] - A[1][0] * A[0][1];
        } else {
            for (int j1 = 0; j1 < N; j1++) {
                Calculate calculate = new Calculate(A, N, j1);
//                calculate.setcMatrix(this); //todo: you may call callback from other thread
                Future<Double[][]> result = executorService.submit(calculate);
                try {
                    callback(A, N, result.get(10, TimeUnit.SECONDS), j1);
                } catch (InterruptedException | ExecutionException | TimeoutException e) {
                    e.printStackTrace();
                }
            }
        }
        if (isMain) {
            executorService.shutdown(); //it just signal. System will wait for all task completed.
            executorService.awaitTermination(60, TimeUnit.MINUTES);
        }
        return det;
    }
}

class Calculate implements Callable<Double[][]> {

    private int N;

    private Double[][] A;

    private int j1;

    public Calculate(Double[][] a, int n, int j1) {
        N = n;
        A = a;
        this.j1 = j1;
    }

    private CMatrix cMatrix;

    public void setcMatrix(CMatrix cMatrix) {
        this.cMatrix = cMatrix;
    }

    public CMatrix getcMatrix() {
        return cMatrix;
    }

    @Override
    public Double[][] call() throws Exception {
        Double[][] m = new Double[N - 1][];
        for (int i = 1; i < N; i++) {//-----Надо это организовать в потоке
            int j2 = 0;
            for (int j = 0; j < N; j++) {
                if (j == j1)
                    continue;
                m[i - 1][j2] = A[i][j];
                j2++;
            }
        }
        return m;
    }
}