如何使用线程数实现矩阵乘法

Question

无法实现具有特定线程数的矩阵乘法。

程序不会停止并显示

  

线程“ Thread-####”中的异常java.lang.NullPointerException

    public Matrix multiply(Matrix a, Matrix b) {
        if (a.cols() != b.rows()) {
          return null;
        }

        threads = new Thread[a.cols()][b.rows()];
        MatrixMultiplication[] vmmworker = new  MatrixMultiplication[this.numThreads];
                Thread[] vmmThreads = new Thread[this.numThreads];
                barriere = new CyclicBarrier(this.numThreads, new Runnable() {
                public void run() {


                }});
        Matrix c = new Matrix(a.rows(), b.cols());

        int n = a.cols();
        for (int f = 0; f < this.numThreads; f++) {
                    int blocksize = (int) Math.ceil((double) a.cols() / this.numThreads ) ;
                    int start = f * blocksize;
                    int end = Math.min((f+1)*blocksize, n);
                    for (int i = start; i < end; i++) {
                        for (int j = 0; j<b.cols(); j++) {
                            threads[i][j] = new Thread(new MatrixMultiplication(a,b,c,start,end));
                            threads[i][j].start();
                        }
                    }

                    vmmworker[f] = new MatrixMultiplication(a, b, c, start, end);
                    vmmThreads[f] = new Thread(vmmworker[f]);
                    vmmThreads[f].start();
    }

    public void run() {
        for (int i = start; i < end; i++) {
        for (int j = 0; j<b.cols(); j++) {
            for (int k = 0; k < a.cols(); k++) {
                double cij = c.get(i, j);
                double aik = a.get(i, k);
                double bkj = b.get(k, j);
                c.set(i, j, cij + aik  * bkj);
            }
        }
        try { barriere.await(); }
        catch (InterruptedException e) { e.printStackTrace(); }
        catch (BrokenBarrierException e) { e.printStackTrace(); }}

我想创建ijk循环，并以其开头和结尾。