c++ - 如何使用 MPI_Sendrecv 进行矩阵转置？

Question

我想使用 MPI_Sendrecv 执行矩阵转置，但在运行时，它等待并且程序没有结束。这是我的代码:

...

void sendrecvelem(int **A, int **R, int p, int elements, int part) {
  int i,j,c=0;
  for(i=1;i<p;i++) {
    for(j=0;j<part;j++) {
      MPI_Sendrecv(A[c*part], j, MPI_INT, i, j, &R[elements][c*part], j, MPI_INT, i, j, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
    }
    c++;
  }
}

int main(int argc, char ** argv) {
  MPI_Init(&argc, &argv);
  int p,id;
  MPI_Comm_size(MPI_COMM_WORLD, &p);
  MPI_Comm_rank(MPI_COMM_WORLD, &id);
  int ** data=NULL;
  int elements=10,i,j;
  int **A=NULL;
  int part=elements/(p-1);
  int **R=NULL;

  if(id == 0) {
    A = allocMatrix(elements,elements);
    R = allocMatrix(elements, elements);
    init(A,elements,elements);
    printelements(A, elements, elements);
    sendrecvelem(A, R, p, elements, part);
    printelements(R, elements, elements);
  }

  MPI_Finalize();
  return 0;
}

Answer 1

MPI_Sendrecv 是一个阻塞操作，只有总大小 p 中的 rank o 调用它，因此阻塞了应用程序。

MPI_Comm_rank(MPI_COMM_WORLD, &id);
if(id == 0) {
    A = allocMatrix(elements,elements);
    R = allocMatrix(elements, elements);
    init(A,elements,elements);
    printelements(A, elements, elements);

    sendrecvelem(A, R, p, elements, part);

    /* MPI_Sendrecv is called only by rank 0. Rank 0 sends part of array to next rank 
    and since MPI_Sendrecv is blocking, it waits for other process to receive data. 
    Since this entire function is only called by rank 0 (if(id == 0)), 
    the application will wait which is an expected behaviour in this case. */


    printelements(R, elements, elements);
  } else {
   /* one solution is to put an else block (which will be called by all prcess other than 0)
   and call MPI_Sendrecv */
   sendrecvelem(A, R, p, elements, part);

  }