Question

我试图以并行方式生成导数矩阵。我有整个热方程求解器使用两个线程，但现在我试图找出如何将底行发送到下一个等级的rec2，并将顶行发送到前一个等级的rec1。我试图在请求矩阵中使用数字，但没有任何效果。出于某种原因，我被告知，通过iSend，两个不同的接收器具有相同的请求。

任何修复此问题的建议或帮助我更好地理解这一点都会很棒。

  double** change = alloc(sizeX,sizeY); 
  double*    rec1;
  double*    rec2;
  int rank,size;
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  MPI_Comm_size(MPI_COMM_WORLD, &size);
  MPI_Request req[4];


  if(rank != 0)
  {
    rec1 = calloc(sizeY,sizeof(double));
  }
  if(rank != size-1)
  {
    rec2 = calloc(sizeY,sizeof(double));
  }

  if ( rank == 0 )
  {
    MPI_Irecv(rec2, sizeY, MPI_DOUBLE, rank+1, 1244, MPI_COMM_WORLD, &req[1]);
    MPI_Isend(u[sizeX-1], sizeY, MPI_DOUBLE, rank+1, 1244, MPI_COMM_WORLD, &req[0]);
  }
  else if ( rank == size-1 )
  {
    MPI_Irecv(rec1, sizeY, MPI_DOUBLE, rank - 1, 1244, MPI_COMM_WORLD, &req[2]);
    MPI_Isend(u[0], sizeY, MPI_DOUBLE, rank - 1, 1244, MPI_COMM_WORLD, &req[3]);
  }
  else if ( rank != 0 && rank != size -1)
  {
    MPI_Irecv(rec1, sizeY, MPI_DOUBLE, rank-1, 1234, MPI_COMM_WORLD, &req[1]);
    MPI_Isend(u[0], sizeY, MPI_DOUBLE, rank-1, 1234, MPI_COMM_WORLD, &req[0]);

    MPI_Irecv(rec2, sizeY, MPI_DOUBLE, rank+1, 1234, MPI_COMM_WORLD, &req[2]);
    MPI_Isend(u[sizeX-1], sizeY, MPI_DOUBLE, rank+1, 1234, MPI_COMM_WORLD, &req[3]);

  }
  // setting elements of most of the points

  int xStart = 1;
  int xBound = sizeX-1;

  for(int x = xStart; x < xBound; x++)
  { 
    for(int y = 1; y < sizeY-1; y++)
    {
      change[x][y] = fpp(u[x-1][y],u[x][y],u[x+1][y],dx)
      + fpp(u[x][y-1],u[x][y],u[x][y+1],dx);
    }
  }

  MPI_Waitall(size+1,req,MPI_STATUSES_IGNORE );

Answer 1

观察请求数量及其开始！ rank 0和rank size-1处理2条消息，而其他处理4条消息。这可能会导致MPI_Waitall（）出现问题。并且rank size-1不初始化req [0]和req [1]

使用@JonathanDursi的reqcnt技巧：

 int nbreq=0;
 if(rank!=0 && size>1){
   MPI_Irecv(rec1, sizeY, MPI_DOUBLE, rank - 1, 1244, MPI_COMM_WORLD, &req[nbreq]);
   nbreq++;
   MPI_Isend(u[0], sizeY, MPI_DOUBLE, rank - 1, 1244, MPI_COMM_WORLD, &req[nbreq]);
   nbreq++;
 }
 if(rank!=size-1){
   MPI_Irecv(rec2, sizeY, MPI_DOUBLE, rank+1, 1244, MPI_COMM_WORLD, &req[nbreq]);
   nbreq++;
   MPI_Isend(u[sizeX-1], sizeY, MPI_DOUBLE, rank+1, 1244, MPI_COMM_WORLD, &req[nbreq]);
   nbreq++;
 }
 ...
 MPI_Waitall(nbreq,req,MPI_STATUSES_IGNORE );

使用带有ISend和IRecv的三个线程使用MPI发送消息

1 个答案: