MPI - 发送数组的片段

Question

所以我有一个双打数组。我希望每5分钟发送一次，以便接收进程。所以基本上，我需要一种发送特定双打的方式，在它们之间迈进。除了将双打存储到发送缓冲区之外，是否有这样的功能？制作我自己的派生类型会更好吗？

Answer 1

您应该创建一个MPI数据类型;它给人的MPI库的机会，以避免额外的副本从数组编组，这是非常简单的使用做，在这种情况下，MPI_Type_vector()：

#include <stdio.h> 
#include <stdlib.h> 
#include <mpi.h> 

int main(int argc, char** argv) 
{ 
    int size, rank; 
    const int bigsize=50; 
    const int stride = 5; 
    const int count = (bigsize + stride - 1)/stride; 

    const int sender = 0; 
    const int receiver = 1; 
    const int mytag = 1; 

    MPI_Init(&argc,&argv); 
    MPI_Comm_size(MPI_COMM_WORLD,&size); 
    MPI_Comm_rank(MPI_COMM_WORLD,&rank); 

    if (size < 2) { 
     fprintf(stderr,"%s: Require at least two processors.\n", argv[0]); 
     MPI_Finalize(); 
     exit(-1); 
    } 


    if(rank == sender) 
    { 
     double bigarray[bigsize]; 
     for (int i=0; i<bigsize; i++) 
      bigarray[i] = 0.; 

     for (int i=0; i<bigsize; i+=stride) 
      bigarray[i] = i/stride; 

     printf("[%d]: ", rank); 
     for (int i=0; i<bigsize; i++) 
      printf("%lf ", bigarray[i]); 
     printf("\n"); 

     MPI_Datatype everyfifth; 

     MPI_Type_vector(count, 1, stride, MPI_DOUBLE, &everyfifth); 
     MPI_Type_commit(&everyfifth); 

     MPI_Send(bigarray, 1, everyfifth, receiver, mytag, MPI_COMM_WORLD); 

     MPI_Type_free(&everyfifth); 
    } 
    else if(rank == receiver) 
    { 
     double littlearray[count]; 

     MPI_Status status; 

     MPI_Recv(littlearray, count, MPI_DOUBLE, sender, mytag, 
        MPI_COMM_WORLD, &status); 

     printf("[%d]: ", rank); 
     for (int i=0; i<count; i++) 
      printf("%lf ", littlearray[i]); 
     printf("\n"); 
    } 

    MPI_Finalize(); 

    return 0; 
} 

编译和运行提供了

$ mpicc -o vector vector.c -std=c99 
$ mpirun -np 2 ./vector 
[0]: 0.000000 0.000000 0.000000 0.000000 0.000000 1.000000 0.000000 0.000000 0.000000 0.000000 2.000000 0.000000 0.000000 0.000000 0.000000 3.000000 0.000000 0.000000 0.000000 0.000000 4.000000 0.000000 0.000000 0.000000 0.000000 5.000000 0.000000 0.000000 0.000000 0.000000 6.000000 0.000000 0.000000 0.000000 0.000000 7.000000 0.000000 0.000000 0.000000 0.000000 8.000000 0.000000 0.000000 0.000000 0.000000 9.000000 0.000000 0.000000 0.000000 0.000000 
[1]: 0.000000 1.000000 2.000000 3.000000 4.000000 5.000000 6.000000 7.000000 8.000000 9.000000