c-对结构数组执行MPI send/recv的正确方法

Question

我已经用树莓pis建立了一个四节点mpi集群。据我所知，我只关注最后一个主要问题，那就是如何将每个工人的结构数组发送给经理。我已经将代码裁剪到下面，但这可能需要几次尝试，因为我可能裁剪得太多了。尽管如此，我仍然会遇到同样的错误(seg错误，表示地址未映射(，但如果有一点第四和第四个错误，我很抱歉。

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <mpi.h>
struct ticknrank
{
char * ticker;
int errors;
int rank;
};
int main() //Designed for one master, three slaves
{
// i am under the impression the problem lies somewhere in this beginning section, before the commit.
int my_id;
MPI_Init(NULL,NULL);
MPI_Comm_rank(MPI_COMM_WORLD, &my_id);
MPI_Status status;
MPI_Datatype types[3] = {MPI_CHAR,MPI_INT,MPI_INT};
MPI_Datatype MPI_ticknrank, MPI_tmp;
int blocklengths[3] ={8,1,1};
MPI_Aint offsets[3];
offsets[0] = offsetof(struct ticknrank,ticker);
offsets[1] = offsetof(struct ticknrank,errors);
offsets[2]= offsetof(struct ticknrank,rank);
MPI_Aint lb, extent;
MPI_Type_create_struct(3,blocklengths, offsets, types, &MPI_tmp);
MPI_Type_get_extent(MPI_tmp, &lb, &extent);
MPI_Type_create_resized(MPI_tmp, lb, extent, &MPI_ticknrank);
MPI_Type_commit(&MPI_ticknrank);
//  NOTE: sizeof(ticknrank) = 12, while MPI_Type_size(ticknrank) = 16. Not sure what to do about that.
if(my_id == 0) // meaning this process is a host job
{
//NOTE: NodethrRes and fou can be ommitted, I was just lazy and didn't wanna delete them
//on my cluster.
int length = 2;
struct ticknrank * NodeTwoRes = (struct ticknrank *)malloc(length * sizeof(struct ticknrank));
struct ticknrank * NodeThrRes = (struct ticknrank *)malloc(length * sizeof(struct ticknrank));
struct ticknrank * NodeFouRes = (struct ticknrank *)malloc(length * sizeof(struct ticknrank));

MPI_Recv(NodeTwoRes, length, MPI_ticknrank,1,MPI_ANY_TAG, MPI_COMM_WORLD, &status);
MPI_Recv(NodeThrRes, length, MPI_ticknrank,2,MPI_ANY_TAG, MPI_COMM_WORLD, &status);
MPI_Recv(NodeFouRes, length, MPI_ticknrank,3,MPI_ANY_TAG, MPI_COMM_WORLD, &status);
printf("%sn", NodeTwoRes[0].ticker);

}
else
{
int myLen = 2;
struct ticknrank * results = malloc(myLen * sizeof(struct ticknrank));
results[0].ticker = strdup("FIRST");
results[0].rank = 4;
results[0].errors = 7;
results[1].ticker = strdup("SECON");
results[1].rank = 3;
results[1].errors = 15;
MPI_Send(results,myLen,MPI_ticknrank,0,1,MPI_COMM_WORLD);
}
MPI_Type_free(&MPI_ticknrank);
MPI_Finalize();
return 0;
}

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Answer 1

C结构是char * ticker(如果运行32位，则为4字节(，但派生的数据类型是char ticker[8]，实际上是8字节。

如果您想在一个快照中发送多个struct ticknrank，那么数据应该在连续内存中，这意味着从char * ticker移动到char ticker[8]，并用strcpy()替换strdup()(由您来确保没有缓冲区溢出(。