MPI_Bcast 进入 while 循环

Question

我有这段代码：

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

struct fields{
  int hostNumber;
  int *numberArray;
}; 

struct fields *start(int);
struct fields *gatherData(int);

int main(int argc, char** argv) {
    int rank, size, count, *tmpArray, tmpNumOfArray;
     
    struct fields *myFields;      
    setbuf(stdout, NULL);        
    
    MPI_Init(&argc, &argv);
    MPI_Status status;
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &size);        
   
    while(1){            
        if (rank == 0){
            //printf("I am parent-process with rank = %d, size = %d\n", rank, size);
                     
            myFields = start(rank);
            //for (int i = 0 ; i < myFields->hostNumber ; i++) printf("%d\n",((myFields->numberArray)[i]));
                           
            if ((myFields->hostNumber) < size){
                printf("Error!!! Number of Processes is more than number of Elements.\n");
                MPI_Abort(MPI_COMM_WORLD, 0);  
            }

            if ((myFields->hostNumber) < (2 * size)){
                printf("Error!!! The Host of Numbers should be at least double of the number  of Processes!!!\n");
                MPI_Abort(MPI_COMM_WORLD, 0);  
            }
      
            tmpNumOfArray = myFields->hostNumber;
            MPI_Bcast(&tmpNumOfArray, 1, MPI_INT, 0, MPI_COMM_WORLD);
        }
        
        MPI_Barrier(MPI_COMM_WORLD);            
        printf("process = %d, tmpNumOfArray = %d\n", rank, tmpNumOfArray);
        sleep(5);    
    }
    
    MPI_Finalize(); 
    return 0;
}

struct fields *start(int rank){
  int input;
  struct fields *myFields;
  system("clear");
  printf("1) Type 1 For Execution\n");
  printf("2) Type 2 For Exit\n");
  printf("Give your choice:");     
  scanf("%d",&input);

  switch(input){
    case 1:
        myFields = gatherData(rank);
        break;
    case 2:
    default:
        MPI_Abort(MPI_COMM_WORLD, 0); 
}
  return myFields;
}

struct fields *gatherData(int rank){
int host;
struct fields *myFields;

myFields = (struct fields *)malloc(sizeof(struct fields));    
if (myFields == NULL){
    printf("Cannot allocate memory for myFields struct!\n");
    MPI_Abort(MPI_COMM_WORLD, 0);     
}

if (rank == 0){
    printf("Give the host of the numbers to be statically checked: ");
    scanf("%d",&host);

    int *nmbArray = (int *)malloc(sizeof(nmbArray) * host);   
    for (int i = 0; i < host; i++){
        printf("Give the %d number:", i);
        scanf("%d", (&(nmbArray[i])));
    }  
    
    myFields->hostNumber = host;
    myFields->numberArray = &nmbArray[0];
}
  return myFields;      
}

当我运行它时，我得到以下信息：

process = 2, tmpNumOfArray = 0
process = 0, tmpNumOfArray = 10
process = 1, tmpNumOfArray = 0
process = 3, tmpNumOfArray = 0

我是什么：

process = 2, tmpNumOfArray = 10
process = 0, tmpNumOfArray = 10
process = 1, tmpNumOfArray = 10
process = 3, tmpNumOfArray = 10

有什么建议吗？不要专注于 gatherData() 和 start() 函数，因为它们运行完美，问题在于 main() 到 MPI_Bcast() 函数。我也试过 MPI_COMM_SPAWN 但我认为它不能从父母广播给孩子。 先谢谢了！！！

Answer 1

MPI_Bcast

将消息从具有“root”等级的进程广播到所有其他进程 沟通者的进程

MPI_Bcast 广播例程是集体通信。 Hence:

集体沟通是一种沟通方式，它涉及 一个通信器中所有进程的参与。

您的代码的问题是只有rank=0 的进程正在调用MPI_Bcast；相反，所有涉及的进程也应该调用该 MPI 例程。

通过相应地移动该调用来修复您的代码，即：

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

struct fields{
  int hostNumber;
  int *numberArray;
}; 

struct fields *start(int);
struct fields *gatherData(int);

int main(int argc, char** argv) {
    int rank, size, count, *tmpArray, tmpNumOfArray;
     
    struct fields *myFields;      
    setbuf(stdout, NULL);        
    
    MPI_Init(&argc, &argv);
    MPI_Status status;
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &size);        
   
    while(1){            
        if (rank == 0)
        {          
            myFields = start(rank);
            if ((myFields->hostNumber) < size){
                printf("Error!!! Number of Processes is more than number of Elements.\n");
                MPI_Abort(MPI_COMM_WORLD, 0);  
            }

            if ((myFields->hostNumber) < (2 * size)){
                printf("Error!!! The Host of Numbers should be at least double of the number  of Processes!!!\n");
                MPI_Abort(MPI_COMM_WORLD, 0);  
            }
            tmpNumOfArray = myFields->hostNumber;
        }
        
        MPI_Bcast(&tmpNumOfArray, 1, MPI_INT, 0, MPI_COMM_WORLD); // Move this part
        MPI_Barrier(MPI_COMM_WORLD);            
        printf("process = %d, tmpNumOfArray = %d\n", rank, tmpNumOfArray);
        sleep(5); 
    }
    
    MPI_Finalize(); 
    return 0;
}

struct fields *start(int rank){
  int input;
  struct fields *myFields;
  system("clear");
  printf("1) Type 1 For Execution\n");
  printf("2) Type 2 For Exit\n");
  printf("Give your choice:");     
  scanf("%d",&input);

  switch(input){
    case 1:
        myFields = gatherData(rank);
        break;
    case 2:
    default:
        MPI_Abort(MPI_COMM_WORLD, 0); 
  }
  return myFields;
}

struct fields *gatherData(int rank){
int host;
struct fields *myFields;

myFields = (struct fields *)malloc(sizeof(struct fields));    
if (myFields == NULL){
    printf("Cannot allocate memory for myFields struct!\n");
    MPI_Abort(MPI_COMM_WORLD, 0);     
}

if (rank == 0){
    printf("Give the host of the numbers to be statically checked: ");
    scanf("%d",&host);

    int *nmbArray = (int *)malloc(sizeof(nmbArray) * host);   
    for (int i = 0; i < host; i++){
        printf("Give the %d number:", i);
        scanf("%d", (&(nmbArray[i])));
    }  
    
    myFields->hostNumber = host;
    myFields->numberArray = &nmbArray[0];
}
  return myFields;      
}