Send over MPI_Bcast an MPI_PACKED message - c

Question

I have a message that I want to send in broadcast by using MPI_Bcast.
I have two structs with, near the others, dynamic arrays, and because of that I decided to use MPI_Pack and MPI_Unpack.
Here below my solution.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <mpi.h>
#include <stddef.h>
#define DEBUG 0
typedef struct Code {
char character;
int length;
char *code;
} Code;
typedef struct CodeDictionary {
int codesNr;
Code *codes;
} CodeDictionary;
typedef struct Header {
int size; // size of the message in bytes
MPI_Datatype *type; // message type
int position; // position in the buffer
} Header;
typedef unsigned char BYTE;
int getRand(const int from, const int to)
{
int num = (rand() % (to - from + 1)) + from;
return num;
}
void buildCodeDictionaryType(MPI_Datatype *CodeDictType) {
int blockLengths[] = {1, 1};
MPI_Datatype types[] = {MPI_CHAR, MPI_INT};
MPI_Aint offsets[2];
offsets[0] = offsetof(Code, character);
offsets[1] = offsetof(Code, length);
MPI_Type_create_struct(2, blockLengths, offsets, types, CodeDictType);
MPI_Type_commit(CodeDictType);
}
BYTE* buildCodeDictionaryMsg(Header *header, CodeDictionary *dict) {
header->size = sizeof(int);
BYTE *buffer = malloc(sizeof(BYTE) * (header->size));
MPI_Pack(&dict->codesNr, 1, MPI_INT, buffer, header->size, &header->position, MPI_COMM_WORLD);
if (DEBUG == 1) {
printf("\ndict->codesNr = %d\n", dict->codesNr);
printf("header->size = %d\n", header->size);
printf("header->position = %d\n\n", header->position);
}
for (int i = 0; i < dict->codesNr; i++) {
header->size += sizeof(char) + sizeof(int) + (sizeof(char) * (dict->codes[i].length+1));
buffer = realloc(buffer, header->size);
MPI_Pack(&dict->codes[i], 1, *header->type, buffer, header->size, &header->position, MPI_COMM_WORLD);
if (DEBUG == 1) {
printf("before pack array - header->size = %d\n", header->size);
printf("before pack array - header->position = %d\n", header->position);
}
MPI_Pack(dict->codes[i].code, (dict->codes[i].length+1), MPI_CHAR, buffer, header->size, &header->position, MPI_COMM_WORLD);
if (DEBUG == 1) {
printf("after pack array - header->size = %d\n", header->size);
printf("after pack array - header->position = %d\n", header->position);
printf("\n");
}
}
return buffer;
}
void buildCodeDictionary(Header *header, CodeDictionary *dict, BYTE* buffer) {
MPI_Unpack(buffer, header->size, &header->position, &dict->codesNr, 1, MPI_INT, MPI_COMM_WORLD);
if (DEBUG == 1) {
printf("dict->codesNr = %d\n", dict->codesNr);
printf("header->size = %d\n", header->size);
printf("header->position = %d\n\n", header->position);
}
dict->codes = malloc(sizeof(Code) * dict->codesNr);
// I do it just for the first element because of test
MPI_Unpack(buffer, header->size, &header->position, &dict->codes[0], 1, *header->type, MPI_COMM_WORLD);
if (DEBUG == 1) {
printf("before unpack - header->size = %d\n", header->size);
printf("before unpack - header->position = %d\n", header->position);
}
dict->codes[0].code = malloc(sizeof(char) * (dict->codes[0].length+1));
MPI_Unpack(buffer, header->size, &header->position, &dict->codes[0].code, (dict->codes[0].length+1), MPI_CHAR, MPI_COMM_WORLD);
if (DEBUG == 1) {
printf("after unpack - header->size = %d\n", header->size);
printf("after unpack - header->position = %d\n", header->position);
}
// just for test
printf("character: %c\tlength: %d\tcode: ",
dict->codes[0].character,
dict->codes[0].length);
printf("%s\n", dict->codes[0].code); // it crashes here
// if it works do a for in order to unpack all the data
// ...
}
int main(int argc, char** argv) {
MPI_Init(NULL, NULL);
// Get the number of processes
int world_size;
MPI_Comm_size(MPI_COMM_WORLD, &world_size);
// Get the rank of the process
int world_rank;
MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);
// Create a CodeDictionary variable
CodeDictionary dict;
if (world_rank == 0)
printf("sending\n\n");
if (world_rank == 0) {
dict.codesNr = getRand(5, 9);
dict.codes = malloc(sizeof(Code) * dict.codesNr);
// create some fake values
for (int i = 0; i < dict.codesNr; i++) {
dict.codes[i].character = 'a' + i;
dict.codes[i].length = getRand(1, 9);
dict.codes[i].code = malloc(sizeof(char) * (dict.codes[i].length+1));
for (int j = 0; j < dict.codes[i].length; j++) {
int randChar = getRand('a', 'z');
dict.codes[i].code[j] = randChar + j;
}
dict.codes[i].code[dict.codes[i].length] = '\0';
if (DEBUG == 1)
printf("strlen(dict.charEncoding[%d].encoding): %d\n", i, strlen(dict.codes[i].code));
}
printf("source data\n");
for (int i = 0; i < dict.codesNr; i++) {
printf("codes[%d]:\n\t", i);
printf("character: %c\tlength: %d\tcode: ", dict.codes[i].character, dict.codes[i].length);
for (int j = 0; j < dict.codes[i].length; j++)
printf("%c", dict.codes[i].code[j]);
printf("\n");
}
}
MPI_Datatype codeDictType;
buildCodeDictionaryType(&codeDictType);
Header header = {.size = 0, .position = 0, .type = NULL};
header.type = &codeDictType;
BYTE *buffer = NULL;
if (world_rank == 0)
buffer = buildCodeDictionaryMsg(&header, &dict);
MPI_Bcast(&header.size, 1, MPI_INT, 0, MPI_COMM_WORLD);
if (DEBUG == 1)
printf("rank %d: header.size = %d\n", world_rank, header.size);
if (world_rank != 0)
buffer = calloc(header.size, sizeof(BYTE));
MPI_Bcast(buffer, header.size, MPI_PACKED, 0, MPI_COMM_WORLD);
if (world_rank != 0) {
printf("\nreceiving\n\n");
buildCodeDictionary(&header, &dict, buffer);
// printf("received data\n");
// for (int i = 0; i < dict.codesNr; i++) {
// printf("codes[%d]:\n\t", i);
// printf("character: %c\tlength: %d\tcode: ", dict.codes[i].character, dict.codes[i].length);
// for (int j = 0; j < dict.codes[i].length; j++)
// printf("%c", dict.codes[i].code[j]);
// printf("\n");
// }
}
free(buffer);
MPI_Type_free(&codeDictType);
for (int i = 0; i < dict.codesNr; i++)
free(dict.codes[i].code);
free(dict.codes);
MPI_Finalize();
return 0;
}
For some reason this line of code doesn't work MPI_Unpack(buffer, header->size, &header->position, &dict->codes[0].code, (dict->codes[0].length+1), MPI_CHAR, MPI_COMM_WORLD); because if I try to print the received array, the run crashes with segmentation fault as error.
I don't understand why it happens, I take care of the memory by allocating the right size, \0 character included.
Do you know what is the problem?