Large Data Array MPI Send

Question

Send an array larger than 250 using send / recv the MPI. How should I proceed? With this kind of attribute it gives buffer error.

My arrays are text1, text2, Text3. Thanks =D

#include <stdio.h>
#include <mpi.h>
#include <time.h>
#include <math.h>
#include <string.h>
#define maxn 12000 //AoLéo
#include <stdlib.h>

int max(int a,int b);
int LongestCommonSubsequence(char text[]);


static char search[] = "ab"; //array que irá ser buscado nos arrays
static const char alphanum[]               ="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
int stringLength = sizeof(alphanum) - 1;



int max(int a,int b)
{
    return a>b?a:b;
}

   int LongestCommonSubsequence(char text[]){



    int Slength = strlen(search); //Procurado
    int Tlength = strlen(text); //Procura
    int iter,jter=0;


   int common[Slength+1][Tlength+1];


    for(iter=0; iter<=Slength; iter++){
            for(jter=0; jter<=Tlength; jter++){

                    if(iter == 0 || jter == 0){
                        common[iter][jter] = 0;
                    }

                    else if(search[iter-1] == text[jter-1] ){
                            common[iter][jter] = common[iter-1][jter-1] + 1;
                    }
                    else{
                            common[iter][jter]= max(common[iter][jter-1],common[iter-1][jter]);


                    }

            }
    }


 return common[Slength][Tlength];

}



 main(int argc, char **argv)
{   
double startwtime = 0.0, endwtime; //var de tempo de execução
int id;//id : Rank de um processo
int p;//p : Numero de Processos


char texto1[maxn];
char texto2[maxn];
char texto3[maxn];



    //Inicializa os processos.
MPI_Init(&argc,&argv);
//determina o rank de um processo
MPI_Comm_rank(MPI_COMM_WORLD,&id);
//determina o numero de processos executando
MPI_Comm_size(MPI_COMM_WORLD,&p);
MPI_Status status;
    //mostra dados
 printf("Processo iniciado do id: %d\n ",id);
     printf("Numeros de processos p: %d \n",p);
if(id==0)
{
startwtime = MPI_Wtime();//iniciando o contador de tempo

strcpy(texto1,"auhauhsushauhs");
strcpy(texto2, "oplpadasdasdasdasdafadvalk");
strcpy(texto3, "cbfgrwtgjyunyhs");

int lengthText1 = strlen(texto1);//Atribuindo o tamanho do vetor
int lengthText2 = strlen(texto2);//Atribuindo o tamanho do vetor        
int lengthText3 = strlen(texto3);//Atribuindo o tamanho do vetor
printf("TAMANHO DO VETOR 1 >>>%d<<<", lengthText1);

printf("Enviando o tamanho dos vetores para os %d processadores....\n", p);
MPI_Send(&lengthText1, 1, MPI_CHAR, 1, 0, MPI_COMM_WORLD);  
MPI_Send(&lengthText2, 1, MPI_CHAR, 2, 0, MPI_COMM_WORLD);
MPI_Send(&lengthText3, 1, MPI_CHAR, 3, 0, MPI_COMM_WORLD);


printf("Enviando os dados para os %d processadores....\n", p);
MPI_Send(texto1, lengthText1, MPI_CHAR, 1, 0, MPI_COMM_WORLD);  
MPI_Send(texto2, lengthText2, MPI_CHAR, 2, 0, MPI_COMM_WORLD);
MPI_Send(texto3, lengthText3, MPI_CHAR, 3, 0, MPI_COMM_WORLD);
printf("Dados enviados com sucesso!\n");


}

if(id == 1){
int answer; 
int lengthText1;
MPI_Recv(&lengthText1, 1, MPI_CHAR, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);//Recebendo o tamanho do vetor
MPI_Recv(texto1, lengthText1, MPI_CHAR, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);//Recebendo o vetor
printf("Dados recebidos com sucesso no processador: %d \n", id);

answer = LongestCommonSubsequence(texto1);
printf("Resposta do processador %d eh de %d incidencias\n", id, answer);
MPI_Send(&answer, 1, MPI_INT, 0, 0, MPI_COMM_WORLD);
}

if(id == 2){
int answer;
int lengthText2;
MPI_Recv(&lengthText2, 1, MPI_CHAR, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);//Recebendo o tamanho do vetor
MPI_Recv(texto2, lengthText2, MPI_CHAR, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);//Recebendo o vetor
printf("Dados recebidos com sucesso no processador: %d \n", id);

answer = LongestCommonSubsequence(texto2);
printf("Resposta do processador %d eh de %d incidencias\n", id, answer);
MPI_Send(&answer, 1, MPI_INT, 0, 0, MPI_COMM_WORLD);
}

if(id == 3){
int answer; 
int lengthText3;
MPI_Recv(&lengthText3, 1, MPI_CHAR, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);//Recebendo o tamanho do vetor
MPI_Recv(texto3, lengthText3, MPI_CHAR, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);//Recebendo o vetor
printf("Dados recebidos com sucesso no processador: %d \n", id);

answer = LongestCommonSubsequence(texto3);
printf("Resposta do processador %d eh de %d incidencias\n", id, answer);
MPI_Send(&answer, 1, MPI_INT, 0, 0, MPI_COMM_WORLD);
}




//Retorno do Jedi
if(id == 0 ){
int answer=0;
int i;
int respostas[2];
endwtime = MPI_Wtime();

printf("Recebendo dados dos processadores\n");
for(i=1; i<4; i++){
MPI_Recv(&answer, 1, MPI_INT, i, MPI_ANY_TAG, MPI_COMM_WORLD, &status);
respostas[i] = answer;
answer=0;
}
printf("Dados recebidos com sucesso no servidor!\n");
for(i=1; i<4; i++){
printf("Incidencias no noh %d foi de: %d\n", i, respostas[i]);



}
printf("\n\n************ Tempo de execucao foi de %.4f segundos ***********\n", endwtime-startwtime);
  }


MPI_Finalize(); //Finalizar MPI
}

I'm using dynamic programming and I'm 3 knots + server.

Patrick · Accepted Answer · 2015-05-28 04:03:58Z

2

This is no surprise. You are using the MPI datatype MPI_CHAR for sending and receiving the string lengths. This sends only 1 byte. Use MPI_INT as the MPI datatype instead to send the full 4 byte integer:

// what you are doing:
MPI_Send(&lengthText1, 1, MPI_CHAR, 1, 0, MPI_COMM_WORLD);
// ... and
MPI_Recv(&lengthText1, 1, MPI_CHAR, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);

// what you should be doing:
MPI_Send(&lengthText1, 1, MPI_INT, 1, 0, MPI_COMM_WORLD);
// ... and
MPI_Recv(&lengthText1, 1, MPI_INT, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);

answered May 28, 2015 at 4:03

Patrick

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4 Comments

Sayoan Oliveira Over a year ago

I am frightened by such inattention. : / Thank you so much for looking so silly .

Rob Latham Over a year ago

if you compile with clang, there are type annotations to catch this sort of mistake

Sayoan Oliveira Over a year ago

I am sending two character sizes with 12k and 1k , When I put 15k + it explodes . Any Suggestion? I am suspicious of LongestCommonSub function, but it makes no sense . 500 and 15k comparisons are valid, but 15k to 15k not.

Patrick Over a year ago

What do you mean by 'explode'? Your LongestCommonSub function is quadratic in time and memory complexity. It will require much more time and memory for the 15k*15k case (~1GB Ram) than for the 500*15k case.

xamid · Accepted Answer · 2023-04-01 18:23:46Z

It should be noted that there is MPI_Probe to obtain the size of an array before sending. There do not have to be two MPI_Send calls. Furthermore, you can use arrays of dynamic size conforming to the C++ standard, and simply use std::string.

For example:

template<typename T>
struct ManagedArray { // for RAII on dynamic arrays
    T* data;
    ManagedArray() : data(nullptr) { }
    ManagedArray(size_t size) : data(new T[size]) { }
    ~ManagedArray() { delete data; }
};

string mpi_recvString(int rank, int source) {
    MPI_Status status_recv;
    MPI_Probe(source, 0, MPI_COMM_WORLD, &status_recv);
    int size;
    MPI_Get_count(&status_recv, MPI_CHAR, &size);
    cout << rank << ": Will receive " << size << " chars." << endl;
    ManagedArray<char> arr(size);
    MPI_Recv(arr.data, size, MPI_CHAR, source, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
    cout << rank << ": Received: " << arr.data << ". (length " << string(arr.data).length() << ")" << endl;
    return arr.data;
}

In case anyone would like to see the mpi_sendString as well:

void mpi_sendString(int rank, const string& s, int dest) {
    cout << rank << ": Sending " << s << ". (length " << s.length() << ")" << endl;
    // Actually send s.size() + 1 chars, since s.c_str() is null-terminated.
    MPI_Send(s.c_str(), s.size() + 1, MPI_CHAR, dest, 0, MPI_COMM_WORLD);
}

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