Why do i get the failed to attach to a bootstrap queue for this MPI code?-CodePudding

The exercise I'm trying to do asks us to build a ring of processes where each of them passes the number x to the following process, only the process with rank=0 decreases the x. When x is equal to zero the program ends. The working code is the following:

#include <stdio.h>
#include <stddef.h>
#include <string.h>
#include "mpi.h"

int main(int argc, char** argv) {

int x = 0;
int tag = 99;

MPI_Status status;

MPI_Init(&argc, &argv);

int myRank;
MPI_Comm_rank(MPI_COMM_WORLD, &myRank);

int size;
MPI_Comm_size(MPI_COMM_WORLD, &size);

if (myRank == 0) {
    printf("Process %d enter a value: \n", myRank);
    fflush(stdout);
    scanf_s("%d", &x);

    while (x>0) {
        MPI_Send(&x, 1, MPI_INT, 1, tag, MPI_COMM_WORLD);
        MPI_Recv(&x, 1, MPI_INT, MPI_ANY_SOURCE, tag, MPI_COMM_WORLD, &status);
        printf("Process %d : lap number %d \n", myRank, x);
        x--;
    } 


}
else {

    do {

        
        MPI_Recv(&x, 1, MPI_INT, MPI_ANY_SOURCE, tag, MPI_COMM_WORLD, &status);
        printf("Process %d : lap number %d \n", myRank, x);
        MPI_Send(&x, 1, MPI_INT, (myRank   1) % size, tag, MPI_COMM_WORLD); 
    } while (x > 1);
}

MPI_Finalize();
return 0;
}

but if i change the last do while cycle like this:

#include <stdio.h>
#include <stddef.h>
#include <string.h>
#include "mpi.h"

int main(int argc, char** argv) {

int x = 0;
int tag = 99;

MPI_Status status;

MPI_Init(&argc, &argv);

int myRank;
MPI_Comm_rank(MPI_COMM_WORLD, &myRank);

int size;
MPI_Comm_size(MPI_COMM_WORLD, &size);

if (myRank == 0) {
    printf("Process %d enter a value: \n", myRank);
    fflush(stdout);
    scanf_s("%d", &x);

    while (x>0) {
        MPI_Send(&x, 1, MPI_INT, 1, tag, MPI_COMM_WORLD);
        MPI_Recv(&x, 1, MPI_INT, MPI_ANY_SOURCE, tag, MPI_COMM_WORLD, &status);
        printf("Processo %d : giro numero %d \n", myRank, x);
        x--;
    } 


}
else {

    while (x>0) {

        
        MPI_Recv(&x, 1, MPI_INT, MPI_ANY_SOURCE, tag, MPI_COMM_WORLD, &status);
        printf("Processo %d : giro numero %d \n", myRank, x);
        MPI_Send(&x, 1, MPI_INT, (myRank   1) % size, tag, MPI_COMM_WORLD); 
    } 
}

MPI_Finalize();
return 0;
}

I get this error:

job aborted:
[ranks] message

[0] fatal error
Fatal error in MPI_Send: Other MPI error, error stack:
MPI_Send(buf=0x000000F6100FF514, count=1, MPI_INT, dest=1, tag=99, MPI_COMM_WORLD) failed
failed to attach to a bootstrap queue - 10616:296

[1-2] terminated

But I don't understand why... Shouldn't the two codes be equivalent?

CodePudding user response：

You set x to zero, and then all processes but zero do while (x>0) { stuff }. So they don't do anything.