Hi all,
I'm using MPI_Comm_spawn to start new child process.
I found that if the parent process execute MPI_Finalize before the child
process, the child process core dump on MPI_Finalize.
I couldn't find the correct way to have a clean shutdown of all processes
( parent and child ).
What that I found is that sleep(2) in the parent process just before
calling MPI_Finalize, gives the CPU cycle for the child process to finish
its own MPI_Finalize, and only then there is no core dump.
Although this resolve the issue, I can't accept this as acceptable solution.
I guess I'm doing something wrong ( implementation or design ), so this is
why I'm sending this email to the group ( and yes, I did check the FAQ,
and done some search on the distribution list archive ).
Here is the entire code to reproduce the issue :
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <mpi.h>
#include <stdlib.h>
int main(int argc, char* argv[]){
int my_rank; /* rank of process */
int p; /* number of processes */
int source; /* rank of sender */
int dest; /* rank of receiver */
int tag=0; /* tag for messages */
char message[100]; /* storage for message */
MPI_Status status ; /* return status for receive */
/* start up MPI */
MPI_Init(&argc, &argv);
/* find out process rank */
MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
fprintf(stderr,"My rank is : %d\n",my_rank);
/* find out number of processes */
MPI_Comm_size(MPI_COMM_WORLD, &p);
MPI_Comm parent;
MPI_Comm_get_parent(&parent);
if ( parent != MPI_COMM_NULL){
/* create message */
dest = 0;
/* use strlen+1 so that '\0' get transmitted */
MPI_Recv(message, 100, MPI_CHAR, 0, tag,parent, &status);
fprintf(stderr,"Got [%s] from root\n",message);
/* shut down MPI */
MPI_Finalize();
}
else{
printf("Hello MPI World From process 0: Num processes: %d\n",p);
MPI_Comm everyone;
MPI_Comm_spawn("mpitest",MPI_ARGV_NULL,1,MPI_INFO_NULL,0,
MPI_COMM_SELF,&everyone,
MPI_ERRCODES_IGNORE);
/* find out number of processes */
MPI_Comm_size(everyone, &p);
fprintf(stderr,"New world size:%d\n",p);
for (source = 0; source < p; source++) {
sprintf(message, "Hello MPI World from root to process
%d!", source);
MPI_Send(message, strlen(message)+1, MPI_CHAR,source,
tag, everyone);
}
/**
* Why this sleep resolve my core dump issues ?
* Any timing between the parent to child process ?
* Based on the document, and FAQ, I couldn't not find an
answer for
this issue.
*
* If you comment out the sleep(2), the child process will
crash on the
MPI_Finalize with
* singal 11, Segmentation fault.
*/
//sleep(2); //un-comment this line to have the sleep, and avoid
the core
dumps.
/* shut down MPI */
MPI_Finalize();
}
return 0;
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Anyone for the rescue ?
Thank you,
Roy Avidor
