You need to disconnect the parent/child from each other prior to finalizing - see the attached example
simple_spawn.c
Description: Binary data
On Aug 31, 2014, at 9:44 PM, Roy <open...@jsp.selfip.org> wrote:
> 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
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