[mpich2-dev] Parent terminates when the spawned child terminates

[Lisandro Dalcin]

On 15 December 2010 19:11, Suraj Prabhakaran
<suraj.prabhakaran at gmail.com> wrote:
> Thank you guys for all the reply. Thanks Pavan for hinting at the auto
> cleanup option. This does what I wanted it to do. Just adding to the
> discussion, I agree with your comments on the portable program's assumption
> part. The standard states that one program's error may affect the other only
> if they somehow belong in an intra or inter communicator. And in my case,
> the parent spawns the child and disconnects the communicator. The child also
> as soon as init, gets the parent and disconnects from the parent. The sample
> code is given below.
>
> Parent:
>
> int main (int argc, char *argv[])
> {
>    MPI_Init(&argc, &argv);
>    MPI_Errhandler_set(MPI_COMM_WORLD, MPI_ERRORS_RETURN);
>    MPI_Comm child_comm;
>    MPI_Comm_spawn("./child", MPI_ARGV_NULL, 1, MPI_INFO_NULL, 0,
> MPI_COMM_SELF, &child_comm, MPI_ERRCODES_IGNORE);
>    MPI_Errhandler_set(child_comm, MPI_ERRORS_RETURN);
>    printf("spawned a child\n");
>    MPI_Comm_disconnect(&child_comm);
>    printf("Disconnected from the child\n");
>    sleep(5000);
>    MPI_Finalize();
>    return 0;
> }
>
> Child:
>
> int main (int argc, char *argv[])
> {
>    MPI_Init(&argc, &argv);
>    MPI_Comm parent, parent1;
>    MPI_Comm_get_parent(&parent);
>    MPI_Comm_disconnect(&parent);
>    if(parent == MPI_COMM_NULL)
>    printf("Child: Disconnected from the parent, Exiting\n\n");
>
>    MPI_Comm_get_parent(&parent1);
>
>    if(parent1 != MPI_COMM_NULL)
>    printf("Child: yes, i got my parent again\n");
>
>    exit(1);
>
>    MPI_Finalize();
>    return 0;
> }
>
> If you see here, the child's first message will be displayed while the
> second printf will not be displayed! Which shows that it cant get the parent
> anymore. And when a exit() happens abruptly, it shouldn't affect the parent
> rite (since they now dont have a common communicator, and without any auto
> clean option) ?
> Please correct me if I am wrong.
>

I believe you are right.  For this program, at child exit() time
parent and child are disconnected, and I understand the MPI standard
says that the parent should not be affected. Of course, I'm not a MPI
lawyer, and perhaps I misunderstood the wording...


-- 
Lisandro Dalcin
---------------
CIMEC (INTEC/CONICET-UNL)
Predio CONICET-Santa Fe
Colectora RN 168 Km 472, Paraje El Pozo
Tel: +54-342-4511594 (ext 1011)
Tel/Fax: +54-342-4511169