Re: [mpich-discuss] MPI_Comm_Spawn causing zombies of hydra_pmi_proxy

7 Mar 2013


      I just tried this with the mpich master and it seems to work correctly,
and there are no zombie processes (though I reduced the number of
iterations to 10000, instead of 200000).  This was a problem in mpich
once upon a time, but that was a few years ago.  Are you using the
latest version of mpich (3.0.2)?

 -- Pavan

On 03/07/2013 09:44 AM US Central Time, Silvan Brï¿½ndli wrote:
...
PS: The attached programs are a simplification of my code. They
reproduce the zombie problem. Waiting for the 32k zombies takes a
while... but I expect the same behaviour as with my original code.
Am I missing something when finishing the called program? I just use
MPI_Comm_disconnect and MPI_Finalize.
Best regards
Silvan
main.cpp
#include <mpi.h>;
int main(int argc, char *argv[])
{
  int          myrank;
  int spawnerror;
  int value = 123;
  void *buf = &value;
  MPI_Comm child_comm;
if (MPI_Init(&argc,&argv)!=MPI_SUCCESS)
  {
    printf("MPI_Init failed");
  }
MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
char* hiargv[] = {"23",NULL};
  for(int i = 1; i <= 200000; i++)
  {
    value = i;
    printf("Main before spawn %d\n",i);
    MPI_Comm_spawn("./hi",hiargv, 1, MPI_INFO_NULL, myrank,
MPI_COMM_SELF, &child_comm, &spawnerror);
    MPI_Send(buf, 1, MPI_INTEGER, 0, 1, child_comm);
    MPI_Comm_disconnect(&child_comm);
  }
MPI_Finalize();
  return 0;
}
hi.cpp:
#include <mpi.h>;
int main(int argc, char** argv) {
  MPI_Comm parent;
  MPI_Status status;
  int err;
  int value = -1;
  void* buf= &value;
if (MPI_Init(&argc,&argv)!=MPI_SUCCESS)
  {
    printf("MPI_Init failed");
  }
  MPI_Comm_get_parent(&parent);
  if (parent == MPI_COMM_NULL) printf("No parent!");
MPI_Recv(buf, 1, MPI_INTEGER, 0, MPI_ANY_TAG, parent, &status);
  MPI_Comm_disconnect(&parent);
  err = MPI_Finalize();
  printf("hi finalized %d %d \n",err, value);
  return 0;
}
On 07.03.2013 12:38, Silvan Brï¿½ndli wrote:
...
Dear all,
again I have a question related to spawning processes. I understand the
situation as follows:
My program A spawns program B. Program B spawns program C1, C2 ...
C10000 ...
Program Cx terminates correctly before Cx+1 is called, however returning
1 to mpiexec. To handle this I use the workaround as described in
http://lists.mpich.org/pipermail/discuss/2013-February/000429.html
Now it looks like with every Spawn a "hydra_pmi_proxy" is started, the
calling program is mpiexec. When the program Cx is finished this
"hydra_pmi_proxy" remains as a zombie until the programs A, B and
mpiexec are finished. When approx. 32k of those "hydra_pmi_proxy" exist
I get some problems (too many processes or something similar).
What can I do to finish "hydra_pmi_proxy" while my programs A, B and
mpiexec are still running?
I'm glad about every hint.
Best regards
Silvan
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-- 
Pavan Balaji
http://www.mcs.anl.gov/~balaji