[mpich2-dev] some comments on attribute catching, create/free() keyvals and all that.

[Lisandro Dalcin]

As I've shown in a previous emal, MPICH2 likely implement
create()/free() for keyvals using a counter that is incr/decr ...

Now, give a try to the code pasted below. This shows that (at least in
MPICH2), MPI_Keyval_free() have to be used with great care as it is
IMHO dangerous, and basically these calls should be all done near
MPI_Finalize() time... or bad things could happen...

The only reference I can found in the MPI standard is at
(http://www.mpi-forum.org/docs/mpi21-report-bw/node147.htm#Node147)
where MPI_Comm_free_keyval() is explained... However, I believe that
description is talking about different things...

Should MPICH2 stop decrefing the keyval counter? You know, about 2<<31
values should be enough, right ;-) ?
But then.. What the pourpose of having MPI_Keyval_free()? Just to
invalidate de passed value by setting it to KEYVAL_INVALID?


#include <mpi.h>
#include <stdio.h>

int free_KeyVal(MPI_Comm c, int k, void *v,void *ctx)
{
  printf("free_KeyVal()\n");
  return MPI_SUCCESS;
}

int main( int argc, char ** argv ) {
  int Key1, Key2, Val1=1, Val2=2, ValOut;
  MPI_Init(&argc, &argv);

  MPI_Keyval_create(MPI_NULL_COPY_FN, free_KeyVal, &Key1,(void *) 0);
  MPI_Attr_put(MPI_COMM_SELF, Key1, &Val1);
  MPI_Keyval_free(&Key1);

  MPI_Keyval_create(MPI_NULL_COPY_FN, MPI_NULL_DELETE_FN, &Key2,(void *) 0);
  MPI_Attr_put(MPI_COMM_SELF, Key2, &Val2);
  MPI_Keyval_free(&Key2);

  MPI_Finalize();

  return 0;
}


-- 
Lisandro Dalcín
---------------
Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
PTLC - Güemes 3450, (3000) Santa Fe, Argentina
Tel/Fax: +54-(0)342-451.1594