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

[Dave Goodell]

Lisandro,

Have you seen our recent commits on this issue?  I believe that the  
issues you pointed out were resolved in the following changesets:  
r4025-r4030, r4044, r4048.

Related trac tickets: #222, #449

-Dave

On Mar 13, 2009, at 1:01 PM, Lisandro Dalcin wrote:

> 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)
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> Tel/Fax: +54-(0)342-451.1594