[MPICH] Freeing Userdefined resources (Datatypes, Communicators, ... ) properly with C++

[Martin Schwinzerl]

Dear Rajeev!
> MPI_Finalize does not deallocate user-created objects. 
>   
Thanks for clearing this up. I was a little bit uncertain about this,
as the MPI-2 standard states in the clarification to MPI_FINALIZE that

"This routine cleans up all MPI state."

But (if I'm not mistaken) it does not elaborate what exactly qualifies as
 "state". Since these user allocated resources are already handles
by nature (e.g. assigning

MPI::Intracomm m_commA =  /* ... */
MPI::Intracomm m_commB = commA

performs no deep copy), I had speculations that MPI::Finalize()
would perhaps free all raw resources automatically, since these
are obviously handled already at a global level
somewhere in the MPI namespace. Would have been a nice
time and effort saver :-)

Just out of curiosity: Are there any special reasons/obstacles for not
doing this
in MPI::Finalize() ? If I understand the Finalize() and Free() mechanism
correctly, then Free() directives have no immediate influence on currently
active jobs (e.g. they just hinder new operations from accessing the
resource in
question and keep the resource intact as long as it is needed by active
operations).
Would there been (too much) communication / synchronisation overhead
necessary between the different processes to decide when to explicitly
remove
the resource ?
> MPI_Finalized is an MPI-2 function. There is no equivalent in MPI-1.2. But
> in practice, this may not be a problem as most implementation support at
> least some MPI-2 functions, and hence may support MPI_Finalized.
>   
Ah! MPICH-1.2.6 / 1.2.7 has problems with MPI::Is_finalized() but can handle
MPI_Finalized() as it seems.

Best regards & Thank your for your support !

Martin