From dalcinl@XXXXXXXXX Thu Nov 29 08:13:43 2007
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Date: Thu, 29 Nov 2007 11:13:39 -0300
From: "Lisandro Dalcin" <dalcinl@XXXXXXXXX>
To: "William Gropp" <gropp@XXXXXXXXXXX>
Subject: mpi-2 clarifications
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Bill, here goes an issue I faced in developing mpi4py.

Group operations are supposed to return new groups, so the used has to
free the result. Additionally, the standard say that those operations
may return the empty group. Then the issue: if the empty group is
returned, the user should or should not call MPI_Group_free()??. I
could not find any part of the standard about freeing MPI_GROUP_EMPTY.

This issue is very similar to the one in MPI-1 related to error handlers.

I believe the standard should be a bit stricter here, but many
possibilities are:

* MPI_GROUP_EMPTY must be freed it it is the result of a group
operation. This way similar to the management of predefined error
handlers.

* MPI_GROUP_EMPTY cannot be freed, as it is a predefined handle. Users
have to always check if the result of a group operation is
MPI_GROUP_EMPTY to know if they can or cannot free them. This way is
similar to the current management of predefined datatypes.



--=20
Lisandro Dalc=EDn
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