On May 28, 2014, at 4:31 AM, Jeff Squyres (jsquyres) <jsquy...@cisco.com> wrote:
> On May 27, 2014, at 9:11 PM, Gilles Gouaillardet > <gilles.gouaillar...@gmail.com> wrote: > >> in the case of intercomm_create, the children free all the communicators and >> then MPI_Disconnect() and then MPI_Finalize() and exits. >> the parent only MPI_Disconnect() without freeing all the communicators. >> MPI_Finalize() tries to disconnect and communicate with already exited >> processes. >> >> my understanding is that there are two ways of seeing things : >> a) the "R-way" : the problem is the parent should not try to communicate to >> already exited processes >> b) the "J-way" : the problem is the children should have waited either in >> MPI_Comm_free() or MPI_Finalize() > > I didn't ignore Ralph's email; I was just pulling you chain, Jeff :-) > I was pointing out what the MPI semantics are supposed to be. > > I had only a short time this morning to look at the intercomm_create test > program, and it looks like Gilles might be correct -- the children are > freeing all relevant communicators *but the parent is not*. If this is, > indeed, correct, then a) OMPI's implementation might be fine because the test > program is erroneous (i.e., the children *think* that they are disconnected > and therefore allow themselves to exit, but the parents *think* that they are > still connected and therefore try to contact the children during the parents' > MPI_FINALIZE), and b) his original patch to the test program could well be > correct. Agreed - however, I find it concerning that loop_spawn, which does have every process calling comm_free, is showing the same symptom upon the parent calling finalize. > > I won't have time to investigate this today; if someone else could look at > the test code and confirm whether this is correct or not, that would be > appreciated. > >> as far as i am concerned, i have no opinion on which of a) or b) is the >> correct/most appropriate approach. > > To be totally clear: MPI says it is erroneous for only some (not all) > processes in a communicator to call MPI_COMM_FREE. So if that's the real > problem, then the discussion about why the parent(s) is(are) trying to > contact the children is moot -- the test is erroneous, and erroneous > application behavior is undefined. > > All that being said, if we want to make this error case a bit friendlier to > the user, that would be great (i.e., a show_help something like "It looks > like an MPI process is trying to contact another MPI process that has already > exited/called MPI_FINALIZE. This is almost certainly an error in the > application..."). Also agreed, assuming we can find the right place to correctly determine that is what is happening. > But that's definitely extra bonus points, and not required. > > -- > Jeff Squyres > jsquy...@cisco.com > For corporate legal information go to: > http://www.cisco.com/web/about/doing_business/legal/cri/ > > _______________________________________________ > devel mailing list > de...@open-mpi.org > Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/devel > Link to this post: > http://www.open-mpi.org/community/lists/devel/2014/05/14883.php
