[Mpi-forum] Question about the semantics of MPI_Comm_disconnect

[Rajeev Thakur]

As George said, it seems to be covered by lines 29-40 on pg 399 and 35-40 on 400.

Rajeev

On Nov 13, 2013, at 3:00 PM, Jeff Squyres (jsquyres) <jsquyres at cisco.com> wrote:

> On Nov 12, 2013, at 5:40 PM, Rajeev Thakur <thakur at mcs.anl.gov> wrote:
> 
>> Think of Comm_disconnect as "whatever connection was there between client and server is gone".
> 
> 
> Rajeev --
> 
> This sentence has been bugging me, and I just figured out why.  
> 
> I've always thought of COMM_DISCONNECT just as you describe: whatever connection was there between client and server is gone.  But what about other types of MPI handles -- like MPI_File and MPI_Window?  For example:
> 
> -----
> MPI_Comm_spawn(..., &child);
> MPI_Intercomm_merge(child, 0, &child_intra);
> MPI_File_open(child_intra, ..., &file);
> MPI_Comm_disconnect(&child_intra);
> MPI_Comm_disconnect(&child);
> -----
> 
> At this point, all communicators between parent and child are gone, but there's still a File (the same example could be done with an RMA window).
> 
> So the processes are *not* actually disconnected (in the MPI sense of the word "disconnected).  Indeed, in the above example, if there was no File, you still have to do *2* disconnects before the parent and child are truly disconnected.
> 
> Hence, I think that this is a very poorly named function -- it *doesn't* necessarily disconnect MPI processes.  It really performs and operation that is something like MPI_COMM_FREE_WAIT.
> 
> I wonder if this is worth an AtoU...
> 
> -- 
> Jeff Squyres
> jsquyres at cisco.com
> For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/
> 
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