[Mpi3-ft] Stabilization Updated & MPI_Comm_size question

Richard Treumann treumann at us.ibm.com
Mon Sep 20 13:54:44 CDT 2010

The MPI Standard currently states that communicator creation is collective 
and deterministic. (I did not go back and read the wording so I may be 
missing some nuance).  To me that means that when a communicator handle is 
returned, every process has certain pieces of information encoded in the 
opaque communicator object  that it can assume match at every member. This 
shared view includes the number of processes negotiated and an agreement 
on which process corresponds to each rank. It does not mean that every 
process that was intended to be in the communicator is still alive and 

Are you changing the rule that "communicator creation is collective and 
deterministic"?  If not, there are things which can occur before the 
"collective and deterministic" commit point and things that occur after. 

It seems to me that MPI_Comm_size must return the number that was 
committed and if you need to find how many are left after post-commit 
problems, it demands a different call. If you need to find out how many 
were desired when fewer may have been committed, that too is another call.


Dick Treumann  -  MPI Team 
IBM Systems & Technology Group
Dept X2ZA / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
Tele (845) 433-7846         Fax (845) 433-8363
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