Subject: Re: MPI_FINALIZE To: mpi-21@XXXXXXXXXXXXX X-Mailer: Lotus Notes Release 5.0.5 September 22, 2000 From: "Richard Treumann" Date: Tue, 15 May 2001 14:40:59 -0400 X-MIMETrack: Serialize by Router on D01ML077/01/M/IBM(Release 5.0.7 SPR #MIAS4UTJ8H &S/390 SPR #JHEG4V8UT5|April 5, 2001) at 05/15/2001 02:42:28 PM MIME-Version: 1.0 Content-type: text/plain; charset=us-ascii Sender: owner-mpi-21@XXXXXXXXXXXXX Precedence: bulk Reply-To: mpi-21@XXXXXXXXXXXXX MPI_Bcast is collective but I would be surprised if a implementation chose to make the tasks close to root block while waiting for the tasks farther out to process a correct call. When MPI states that only MPI_Barrier __promises__ a synchronization, the reason is that in many collectives making all calls wait to confirm all others had occured correctly would reduce performance and add little value. MPI_Bcast on an intercommunicator is collective but involves calls by tasks which have no participation in the operation at all. These tasks pass MPI_PROC_NULL as root and an MPI implementation that made these calls into local no-ops could be valid. A program that __presumed__ they were local no-ops and could be omitted would be invalid. Dick Treumann RS/6000 SP Development IBM Poughkeepsie Unix Development Lab Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 "Andrew Lumsdaine" To: , "Jeff Squyres" > cc: Sent by: Subject: Re: MPI_FINALIZE owner-mpi-21@mpi -forum.org 05/10/2001 02:07 PM Please respond to mpi-21 Hum. If I understand the idea of "collective" properly, then I don't see how this can be accomplished without something like a barrier occurring. Does not the requirement that all the processes have to call the MPI routine also imply that it is an error if they do not all do so? Does not that also imply that each process needs to wait until all processes have made the collective call in order to know whether the collective call has been properly made or not? Otherwise, I don't think MPI_Finalize would be truly collective. I.e., if one can call it and receive indication of success regardless of whether anyone else ever calls it or not, then it seems like a local procedure.