[mpich-discuss] mpich2 and sending message from a task to itself

[Bryan Putnam]

On Thu, 29 May 2008, Rajeev Thakur wrote:

> The send-to-yourself needs to be either a nonblocking send or the receive
> must be posted before the send. MPI_Send will block for the receive to be
> posted. 
> 
> Rajeev

Rajeev,

One of my co-workers makes the following comment:

That contradicts Section 2.2 in MPI: The Complete Reference (Blocking Send 
and Receive Operations), which specifically says on page I-37 that a 
process may use MPI_SEND to send a message to itself. I see nothing there 
about a need to post a receive before the send, and at any rate, 
nonblocking sends and receives are not discussed until section 2.8.

Thanks,
Bryan

> 
> 
> > -----Original Message-----
> > From: owner-mpich-discuss at mcs.anl.gov 
> > [mailto:owner-mpich-discuss at mcs.anl.gov] On Behalf Of Bryan Putnam
> > Sent: Thursday, May 29, 2008 3:26 PM
> > To: mpich-discuss at mcs.anl.gov
> > Subject: [mpich-discuss] mpich2 and sending message from a 
> > task to itself
> > 
> > Hi,
> > 
> > I've found that if I take a standard "hello, world" program 
> > (where master 
> > sends "hello" to all tasks except itself), and modify it so 
> > that master 
> > sends "hello" to all tasks including itself, I get a 
> > "MPI_Send" error when 
> > using mpich2-1.0.7, of the form
> > 
> > Fatal error in MPI_Send: Error message texts are not 
> > available[cli_0]: 
> > aborting job:
> > 
> > From what we can tell, sending a message to yourself is 
> > allowed by the MPI 
> > standard:
> > 
> > From MPI: The Complete Reference (I-37):
> > 
> > +++++++++++++++
> > The range of valid values for [the destination argument] is 0..n-1,
> > where n is the number of processes in the group. This range includes
> > the rank of the sender: if [the communicator] is an intracommunicator,
> > then a process may send a message to itself.
> > 
> > MPI::COMM_WORLD is indeed an intracommunicator.
> > +++++++++++++++
> > 
> > For your enjoyment, I've included my original code, and followed it 
> > by the modified code.
> > 
> > Thanks!
> > Bryan
> > 
> > 
> >       program hellof
> >       include 'mpif.h'
> >       integer me, nt, mpierr, status(MPI_STATUS_SIZE)
> >       integer tag
> >       character*12  message, inmsg
> >   
> >       call MPI_INIT(mpierr)
> >       call MPI_COMM_SIZE(MPI_COMM_WORLD, nt, mpierr)
> >       call MPI_COMM_RANK(MPI_COMM_WORLD, me, mpierr)
> >       tag = 1
> >   
> >       if(me .eq. 0) then
> >         message = 'Hello world!'
> >         do i=1,nt-1
> >            call MPI_SEND(message, 12, MPI_CHARACTER, i, tag,
> >      &                   MPI_COMM_WORLD, mpierr)
> >         enddo
> >         write(6,*) 'node', me, ': ', message
> >       else
> >         call MPI_RECV(inmsg, 12, MPI_CHARACTER, 0, tag,
> >      &                MPI_COMM_WORLD, status, mpierr)
> >         write(6,*) 'node', me, ': ', inmsg
> >       endif
> >       call MPI_FINALIZE(mpierr)
> >       end 
> > 
> > 
> > Modified code:
> > 
> > 
> >       program hellof
> >       include 'mpif.h'
> >       integer me, nt, mpierr, status(MPI_STATUS_SIZE)
> >       integer tag
> >       character*12  message, inmsg
> >   
> >       call MPI_INIT(mpierr)
> >       call MPI_COMM_SIZE(MPI_COMM_WORLD, nt, mpierr)
> >       call MPI_COMM_RANK(MPI_COMM_WORLD, me, mpierr)
> >       tag = 1
> >   
> >       if(me .eq. 0) then
> >         message = 'Hello world!'
> >         do i=0,nt-1
> >            call MPI_SEND(message, 12, MPI_CHARACTER, i, tag,
> >      &                   MPI_COMM_WORLD, mpierr)
> >         enddo
> >         write(6,*) 'node', me, ': ', message
> >       endif
> >       call MPI_RECV(inmsg, 12, MPI_CHARACTER, 0, tag,
> >      &              MPI_COMM_WORLD, status, mpierr)
> >         write(6,*) 'node', me, ': ', inmsg
> >       call MPI_FINALIZE(mpierr)
> >       end
> > 
> > 
> > 
> 
>