I have modified the code so that all the terminal outputs are done by one executable.  I have attached the source files, after compiling type "make go" and the code will execute.

The previous code output was from a supercomputer cluster where the two processes resides on two different nodes.  When running the same code on a regular-multiprocessor machine (mac mini in this case), I got this output:
 F
 F
 T
           1
 F
 T
           2
 F
 T
           3
 F
 T
           4

If I'm sending a message every 2 seconds and I'm polling every 0.05 second, I would expect 39 F and 1 T between each number.  At least when I ran it on the supercomputer, this is true during the very beginning; however I don't even see this when I'm running the code on my mac mini.

On Sat, Jun 5, 2010 at 2:44 PM, David Zhang <solarbikedz@gmail.com> wrote:
Dear all:

I'm using mpi_iprobe to serve as a way to send signals between different mpi executables. I'm using the following test codes (fortran):

#1
program send
implicit none
        include 'mpif.h'

real*8 :: vec(20000)=1.0
integer :: ierr,i=0,request(1)

        call mpi_init(ierr)
        do
                call mpi_isend(vec,20000,mpi_real8,
0,1,mpi_comm_world,request(1),ierr)
                i=i+1
                print *,i
                vec=-vec
                call usleep_fortran(2.d0)
                call mpi_wait(request(1),MPI_STATUS_IGNORE,ierr)
        end do

end program send
--------------------------------------------------
#2
program send
implicit none
        include 'mpif.h'

real*8 :: vec(20000)
integer :: ierr

        call mpi_init(ierr)
        do
                if(key_present()) then
                        call mpi_recv(vec,20000,mpi_real8,1,1,mpi_comm_world,MPI_STATUS_IGNORE,ierr)
                end if
                call usleep_fortran(0.05d0)

        end do

contains

function key_present()
implicit none
  logical :: key_present

        key_present = .false.
        call mpi_iprobe(1,1,mpi_comm_world,key_present,MPI_STATUS_IGNORE,ierr)
        print *, key_present

end function key_present

end program send
-----------------------------------
The usleep_fortran is a routine I've written to pause the program for that amount of time (in seconds).  As you can see, on the receiving end I'm probing to see whether the message has being received every 0.05 seconds, where each probing would result a print of the probing result; while the sending is once every 2 seconds. 

Doing
mpirun -np 1 recv : -np 1 send
 Naturally I expect the output to be something like:

1
(fourty or so F)
T
2
(another fourty or so F)
T
3

however this is the output I get:

1
(fourty or so F)
T
2
(about a two second delay)
T
3

It seems to me that after the first set of probes, once the message was received, the non-blocking mpi probe becomes blocking for some strange reason.  I'm using mpi_iprobe for the first time, so I'm not sure if I'm doing something blatantly wrong.


--
David Zhang
University of California, San Diego



--
David Zhang
University of California, San Diego
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