[mpich-discuss] MPI_Wait status array and non-blocking sends

[Helvio Vairinhos]

Yes, sorry for not having posted the whole test code before. I had done
what you suggest, and the status comes out empty. My test code is the
following:

PROGRAM mpitest
    IMPLICIT NONE
    INCLUDE "mpif.h"
   INTEGER:: ierr, rank, buf, req
   INTEGER,DIMENSION(MPI_STATUS_SIZE):: status

    CALL MPI_INIT(ierr)
    CALL MPI_COMM_RANK(MPI_COMM_WORLD, rank, ierr)

   IF( rank==0 ) THEN
      buf=23
      CALL MPI_ISEND(buf, 1, MPI_INTEGER, 1, 99, MPI_COMM_WORLD, req, ierr)
      CALL MPI_WAIT(req, status, ierr)
      WRITE(*,*) "MPI_ISEND status:", status
   ELSE IF( rank==1 ) THEN
      buf=0
      CALL MPI_IRECV(buf, 1, MPI_INTEGER, 0, 99, MPI_COMM_WORLD, req, ierr)
      CALL MPI_WAIT(req, status, ierr)
      WRITE(*,*) "MPI_IRECV status:", status
      WRITE(*,*) "Incoming message:", buf
   ENDIF

   CALL MPI_FINALIZE(ierr)

    STOP
END PROGRAM mpitest

I compile the code with gfortran, via the mpif90 wrapper from
MPICH2-1.3.4 (built in the latest Cygwin release):

$ mpif90 mpitest.F90
$ mpiexec -n 2 ./a.exe

The output result is still empty for MPI_ISEND, and it's o.k. for MPI_IRECV:

 MPI_ISEND status:           0           0           0          
0           0
 MPI_IRECV status:           4           0           0         
99           0
 Incoming message:         23

Best,
Helvio.


On 02-08-2011 17:38, Rajeev Thakur wrote:
> Make sure you have declared the status variable as "integer status(MPI_STATUS_SIZE)". If the status is still empty, send us a small test program that demonstrates the error.
>
> Rajeev
>
>
> On Aug 2, 2011, at 6:07 AM, Helvio Vairinhos wrote:
>
>> Hi,
>>
>> I'm new to MPI and I'd like to understand something about non-blocking
>> sends/receives and MPI_WAIT that I quite don't understand, if not only
>> for curiosity. I use the MPICH2-1.3.2p1 implementation of MPI for
>> Cygwin. Consider the following snippet of F90 code, which does basic
>> non-blocking send and receive, and waits for the completion of each one
>> of them:
>>
>>   IF (rank==0) THEN
>>      buf=1
>>      CALL MPI_ISEND(buf, 1, MPI_INTEGER, 1, 99, MPI_COMM_WORLD, req, ierr)
>>      CALL MPI_WAIT(req, status, ierr)
>>      WRITE(*,*) "MPI_ISEND status:", status
>>   ELSE IF (rank==1) THEN
>>      buf=0
>>      CALL MPI_IRECV(buf, 1, MPI_INTEGER, 0, 99, MPI_COMM_WORLD, req, ierr)
>>      CALL MPI_WAIT(req, status, ierr)
>>      WRITE(*,*) "MPI_IRECV status:", status
>>      WRITE(*,*) "Incoming message:", buf
>>   ENDIF
>>
>> The output is:
>>
>> $ mpif90 mpitest.F90
>> $ mpiexec -n 2 ./a.exe
>> MPI_Isend status:           0           0           0          
>> 0           0
>> MPI_Irecv status:           4           0           0         
>> 99           0
>> Incoming message:           1
>>
>> I don't understand why the MPI_WAIT that waits for the completion of the
>> non-blocking send does not return a proper STATUS array (the STATUS
>> array is always returned with zero components, regardless of the sending
>> mode being basic, synchronous, ready or buffered). I thought that
>> information like tag, size and destination rank would still be encoded
>> in STATUS at the sending end, after the send is completed. I know that
>> STATUS makes more sense in the receiving end, but I just wanted to know
>> if this is normal, i.e. if the MPI_WAIT always completes a sending
>> routine and returns a zero STATUS array, or if I'm doing something wrong.
>>
>> Thanks,
>> Helvio
>> _______________________________________________
>> mpich-discuss mailing list
>> mpich-discuss at mcs.anl.gov
>> https://lists.mcs.anl.gov/mailman/listinfo/mpich-discuss
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