[mpich-discuss] Duplicate reception of messages

[Thakur, Rajeev]

To help narrow down the problem, can you try your code with some other MPI implementation on any system? If it works, can you send us a small test program that reproduces the problem?

Rajeev


From: "Mccall, Kurt E. (MSFC-EV41) via discuss" <discuss at mpich.org>
Reply-To: "discuss at mpich.org" <discuss at mpich.org>
Date: Wednesday, June 14, 2023 at 4:13 PM
To: "discuss at mpich.org" <discuss at mpich.org>
Cc: "Mccall, Kurt E. (MSFC-EV41)" <kurt.e.mccall at nasa.gov>
Subject: [mpich-discuss] Duplicate reception of messages

My code seems to be receiving particular messages more than once -- I can tell from the unique variables they contain.
I have verified that each unique variable is being sent exactly once.   The sender simply calls MPI_ISend to send a single
message containing an array of variables.

The receiver pseudo-code is as follows.   Have I made a mistake in my use of MPI_Iprobe?

MPI_Status status;
int flag;

// loop in case there was more than one message queued up due to asynchrony between
// sender and receiver.   Most of the time, there is only one message.
do {
    flag =  false;
    MPI_Iprobe (sender_rank, tag, intercom,  &flag, &status);

    if (flag)
    {
         int len;
         MPI_Get_count (&status, data_type, &len);

         MPI_Recv (buffer, len, data_type, sender_rank, tag, intercom, MPI_STATUS_IGNORE);

         // at this point, sometimes I see duplicate variable values in the buffer, in different
         // calls to MPI_Recv.  That is, s supposedly unique variable appears in two different
         // message.
    }
} while(flag);


Thanks for your help.   Here is my build information:

MPICH Version:          4.0.1
MPICH Release date:     Tue Feb 22 16:37:51 CST 2022
MPICH Device:           ch3:nemesis
MPICH configure:        --prefix=/opt/mpich --with-device=ch3:nemesis --with-slurm --disable-fortran -enable-debuginfo --enable-g=debug
MPICH CC:       gcc    -g -O2
MPICH CXX:      g++   -g -O2
MPICH F77:         -g
MPICH FC:          -g
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