[mpich-discuss] MPI_Cancel + MPI_Wait stalls when using ch4, not when using ch3

[Zhou, Hui]

Thanks for reporting. We'll fix this. Tracking issue: https://github.com/pmodels/mpich/issues/5775
[https://opengraph.githubassets.com/abeb43664f034115c44e99f3e273e49dbfdeb9ebcc478dd9ede9ca4d439f78ab/pmodels/mpich/issues/5775]<https://github.com/pmodels/mpich/issues/5775>
ch4: MPI_Cancel stalls MPI_Wait · Issue #5775 · pmodels/mpich<https://github.com/pmodels/mpich/issues/5775>
Reported on discuss mailinglist: ---- quote ---- Hi, Running one of our test programs using MPICH 3.4.3 and ch4:ofi, I notice that MPI_Wait on an MPI_Request that has been MPI_Cancelled never compl...
github.com

________________________________
From: Edric Ellis via discuss <discuss at mpich.org>
Sent: Wednesday, January 19, 2022 11:21 AM
To: discuss at mpich.org <discuss at mpich.org>
Cc: Edric Ellis <eellis at mathworks.com>
Subject: [mpich-discuss] MPI_Cancel + MPI_Wait stalls when using ch4, not when using ch3

Hi,

Running one of our test programs using MPICH 3.4.3 and ch4:ofi, I notice that MPI_Wait on an MPI_Request that has been MPI_Cancelled never completes (it does when using ch3). (The documentation for MPI_Cancel states "If a communication is marked for cancellation, then a MPI_WAIT call for that communication is guaranteed to return, irrespective of the activities of other processes (i.e., MPI_WAIT behaves as a local function)")

Here's a simple example:

#include <mpi.h>
#include <stdio.h>
#include <stdlib.h>

void check(int const value) {
    if (value != MPI_SUCCESS) {
        fprintf(stderr, "Failed.\n");
        exit(1);
    }
}

int main(int argc, char** argv) {
    MPI_Request r1;
    int payload = 42;
    int result;

    check(MPI_Init(0,0));
    check(MPI_Issend(&payload, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, &r1));
    check(MPI_Test(&r1, &result, MPI_STATUS_IGNORE));
    fprintf(stdout, "MPI_Test result: %d\n", result);
    check(MPI_Cancel(&r1));
    check(MPI_Wait(&r1, MPI_STATUS_IGNORE));
    MPI_Finalize();
    return 0;
}

This stalls in MPI_Wait when executed using "mpiexec -n 1 ./a.out".

Cheers,
Edric.

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