Hello wg-persistence,

Looking at the MPI 4.0 document, it is not clear to us, whether it is
allowed to call a completion call for a partitioned communication
request before all partitions are marked ready. A simple single-threaded
example would be:

```C
MPI_Psend_init(message, partitions, COUNT, MPI_DOUBLE, dest, tag,
                MPI_COMM_WORLD, MPI_INFO_NULL, &request);
MPI_Start(&request);
for(i = 0; i < partitions-1; ++i)
{
     MPI_Pready(i, request);
}
MPI_Test(&request, &flag, MPI_STATUS_IGNORE); // flag will always be 0
MPI_Pready(partitions-1, request);
MPI_Wait(&request, MPI_STATUS_IGNORE);
MPI_Request_free(&request);
```

The question becomes more relevant in a multi-threaded context. One
thread could finish the work early and call MPI_Wait to detect when all
partitions were sent.

 From my understanding, the only requirement is that all partitions must
be marked ready with explicit ready calls before the operation can
complete. Replacing the test in above example with a wait call would
result in deadlock.

Best
Joachim

--
Dr. rer. nat. Joachim Jenke

IT Center
Group: High Performance Computing
Division: Computational Science and Engineering
RWTH Aachen University
Seffenter Weg 23
D 52074  Aachen (Germany)
Tel: +49 241 80- 24765
Fax: +49 241 80-624765
protze@itc.rwth-aachen.de
www.itc.rwth-aachen.de
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