[Mpi-forum] Progress Question

[Thakur, Rajeev]

Jim,
      I don’t fully understand your question. Is it “If all processes reach MPI_Barrier, are they guaranteed to exit the barrier without the need for any other MPI function to be called on any process?” I would say yes.

Rajeev


From: mpi-forum <mpi-forum-bounces at lists.mpi-forum.org> on behalf of Jim Dinan via mpi-forum <mpi-forum at lists.mpi-forum.org>
Reply-To: Main MPI Forum mailing list <mpi-forum at lists.mpi-forum.org>
Date: Saturday, October 10, 2020 at 12:31 PM
To: Main MPI Forum mailing list <mpi-forum at lists.mpi-forum.org>
Cc: Jim Dinan <james.dinan at gmail.com>
Subject: [Mpi-forum] Progress Question

Hi All,

A colleague recently asked a question that I wasn't able to answer definitively. Is the following code guaranteed to make progress?

MPI_Barrier();
if rank == 1
  create_file("test")
if rank == 0
   while not_exists("test")
       sleep(1);

That is, can rank 1 require rank 0 to make MPI calls after its return from the barrier, in order for rank 1 to complete the barrier? If the code were written as follows:

isend(..., other_rank, &req[0])
irecv(..., other_rank, &req[1])
waitall(2, req)
if rank == 1
  create_file("test")
if rank == 0
   while not_exists("test")
       sleep(1);

I think it would clearly not guarantee progress since the send data can be buffered. Is the same true for barrier?

Cheers,
 ~Jim.
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