Thank you Kenneth. I figured as much. No matter how long i searched, it seems this question keeps popping up and there is no solution to date.

On the bright side i figured, oh well, we can launch the separate workers, configure them into one intra communicator via MPI_Comm_accept() and intracomm_merge() and pass in the task via shared memory. It seems to be working although direct in-process control over task data hand-off would be nicer still.

Thank you for the issue tracker!

-dmitriy

On Tue, Apr 26, 2016 at 8:18 AM, Kenneth Raffenetti <raffenet@mcs.anl.gov> wrote:

Hi Dmitriy,

mpiexec is still needed for this type of operation with MPICH today. This ticket has some of the previous discussion about singleton init and spawn, but there hasn't been much demand for the feature. https://trac.mpich.org/projects/mpich/ticket/1074

Ken

On 04/21/2016 12:18 AM, Dmitriy Lyubimov wrote:

Hi,

I guess i need to be asking more specific questions.

I saw the same issue has been raised a few years ago and apparently
there was no solution for it back then, so i thought i'd check again.

The question is about bypassing mpiexec and trying to connect already
running processes (which already have some data in memory to share with
mpi tasks) into a single communicator without having to spawn yet
another process with mpiexec.

Suppose one of this processes uses MPI_Comm_accept, and the other
somehow know the mpi port name and would use MPI_Comm_connect() to
connect to it.

Everything works as long as both server and client started with mpiexec
-n 1. However, without mpiexec, the same attempts cause errors and
connection never happens:

mpiexec@Intel-Kubu] match_arg (utils/args/args.c:159): unrecognized
argument pmi_args
[mpiexec@Intel-Kubu] HYDU_parse_array (utils/args/args.c:174): argument
matching returned error
[mpiexec@Intel-Kubu] parse_args (ui/mpich/utils.c:1596): error parsing
input array
[mpiexec@Intel-Kubu] HYD_uii_mpx_get_parameters (ui/mpich/utils.c:1648):
unable to parse user arguments
[mpiexec@Intel-Kubu] main (ui/mpich/mpiexec.c:153): error parsing parameters

So, there's no way of working around the necessity to spawn an entirely
new process with mpiexec?

Thank you very much for your help.
-Dmitriy

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