Add capability to launch serial jobs through wrapper

[climbfuji]

We've come across an unusual system where you can't run an executable that was compiled with an MPI wrapper without srun, even if you want to execute it as a non-MPI (serial, 1 process) application.

For this, it would be nice to be able to launch serial jobs through a wrapper, similar to how MPI jobs are launched. I made the following changes for the latest ecbuild code in this repository:

https://github.com/ecmwf/ecbuild/compare/develop...climbfuji:feature/serexec

I then used

ecbuild -DMPIEXEC_EXECUTABLE="/usr/bin/srun" -DMPIEXEC_NUMPROC_FLAG="-n" -DSEREXEC="/usr/bin/srun" -DSEREXEC_NUMPROC_FLAG="-n" ..
make
ctest

and it worked like a charm.

I am happy to issue a pull request and, if so desired, change the names of the new flags (e.g. one could use -DSEREXEC_EXECUTABLE and -DSEREXEC_NUMPROC_FLAG or something else if SEREXEC sounds bad).

If there is already a solution in place that I haven't seen (I read through the entire file cmake/ecbuild_add_test.cmake), then please let me know.

[wdeconinck]

This is not a ecbuild issue per se. I usually solve it with https://cmake.org/cmake/help/latest/variable/CMAKE_CROSSCOMPILING_EMULATOR.html To do this:

echo 'srun -n 1 "$''@"'   > serial_run
chmod 755 serial_run

Then configure (or reconfigure) with

cmake . -DCMAKE_CROSSCOMPILING_EMULATOR=${PWD}/serial_run -DMPIEXEC_EXECUTABLE="/usr/bin/srun" -DMPIEXEC_NUMPROC_FLAG="-n"

Now ctest should work.

[wdeconinck]

Following simpler approach will also work as of cmake 3.15:

cmake . -DCMAKE_CROSSCOMPILING_EMULATOR=/usr/bin/srun;-n;1 -DMPIEXEC_EXECUTABLE="/usr/bin/srun" -DMPIEXEC_NUMPROC_FLAG="-n"

[climbfuji]

Thanks @wdeconinck, I will try that and report back. I also asked the sysadmins on Gaea if they can change their system settings so that this won't be needed.

[climbfuji]

@wdeconinck Finally got around to test your suggestion, and it works fine. Closing this issue.