OpenMPI Download and CMake Compilation Errors with C++

[Nicholas Brunk <nbrunk at iu dot edu>]

 I am trying to use Cygwin with hybrid OMP/MPI parallelization, which
worked previously with OpenMP version 1.10.7-1.  However, upon updating
this in Cygwin, the removal of the C++ compiler functionality with OMP 3+
(as reported here <https://sourceware.org/ml/cygwin/2018-09/msg00180.html>)
has caused problems.

I have tried many steps to rectify this without success, with my IDE
(CLion) always reporting during the CMake process that it "Could not find
MPI_CXX (missing:  MPI_CXX_WORKS)" and "Could not find MPI (missing:
MPI_CXX_FOUND)".  [My cygcheck file is over 1MB and the mailer daemon for
the listserver doesn't allow it to be attached.]

First, I tried simply reverting the update to the version of openmpi in
which the C++ compiler functionality was not yet deprecated, listed as
"openmpi-1.10.7-1" in the Cygwin installer.  However, regardless of mirror,
the Cygwin installer reports "The following package had download errors."
So there seems to be a download bug preventing users from installing the
listed previous version of the OpenMPI package I was using previously.
While OpenMP version 1.10.7 can be downloaded directly from the OMP website
here <https://www.open-mpi.org/software/ompi/v1.10/>, I do not know how to
install it properly into Cygwin or otherwise make my IDE (CLion) work with
the two.

Trying to get any of the new versions of openmpi (that may be downloaded
via Cygwin) working also had problems.  I see here
<https://www.open-mpi.org/software/ompi/v1.10/> others reporting this
issue, and a support person stated one can "reinstate the mpicxx wrapper
yourself," but I have no idea what this means (I'm just a physicist).  I
then saw the post here
<https://sourceware.org/ml/cygwin/2018-09/msg00216.html> stating a certain
(available) version was "reverting the removal of the C++ compiler
invocation," but installing that version does not change the errors
reported at all.  I've also seen people saying (e.g. here
<https://sourceware.org/ml/cygwin/2018-08/msg00363.html>) that
configuration of OpenMP can be done in such a way as to restore
functionality.  However, I have no idea how to actually do this within
either Cygwin or my IDE.

Can either 1) the ability to successfully download and install the older
listed version of OpenMP, be restored, or 2) a clear set of instructions
(or CMake script) that enables the new version of OpenMPI to compile with a
C++ project be provided?

Thank you so much,

Nicholas

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