ENH: support external MPI initialize / finalize (#1266)

applications/test/parallel-external-init/Test-parallel-external-init.C

@@ -0,0 +1,106 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2019 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Application
+    Test-parallel-external-init
+
+Description
+    Simulate starting MPI outside of OpenFOAM
+
+\*---------------------------------------------------------------------------*/
+
+#include "argList.H"
+#include "Time.H"
+#include "IPstream.H"
+#include "OPstream.H"
+#include "vector.H"
+#include "IOstreams.H"
+#include "Pstream.H"
+
+#include <mpi.h>
+#include <iostream>
+
+using namespace Foam;
+
+
+bool startMPI()
+{
+    int nprocs = 0, rank = 0;
+
+    MPI_Init(nullptr, nullptr);
+
+    MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
+    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+
+    if (nprocs && rank == 0)
+    {
+        std::cout<< nl << "Using MPI with " << nprocs << " procs" << nl << nl;
+    }
+
+    return true;
+}
+
+
+bool stopMPI()
+{
+    Info<< nl << "Stopping MPI" << nl << nl;
+
+    MPI_Finalize();
+
+    return true;
+}
+
+
+string message()
+{
+    return
+    (
+        "rank " + name(Pstream::myProcNo())
+      + " / " + name(Pstream::nProcs()) + "\n"
+    );
+}
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+int main(int argc, char *argv[])
+{
+    argList::noCheckProcessorDirectories();
+
+    UPstream::debug = 1;
+
+    startMPI();
+
+    #include "setRootCase.H"
+
+    Pout<< message().c_str();
+
+    stopMPI();
+
+    Info<< "\nEnd\n" << endl;
+
+    return 0;
+}
+
+
+// ************************************************************************* //