In the singleton class Mpi: added method Mpi::Init_thread that

performs MPI initialization using MPI_Init_thread; added method
Mpi::Init_auto that selects what MPI init mode to use based on
the configured external packages used by MFEM -- currently it
calls Mpi::Init_thread(MPI_THREAD_MULTIPLE) when using STRUMPACK
built with SLATE or PT-Scotch, otherwise it calls Mpi::Init.

In the examples that can use STRUMPACK, use Mpi::Init_auto instead
of Mpi::Init.

Fix a small unrelated issue noticed during testing: in
miniapps/multidomain/multidomain.cpp, do not open GLVis socket
connections when visualization is disabled.

examples/ex11p.cpp

@@ -58,7 +58,7 @@ using namespace mfem;
 int main(int argc, char *argv[])
 {
    // 1. Initialize MPI and HYPRE.
-   Mpi::Init(argc, argv);
+   Mpi::Init_auto();
    int num_procs = Mpi::WorldSize();
    int myid = Mpi::WorldRank();
    Hypre::Init();

examples/ex25p.cpp

@@ -155,7 +155,7 @@ prob_type prob;
 int main(int argc, char *argv[])
 {
    // 1. Initialize MPI and HYPRE.
-   Mpi::Init(argc, argv);
+   Mpi::Init_auto();
    int num_procs = Mpi::WorldSize();
    int myid = Mpi::WorldRank();
    Hypre::Init();

examples/petsc/ex11p.cpp

@@ -42,7 +42,7 @@ using namespace mfem;
 int main(int argc, char *argv[])
 {
    // 1. Initialize MPI and HYPRE.
-   Mpi::Init(argc, argv);
+   Mpi::Init_auto();
    int num_procs = Mpi::WorldSize();
    int myid = Mpi::WorldRank();
    Hypre::Init();

general/communication.cpp

@@ -26,6 +26,10 @@
 #include "sort_pairs.hpp"
 #include "globals.hpp"
 
+#ifdef MFEM_USE_STRUMPACK
+#include <StrumpackConfig.hpp> // STRUMPACK_USE_PTSCOTCH, etc
+#endif
+
 #include <iostream>
 #include <map>
 
@@ -34,6 +38,51 @@ using namespace std;
 namespace mfem
 {
 
+// static private method
+void Mpi::Init_(int *argc, char ***argv)
+{
+   MFEM_VERIFY(!IsInitialized(), "MPI already initialized!")
+#if defined(MFEM_USE_STRUMPACK)
+#if defined(STRUMPACK_USE_PTSCOTCH) || defined(STRUMPACK_USE_SLATE_SCALAPACK)
+   if (Root())
+   {
+      MFEM_WARNING("STRUMPACK built with SLATE or PT-Scotch may require "
+                   "MPI_Init_thread with MPI_THREAD_MULTIPLE!");
+   }
+#endif
+#endif
+   int mpi_err = MPI_Init(argc, argv);
+   MFEM_VERIFY(!mpi_err, "error in MPI_Init()!");
+   // The Mpi singleton object below needs to be created after MPI_Init() for
+   // some MPI implementations
+   Singleton();
+}
+
+// static public method
+void Mpi::Init_thread(int required, int *provided)
+{
+   MFEM_VERIFY(!IsInitialized(), "MPI already initialized!")
+   int provided_;
+   int mpi_err = MPI_Init_thread(nullptr, nullptr, required,
+                                 provided ? provided : &provided_);
+   MFEM_VERIFY(!mpi_err, "error in MPI_Init_thread()!");
+   // The Mpi singleton object below needs to be created after MPI_Init() for
+   // some MPI implementations
+   Singleton();
+}
+
+// static public method
+void Mpi::Init_auto()
+{
+#if defined(MFEM_USE_STRUMPACK) && \
+    (defined(STRUMPACK_USE_PTSCOTCH) || defined(STRUMPACK_USE_SLATE_SCALAPACK))
+   Mpi::Init_thread(MPI_THREAD_MULTIPLE);
+#else
+   Mpi::Init();
+#endif
+}
+
+
 GroupTopology::GroupTopology(const GroupTopology &gt)
    : MyComm(gt.MyComm),
      group_lproc(gt.group_lproc)

general/communication.hpp

@@ -36,6 +36,18 @@ public:
    static void Init() { Init_(NULL, NULL); }
    /// Singleton creation with Mpi::Init(argc,argv);
    static void Init(int &argc, char **&argv) { Init_(&argc, &argv); }
+   /// Singleton creation; MPI is initialized using MPI_Init_thread.
+   /** For a description of the parameters @a required and @a provided, see the
+       documentation for MPI_Init_thread. When the parameter @a provided is
+       @c nullptr (default), no output value is returned. */
+   static void Init_thread(int required, int *provided = nullptr);
+   /** @brief Singleton creation; MPI is initialized appropriately for all
+       configured external libraries used by MFEM. */
+   /** @note In some cases, this method may not be able to select the correct
+       MPI initialization method. In such cases, initialization with Mpi::Init()
+       or Mpi::Init_thread() is recommended based on the needs of the
+       application. */
+   static void Init_auto();
    /// Finalize MPI (if it has been initialized and not yet already finalized).
    static void Finalize()
    {
@@ -72,23 +84,14 @@ public:
    /// Return true if the rank in MPI_COMM_WORLD is zero.
    static bool Root() { return WorldRank() == 0; }
 private:
-   /// Initialize MPI
-   static void Init_(int *argc, char ***argv)
+   /// Initialize the Mpi singleton.
+   static Mpi &Singleton()
    {
-      MFEM_VERIFY(!IsInitialized(), "MPI already initialized!")
-#if defined(MFEM_USE_STRUMPACK)
-#if defined(STRUMPACK_USE_PTSCOTCH) || defined(STRUMPACK_USE_SLATE_SCALAPACK)
-      if (Root())
-      {
-         MFEM_WARNING("STRUMPACK built with SLATE or PT-Scotch may require MPI_Init_thread with MPI_THREAD_MULTIPLE!");
-      }
-#endif
-#endif
-      MPI_Init(argc, argv);
-      // The "mpi" object below needs to be created after MPI_Init() for some
-      // MPI implementations
       static Mpi mpi;
+      return mpi;
    }
+   /// Initialize MPI using MPI_Init()
+   static void Init_(int *argc, char ***argv);
    /// Finalize MPI
    ~Mpi() { Finalize(); }
    /// Prevent direct construction of objects of this class

miniapps/multidomain/multidomain.cpp

@@ -322,17 +322,19 @@ int main(int argc, char *argv[])
 
    char vishost[] = "localhost";
    int  visport   = 19916;
-   socketstream cyl_sol_sock(vishost, visport);
+   socketstream cyl_sol_sock;
    if (visualization)
    {
+      cyl_sol_sock.open(vishost, visport);
       cyl_sol_sock << "parallel " << num_procs << " " << myid << "\n";
       cyl_sol_sock.precision(8);
       cyl_sol_sock << "solution\n" << cylinder_submesh << temperature_cylinder_gf <<
                    "pause\n" << std::flush;
    }
-   socketstream block_sol_sock(vishost, visport);
+   socketstream block_sol_sock;
    if (visualization)
    {
+      block_sol_sock.open(vishost, visport);
       block_sol_sock << "parallel " << num_procs << " " << myid << "\n";
       block_sol_sock.precision(8);
       block_sol_sock << "solution\n" << block_submesh << temperature_block_gf <<