provide access to mpi comm handle for python extracts (#71)

src/ascent/runtimes/ascent_main_runtime.cpp

@@ -428,10 +428,10 @@ AscentRuntime::ConvertExtractToFlow(const conduit::Node &extract,
        // read script only on rank 0 
        if(rank == 0)
        {
+         ostringstream py_src; 
          std::string script_fname = params["file"].as_string();
          ifstream ifs(script_fname.c_str());
-
-         ostringstream py_src;
+
          py_src << "# script from: " << script_fname << std::endl;
          copy(istreambuf_iterator<char>(ifs),
               istreambuf_iterator<char>(),
@@ -449,6 +449,17 @@ AscentRuntime::ConvertExtractToFlow(const conduit::Node &extract,
        params.remove("file");
        params["source"] = n_py_src;
      }
+
+     // inject helper that provides the mpi comm handle
+     ostringstream py_src_final;
+     py_src_final << "# ascent mpi comm helper function" << std::endl
+                  << "def ascent_mpi_comm_id():" << std::endl
+                  << "    return " << comm_id << std::endl
+                  << std::endl
+                  << params["source"].as_string(); // now include user's script
+
+     params["source"] = py_src_final.str();
+
 #endif
 
     // todo, inspect args, if passed via file, read on root proc and broadcast

src/tests/ascent/t_ascent_mpi_python_extract.cpp

@@ -66,7 +66,13 @@ using ascent::Ascent;
 
 std::string py_script = "\n"
 "v = input()\n"
-"print(v['state'])\n";
+"print(v['state'])\n"
+"\n"
+"from mpi4py import MPI\n"
+"print(ascent_mpi_comm_id())\n"
+"comm = MPI.Comm.f2py(ascent_mpi_comm_id())\n"
+"print('COMM SIZE = {}'.format(comm.Get_size()))\n"
+"\n";
 
 //-----------------------------------------------------------------------------
 TEST(ascent_mpi_runtime, test_pyhton_script_extract_src)