Use MPI_Init_thread if OpenMP is enabled

If MPI is used in a multi-threaded environment the MPI implementation has
to be aware of the calling context of MPI methods. Therefore, initialize
the MPI environment with MPI_Init_thread requesting the desired thread
support level. So far ls1 makes MPI calls only from the main thread, i.e., uses
MPI_THREAD_FUNNELED. For details see the MPI standard.

Signed-off-by: Christoph Niethammer <[email protected]>

src/MarDyn.cpp

@@ -132,8 +132,18 @@ int run_unit_tests(const Values &options, const std::vector<std::string> &args)
  */
 int main(int argc, char** argv) {
 #ifdef ENABLE_MPI
+#if defined(_OPENMP)
+	int thread_support_level_requested = MPI_THREAD_FUNNELED; /* So far only the main thread makes MPI calls */
+	int thread_support_level_provided = MPI_THREAD_SINGLE;
+	MPI_Init_thread(&argc, &argv, thread_support_level_requested, &thread_support_level_provided);
+	if (thread_support_level_requested < thread_support_level_provided) {
+		std::cerr << "Error: MPI implementation does not support the requested thread support level." << std::endl;
+		std::exit(EXIT_FAILURE);
+	}
+#else
 	MPI_Init(&argc, &argv);
-#endif
+#endif /* _OPENMP */
+#endif /* ENABLE_MPI */
 
 	/* Initialize the global log file */
 	Log::global_log = new Log::Logger(Log::Info);