Add new CLI option to allow parallel output

src/utils/Messenger.cpp

@@ -9,10 +9,10 @@ namespace parallel
 Messenger* Messenger::m_instance = nullptr;
 
 void
-Messenger::create(int& argc, char* argv[])
+Messenger::create(int& argc, char* argv[], bool parallel_output)
 {
   if (Messenger::m_instance == nullptr) {
-    Messenger::m_instance = new Messenger(argc, argv);
+    Messenger::m_instance = new Messenger(argc, argv, parallel_output);
   } else {
     throw UnexpectedError("Messenger already created");
   }
@@ -28,7 +28,7 @@ Messenger::destroy()
   }
 }
 
-Messenger::Messenger([[maybe_unused]] int& argc, [[maybe_unused]] char* argv[])
+Messenger::Messenger([[maybe_unused]] int& argc, [[maybe_unused]] char* argv[], bool parallel_output)
 {
 #ifdef PUGS_HAS_MPI
   MPI_Init(&argc, &argv);
@@ -66,7 +66,7 @@ Messenger::Messenger([[maybe_unused]] int& argc, [[maybe_unused]] char* argv[])
     return size;
   }();
 
-  if (m_rank != 0) {
+  if ((not parallel_output) and (m_rank != 0)) {
     // LCOV_EXCL_START
     std::cout.setstate(std::ios::badbit);
     std::cerr.setstate(std::ios::badbit);