Fix CI: the app needs to be able to work without MPI support

runtime/cudaq.h

@@ -219,6 +219,9 @@ std::size_t get_random_seed();
 int num_available_gpus();
 
 namespace mpi {
+/// @brief Return true if CUDA Quantum has MPI plugin support.
+bool available();
+
 /// @brief Initialize MPI if available. This function
 /// is a no-op if there CUDA Quantum has not been built
 /// against MPI.

runtime/cudaq/cudaq.cpp

@@ -116,6 +116,11 @@ cudaq::MPIPlugin *getMpiPlugin(bool unsafe) {
   return g_plugin.get();
 };
 
+bool available() {
+  auto *commPlugin = getMpiPlugin(true);
+  return commPlugin != nullptr;
+}
+
 void initialize() {
   auto *commPlugin = getMpiPlugin();
   commPlugin->initialize();

tools/cudaq-qpud/RestServerMain.cpp

@@ -15,6 +15,7 @@ namespace cudaq {
 namespace mpi {
 void initialize();
 void finalize();
+bool available();
 } // namespace mpi
 } // namespace cudaq
 
@@ -28,9 +29,11 @@ static llvm::cl::opt<int>
 
 int main(int argc, char **argv) {
   llvm::cl::ParseCommandLineOptions(argc, argv, "CUDA Quantum REST server\n");
-  cudaq::mpi::initialize();
+  if (cudaq::mpi::available())
+    cudaq::mpi::initialize();
   auto restServer = cudaq::registry::get<cudaq::RemoteRuntimeServer>("rest");
   restServer->init({{"port", std::to_string(port)}});
   restServer->start();
-  cudaq::mpi::finalize();
+  if (cudaq::mpi::available())
+    cudaq::mpi::finalize();
 }