From 24c38421586e891197b0e47eeef6ba919cc3612e Mon Sep 17 00:00:00 2001
From: Alexander Liemen <47395086+aliemen@users.noreply.github.com>
Date: Thu, 17 Sep 2026 13:20:21 +0200
Subject: [PATCH] Resolve include loop in ParallelDispatch and datatypes.h. Add
 small compile check as a unit test for this specific include order

---
 src/Manager/datatypes.h                   | 15 ++++++++-------
 src/Utility/ParallelDispatch.h            |  6 ++++--
 unit_tests/Utility/CMakeLists.txt         |  1 +
 unit_tests/Utility/HeaderIncludeOrder.cpp | 13 +++++++++++++
 4 files changed, 26 insertions(+), 9 deletions(-)
 create mode 100644 unit_tests/Utility/HeaderIncludeOrder.cpp

diff --git a/src/Manager/datatypes.h b/src/Manager/datatypes.h
index cabcc7da3a..60046719ad 100644
--- a/src/Manager/datatypes.h
+++ b/src/Manager/datatypes.h
@@ -1,12 +1,14 @@
 #ifndef IPPL_DATATYPES_H
 #define IPPL_DATATYPES_H
 
+#include "Ippl.h"
+
+#include "PoissonSolvers/FEMPoissonSolver.h"
 #include "PoissonSolvers/FFTOpenPoissonSolver.h"
 #include "PoissonSolvers/FFTPeriodicPoissonSolver.h"
 #include "PoissonSolvers/FFTTruncatedGreenPeriodicPoissonSolver.h"
 #include "PoissonSolvers/NullSolver.h"
 #include "PoissonSolvers/PoissonCG.h"
-#include "PoissonSolvers/FEMPoissonSolver.h"
 #include "PoissonSolvers/PreconditionedFEMPoissonSolver.h"
 
 // some typedefs
@@ -67,16 +69,15 @@ using OpenSolver_t =
     ConditionalType<Dim == 3, ippl::FFTOpenPoissonSolver<VField_t<T, Dim>, Field_t<Dim>>>;
 
 template <typename T = double, unsigned Dim = 3>
-using FEMSolver_t = ippl::FEMPoissonSolver<Field<T, Dim>, Field<T, Dim>>; 
+using FEMSolver_t = ippl::FEMPoissonSolver<Field<T, Dim>, Field<T, Dim>>;
 
 template <typename T = double, unsigned Dim = 3>
-using FEMPreconSolver_t = ippl::PreconditionedFEMPoissonSolver<Field<T, Dim>, Field<T, Dim>>; 
+using FEMPreconSolver_t = ippl::PreconditionedFEMPoissonSolver<Field<T, Dim>, Field<T, Dim>>;
 
 template <typename T = double, unsigned Dim = 3>
-using Solver_t = VariantFromConditionalTypes<CGSolver_t<T, Dim>, FFTSolver_t<T, Dim>,
-                                             FFTTruncatedGreenSolver_t<T, Dim>,
-                                             OpenSolver_t<T, Dim>, NullSolver_t<T, Dim>,
-                                             FEMSolver_t<T, Dim>, FEMPreconSolver_t<T, Dim>>;
+using Solver_t = VariantFromConditionalTypes<
+    CGSolver_t<T, Dim>, FFTSolver_t<T, Dim>, FFTTruncatedGreenSolver_t<T, Dim>,
+    OpenSolver_t<T, Dim>, NullSolver_t<T, Dim>, FEMSolver_t<T, Dim>, FEMPreconSolver_t<T, Dim>>;
 
 extern const char* TestName;
 
diff --git a/src/Utility/ParallelDispatch.h b/src/Utility/ParallelDispatch.h
index 4e342aa028..d5cf36ba79 100644
--- a/src/Utility/ParallelDispatch.h
+++ b/src/Utility/ParallelDispatch.h
@@ -7,8 +7,8 @@
 #define IPPL_PARALLEL_DISPATCH_H
 
 #include <Kokkos_Core.hpp>
-#include "Ippl.h"
 
+#include <mpi.h>
 #include <tuple>
 
 #include "Types/Vector.h"
@@ -198,7 +198,9 @@ namespace ippl {
         template <typename F>
         void parallelForMPI(size_t n, F&& f) {
             constexpr bool useGPU = isGPUSpace<Kokkos::DefaultExecutionSpace>;
-            const bool threadSafe = Env->threadMultiple();
+            int provided          = MPI_THREAD_SINGLE;
+            MPI_Query_thread(&provided);
+            const bool threadSafe = provided >= MPI_THREAD_MULTIPLE;
 
             if constexpr (useGPU) {
                 if (threadSafe) {
diff --git a/unit_tests/Utility/CMakeLists.txt b/unit_tests/Utility/CMakeLists.txt
index 687806dd2b..aa3765a3ee 100644
--- a/unit_tests/Utility/CMakeLists.txt
+++ b/unit_tests/Utility/CMakeLists.txt
@@ -2,3 +2,4 @@ file(RELATIVE_PATH _relPath "${PROJECT_SOURCE_DIR}" "${CMAKE_CURRENT_SOURCE_DIR}
 message(STATUS "Adding unit tests found in ${_relPath}")
 
 add_ippl_test(ParameterList)
+add_ippl_test(HeaderIncludeOrder COMPILE_ONLY)
diff --git a/unit_tests/Utility/HeaderIncludeOrder.cpp b/unit_tests/Utility/HeaderIncludeOrder.cpp
new file mode 100644
index 0000000000..17e90b5456
--- /dev/null
+++ b/unit_tests/Utility/HeaderIncludeOrder.cpp
@@ -0,0 +1,13 @@
+/**
+ * @file HeaderIncludeOrder.cpp
+ * @brief Verifies that Manager/datatypes.h compiles without a preceding Ippl.h include.
+ * 
+ * This small test verifies that we don't get a compiler error in OPALX when including 
+ * `datatypes.h` without first including `Ippl.h`. 
+ */
+
+#include "Manager/datatypes.h"
+
+int main() {
+    return 0;
+}