From 6fdfe4ff4c2697c77528d66546342d00d427c24a Mon Sep 17 00:00:00 2001
From: Vitor Sessak <vsessak@google.com>
Date: Thu, 3 Sep 2026 12:27:04 +0000
Subject: [PATCH] Provide std::mutex fallback for omp_mutex_t when OpenMP is
 disabled

When compiling without OpenMP, provide standard library std::mutex fallback
wrapper functions to allow compiling omp_mutex_t locks.
---
 cpp/src/utilities/omp_helpers.hpp | 37 ++++++++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/cpp/src/utilities/omp_helpers.hpp b/cpp/src/utilities/omp_helpers.hpp
index 3fd31d169e..22a8164a5e 100644
--- a/cpp/src/utilities/omp_helpers.hpp
+++ b/cpp/src/utilities/omp_helpers.hpp
@@ -24,13 +24,47 @@ std::pair<i_t, i_t> calculate_index_range(i_t k, double total, double n)
 }  // namespace cuopt
 
 #ifdef _OPENMP
-
 #include <omp.h>
+#else
+#include <mutex>
+#endif
 #include <memory>
 #include <utility>
 
 namespace cuopt {
 
+#ifndef _OPENMP
+class omp_mutex_t {
+ public:
+  omp_mutex_t() : mutex(new std::mutex()) { }
+
+  omp_mutex_t(const omp_mutex_t&) = delete;
+
+  omp_mutex_t(omp_mutex_t&& other) { *this = std::move(other); }
+
+  omp_mutex_t& operator=(const omp_mutex_t&) = delete;
+
+  omp_mutex_t& operator=(omp_mutex_t&& other)
+  {
+    if (&other != this) {
+      mutex = std::move(other.mutex);
+    }
+    return *this;
+  }
+
+  void lock() { mutex->lock(); }
+
+  void unlock() { mutex->unlock(); }
+
+  bool try_lock() { return mutex->try_lock(); }
+
+ private:
+  std::unique_ptr<std::mutex> mutex;
+};
+#endif  // !_OPENMP
+
+#ifdef _OPENMP
+
 // Wrapper of omp_lock_t. Optionally, you can provide a hint as defined in
 // https://www.openmp.org/spec-html/5.1/openmpse39.html#x224-2570003.9
 class omp_mutex_t {
@@ -67,6 +101,7 @@ class omp_mutex_t {
  private:
   std::unique_ptr<omp_lock_t> mutex;
 };
+#endif  // _OPENMP
 
 // Empty class with the same methods as `omp_mutex_t`. This is mainly used for cleanly disabling
 // the `omp_mutex_t` via type alias (`lock` and `unlock` are replaced by NOOPs).