diff --git a/GridKit/Model/PhasorDynamics/Controller/REECB/ReecbImpl.hpp b/GridKit/Model/PhasorDynamics/Controller/REECB/ReecbImpl.hpp
index 2ed478014c..5917d14b22 100644
--- a/GridKit/Model/PhasorDynamics/Controller/REECB/ReecbImpl.hpp
+++ b/GridKit/Model/PhasorDynamics/Controller/REECB/ReecbImpl.hpp
@@ -8,7 +8,7 @@
 
 #include <algorithm>
 #include <array>
-#include <mutex>
+#include <atomic>
 #include <variant>
 
 #include <GridKit/Model/PhasorDynamics/BusBase.hpp>
@@ -1378,8 +1378,8 @@ namespace GridKit
       /**
        * @brief Static method to log time constant warnings
        *
-       * @note Used in combination with static std:once_flag and std:call_once,
-       *       to reduce the number of times the warning is printed.
+       * @note Guarded by a static std::atomic<bool> flag so the warning is
+       *       printed at most once per model type.
        */
       template <typename scalar_type, typename index_type>
       void Reecb<scalar_type, index_type>::logTimeConstantWarning()
@@ -1408,9 +1408,11 @@ namespace GridKit
 
         if (floor_warning)
         {
-          static std::once_flag time_constant_warning_flag_;
-          std::call_once(time_constant_warning_flag_,
-                         &logTimeConstantWarning);
+          static std::atomic<bool> time_constant_warning_flag_{false};
+          if (!time_constant_warning_flag_.exchange(true))
+          {
+            logTimeConstantWarning();
+          }
         }
 
         if (PfFlag_ && QFlag_)
diff --git a/GridKit/Model/PhasorDynamics/Controller/REPCA/RepcaImpl.hpp b/GridKit/Model/PhasorDynamics/Controller/REPCA/RepcaImpl.hpp
index df9da208a3..1e266055db 100644
--- a/GridKit/Model/PhasorDynamics/Controller/REPCA/RepcaImpl.hpp
+++ b/GridKit/Model/PhasorDynamics/Controller/REPCA/RepcaImpl.hpp
@@ -7,7 +7,7 @@
 #pragma once
 
 #include <algorithm>
-#include <mutex>
+#include <atomic>
 #include <variant>
 
 #include <GridKit/Model/PhasorDynamics/BusBase.hpp>
@@ -960,8 +960,8 @@ namespace GridKit
       /**
        * @brief Static method to log time constant warnings
        *
-       * @note Used in combination with static std:once_flag and std:call_once,
-       *       to reduce the number of times the warning is printed.
+       * @note Guarded by a static std::atomic<bool> flag so the warning is
+       *       printed at most once per model type.
        */
       template <typename scalar_type, typename index_type>
       void Repca<scalar_type, index_type>::logTimeConstantWarning()
@@ -1000,9 +1000,11 @@ namespace GridKit
         if (Tfltr_ < TIME_CONSTANT_MINIMUM || Tfv_ < TIME_CONSTANT_MINIMUM
             || Tp_ < TIME_CONSTANT_MINIMUM || Tlag_ < TIME_CONSTANT_MINIMUM)
         {
-          static std::once_flag time_constant_warning_flag_;
-          std::call_once(time_constant_warning_flag_,
-                         &logTimeConstantWarning);
+          static std::atomic<bool> time_constant_warning_flag_{false};
+          if (!time_constant_warning_flag_.exchange(true))
+          {
+            logTimeConstantWarning();
+          }
         }
 
         Tfltr_ = std::max(Tfltr_, TIME_CONSTANT_MINIMUM);
diff --git a/GridKit/Model/PhasorDynamics/Converter/REGCA/RegcaImpl.hpp b/GridKit/Model/PhasorDynamics/Converter/REGCA/RegcaImpl.hpp
index 233a5be867..cf585b6bd0 100644
--- a/GridKit/Model/PhasorDynamics/Converter/REGCA/RegcaImpl.hpp
+++ b/GridKit/Model/PhasorDynamics/Converter/REGCA/RegcaImpl.hpp
@@ -7,8 +7,8 @@
 #pragma once
 
 #include <algorithm>
+#include <atomic>
 #include <cmath>
-#include <mutex>
 #include <variant>
 
 #include <GridKit/Model/PhasorDynamics/BusBase.hpp>
@@ -66,8 +66,8 @@ namespace GridKit
       /**
        * @brief Static method to log time constant warnings
        *
-       * @note Used in combination with static std:once_flag and std:call_once,
-       *       to reduce the number of times the warning is printed.
+       * @note Guarded by a static std::atomic<bool> flag so the warning is
+       *       printed at most once per model type.
        */
       template <typename scalar_type, typename index_type>
       void Regca<scalar_type, index_type>::logTimeConstantWarning()
@@ -89,9 +89,11 @@ namespace GridKit
       {
         if (Tg_ < TIME_CONSTANT_MINIMUM || TM_ < TIME_CONSTANT_MINIMUM)
         {
-          static std::once_flag time_constant_warning_flag_;
-          std::call_once(time_constant_warning_flag_,
-                         &logTimeConstantWarning);
+          static std::atomic<bool> time_constant_warning_flag_{false};
+          if (!time_constant_warning_flag_.exchange(true))
+          {
+            logTimeConstantWarning();
+          }
         }
 
         Tg_          = std::max(Tg_, TIME_CONSTANT_MINIMUM);
diff --git a/GridKit/Model/PhasorDynamics/Exciter/ESDC1A/Esdc1aImpl.hpp b/GridKit/Model/PhasorDynamics/Exciter/ESDC1A/Esdc1aImpl.hpp
index a4af51239a..505fc83d7f 100644
--- a/GridKit/Model/PhasorDynamics/Exciter/ESDC1A/Esdc1aImpl.hpp
+++ b/GridKit/Model/PhasorDynamics/Exciter/ESDC1A/Esdc1aImpl.hpp
@@ -7,7 +7,7 @@
 #pragma once
 
 #include <algorithm>
-#include <mutex>
+#include <atomic>
 #include <variant>
 
 #include <GridKit/Model/PhasorDynamics/BusBase.hpp>
@@ -771,8 +771,8 @@ namespace GridKit
       /**
        * @brief Static method to log time constant warnings
        *
-       * @note Used in combination with static std:once_flag and std:call_once,
-       *       to reduce the number of times the warning is printed.
+       * @note Guarded by a static std::atomic<bool> flag so the warning is
+       *       printed at most once per model type.
        */
       template <typename scalar_type, typename index_type>
       void Esdc1a<scalar_type, index_type>::logTimeConstantWarning()
@@ -817,9 +817,11 @@ namespace GridKit
             || Tb_ < TIME_CONSTANT_MINIMUM || Te_ < TIME_CONSTANT_MINIMUM
             || Tf1_ < TIME_CONSTANT_MINIMUM)
         {
-          static std::once_flag time_constant_warning_flag_;
-          std::call_once(time_constant_warning_flag_,
-                         &logTimeConstantWarning);
+          static std::atomic<bool> time_constant_warning_flag_{false};
+          if (!time_constant_warning_flag_.exchange(true))
+          {
+            logTimeConstantWarning();
+          }
         }
 
         Tr_  = std::max(Tr_, TIME_CONSTANT_MINIMUM);
diff --git a/GridKit/Model/PhasorDynamics/Exciter/IEEET1/Ieeet1Impl.hpp b/GridKit/Model/PhasorDynamics/Exciter/IEEET1/Ieeet1Impl.hpp
index 6be4cf1ebb..0074d0e33b 100644
--- a/GridKit/Model/PhasorDynamics/Exciter/IEEET1/Ieeet1Impl.hpp
+++ b/GridKit/Model/PhasorDynamics/Exciter/IEEET1/Ieeet1Impl.hpp
@@ -8,8 +8,8 @@
  */
 
 #include <algorithm>
+#include <atomic>
 #include <iostream>
-#include <mutex>
 
 #include <GridKit/Model/PhasorDynamics/Bus/Bus.hpp>
 #include <GridKit/Model/PhasorDynamics/Exciter/IEEET1/Ieeet1.hpp>
@@ -550,8 +550,8 @@ namespace GridKit
       /**
        * @brief Static method to log time constant warnings
        *
-       * @note Used in combination with static std:once_flag and std:call_once,
-       *       to reduce the number of times the warning is printed.
+       * @note Guarded by a static std::atomic<bool> flag so the warning is
+       *       printed at most once per model type.
        */
       template <typename scalar_type, typename index_type>
       void Ieeet1<scalar_type, index_type>::logTimeConstantWarning()
@@ -570,9 +570,11 @@ namespace GridKit
         if (Tr_ < TIME_CONSTANT_MINIMUM || Ta_ < TIME_CONSTANT_MINIMUM
             || Te_ < TIME_CONSTANT_MINIMUM || Tf_ < TIME_CONSTANT_MINIMUM)
         {
-          static std::once_flag time_constant_warning_flag_;
-          std::call_once(time_constant_warning_flag_,
-                         &logTimeConstantWarning);
+          static std::atomic<bool> time_constant_warning_flag_{false};
+          if (!time_constant_warning_flag_.exchange(true))
+          {
+            logTimeConstantWarning();
+          }
         }
 
         Tr_ = std::max(Tr_, TIME_CONSTANT_MINIMUM);
diff --git a/GridKit/Model/PhasorDynamics/Governor/GASTPTI/GastPtiImpl.hpp b/GridKit/Model/PhasorDynamics/Governor/GASTPTI/GastPtiImpl.hpp
index e35cc8a2a1..92aa4f1e0b 100644
--- a/GridKit/Model/PhasorDynamics/Governor/GASTPTI/GastPtiImpl.hpp
+++ b/GridKit/Model/PhasorDynamics/Governor/GASTPTI/GastPtiImpl.hpp
@@ -7,8 +7,8 @@
 #pragma once
 
 #include <algorithm>
+#include <atomic>
 #include <cassert>
-#include <mutex>
 #include <variant>
 
 #include <GridKit/Model/PhasorDynamics/Governor/GASTPTI/GastPti.hpp>
@@ -703,8 +703,8 @@ namespace GridKit
       /**
        * @brief Static method to log time constant warnings
        *
-       * @note Used in combination with static std:once_flag and std:call_once,
-       *       to reduce the number of times the warning is printed.
+       * @note Guarded by a static std::atomic<bool> flag so the warning is
+       *       printed at most once per model type.
        */
       template <typename scalar_type, typename index_type>
       void GastPti<scalar_type, index_type>::logTimeConstantWarning()
@@ -735,9 +735,11 @@ namespace GridKit
 
         if (floor_warning)
         {
-          static std::once_flag time_constant_warning_flag_;
-          std::call_once(time_constant_warning_flag_,
-                         &logTimeConstantWarning);
+          static std::atomic<bool> time_constant_warning_flag_{false};
+          if (!time_constant_warning_flag_.exchange(true))
+          {
+            logTimeConstantWarning();
+          }
         }
 
         Vmin_response_ = Vmin_;
diff --git a/GridKit/Model/PhasorDynamics/Governor/HYGOV/HygovImpl.hpp b/GridKit/Model/PhasorDynamics/Governor/HYGOV/HygovImpl.hpp
index 71ada99e05..1ad51b4240 100644
--- a/GridKit/Model/PhasorDynamics/Governor/HYGOV/HygovImpl.hpp
+++ b/GridKit/Model/PhasorDynamics/Governor/HYGOV/HygovImpl.hpp
@@ -7,7 +7,7 @@
 #pragma once
 
 #include <algorithm>
-#include <mutex>
+#include <atomic>
 #include <numeric>
 #include <variant>
 
@@ -753,8 +753,8 @@ namespace GridKit
       /**
        * @brief Static method to log time constant warnings
        *
-       * @note Used in combination with static std:once_flag and std:call_once,
-       *       to reduce the number of times the warning is printed.
+       * @note Guarded by a static std::atomic<bool> flag so the warning is
+       *       printed at most once per model type.
        */
       template <typename scalar_type, typename index_type>
       void Hygov<scalar_type, index_type>::logTimeConstantWarning()
@@ -816,9 +816,11 @@ namespace GridKit
             || Tg_ < TIME_CONSTANT_MINIMUM || Tw_ < TIME_CONSTANT_MINIMUM
             || Tnp_ < TIME_CONSTANT_MINIMUM)
         {
-          static std::once_flag time_constant_warning_flag_;
-          std::call_once(time_constant_warning_flag_,
-                         &logTimeConstantWarning);
+          static std::atomic<bool> time_constant_warning_flag_{false};
+          if (!time_constant_warning_flag_.exchange(true))
+          {
+            logTimeConstantWarning();
+          }
         }
 
         // HYGOV residuals solve explicitly for the state derivatives to preserve
diff --git a/GridKit/Model/PhasorDynamics/Governor/Tgov1/Tgov1Impl.hpp b/GridKit/Model/PhasorDynamics/Governor/Tgov1/Tgov1Impl.hpp
index 01843aa0fc..a50c3a2748 100644
--- a/GridKit/Model/PhasorDynamics/Governor/Tgov1/Tgov1Impl.hpp
+++ b/GridKit/Model/PhasorDynamics/Governor/Tgov1/Tgov1Impl.hpp
@@ -9,7 +9,7 @@
  */
 
 #include <algorithm>
-#include <mutex>
+#include <atomic>
 
 #include <GridKit/Model/PhasorDynamics/Governor/Tgov1/Tgov1.hpp>
 #include <GridKit/Model/PhasorDynamics/Governor/Tgov1/Tgov1Data.hpp>
@@ -134,8 +134,8 @@ namespace GridKit
       /**
        * @brief Static method to log time constant warnings
        *
-       * @note Used in combination with static std:once_flag and std:call_once,
-       *       to reduce the number of times the warning is printed.
+       * @note Guarded by a static std::atomic<bool> flag so the warning is
+       *       printed at most once per model type.
        */
       template <typename scalar_type, typename index_type>
       void Tgov1<scalar_type, index_type>::logTimeConstantWarning()
@@ -149,9 +149,11 @@ namespace GridKit
       {
         if (T1_ < TIME_CONSTANT_MINIMUM || T3_ < TIME_CONSTANT_MINIMUM)
         {
-          static std::once_flag time_constant_warning_flag_;
-          std::call_once(time_constant_warning_flag_,
-                         &logTimeConstantWarning);
+          static std::atomic<bool> time_constant_warning_flag_{false};
+          if (!time_constant_warning_flag_.exchange(true))
+          {
+            logTimeConstantWarning();
+          }
         }
 
         T1_ = std::max(T1_, TIME_CONSTANT_MINIMUM);