feat(ntp): update NTP time service singleton

Refactor the NTP time service to use the eternal singleton pattern with optional DLL support.
Add an ODR test target covering DLL singleton macros and adjust test setup.

Author: NewYaroslav

include/time_shield/ntp_time_service.hpp

@@ -179,15 +179,42 @@ namespace time_shield {
         };
 #endif // _TIME_SHIELD_TEST_FAKE_NTP
 
-#ifndef TIME_SHIELD_CPP17
 #if defined(TIME_SHIELD_TEST_FAKE_NTP)
         using RunnerAlias = detail::FakeNtpRunner;
 #else
         using RunnerAlias = NtpClientPoolRunner;
 #endif
 
-        extern NtpTimeServiceT<RunnerAlias> g_ntp_time_service;
-#endif // !TIME_SHIELD_CPP17
+#if defined(TIME_SHIELD_NTP_TIME_SERVICE_USE_DLL_SINGLETON)
+#if defined(_WIN32) || defined(__CYGWIN__)
+#ifdef TIME_SHIELD_NTP_TIME_SERVICE_DLL_EXPORTS
+#define TIME_SHIELD_NTP_TIME_SERVICE_API __declspec(dllexport)
+#else
+#define TIME_SHIELD_NTP_TIME_SERVICE_API __declspec(dllimport)
+#endif
+#else
+#define TIME_SHIELD_NTP_TIME_SERVICE_API
+#endif
+
+        extern "C" TIME_SHIELD_NTP_TIME_SERVICE_API NtpTimeServiceT<RunnerAlias>& ntp_time_service_instance() noexcept;
+#endif
+
+        template <class RunnerT>
+        struct NtpTimeServiceSingleton final {
+            static NtpTimeServiceT<RunnerT>& instance() noexcept {
+                static NtpTimeServiceT<RunnerT>* p_instance = new NtpTimeServiceT<RunnerT>{};
+                return *p_instance;
+            }
+        };
+
+#if defined(TIME_SHIELD_NTP_TIME_SERVICE_USE_DLL_SINGLETON)
+        template <>
+        struct NtpTimeServiceSingleton<RunnerAlias> final {
+            static NtpTimeServiceT<RunnerAlias>& instance() noexcept {
+                return ntp_time_service_instance();
+            }
+        };
+#endif
     } // namespace detail
 
     /// \ingroup ntp
@@ -202,11 +229,7 @@ namespace time_shield {
         /// \brief Return the singleton instance.
         /// \return Singleton instance.
         static NtpTimeServiceT& instance() noexcept {
-#ifdef TIME_SHIELD_CPP17
-            return m_instance;
-#else
-            return detail::g_ntp_time_service;
-#endif
+            return detail::NtpTimeServiceSingleton<RunnerT>::instance();
         }
 
         NtpTimeServiceT(const NtpTimeServiceT&) = delete;
@@ -532,21 +555,14 @@ namespace time_shield {
 
         std::unique_ptr<RunnerT> m_runner;
 
-#ifdef TIME_SHIELD_CPP17
-        static NtpTimeServiceT m_instance;
-#endif
     };
 
-#ifdef TIME_SHIELD_CPP17
-    template <class RunnerT>
-    inline NtpTimeServiceT<RunnerT> NtpTimeServiceT<RunnerT>::m_instance{};
-#endif
-
-#ifndef TIME_SHIELD_CPP17
+#if defined(TIME_SHIELD_NTP_TIME_SERVICE_USE_DLL_SINGLETON) && defined(TIME_SHIELD_NTP_TIME_SERVICE_DLL_IMPLEMENTATION)
 namespace detail {
-#if defined(TIME_SHIELD_NTP_TIME_SERVICE_DEFINE)
-    NtpTimeServiceT<RunnerAlias> g_ntp_time_service;
-#endif
+    extern "C" TIME_SHIELD_NTP_TIME_SERVICE_API NtpTimeServiceT<RunnerAlias>& ntp_time_service_instance() noexcept {
+        static NtpTimeServiceT<RunnerAlias>* p_instance = new NtpTimeServiceT<RunnerAlias>{};
+        return *p_instance;
+    }
 } // namespace detail
 #endif
 

tests/ntp_time_service_test.cpp

@@ -2,7 +2,6 @@
 
 #if TIME_SHIELD_ENABLE_NTP_CLIENT
 #define TIME_SHIELD_TEST_FAKE_NTP
-#define TIME_SHIELD_NTP_TIME_SERVICE_DEFINE
 #include <time_shield/ntp_time_service.hpp>
 
 #include <cassert>

tests/odr/CMakeLists.txt

@@ -14,3 +14,14 @@ target_link_libraries(odr_cxx17 PRIVATE time_shield::time_shield)
 set_target_properties(odr_cxx17 PROPERTIES CXX_STANDARD 17 CXX_STANDARD_REQUIRED YES)
 
 add_test(NAME odr_cxx17 COMMAND odr_cxx17)
+
+set(NTP_TIME_SERVICE_DLL_SOURCES
+    ntp_time_service_dll_a.cpp
+    ntp_time_service_dll_b.cpp
+)
+
+add_executable(ntp_time_service_dll_odr ${NTP_TIME_SERVICE_DLL_SOURCES})
+target_link_libraries(ntp_time_service_dll_odr PRIVATE time_shield::time_shield)
+set_target_properties(ntp_time_service_dll_odr PROPERTIES CXX_STANDARD 11 CXX_STANDARD_REQUIRED YES)
+
+add_test(NAME ntp_time_service_dll_odr COMMAND ntp_time_service_dll_odr)

tests/odr/ntp_time_service_dll_a.cpp

@@ -0,0 +1,22 @@
+#include <time_shield/config.hpp>
+
+#if TIME_SHIELD_ENABLE_NTP_CLIENT
+#define TIME_SHIELD_TEST_FAKE_NTP
+#define TIME_SHIELD_NTP_TIME_SERVICE_USE_DLL_SINGLETON
+#define TIME_SHIELD_NTP_TIME_SERVICE_DLL_EXPORTS
+#define TIME_SHIELD_NTP_TIME_SERVICE_DLL_IMPLEMENTATION
+#include <time_shield/ntp_time_service.hpp>
+
+int ntp_time_service_dll_helper();
+
+int main() {
+    auto& service = time_shield::NtpTimeService::instance();
+    service.shutdown();
+    (void)ntp_time_service_dll_helper();
+    return 0;
+}
+#else
+int main() {
+    return 0;
+}
+#endif

tests/odr/ntp_time_service_dll_b.cpp

@@ -0,0 +1,16 @@
+#include <time_shield/config.hpp>
+
+#if TIME_SHIELD_ENABLE_NTP_CLIENT
+#define TIME_SHIELD_TEST_FAKE_NTP
+#define TIME_SHIELD_NTP_TIME_SERVICE_USE_DLL_SINGLETON
+#define TIME_SHIELD_NTP_TIME_SERVICE_DLL_EXPORTS
+#include <time_shield/ntp_time_service.hpp>
+
+int ntp_time_service_dll_helper() {
+    return time_shield::NtpTimeService::instance().running() ? 1 : 0;
+}
+#else
+int ntp_time_service_dll_helper() {
+    return 0;
+}
+#endif