From 8bb9197adcb5b40edb10fa0359cc59f2cf9e9937 Mon Sep 17 00:00:00 2001
From: Jeffrey Walton <noloader@gmail.com>
Date: Mon, 2 May 2016 23:38:10 -0400
Subject: [PATCH] Add atomics support

---
 config.h         | 13 +++++++++++++
 config.recommend | 13 +++++++++++++
 misc.h           | 32 +++++++++++++++++++++++++++++++-
 stdcpp.h         |  4 ++++
 4 files changed, 61 insertions(+), 1 deletion(-)

diff --git a/config.h b/config.h
index 2e71bcb8..3d4673ea 100644
--- a/config.h
+++ b/config.h
@@ -664,6 +664,19 @@ NAMESPACE_END
 // C++11 or C++14 is available
 #if defined(CRYPTOPP_CXX11) 
 
+// atomics: MS at VS2012 (17.00); GCC at 4.4; Clang at 3.1/3.2; and Intel 13.0.
+#if (CRYPTOPP_MSC_VERSION >= 1700)
+#  define CRYPTOPP_CXX11_ATOMICS 1
+#elif defined(__INTEL_COMPILER) && (__INTEL_COMPILER >= 1300)
+#  define CRYPTOPP_CXX11_ATOMICS 1
+#elif defined(__clang__)
+#  if __has_feature(cxx_atomic)
+#    define CRYPTOPP_CXX11_ATOMICS 1
+#  endif
+#elif (CRYPTOPP_GCC_VERSION >= 40400)
+#  define CRYPTOPP_CXX11_ATOMICS 1
+#endif // atomics
+
 // alignof/alignas: MS at VS2013 (19.00); GCC at 4.8; Clang at 3.3; and Intel 15.0.
 #if (CRYPTOPP_MSC_VERSION >= 1900)
 #  define CRYPTOPP_CXX11_ALIGNAS 1
diff --git a/config.recommend b/config.recommend
index ad845e88..66a69fd3 100644
--- a/config.recommend
+++ b/config.recommend
@@ -664,6 +664,19 @@ NAMESPACE_END
 // C++11 or C++14 is available
 #if defined(CRYPTOPP_CXX11) 
 
+// atomics: MS at VS2012 (17.00); GCC at 4.4; Clang at 3.1/3.2; and Intel 13.0.
+#if (CRYPTOPP_MSC_VERSION >= 1700)
+#  define CRYPTOPP_CXX11_ATOMICS 1
+#elif defined(__INTEL_COMPILER) && (__INTEL_COMPILER >= 1300)
+#  define CRYPTOPP_CXX11_ATOMICS 1
+#elif defined(__clang__)
+#  if __has_feature(cxx_atomic)
+#    define CRYPTOPP_CXX11_ATOMICS 1
+#  endif
+#elif (CRYPTOPP_GCC_VERSION >= 40400)
+#  define CRYPTOPP_CXX11_ATOMICS 1
+#endif // atomics
+
 // alignof/alignas: MS at VS2013 (19.00); GCC at 4.8; Clang at 3.3; and Intel 15.0.
 #if (CRYPTOPP_MSC_VERSION >= 1900)
 #  define CRYPTOPP_CXX11_ALIGNAS 1
diff --git a/misc.h b/misc.h
index d9f98cad..291b8dc1 100644
--- a/misc.h
+++ b/misc.h
@@ -218,7 +218,9 @@ struct NewObject
 //!   <tt>_ReadWriteBarrier()</tt> or <tt>__asm__("" ::: "memory")</tt>.
 #define MEMORY_BARRIER ...
 #else
-#if (_MSC_VER >= 1400)
+#if defined(CRYPTOPP_CXX11_ATOMICS)
+# define MEMORY_BARRIER() std::atomic_thread_fence(std::memory_order_acq_rel)
+#elif (_MSC_VER >= 1400)
 # pragma intrinsic(_ReadWriteBarrier)
 # define MEMORY_BARRIER() _ReadWriteBarrier()
 #elif defined(__INTEL_COMPILER)
@@ -254,6 +256,33 @@ private:
 //! \brief Return a reference to the inner Singleton object
 //! \details Ref() is used to create the object using the object factory. The
 //!   object is only created once with the limitations discussed in the class documentation.
+#if defined(CRYPTOPP_CXX11_ATOMICS)
+template <class T, class F, int instance>
+  const T & Singleton<T, F, instance>::Ref(CRYPTOPP_NOINLINE_DOTDOTDOT) const
+{
+	static volatile simple_ptr<T> s_pObject;
+	T *p = s_pObject.m_p;
+	std::atomic_thread_fence(std::memory_order_acquire);
+
+	if (p)
+		return *p;
+
+	T *newObject = m_objectFactory();
+	p = s_pObject.m_p;
+	std::atomic_thread_fence(std::memory_order_acquire);
+
+	if (p)
+	{
+		delete newObject;
+		return *p;
+	}
+
+	s_pObject.m_p = newObject;
+	std::atomic_thread_fence(std::memory_order_release);
+
+	return *newObject;
+}
+#else
 template <class T, class F, int instance>
 const T & Singleton<T, F, instance>::Ref(CRYPTOPP_NOINLINE_DOTDOTDOT) const
 {
@@ -279,6 +308,7 @@ const T & Singleton<T, F, instance>::Ref(CRYPTOPP_NOINLINE_DOTDOTDOT) const
 
 	return *newObject;
 }
+#endif
 
 // ************** misc functions ***************
 
diff --git a/stdcpp.h b/stdcpp.h
index 66efc203..22cee7a2 100644
--- a/stdcpp.h
+++ b/stdcpp.h
@@ -32,6 +32,10 @@ namespace std {
 #include <iterator>
 #endif
 
+#if defined(CRYPTOPP_CXX11_ATOMICS)
+#include <atomic>
+#endif
+
 #include <cstdlib>
 #include <cstddef>
 #include <cstring>