Merge Atomics branch into Master

config.h

@@ -759,6 +759,18 @@ NAMESPACE_END
 #  define CRYPTOPP_CXX11_ATOMICS 1
 #endif // atomics
 
+// synchronization: MS at VS2012 (17.00); GCC at 4.4; Clang at 3.3; Xcode 5.0; and Intel 12.0.
+// TODO: verify Clang and Intel versions; find __has_feature(x) extension for Clang
+#if (CRYPTOPP_MSC_VERSION >= 1700)
+#  define CRYPTOPP_CXX11_SYNCHRONIZATION 1
+#elif defined(__INTEL_COMPILER) && (__INTEL_COMPILER >= 1200)
+#  define CRYPTOPP_CXX11_SYNCHRONIZATION 1
+#elif (CRYPTOPP_CLANG_VERSION >= 30300) || (CRYPTOPP_APPLE_CLANG_VERSION >= 50000)
+#  define CRYPTOPP_CXX11_SYNCHRONIZATION 1
+#elif (CRYPTOPP_GCC_VERSION >= 40400)
+#  define CRYPTOPP_CXX11_SYNCHRONIZATION 1
+#endif // synchronization
+
 // alignof/alignas: MS at VS2015 (19.00); GCC at 4.8; Clang at 3.3; and Intel 15.0.
 #if (CRYPTOPP_MSC_VERSION >= 1900)
 #  define CRYPTOPP_CXX11_ALIGNAS 1
@@ -767,8 +779,10 @@ NAMESPACE_END
 #  define CRYPTOPP_CXX11_ALIGNAS 1
 #  define CRYPTOPP_CXX11_ALIGNOF 1
 #elif defined(__clang__)
-#  if __has_feature(cxx_alignof)
+#  if __has_feature(cxx_alignas)
 #  define CRYPTOPP_CXX11_ALIGNAS 1
+#  endif
+#  if __has_feature(cxx_alignof)
 #  define CRYPTOPP_CXX11_ALIGNOF 1
 #  endif
 #elif (CRYPTOPP_GCC_VERSION >= 40800)

config.recommend

@@ -757,6 +757,18 @@ NAMESPACE_END
 #  define CRYPTOPP_CXX11_ATOMICS 1
 #endif // atomics
 
+// synchronization: MS at VS2012 (17.00); GCC at 4.4; Clang at 3.3; Xcode 5.0; and Intel 12.0.
+// TODO: verify Clang and Intel versions; find __has_feature(x) extension for Clang
+#if (CRYPTOPP_MSC_VERSION >= 1700)
+#  define CRYPTOPP_CXX11_SYNCHRONIZATION 1
+#elif defined(__INTEL_COMPILER) && (__INTEL_COMPILER >= 1200)
+#  define CRYPTOPP_CXX11_SYNCHRONIZATION 1
+#elif (CRYPTOPP_CLANG_VERSION >= 30300) || (CRYPTOPP_APPLE_CLANG_VERSION >= 50000)
+#  define CRYPTOPP_CXX11_SYNCHRONIZATION 1
+#elif (CRYPTOPP_GCC_VERSION >= 40400)
+#  define CRYPTOPP_CXX11_SYNCHRONIZATION 1
+#endif // synchronization
+
 // alignof/alignas: MS at VS2015 (19.00); GCC at 4.8; Clang at 3.3; and Intel 15.0.
 #if (CRYPTOPP_MSC_VERSION >= 1900)
 #  define CRYPTOPP_CXX11_ALIGNAS 1
@@ -765,8 +777,10 @@ NAMESPACE_END
 #  define CRYPTOPP_CXX11_ALIGNAS 1
 #  define CRYPTOPP_CXX11_ALIGNOF 1
 #elif defined(__clang__)
-#  if __has_feature(cxx_alignof)
+#  if __has_feature(cxx_alignas)
 #  define CRYPTOPP_CXX11_ALIGNAS 1
+#  endif
+#  if __has_feature(cxx_alignof)
 #  define CRYPTOPP_CXX11_ALIGNOF 1
 #  endif
 #elif (CRYPTOPP_GCC_VERSION >= 40800)

misc.h

@@ -236,10 +236,12 @@ struct NewObject
 //! \tparam T the class or type
 //! \tparam F the object factory for T
 //! \tparam instance the initiali instance count
-//! \details This class safely initializes a static object in a multithreaded environment
+//! \details This class safely initializes a static object in a multithreaded environment. For C++03
-//!   without using locks (for portability). Note that if two threads call Ref() at the same
+//!   and below it will do so without using locks for portability. If two threads call Ref() at the same
-//!   time, they may get back different references, and one object may end up being memory
+//!   time, they may get back different references, and one object may end up being memory leaked. This
-//!   leaked. This is by design.
+//!   is by design. For C++11 and above, a standard double-checked locking pattern with memory fences
+//!   is used. The locks and fences are standard and do not hinder portability.
+//! \sa <A HREF="http://preshing.com/20130930/double-checked-locking-is-fixed-in-cpp11/">Double-Checked Locking is Fixed In C++11</A>
 template <class T, class F = NewObject<T>, int instance=0>
 class Singleton
 {
@@ -256,28 +258,29 @@ 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)
+//! \sa <A HREF="http://preshing.com/20130930/double-checked-locking-is-fixed-in-cpp11/">Double-Checked Locking is Fixed In C++11</A>
+#if defined(CRYPTOPP_CXX11_ATOMICS) && defined(CRYPTOPP_CXX11_SYNCHRONIZATION)
 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;
+	static std::mutex s_mutex;
-	T *p = s_pObject.m_p;
+	static std::atomic<T*> s_pObject;
+
+	T *p = s_pObject.load(std::memory_order_relaxed);
+	std::atomic_thread_fence(std::memory_order_acquire);
+
+	if (p)
+		return *p;
+
+	std::lock_guard<std::mutex> lock(s_mutex);
+	p = s_pObject.load(std::memory_order_relaxed);
 	std::atomic_thread_fence(std::memory_order_acquire);
 
 	if (p)
 		return *p;
 
 	T *newObject = m_objectFactory();
-	p = s_pObject.m_p;
+	s_pObject.store(newObject, std::memory_order_relaxed);
-	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;

stdcpp.h

@@ -36,6 +36,10 @@ namespace std {
 #include <atomic>
 #endif
 
+#if defined(CRYPTOPP_CXX11_SYNCHRONIZATION)
+#include <mutex>
+#endif
+
 #include <cstdlib>
 #include <cstddef>
 #include <cstring>