Locked<T>: optimistically use SpinMutex for intrusive_ptr to consume …

…less RAM

std::mutex is 5 pointers large on x64, whereas std::atomic_flag at most one.

lib/base/atomic.hpp

@@ -4,6 +4,7 @@
 #define ATOMIC_H
 
 #include <atomic>
+#include <boost/smart_ptr/intrusive_ptr.hpp>
 #include <mutex>
 #include <type_traits>
 #include <utility>
@@ -66,6 +67,24 @@ class SpinMutex
 	std::atomic_flag m_State = ATOMIC_FLAG_INIT;
 };
 
+template<typename T>
+struct LockedMutex
+{
+	using Mutex = std::mutex;
+};
+
+/**
+ * SpinMutex is 5 times smaller than std::mutex on x86_64.
+ * Also, it's fine for boost::intrusive_ptr which basically only performs atomic refcounting.
+ *
+ * @ingroup base
+ */
+template<typename T>
+struct LockedMutex<boost::intrusive_ptr<T>>
+{
+	using Mutex = SpinMutex;
+};
+
 /**
  * Wraps any T into a std::atomic<T>-like interface that locks using a mutex.
  *
@@ -80,20 +99,20 @@ class Locked
 public:
 	inline T load() const
 	{
-		std::unique_lock<std::mutex> lock(m_Mutex);
+		std::unique_lock lock (m_Mutex);
 
 		return m_Value;
 	}
 
 	inline void store(T desired)
 	{
-		std::unique_lock<std::mutex> lock(m_Mutex);
+		std::unique_lock lock (m_Mutex);
 
 		m_Value = std::move(desired);
 	}
 
 private:
-	mutable std::mutex m_Mutex;
+	mutable typename LockedMutex<T>::Mutex m_Mutex;
 	T m_Value;
 };