Add locked_access

CMakeLists.txt

@@ -54,6 +54,7 @@ target_sources(concurrent PUBLIC
 	BASE_DIRS "${CMAKE_CURRENT_SOURCE_DIR}"
 	FILES
 		source/concurrent.cpp
+		source/locked_access.cpp
 		source/queue.cpp
 )
 

source/concurrent.cpp

@@ -5,4 +5,5 @@
 
 export module concurrent;
 
+export import concurrent.locked_access;
 export import concurrent.queue;

source/locked_access.cpp

@@ -0,0 +1,48 @@
+// Copyright David Stone 2023.
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+export module concurrent.locked_access;
+
+import std_module;
+
+namespace concurrent {
+
+template<typename T, typename Mutex>
+struct locked_t {
+	static_assert(std::is_reference_v<T>);
+	constexpr locked_t(T value_, Mutex & mutex):
+		m_value(value_),
+		m_lock(mutex)
+	{
+	}
+	constexpr auto value() const & -> T {
+		return m_value;
+	}
+	auto value() && = delete;
+private:
+	T m_value;
+	std::unique_lock<Mutex> m_lock;
+};
+template<typename T, typename Mutex>
+locked_t(T &, Mutex &) -> locked_t<T &, Mutex>;
+
+export template<typename T, typename Mutex = std::mutex>
+struct locked_access {
+	constexpr auto locked() & {
+		return locked_t(m_value, m_mutex);
+	}
+	constexpr auto locked() const & {
+		return locked_t(m_value, m_mutex);
+	}
+	constexpr auto unlocked() const -> T const & {
+		return m_value;
+	}
+
+private:
+	mutable Mutex m_mutex;
+	[[no_unique_address]] T m_value;
+};
+
+} // namespace concurrent