From 507ad06302c2345bed8f57e0ddf6092c6cf5cbbf Mon Sep 17 00:00:00 2001
From: David Stone <davidfromonline@gmail.com>
Date: Sun, 24 Dec 2023 14:01:05 -0700
Subject: [PATCH] Add `locked_access`

---
 CMakeLists.txt           |  1 +
 source/concurrent.cpp    |  1 +
 source/locked_access.cpp | 48 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 50 insertions(+)
 create mode 100644 source/locked_access.cpp

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4d7514d..0b37308 100644
--- a/CMakeLists.txt
+++ b/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
 )
 
diff --git a/source/concurrent.cpp b/source/concurrent.cpp
index 3a990b6..201ab7d 100644
--- a/source/concurrent.cpp
+++ b/source/concurrent.cpp
@@ -5,4 +5,5 @@
 
 export module concurrent;
 
+export import concurrent.locked_access;
 export import concurrent.queue;
\ No newline at end of file
diff --git a/source/locked_access.cpp b/source/locked_access.cpp
new file mode 100644
index 0000000..c3d9939
--- /dev/null
+++ b/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
\ No newline at end of file