added preliminary rwlock for #18

substrate/rwlock

@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: BSD-3-Clause
+#ifndef SUBSTRATE_RWLOCK
+#define SUBSTRATE_RWLOCK
+
+#if __cplusplus < 201703L
+#error "rwlock is on available on C++17 and above"
+#endif
+
+#include <substrate/internal/defs>
+
+#include <utility>
+#include <mutex>
+#include <shared_mutex>
+
+namespace substrate
+{
+	template<typename T>
+	struct rwlock final {
+	private:
+		template<typename U, template<typename> typename lock_t>
+		struct lock_result final {
+		private:
+			lock_t<std::shared_mutex> _lock;
+			U& _obj;
+		public:
+			constexpr lock_result(std::shared_mutex& mut, U& obj) noexcept :
+				_lock{mut}, _obj{obj} { }
+
+			SUBSTRATE_NO_DISCARD(U* operator->() noexcept { return &_obj; })
+			SUBSTRATE_NO_DISCARD(U& operator*() noexcept { return _obj; })
+		};
+		std::shared_mutex _mutex{};
+		T _obj;
+	public:
+		template<typename ...args_t>
+		constexpr rwlock(args_t&&... args) noexcept :
+			_obj{std::forward<args_t>(args)...} { }
+
+		SUBSTRATE_NO_DISCARD(lock_result<const T, std::shared_lock> read() noexcept {
+			return {_mutex, _obj};
+		})
+		SUBSTRATE_NO_DISCARD(lock_result<T, std::unique_lock> write() noexcept {
+			return {_mutex, _obj};
+		})
+	};
+}
+
+#endif /* SUBSTRATE_RWLOCK */
+/* vim: set ft=cpp ts=4 sw=4 noexpandtab: */