fx-sync/include/condvar.hh

//! A value-wrapping condvar, controlled via mutex / rw-lock 
#pragma once

#include <condition_variable>

#include "error.hh"
#include "mutex.hh"

namespace fx::condvar {
	template< typename Mutex, typename T = void> 
	struct mutex_cond;

	template<typename T> 
	struct mutex_cond<std::shared_mutex, T> {
		using wrapper_type = shared::Mutex<T>;
		using condvar_type = std::condition_variable_any;
		using mutex_type = std::shared_mutex;
	};

	template<typename T>
	struct mutex_cond<std::mutex, T> {
		using wrapper_type = Mutex<T>;
		using condvar_type = std::condition_variable;
		using mutex_type = std::mutex;
	};

	template<typename T>
	struct mutex_cond<Mutex<T>, T> : mutex_cond<std::mutex, T> {};

	template<typename T>
	struct mutex_cond<shared::Mutex<T>, T> : mutex_cond<std::shared_mutex, T> {};

	/*template<typename M, typename T>
	struct mutex_cond<mutex::Mutex<M, T>, T> {
		using wrapper_type = mutex::Mutex<M, T>;
		using mutex_type = typename wrapper_type::mutex_type;
	};*/

	template<typename M>
	concept CondMutex = requires{ typename mutex_cond<M>::condvar_type; };

	template<typename M, typename T>
	struct CondVar : public mutex_cond<M, T>::wrapper_type {
		using condvar_type = mutex_cond<M, T>::condvar_type;
	
		using mutex_cond<M, T>::wrapper_type::wrapper_type;
		using mutex_cond<M, T>::wrapper_type::with_lock;
		
		inline void notify_one() { m_cond.notify_one(); }
		inline void notify_all() { m_cond.notify_all(); }

		template<typename F>
			requires(std::is_invocable_v<F, T&>)
		inline decltype(auto) wait_then(F&& func)
			noexcept(std::is_nothrow_invocable_v<F, T&>)
		{
			std::unique_lock ulk{ this->m_mutex };
			m_cond.wait(ulk);
			// Unique lock makes this raw access safe
			return std::forward<F>(func)(*this->get_raw_ptr());
		}

		template<typename F>
		inline decltype(auto) wait_then(F&& func, auto const& predicate)
			noexcept(std::is_nothrow_invocable_v<F, T&> and std::is_nothrow_invocable_v<decltype(predicate), T const&>)
			requires(std::is_invocable_v<F, T&> and std::is_invocable_v<decltype(predicate), T const&>)
		{
			std::unique_lock ulk{ this->m_mutex };
			m_cond.wait(ulk, [&, this] { return predicate(*this->get_ptr()); });
			// Unique lock makes this raw access safe
			return std::forward<F>(func)(*this->get_raw_ptr());
			
		}

		inline
		condvar_type& get_condvar() noexcept { return m_cond; }

		inline
		condvar_type const& get_condvar() const noexcept { return m_cond; }
	protected:
		condvar_type m_cond{};
	};
}

namespace fx {
	template<typename T>
	struct CondVar final : condvar::CondVar<std::mutex, T> {
		using condvar::CondVar<std::mutex, T>::CondVar;

//		using condvar::CondVar<std::mutex, T>::try_wait_then; // Only available for `shared::CondVar`
		using condvar::CondVar<std::mutex, T>::wait_then;
	};
	
	namespace shared {
		template<typename T>
		struct CondVar final : condvar::CondVar<std::shared_mutex, T> {
			using condvar::CondVar<std::shared_mutex, T>::CondVar;

			using condvar::CondVar<std::shared_mutex, T>::wait_then;

			template<typename F>
			inline bool try_wait_then(F&& func, auto const& predicate, std::stop_token st = std::stop_token{})
				noexcept(std::is_nothrow_invocable_v<F, T&> and std::is_nothrow_invocable_v<decltype(predicate), T const&>)
				requires(std::is_invocable_v<F, T&> and std::is_invocable_v<decltype(predicate), T const&>)
			{
				std::unique_lock ulk{ this->m_mutex };
				if(! this->m_cond.wait(ulk, st, [&, this] { return predicate(*this->get_ptr()); }))
					// Abandon attempt at locking
					return false;
					// Unique lock makes raw access safe
				else if constexpr(std::is_convertible_v<std::invoke_result_t<F, T&>, bool>)
					return std::forward<F>(func)(*this->get_raw_ptr());
				else	std::forward<F>(func)(*this->get_raw_ptr());
				return true;
			}
			template<typename F>
			inline auto wait_then(F&& func, auto const& predicate, std::stop_token st)
				noexcept(std::is_nothrow_invocable_v<F, T&> and std::is_nothrow_invocable_v<decltype(predicate), T const&>)
				requires(std::is_invocable_v<F, T&> and std::is_invocable_v<decltype(predicate), T const&>)
			{
				std::unique_lock ulk{ this->m_mutex };
				if(! this->m_cond.wait(ulk, st, [&, this] { return predicate(*this->get_ptr()); }))
					error::throw_cancelled();
				
				return std::forward<F>(func)(*this->get_raw_ptr());
			}



			//NOTE: _shared() cannot be `const` because `m_cond.wait()` is not `const`. It also takes a signal (`notify_one()`) permit regardless of how that wake is used, so.
			template<typename F>
				requires(std::is_invocable_v<F, const T&>)
			inline decltype(auto) wait_then_shared(F&& func)
				noexcept(std::is_nothrow_invocable_v<F, const T&>)
			{
				std::shared_lock ulk{ this->m_mutex };
				this->m_cond.wait(ulk);
				// Shared lock makes this only `const` access safe
				return std::forward<F>(func)(*this->get_ptr());
			}

			template<typename F>
			inline decltype(auto) wait_then_shared(F&& func, auto const& predicate)
				noexcept(std::is_nothrow_invocable_v<F, const T&> and std::is_nothrow_invocable_v<decltype(predicate), T const&>)
				requires(std::is_invocable_v<F, const T&> and std::is_invocable_v<decltype(predicate), T const&>)
			{
				std::shared_lock ulk{ this->m_mutex };
				this->m_cond.wait(ulk, [&, this] { return predicate(*this->get_ptr()); });
				// Shared lock makes this only `const` access safe
				return std::forward<F>(func)(*this->get_ptr());
				
			}

			template<typename F>
			inline bool try_wait_then_shared(F&& func, auto const& predicate, std::stop_token st = std::stop_token{})
				noexcept(std::is_nothrow_invocable_v<F, const T&> and std::is_nothrow_invocable_v<decltype(predicate), T const&>)
				requires(std::is_invocable_v<F, const T&> and std::is_invocable_v<decltype(predicate), T const&>)
			{
				std::shared_lock ulk{ this->m_mutex };
				if(! this->m_cond.wait(ulk, st, [&, this] { return predicate(*this->get_ptr()); }))
					// Abandon attempt at locking
					return false;
					// Shared lock makes only `const` access safe
				else if constexpr(std::is_convertible_v<std::invoke_result_t<F, T const&>, bool>)
					return std::forward<F>(func)(*this->get_ptr());
				else	std::forward<F>(func)(*this->get_ptr());
				return true;
			}

			template<typename F>
			inline decltype(auto) wait_then_shared(F&& func, auto const& predicate, std::stop_token st)
				noexcept(std::is_nothrow_invocable_v<F, const T&> and std::is_nothrow_invocable_v<decltype(predicate), T const&>)
				requires(std::is_invocable_v<F, const T&> and std::is_invocable_v<decltype(predicate), T const&>)
			{
				std::shared_lock ulk{ this->m_mutex };
				if(! this->m_cond.wait(ulk, st, [&, this] { return predicate(*this->get_ptr()); }))
					error::throw_cancelled();

				return std::forward<F>(func)(*this->get_ptr());
			}

		};
	}
	template<typename T>
	using SharedCondVar = shared::CondVar<T>;
}