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// <future> -- C++ -- // Copyright (C) 2009-2018 Free Software Foundation, Inc. // // This file is part of the GNU ISO C++ Library. This library is free // software; you can redistribute it and/or modify it under the // terms of the GNU General Public License as published by the // Free Software Foundation; either version 3, or (at your option) // any later version. // This library is distributed in the hope that it will be useful, // but WITHOUT ANY WARRANTY; without even the implied warranty of // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the // GNU General Public License for more details. // Under Section 7 of GPL version 3, you are granted additional // permissions described in the GCC Runtime Library Exception, version // 3.1, as published by the Free Software Foundation. // You should have received a copy of the GNU General Public License and // a copy of the GCC Runtime Library Exception along with this program; // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see // <http://www.gnu.org/licenses/>. /** @file include/future * This is a Standard C++ Library header. / #ifndef _GLIBCXX_FUTURE #define _GLIBCXX_FUTURE 1 #pragma GCC system_header #if __cplusplus < 201103L # include <bits/c++0x_warning.h> #else #include <mutex> #include <thread> #include <condition_variable> #include <system_error> #include <atomic> #include <bits/atomic_futex.h> #include <bits/functexcept.h> #include <bits/invoke.h> #include <bits/unique_ptr.h> #include <bits/shared_ptr.h> #include <bits/std_function.h> #include <bits/uses_allocator.h> #include <bits/allocated_ptr.h> #include <ext/aligned_buffer.h> namespace std _GLIBCXX_VISIBILITY(default) { _GLIBCXX_BEGIN_NAMESPACE_VERSION /* * @defgroup futures Futures * @ingroup concurrency * * Classes for futures support. * @{ / /// Error code for futures enum class future_errc { future_already_retrieved = 1, promise_already_satisfied, no_state, broken_promise }; /// Specialization. template<> struct is_error_code_enum<future_errc> : public true_type { }; /// Points to a statically-allocated object derived from error_category. const error_category& future_category() noexcept; /// Overload for make_error_code. inline error_code make_error_code(future_errc __errc) noexcept { return error_code(static_cast<int>(__errc), future_category()); } /// Overload for make_error_condition. inline error_condition make_error_condition(future_errc __errc) noexcept { return error_condition(static_cast<int>(__errc), future_category()); } /* * @brief Exception type thrown by futures. * @ingroup exceptions / class future_error : public logic_error { public: explicit future_error(future_errc __errc) : future_error(std::make_error_code(__errc)) { } virtual ~future_error() noexcept; virtual const char what() const noexcept; const error_code& code() const noexcept { return _M_code; } private: explicit future_error(error_code __ec) : logic_error("std::future_error: " + __ec.message()), _M_code(__ec) { } friend void __throw_future_error(int); error_code _M_code; }; // Forward declarations. template<typename _Res> class future; template<typename _Res> class shared_future; template<typename _Signature> class packaged_task; template<typename _Res> class promise; /// Launch code for futures enum class launch { async = 1, deferred = 2 }; constexpr launch operator&(launch __x, launch __y) { return static_cast<launch>( static_cast<int>(__x) & static_cast<int>(__y)); } constexpr launch operator\|(launch __x, launch __y) { return static_cast<launch>( static_cast<int>(__x) \| static_cast<int>(__y)); } constexpr launch operator^(launch __x, launch __y) { return static_cast<launch>( static_cast<int>(__x) ^ static_cast<int>(__y)); } constexpr launch operator~(launch __x) { return static_cast<launch>(~static_cast<int>(__x)); } inline launch& operator&=(launch& __x, launch __y) { return __x = __x & __y; } inline launch& operator\|=(launch& __x, launch __y) { return __x = __x \| __y; } inline launch& operator^=(launch& __x, launch __y) { return __x = __x ^ __y; } /// Status code for futures enum class future_status { ready, timeout, deferred }; // _GLIBCXX_RESOLVE_LIB_DEFECTS // 2021. Further incorrect usages of result_of template<typename _Fn, typename... _Args> using __async_result_of = typename result_of< typename decay<_Fn>::type(typename decay<_Args>::type...)>::type; template<typename _Fn, typename... _Args> future<__async_result_of<_Fn, _Args...>> async(launch __policy, _Fn&& __fn, _Args&&... __args); template<typename _Fn, typename... _Args> future<__async_result_of<_Fn, _Args...>> async(_Fn&& __fn, _Args&&... __args); #if defined(_GLIBCXX_HAS_GTHREADS) && defined(_GLIBCXX_USE_C99_STDINT_TR1) /// Base class and enclosing scope. struct __future_base { /// Base class for results. struct _Result_base { exception_ptr _M_error; _Result_base(const _Result_base&) = delete; _Result_base& operator=(const _Result_base&) = delete; // _M_destroy() allows derived classes to control deallocation virtual void _M_destroy() = 0; struct _Deleter { void operator()(_Result_base* __fr) const { __fr->_M_destroy(); } }; protected: _Result_base(); virtual ~_Result_base(); }; /// A unique_ptr for result objects. template<typename _Res> using _Ptr = unique_ptr<_Res, _Result_base::_Deleter>; /// A result object that has storage for an object of type _Res. template<typename _Res> struct _Result : _Result_base { private: __gnu_cxx::__aligned_buffer<_Res> _M_storage; bool _M_initialized; public: typedef _Res result_type; _Result() noexcept : _M_initialized() { } ~_Result() { if (_M_initialized) _M_value().~_Res(); } // Return lvalue, future will add const or rvalue-reference _Res& _M_value() noexcept { return _M_storage._M_ptr(); } void _M_set(const _Res& __res) { ::new (_M_storage._M_addr()) _Res(__res); _M_initialized = true; } void _M_set(_Res&& __res) { ::new (_M_storage._M_addr()) _Res(std::move(__res)); _M_initialized = true; } private: void _M_destroy() { delete this; } }; /// A result object that uses an allocator. template<typename _Res, typename _Alloc> struct _Result_alloc final : _Result<_Res>, _Alloc { using __allocator_type = __alloc_rebind<_Alloc, _Result_alloc>; explicit _Result_alloc(const _Alloc& __a) : _Result<_Res>(), _Alloc(__a) { } private: void _M_destroy() { __allocator_type __a(this); __allocated_ptr<__allocator_type> __guard_ptr{ __a, this }; this->~_Result_alloc(); } }; // Create a result object that uses an allocator. template<typename _Res, typename _Allocator> static _Ptr<_Result_alloc<_Res, _Allocator>> _S_allocate_result(const _Allocator& __a) { using __result_type = _Result_alloc<_Res, _Allocator>; typename __result_type::__allocator_type __a2(__a); auto __guard = std::__allocate_guarded(__a2); __result_type* __p = ::new((void)__guard.get()) __result_type{__a}; __guard = nullptr; return _Ptr<__result_type>(__p); } // Keep it simple for std::allocator. template<typename _Res, typename _Tp> static _Ptr<_Result<_Res>> _S_allocate_result(const std::allocator<_Tp>& __a) { return _Ptr<_Result<_Res>>(new _Result<_Res>); } // Base class for various types of shared state created by an // asynchronous provider (such as a std::promise) and shared with one // or more associated futures. class _State_baseV2 { typedef _Ptr<_Result_base> _Ptr_type; enum _Status : unsigned { __not_ready, __ready }; _Ptr_type _M_result; __atomic_futex_unsigned<> _M_status; atomic_flag _M_retrieved = ATOMIC_FLAG_INIT; once_flag _M_once; public: _State_baseV2() noexcept : _M_result(), _M_status(_Status::__not_ready) { } _State_baseV2(const _State_baseV2&) = delete; _State_baseV2& operator=(const _State_baseV2&) = delete; virtual ~_State_baseV2() = default; _Result_base& wait() { // Run any deferred function or join any asynchronous thread: _M_complete_async(); // Acquire MO makes sure this synchronizes with the thread that made // the future ready. _M_status._M_load_when_equal(_Status::__ready, memory_order_acquire); return _M_result; } template<typename _Rep, typename _Period> future_status wait_for(const chrono::duration<_Rep, _Period>& __rel) { // First, check if the future has been made ready. Use acquire MO // to synchronize with the thread that made it ready. if (_M_status._M_load(memory_order_acquire) == _Status::__ready) return future_status::ready; if (_M_is_deferred_future()) return future_status::deferred; if (_M_status._M_load_when_equal_for(_Status::__ready, memory_order_acquire, __rel)) { // _GLIBCXX_RESOLVE_LIB_DEFECTS // 2100. timed waiting functions must also join // This call is a no-op by default except on an async future, // in which case the async thread is joined. It's also not a // no-op for a deferred future, but such a future will never // reach this point because it returns future_status::deferred // instead of waiting for the future to become ready (see // above). Async futures synchronize in this call, so we need // no further synchronization here. _M_complete_async(); return future_status::ready; } return future_status::timeout; } template<typename _Clock, typename _Duration> future_status wait_until(const chrono::time_point<_Clock, _Duration>& __abs) { // First, check if the future has been made ready. Use acquire MO // to synchronize with the thread that made it ready. if (_M_status._M_load(memory_order_acquire) == _Status::__ready) return future_status::ready; if (_M_is_deferred_future()) return future_status::deferred; if (_M_status._M_load_when_equal_until(_Status::__ready, memory_order_acquire, __abs)) { // _GLIBCXX_RESOLVE_LIB_DEFECTS // 2100. timed waiting functions must also join // See wait_for(...) above. _M_complete_async(); return future_status::ready; } return future_status::timeout; } // Provide a result to the shared state and make it ready. // Calls at most once: _M_result = __res(); void _M_set_result(function<_Ptr_type()> __res, bool __ignore_failure = false) { bool __did_set = false; // all calls to this function are serialized, // side-effects of invoking __res only happen once call_once(_M_once, &_State_baseV2::_M_do_set, this, std::__addressof(__res), std::__addressof(__did_set)); if (__did_set) // Use release MO to synchronize with observers of the ready state. _M_status._M_store_notify_all(_Status::__ready, memory_order_release); else if (!__ignore_failure) __throw_future_error(int(future_errc::promise_already_satisfied)); } // Provide a result to the shared state but delay making it ready // until the calling thread exits. // Calls at most once: _M_result = __res(); void _M_set_delayed_result(function<_Ptr_type()> __res, weak_ptr<_State_baseV2> __self) { bool __did_set = false; unique_ptr<_Make_ready> __mr{new _Make_ready}; // all calls to this function are serialized, // side-effects of invoking __res only happen once call_once(_M_once, &_State_baseV2::_M_do_set, this, std::__addressof(__res), std::__addressof(__did_set)); if (!__did_set) __throw_future_error(int(future_errc::promise_already_satisfied)); __mr->_M_shared_state = std::move(__self); __mr->_M_set(); __mr.release(); } // Abandon this shared state. void _M_break_promise(_Ptr_type __res) { if (static_cast<bool>(__res)) { __res->_M_error = make_exception_ptr(future_error(future_errc::broken_promise)); // This function is only called when the last asynchronous result // provider is abandoning this shared state, so noone can be // trying to make the shared state ready at the same time, and // we can access _M_result directly instead of through call_once. _M_result.swap(__res); // Use release MO to synchronize with observers of the ready state. _M_status._M_store_notify_all(_Status::__ready, memory_order_release); } } // Called when this object is first passed to a future. void _M_set_retrieved_flag() { if (_M_retrieved.test_and_set()) __throw_future_error(int(future_errc::future_already_retrieved)); } template<typename _Res, typename _Arg> struct _Setter; // set lvalues template<typename _Res, typename _Arg> struct _Setter<_Res, _Arg&> { // check this is only used by promise<R>::set_value(const R&) // or promise<R&>::set_value(R&) static_assert(is_same<_Res, _Arg&>::value // promise<R&> \|\| is_same<const _Res, _Arg>::value, // promise<R> "Invalid specialisation"); // Used by std::promise to copy construct the result. typename promise<_Res>::_Ptr_type operator()() const { _M_promise->_M_storage->_M_set(_M_arg); return std::move(_M_promise->_M_storage); } promise<_Res> _M_promise; _Arg* _M_arg; }; // set rvalues template<typename _Res> struct _Setter<_Res, _Res&&> { // Used by std::promise to move construct the result. typename promise<_Res>::_Ptr_type operator()() const { _M_promise->_M_storage->_M_set(std::move(_M_arg)); return std::move(_M_promise->_M_storage); } promise<_Res> _M_promise; _Res* _M_arg; }; // set void template<typename _Res> struct _Setter<_Res, void> { static_assert(is_void<_Res>::value, "Only used for promise<void>"); typename promise<_Res>::_Ptr_type operator()() const { return std::move(_M_promise->_M_storage); } promise<_Res>* _M_promise; }; struct __exception_ptr_tag { }; // set exceptions template<typename _Res> struct _Setter<_Res, __exception_ptr_tag> { // Used by std::promise to store an exception as the result. typename promise<_Res>::_Ptr_type operator()() const { _M_promise->_M_storage->_M_error = _M_ex; return std::move(_M_promise->_M_storage); } promise<_Res> _M_promise; exception_ptr* _M_ex; }; template<typename _Res, typename _Arg> static _Setter<_Res, _Arg&&> __setter(promise<_Res>* __prom, _Arg&& __arg) { _S_check(__prom->_M_future); return _Setter<_Res, _Arg&&>{ __prom, std::__addressof(__arg) }; } template<typename _Res> static _Setter<_Res, __exception_ptr_tag> __setter(exception_ptr& __ex, promise<_Res>* __prom) { _S_check(__prom->_M_future); return _Setter<_Res, __exception_ptr_tag>{ __prom, &__ex }; } template<typename _Res> static _Setter<_Res, void> __setter(promise<_Res>* __prom) { _S_check(__prom->_M_future); return _Setter<_Res, void>{ __prom }; } template<typename _Tp> static void _S_check(const shared_ptr<_Tp>& __p) { if (!static_cast<bool>(__p)) __throw_future_error((int)future_errc::no_state); } private: // The function invoked with std::call_once(_M_once, ...). void _M_do_set(function<_Ptr_type()>* __f, bool* __did_set) { _Ptr_type __res = (__f)(); // Notify the caller that we did try to set; if we do not throw an // exception, the caller will be aware that it did set (e.g., see // _M_set_result). __did_set = true; _M_result.swap(__res); // nothrow } // Wait for completion of async function. virtual void _M_complete_async() { } // Return true if state corresponds to a deferred function. virtual bool _M_is_deferred_future() const { return false; } struct _Make_ready final : __at_thread_exit_elt { weak_ptr<_State_baseV2> _M_shared_state; static void _S_run(void); void _M_set(); }; }; #ifdef _GLIBCXX_ASYNC_ABI_COMPAT class _State_base; class _Async_state_common; #else using _State_base = _State_baseV2; class _Async_state_commonV2; #endif template<typename _BoundFn, typename _Res = decltype(std::declval<_BoundFn&>()())> class _Deferred_state; template<typename _BoundFn, typename _Res = decltype(std::declval<_BoundFn&>()())> class _Async_state_impl; template<typename _Signature> class _Task_state_base; template<typename _Fn, typename _Alloc, typename _Signature> class _Task_state; template<typename _BoundFn> static std::shared_ptr<_State_base> _S_make_deferred_state(_BoundFn&& __fn); template<typename _BoundFn> static std::shared_ptr<_State_base> _S_make_async_state(_BoundFn&& __fn); template<typename _Res_ptr, typename _Fn, typename _Res = typename _Res_ptr::element_type::result_type> struct _Task_setter; template<typename _Res_ptr, typename _BoundFn> static _Task_setter<_Res_ptr, _BoundFn> _S_task_setter(_Res_ptr& __ptr, _BoundFn& __call) { return { std::__addressof(__ptr), std::__addressof(__call) }; } }; /// Partial specialization for reference types. template<typename _Res> struct __future_base::_Result<_Res&> : __future_base::_Result_base { typedef _Res& result_type; _Result() noexcept : _M_value_ptr() { } void _M_set(_Res& __res) noexcept { _M_value_ptr = std::addressof(__res); } _Res& _M_get() noexcept { return _M_value_ptr; } private: _Res* _M_value_ptr; void _M_destroy() { delete this; } }; /// Explicit specialization for void. template<> struct __future_base::_Result<void> : __future_base::_Result_base { typedef void result_type; private: void _M_destroy() { delete this; } }; #ifndef _GLIBCXX_ASYNC_ABI_COMPAT // Allow _Setter objects to be stored locally in std::function template<typename _Res, typename _Arg> struct __is_location_invariant <__future_base::_State_base::_Setter<_Res, _Arg>> : true_type { }; // Allow _Task_setter objects to be stored locally in std::function template<typename _Res_ptr, typename _Fn, typename _Res> struct __is_location_invariant <__future_base::_Task_setter<_Res_ptr, _Fn, _Res>> : true_type { }; /// Common implementation for future and shared_future. template<typename _Res> class __basic_future : public __future_base { protected: typedef shared_ptr<_State_base> __state_type; typedef __future_base::_Result<_Res>& __result_type; private: __state_type _M_state; public: // Disable copying. __basic_future(const __basic_future&) = delete; __basic_future& operator=(const __basic_future&) = delete; bool valid() const noexcept { return static_cast<bool>(_M_state); } void wait() const { _State_base::_S_check(_M_state); _M_state->wait(); } template<typename _Rep, typename _Period> future_status wait_for(const chrono::duration<_Rep, _Period>& __rel) const { _State_base::_S_check(_M_state); return _M_state->wait_for(__rel); } template<typename _Clock, typename _Duration> future_status wait_until(const chrono::time_point<_Clock, _Duration>& __abs) const { _State_base::_S_check(_M_state); return _M_state->wait_until(__abs); } protected: /// Wait for the state to be ready and rethrow any stored exception __result_type _M_get_result() const { _State_base::_S_check(_M_state); _Result_base& __res = _M_state->wait(); if (!(__res._M_error == 0)) rethrow_exception(__res._M_error); return static_cast<__result_type>(__res); } void _M_swap(__basic_future& __that) noexcept { _M_state.swap(__that._M_state); } // Construction of a future by promise::get_future() explicit __basic_future(const __state_type& __state) : _M_state(__state) { _State_base::_S_check(_M_state); _M_state->_M_set_retrieved_flag(); } // Copy construction from a shared_future explicit __basic_future(const shared_future<_Res>&) noexcept; // Move construction from a shared_future explicit __basic_future(shared_future<_Res>&&) noexcept; // Move construction from a future explicit __basic_future(future<_Res>&&) noexcept; constexpr __basic_future() noexcept : _M_state() { } struct _Reset { explicit _Reset(__basic_future& __fut) noexcept : _M_fut(__fut) { } ~_Reset() { _M_fut._M_state.reset(); } __basic_future& _M_fut; }; }; /// Primary template for future. template<typename _Res> class future : public __basic_future<_Res> { friend class promise<_Res>; template<typename> friend class packaged_task; template<typename _Fn, typename... _Args> friend future<__async_result_of<_Fn, _Args...>> async(launch, _Fn&&, _Args&&...); typedef __basic_future<_Res> _Base_type; typedef typename _Base_type::__state_type __state_type; explicit future(const __state_type& __state) : _Base_type(__state) { } public: constexpr future() noexcept : _Base_type() { } /// Move constructor future(future&& __uf) noexcept : _Base_type(std::move(__uf)) { } // Disable copying future(const future&) = delete; future& operator=(const future&) = delete; future& operator=(future&& __fut) noexcept { future(std::move(__fut))._M_swap(this); return this; } /// Retrieving the value _Res get() { typename _Base_type::_Reset __reset(this); return std::move(this->_M_get_result()._M_value()); } shared_future<_Res> share() noexcept; }; /// Partial specialization for future<R&> template<typename _Res> class future<_Res&> : public __basic_future<_Res&> { friend class promise<_Res&>; template<typename> friend class packaged_task; template<typename _Fn, typename... _Args> friend future<__async_result_of<_Fn, _Args...>> async(launch, _Fn&&, _Args&&...); typedef __basic_future<_Res&> _Base_type; typedef typename _Base_type::__state_type __state_type; explicit future(const __state_type& __state) : _Base_type(__state) { } public: constexpr future() noexcept : _Base_type() { } /// Move constructor future(future&& __uf) noexcept : _Base_type(std::move(__uf)) { } // Disable copying future(const future&) = delete; future& operator=(const future&) = delete; future& operator=(future&& __fut) noexcept { future(std::move(__fut))._M_swap(this); return this; } /// Retrieving the value _Res& get() { typename _Base_type::_Reset __reset(this); return this->_M_get_result()._M_get(); } shared_future<_Res&> share() noexcept; }; /// Explicit specialization for future<void> template<> class future<void> : public __basic_future<void> { friend class promise<void>; template<typename> friend class packaged_task; template<typename _Fn, typename... _Args> friend future<__async_result_of<_Fn, _Args...>> async(launch, _Fn&&, _Args&&...); typedef __basic_future<void> _Base_type; typedef typename _Base_type::__state_type __state_type; explicit future(const __state_type& __state) : _Base_type(__state) { } public: constexpr future() noexcept : _Base_type() { } /// Move constructor future(future&& __uf) noexcept : _Base_type(std::move(__uf)) { } // Disable copying future(const future&) = delete; future& operator=(const future&) = delete; future& operator=(future&& __fut) noexcept { future(std::move(__fut))._M_swap(this); return this; } /// Retrieving the value void get() { typename _Base_type::_Reset __reset(this); this->_M_get_result(); } shared_future<void> share() noexcept; }; /// Primary template for shared_future. template<typename _Res> class shared_future : public __basic_future<_Res> { typedef __basic_future<_Res> _Base_type; public: constexpr shared_future() noexcept : _Base_type() { } /// Copy constructor shared_future(const shared_future& __sf) noexcept : _Base_type(__sf) { } /// Construct from a future rvalue shared_future(future<_Res>&& __uf) noexcept : _Base_type(std::move(__uf)) { } /// Construct from a shared_future rvalue shared_future(shared_future&& __sf) noexcept : _Base_type(std::move(__sf)) { } shared_future& operator=(const shared_future& __sf) noexcept { shared_future(__sf)._M_swap(this); return this; } shared_future& operator=(shared_future&& __sf) noexcept { shared_future(std::move(__sf))._M_swap(this); return this; } /// Retrieving the value const _Res& get() const { return this->_M_get_result()._M_value(); } }; /// Partial specialization for shared_future<R&> template<typename _Res> class shared_future<_Res&> : public __basic_future<_Res&> { typedef __basic_future<_Res&> _Base_type; public: constexpr shared_future() noexcept : _Base_type() { } /// Copy constructor shared_future(const shared_future& __sf) : _Base_type(__sf) { } /// Construct from a future rvalue shared_future(future<_Res&>&& __uf) noexcept : _Base_type(std::move(__uf)) { } /// Construct from a shared_future rvalue shared_future(shared_future&& __sf) noexcept : _Base_type(std::move(__sf)) { } shared_future& operator=(const shared_future& __sf) { shared_future(__sf)._M_swap(this); return this; } shared_future& operator=(shared_future&& __sf) noexcept { shared_future(std::move(__sf))._M_swap(this); return this; } /// Retrieving the value _Res& get() const { return this->_M_get_result()._M_get(); } }; /// Explicit specialization for shared_future<void> template<> class shared_future<void> : public __basic_future<void> { typedef __basic_future<void> _Base_type; public: constexpr shared_future() noexcept : _Base_type() { } /// Copy constructor shared_future(const shared_future& __sf) : _Base_type(__sf) { } /// Construct from a future rvalue shared_future(future<void>&& __uf) noexcept : _Base_type(std::move(__uf)) { } /// Construct from a shared_future rvalue shared_future(shared_future&& __sf) noexcept : _Base_type(std::move(__sf)) { } shared_future& operator=(const shared_future& __sf) { shared_future(__sf)._M_swap(this); return this; } shared_future& operator=(shared_future&& __sf) noexcept { shared_future(std::move(__sf))._M_swap(this); return this; } // Retrieving the value void get() const { this->_M_get_result(); } }; // Now we can define the protected __basic_future constructors. template<typename _Res> inline __basic_future<_Res>:: __basic_future(const shared_future<_Res>& __sf) noexcept : _M_state(__sf._M_state) { } template<typename _Res> inline __basic_future<_Res>:: __basic_future(shared_future<_Res>&& __sf) noexcept : _M_state(std::move(__sf._M_state)) { } template<typename _Res> inline __basic_future<_Res>:: __basic_future(future<_Res>&& __uf) noexcept : _M_state(std::move(__uf._M_state)) { } // _GLIBCXX_RESOLVE_LIB_DEFECTS // 2556. Wide contract for future::share() template<typename _Res> inline shared_future<_Res> future<_Res>::share() noexcept { return shared_future<_Res>(std::move(this)); } template<typename _Res> inline shared_future<_Res&> future<_Res&>::share() noexcept { return shared_future<_Res&>(std::move(this)); } inline shared_future<void> future<void>::share() noexcept { return shared_future<void>(std::move(this)); } /// Primary template for promise template<typename _Res> class promise { typedef __future_base::_State_base _State; typedef __future_base::_Result<_Res> _Res_type; typedef __future_base::_Ptr<_Res_type> _Ptr_type; template<typename, typename> friend class _State::_Setter; friend _State; shared_ptr<_State> _M_future; _Ptr_type _M_storage; public: promise() : _M_future(std::make_shared<_State>()), _M_storage(new _Res_type()) { } promise(promise&& __rhs) noexcept : _M_future(std::move(__rhs._M_future)), _M_storage(std::move(__rhs._M_storage)) { } template<typename _Allocator> promise(allocator_arg_t, const _Allocator& __a) : _M_future(std::allocate_shared<_State>(__a)), _M_storage(__future_base::_S_allocate_result<_Res>(__a)) { } template<typename _Allocator> promise(allocator_arg_t, const _Allocator&, promise&& __rhs) : _M_future(std::move(__rhs._M_future)), _M_storage(std::move(__rhs._M_storage)) { } promise(const promise&) = delete; ~promise() { if (static_cast<bool>(_M_future) && !_M_future.unique()) _M_future->_M_break_promise(std::move(_M_storage)); } // Assignment promise& operator=(promise&& __rhs) noexcept { promise(std::move(__rhs)).swap(this); return this; } promise& operator=(const promise&) = delete; void swap(promise& __rhs) noexcept { _M_future.swap(__rhs._M_future); _M_storage.swap(__rhs._M_storage); } // Retrieving the result future<_Res> get_future() { return future<_Res>(_M_future); } // Setting the result void set_value(const _Res& __r) { _M_future->_M_set_result(_State::__setter(this, __r)); } void set_value(_Res&& __r) { _M_future->_M_set_result(_State::__setter(this, std::move(__r))); } void set_exception(exception_ptr __p) { _M_future->_M_set_result(_State::__setter(__p, this)); } void set_value_at_thread_exit(const _Res& __r) { _M_future->_M_set_delayed_result(_State::__setter(this, __r), _M_future); } void set_value_at_thread_exit(_Res&& __r) { _M_future->_M_set_delayed_result( _State::__setter(this, std::move(__r)), _M_future); } void set_exception_at_thread_exit(exception_ptr __p) { _M_future->_M_set_delayed_result(_State::__setter(__p, this), _M_future); } }; template<typename _Res> inline void swap(promise<_Res>& __x, promise<_Res>& __y) noexcept { __x.swap(__y); } template<typename _Res, typename _Alloc> struct uses_allocator<promise<_Res>, _Alloc> : public true_type { }; /// Partial specialization for promise<R&> template<typename _Res> class promise<_Res&> { typedef __future_base::_State_base _State; typedef __future_base::_Result<_Res&> _Res_type; typedef __future_base::_Ptr<_Res_type> _Ptr_type; template<typename, typename> friend class _State::_Setter; friend _State; shared_ptr<_State> _M_future; _Ptr_type _M_storage; public: promise() : _M_future(std::make_shared<_State>()), _M_storage(new _Res_type()) { } promise(promise&& __rhs) noexcept : _M_future(std::move(__rhs._M_future)), _M_storage(std::move(__rhs._M_storage)) { } template<typename _Allocator> promise(allocator_arg_t, const _Allocator& __a) : _M_future(std::allocate_shared<_State>(__a)), _M_storage(__future_base::_S_allocate_result<_Res&>(__a)) { } template<typename _Allocator> promise(allocator_arg_t, const _Allocator&, promise&& __rhs) : _M_future(std::move(__rhs._M_future)), _M_storage(std::move(__rhs._M_storage)) { } promise(const promise&) = delete; ~promise() { if (static_cast<bool>(_M_future) && !_M_future.unique()) _M_future->_M_break_promise(std::move(_M_storage)); } // Assignment promise& operator=(promise&& __rhs) noexcept { promise(std::move(__rhs)).swap(this); return this; } promise& operator=(const promise&) = delete; void swap(promise& __rhs) noexcept { _M_future.swap(__rhs._M_future); _M_storage.swap(__rhs._M_storage); } // Retrieving the result future<_Res&> get_future() { return future<_Res&>(_M_future); } // Setting the result void set_value(_Res& __r) { _M_future->_M_set_result(_State::__setter(this, __r)); } void set_exception(exception_ptr __p) { _M_future->_M_set_result(_State::__setter(__p, this)); } void set_value_at_thread_exit(_Res& __r) { _M_future->_M_set_delayed_result(_State::__setter(this, __r), _M_future); } void set_exception_at_thread_exit(exception_ptr __p) { _M_future->_M_set_delayed_result(_State::__setter(__p, this), _M_future); } }; /// Explicit specialization for promise<void> template<> class promise<void> { typedef __future_base::_State_base _State; typedef __future_base::_Result<void> _Res_type; typedef __future_base::_Ptr<_Res_type> _Ptr_type; template<typename, typename> friend class _State::_Setter; friend _State; shared_ptr<_State> _M_future; _Ptr_type _M_storage; public: promise() : _M_future(std::make_shared<_State>()), _M_storage(new _Res_type()) { } promise(promise&& __rhs) noexcept : _M_future(std::move(__rhs._M_future)), _M_storage(std::move(__rhs._M_storage)) { } template<typename _Allocator> promise(allocator_arg_t, const _Allocator& __a) : _M_future(std::allocate_shared<_State>(__a)), _M_storage(__future_base::_S_allocate_result<void>(__a)) { } // _GLIBCXX_RESOLVE_LIB_DEFECTS // 2095. missing constructors needed for uses-allocator construction template<typename _Allocator> promise(allocator_arg_t, const _Allocator&, promise&& __rhs) : _M_future(std::move(__rhs._M_future)), _M_storage(std::move(__rhs._M_storage)) { } promise(const promise&) = delete; ~promise() { if (static_cast<bool>(_M_future) && !_M_future.unique()) _M_future->_M_break_promise(std::move(_M_storage)); } // Assignment promise& operator=(promise&& __rhs) noexcept { promise(std::move(__rhs)).swap(this); return this; } promise& operator=(const promise&) = delete; void swap(promise& __rhs) noexcept { _M_future.swap(__rhs._M_future); _M_storage.swap(__rhs._M_storage); } // Retrieving the result future<void> get_future() { return future<void>(_M_future); } // Setting the result void set_value() { _M_future->_M_set_result(_State::__setter(this)); } void set_exception(exception_ptr __p) { _M_future->_M_set_result(_State::__setter(__p, this)); } void set_value_at_thread_exit() { _M_future->_M_set_delayed_result(_State::__setter(this), _M_future); } void set_exception_at_thread_exit(exception_ptr __p) { _M_future->_M_set_delayed_result(_State::__setter(__p, this), _M_future); } }; template<typename _Ptr_type, typename _Fn, typename _Res> struct __future_base::_Task_setter { // Invoke the function and provide the result to the caller. _Ptr_type operator()() const { __try { (_M_result)->_M_set((_M_fn)()); } __catch(const __cxxabiv1::__forced_unwind&) { __throw_exception_again; // will cause broken_promise } __catch(...) { (_M_result)->_M_error = current_exception(); } return std::move(_M_result); } _Ptr_type* _M_result; _Fn* _M_fn; }; template<typename _Ptr_type, typename _Fn> struct __future_base::_Task_setter<_Ptr_type, _Fn, void> { _Ptr_type operator()() const { __try { (_M_fn)(); } __catch(const __cxxabiv1::__forced_unwind&) { __throw_exception_again; // will cause broken_promise } __catch(...) { (_M_result)->_M_error = current_exception(); } return std::move(_M_result); } _Ptr_type _M_result; _Fn* _M_fn; }; // Holds storage for a packaged_task's result. template<typename _Res, typename... _Args> struct __future_base::_Task_state_base<_Res(_Args...)> : __future_base::_State_base { typedef _Res _Res_type; template<typename _Alloc> _Task_state_base(const _Alloc& __a) : _M_result(_S_allocate_result<_Res>(__a)) { } // Invoke the stored task and make the state ready. virtual void _M_run(_Args&&... __args) = 0; // Invoke the stored task and make the state ready at thread exit. virtual void _M_run_delayed(_Args&&... __args, weak_ptr<_State_base>) = 0; virtual shared_ptr<_Task_state_base> _M_reset() = 0; typedef __future_base::_Ptr<_Result<_Res>> _Ptr_type; _Ptr_type _M_result; }; // Holds a packaged_task's stored task. template<typename _Fn, typename _Alloc, typename _Res, typename... _Args> struct __future_base::_Task_state<_Fn, _Alloc, _Res(_Args...)> final : __future_base::_Task_state_base<_Res(_Args...)> { template<typename _Fn2> _Task_state(_Fn2&& __fn, const _Alloc& __a) : _Task_state_base<_Res(_Args...)>(__a), _M_impl(std::forward<_Fn2>(__fn), __a) { } private: virtual void _M_run(_Args&&... __args) { auto __boundfn = [&] () -> typename result_of<_Fn&(_Args&&...)>::type { return std::__invoke(_M_impl._M_fn, std::forward<_Args>(__args)...); }; this->_M_set_result(_S_task_setter(this->_M_result, __boundfn)); } virtual void _M_run_delayed(_Args&&... __args, weak_ptr<_State_base> __self) { auto __boundfn = [&] () -> typename result_of<_Fn&(_Args&&...)>::type { return std::__invoke(_M_impl._M_fn, std::forward<_Args>(__args)...); }; this->_M_set_delayed_result(_S_task_setter(this->_M_result, __boundfn), std::move(__self)); } virtual shared_ptr<_Task_state_base<_Res(_Args...)>> _M_reset(); struct _Impl : _Alloc { template<typename _Fn2> _Impl(_Fn2&& __fn, const _Alloc& __a) : _Alloc(__a), _M_fn(std::forward<_Fn2>(__fn)) { } _Fn _M_fn; } _M_impl; }; template<typename _Signature, typename _Fn, typename _Alloc> static shared_ptr<__future_base::_Task_state_base<_Signature>> __create_task_state(_Fn&& __fn, const _Alloc& __a) { typedef typename decay<_Fn>::type _Fn2; typedef __future_base::_Task_state<_Fn2, _Alloc, _Signature> _State; return std::allocate_shared<_State>(__a, std::forward<_Fn>(__fn), __a); } template<typename _Fn, typename _Alloc, typename _Res, typename... _Args> shared_ptr<__future_base::_Task_state_base<_Res(_Args...)>> __future_base::_Task_state<_Fn, _Alloc, _Res(_Args...)>::_M_reset() { return __create_task_state<_Res(_Args...)>(std::move(_M_impl._M_fn), static_cast<_Alloc&>(_M_impl)); } template<typename _Task, typename _Fn, bool = is_same<_Task, typename decay<_Fn>::type>::value> struct __constrain_pkgdtask { typedef void __type; }; template<typename _Task, typename _Fn> struct __constrain_pkgdtask<_Task, _Fn, true> { }; /// packaged_task template<typename _Res, typename... _ArgTypes> class packaged_task<_Res(_ArgTypes...)> { typedef __future_base::_Task_state_base<_Res(_ArgTypes...)> _State_type; shared_ptr<_State_type> _M_state; public: // Construction and destruction packaged_task() noexcept { } // _GLIBCXX_RESOLVE_LIB_DEFECTS // 2095. missing constructors needed for uses-allocator construction template<typename _Allocator> packaged_task(allocator_arg_t, const _Allocator& __a) noexcept { } template<typename _Fn, typename = typename __constrain_pkgdtask<packaged_task, _Fn>::__type> explicit packaged_task(_Fn&& __fn) : packaged_task(allocator_arg, std::allocator<int>(), std::forward<_Fn>(__fn)) { } // _GLIBCXX_RESOLVE_LIB_DEFECTS // 2097. packaged_task constructors should be constrained // 2407. [this constructor should not be] explicit template<typename _Fn, typename _Alloc, typename = typename __constrain_pkgdtask<packaged_task, _Fn>::__type> packaged_task(allocator_arg_t, const _Alloc& __a, _Fn&& __fn) : _M_state(__create_task_state<_Res(_ArgTypes...)>( std::forward<_Fn>(__fn), __a)) { } ~packaged_task() { if (static_cast<bool>(_M_state) && !_M_state.unique()) _M_state->_M_break_promise(std::move(_M_state->_M_result)); } // No copy packaged_task(const packaged_task&) = delete; packaged_task& operator=(const packaged_task&) = delete; template<typename _Allocator> packaged_task(allocator_arg_t, const _Allocator&, const packaged_task&) = delete; // Move support packaged_task(packaged_task&& __other) noexcept { this->swap(__other); } template<typename _Allocator> packaged_task(allocator_arg_t, const _Allocator&, packaged_task&& __other) noexcept { this->swap(__other); } packaged_task& operator=(packaged_task&& __other) noexcept { packaged_task(std::move(__other)).swap(this); return this; } void swap(packaged_task& __other) noexcept { _M_state.swap(__other._M_state); } bool valid() const noexcept { return static_cast<bool>(_M_state); } // Result retrieval future<_Res> get_future() { return future<_Res>(_M_state); } // Execution void operator()(_ArgTypes... __args) { __future_base::_State_base::_S_check(_M_state); _M_state->_M_run(std::forward<_ArgTypes>(__args)...); } void make_ready_at_thread_exit(_ArgTypes... __args) { __future_base::_State_base::_S_check(_M_state); _M_state->_M_run_delayed(std::forward<_ArgTypes>(__args)..., _M_state); } void reset() { __future_base::_State_base::_S_check(_M_state); packaged_task __tmp; __tmp._M_state = _M_state; _M_state = _M_state->_M_reset(); } }; /// swap template<typename _Res, typename... _ArgTypes> inline void swap(packaged_task<_Res(_ArgTypes...)>& __x, packaged_task<_Res(_ArgTypes...)>& __y) noexcept { __x.swap(__y); } template<typename _Res, typename _Alloc> struct uses_allocator<packaged_task<_Res>, _Alloc> : public true_type { }; // Shared state created by std::async(). // Holds a deferred function and storage for its result. template<typename _BoundFn, typename _Res> class __future_base::_Deferred_state final : public __future_base::_State_base { public: explicit _Deferred_state(_BoundFn&& __fn) : _M_result(new _Result<_Res>()), _M_fn(std::move(__fn)) { } private: typedef __future_base::_Ptr<_Result<_Res>> _Ptr_type; _Ptr_type _M_result; _BoundFn _M_fn; // Run the deferred function. virtual void _M_complete_async() { // Multiple threads can call a waiting function on the future and // reach this point at the same time. The call_once in _M_set_result // ensures only the first one run the deferred function, stores the // result in _M_result, swaps that with the base _M_result and makes // the state ready. Tell _M_set_result to ignore failure so all later // calls do nothing. _M_set_result(_S_task_setter(_M_result, _M_fn), true); } // Caller should check whether the state is ready first, because this // function will return true even after the deferred function has run. virtual bool _M_is_deferred_future() const { return true; } }; // Common functionality hoisted out of the _Async_state_impl template. class __future_base::_Async_state_commonV2 : public __future_base::_State_base { protected: ~_Async_state_commonV2() = default; // Make waiting functions block until the thread completes, as if joined. // // This function is used by wait() to satisfy the first requirement below // and by wait_for() / wait_until() to satisfy the second. // // [futures.async]: // // — a call to a waiting function on an asynchronous return object that // shares the shared state created by this async call shall block until // the associated thread has completed, as if joined, or else time out. // // — the associated thread completion synchronizes with the return from // the first function that successfully detects the ready status of the // shared state or with the return from the last function that releases // the shared state, whichever happens first. virtual void _M_complete_async() { _M_join(); } void _M_join() { std::call_once(_M_once, &thread::join, &_M_thread); } thread _M_thread; once_flag _M_once; }; // Shared state created by std::async(). // Starts a new thread that runs a function and makes the shared state ready. template<typename _BoundFn, typename _Res> class __future_base::_Async_state_impl final : public __future_base::_Async_state_commonV2 { public: explicit _Async_state_impl(_BoundFn&& __fn) : _M_result(new _Result<_Res>()), _M_fn(std::move(__fn)) { _M_thread = std::thread{ [this] { __try { _M_set_result(_S_task_setter(_M_result, _M_fn)); } __catch (const __cxxabiv1::__forced_unwind&) { // make the shared state ready on thread cancellation if (static_cast<bool>(_M_result)) this->_M_break_promise(std::move(_M_result)); __throw_exception_again; } } }; } // Must not destroy _M_result and _M_fn until the thread finishes. // Call join() directly rather than through _M_join() because no other // thread can be referring to this state if it is being destroyed. ~_Async_state_impl() { if (_M_thread.joinable()) _M_thread.join(); } private: typedef __future_base::_Ptr<_Result<_Res>> _Ptr_type; _Ptr_type _M_result; _BoundFn _M_fn; }; template<typename _BoundFn> inline std::shared_ptr<__future_base::_State_base> __future_base::_S_make_deferred_state(_BoundFn&& __fn) { typedef typename remove_reference<_BoundFn>::type __fn_type; typedef _Deferred_state<__fn_type> __state_type; return std::make_shared<__state_type>(std::move(__fn)); } template<typename _BoundFn> inline std::shared_ptr<__future_base::_State_base> __future_base::_S_make_async_state(_BoundFn&& __fn) { typedef typename remove_reference<_BoundFn>::type __fn_type; typedef _Async_state_impl<__fn_type> __state_type; return std::make_shared<__state_type>(std::move(__fn)); } /// async template<typename _Fn, typename... _Args> future<__async_result_of<_Fn, _Args...>> async(launch __policy, _Fn&& __fn, _Args&&... __args) { std::shared_ptr<__future_base::_State_base> __state; if ((__policy & launch::async) == launch::async) { __try { __state = __future_base::_S_make_async_state( std::thread::__make_invoker(std::forward<_Fn>(__fn), std::forward<_Args>(__args)...) ); } #if __cpp_exceptions catch(const system_error& __e) { if (__e.code() != errc::resource_unavailable_try_again \|\| (__policy & launch::deferred) != launch::deferred) throw; } #endif } if (!__state) { __state = __future_base::_S_make_deferred_state( std::thread::__make_invoker(std::forward<_Fn>(__fn), std::forward<_Args>(__args)...)); } return future<__async_result_of<_Fn, _Args...>>(__state); } /// async, potential overload template<typename _Fn, typename... _Args> inline future<__async_result_of<_Fn, _Args...>> async(_Fn&& __fn, _Args&&... __args) { return std::async(launch::async\|launch::deferred, std::forward<_Fn>(__fn), std::forward<_Args>(__args)...); } #endif // _GLIBCXX_ASYNC_ABI_COMPAT #endif // _GLIBCXX_HAS_GTHREADS && _GLIBCXX_USE_C99_STDINT_TR1 // @} group futures _GLIBCXX_END_NAMESPACE_VERSION } // namespace #endif // C++11 #endif // _GLIBCXX_FUTURE Back

Edit File : future | Size : 49.49 KB

// <future> -*- C++ -*-

// Copyright (C) 2009-2018 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file include/future
 *  This is a Standard C++ Library header.
 */

#ifndef _GLIBCXX_FUTURE
#define _GLIBCXX_FUTURE 1

#pragma GCC system_header

#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else

#include <mutex>
#include <thread>
#include <condition_variable>
#include <system_error>
#include <atomic>
#include <bits/atomic_futex.h>
#include <bits/functexcept.h>
#include <bits/invoke.h>
#include <bits/unique_ptr.h>
#include <bits/shared_ptr.h>
#include <bits/std_function.h>
#include <bits/uses_allocator.h>
#include <bits/allocated_ptr.h>
#include <ext/aligned_buffer.h>

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

/**
   * @defgroup futures Futures
   * @ingroup concurrency
   *
   * Classes for futures support.
   * @{
   */

/// Error code for futures
  enum class future_errc
  {
    future_already_retrieved = 1,
    promise_already_satisfied,
    no_state,
    broken_promise
  };

/// Specialization.
  template<>
    struct is_error_code_enum<future_errc> : public true_type { };

/// Points to a statically-allocated object derived from error_category.
  const error_category&
  future_category() noexcept;

/// Overload for make_error_code.
  inline error_code
  make_error_code(future_errc __errc) noexcept
  { return error_code(static_cast<int>(__errc), future_category()); }

/// Overload for make_error_condition.
  inline error_condition
  make_error_condition(future_errc __errc) noexcept
  { return error_condition(static_cast<int>(__errc), future_category()); }

/**
   *  @brief Exception type thrown by futures.
   *  @ingroup exceptions
   */
  class future_error : public logic_error
  {
  public:
    explicit
    future_error(future_errc __errc)
    : future_error(std::make_error_code(__errc))
    { }

virtual ~future_error() noexcept;

virtual const char*
    what() const noexcept;

const error_code&
    code() const noexcept { return _M_code; }

private:
    explicit
    future_error(error_code __ec)
    : logic_error("std::future_error: " + __ec.message()), _M_code(__ec)
    { }

friend void __throw_future_error(int);

error_code 			_M_code;
  };

// Forward declarations.
  template<typename _Res>
    class future;

template<typename _Res>
    class shared_future;

template<typename _Signature>
    class packaged_task;

template<typename _Res>
    class promise;

/// Launch code for futures
  enum class launch
  {
    async = 1,
    deferred = 2
  };

constexpr launch operator&(launch __x, launch __y)
  {
    return static_cast<launch>(
	static_cast<int>(__x) & static_cast<int>(__y));
  }

constexpr launch operator|(launch __x, launch __y)
  {
    return static_cast<launch>(
	static_cast<int>(__x) | static_cast<int>(__y));
  }

constexpr launch operator^(launch __x, launch __y)
  {
    return static_cast<launch>(
	static_cast<int>(__x) ^ static_cast<int>(__y));
  }

constexpr launch operator~(launch __x)
  { return static_cast<launch>(~static_cast<int>(__x)); }

inline launch& operator&=(launch& __x, launch __y)
  { return __x = __x & __y; }

inline launch& operator|=(launch& __x, launch __y)
  { return __x = __x | __y; }

inline launch& operator^=(launch& __x, launch __y)
  { return __x = __x ^ __y; }

/// Status code for futures
  enum class future_status
  {
    ready,
    timeout,
    deferred
  };

// _GLIBCXX_RESOLVE_LIB_DEFECTS
  // 2021. Further incorrect usages of result_of
  template<typename _Fn, typename... _Args>
    using __async_result_of = typename result_of<
      typename decay<_Fn>::type(typename decay<_Args>::type...)>::type;

template<typename _Fn, typename... _Args>
    future<__async_result_of<_Fn, _Args...>>
    async(launch __policy, _Fn&& __fn, _Args&&... __args);

template<typename _Fn, typename... _Args>
    future<__async_result_of<_Fn, _Args...>>
    async(_Fn&& __fn, _Args&&... __args);

#if defined(_GLIBCXX_HAS_GTHREADS) && defined(_GLIBCXX_USE_C99_STDINT_TR1)

/// Base class and enclosing scope.
  struct __future_base
  {
    /// Base class for results.
    struct _Result_base
    {
      exception_ptr		_M_error;

_Result_base(const _Result_base&) = delete;
      _Result_base& operator=(const _Result_base&) = delete;

// _M_destroy() allows derived classes to control deallocation
      virtual void _M_destroy() = 0;

struct _Deleter
      {
	void operator()(_Result_base* __fr) const { __fr->_M_destroy(); }
      };

protected:
      _Result_base();
      virtual ~_Result_base();
    };

/// A unique_ptr for result objects.
    template<typename _Res>
      using _Ptr = unique_ptr<_Res, _Result_base::_Deleter>;

/// A result object that has storage for an object of type _Res.
    template<typename _Res>
      struct _Result : _Result_base
      {
      private:
	__gnu_cxx::__aligned_buffer<_Res>	_M_storage;
	bool 					_M_initialized;

public:
	typedef _Res result_type;

_Result() noexcept : _M_initialized() { }

~_Result()
	{
	  if (_M_initialized)
	    _M_value().~_Res();
	}

// Return lvalue, future will add const or rvalue-reference
	_Res&
	_M_value() noexcept { return *_M_storage._M_ptr(); }

void
	_M_set(const _Res& __res)
	{
	  ::new (_M_storage._M_addr()) _Res(__res);
	  _M_initialized = true;
	}

void
	_M_set(_Res&& __res)
	{
	  ::new (_M_storage._M_addr()) _Res(std::move(__res));
	  _M_initialized = true;
	}

private:
	void _M_destroy() { delete this; }
    };

/// A result object that uses an allocator.
    template<typename _Res, typename _Alloc>
      struct _Result_alloc final : _Result<_Res>, _Alloc
      {
	using __allocator_type = __alloc_rebind<_Alloc, _Result_alloc>;

explicit
	_Result_alloc(const _Alloc& __a) : _Result<_Res>(), _Alloc(__a)
	{ }

private:
	void _M_destroy()
	{
	  __allocator_type __a(*this);
	  __allocated_ptr<__allocator_type> __guard_ptr{ __a, this };
	  this->~_Result_alloc();
	}
      };

// Create a result object that uses an allocator.
    template<typename _Res, typename _Allocator>
      static _Ptr<_Result_alloc<_Res, _Allocator>>
      _S_allocate_result(const _Allocator& __a)
      {
	using __result_type = _Result_alloc<_Res, _Allocator>;
	typename __result_type::__allocator_type __a2(__a);
	auto __guard = std::__allocate_guarded(__a2);
	__result_type* __p = ::new((void*)__guard.get()) __result_type{__a};
	__guard = nullptr;
	return _Ptr<__result_type>(__p);
      }

// Keep it simple for std::allocator.
    template<typename _Res, typename _Tp>
      static _Ptr<_Result<_Res>>
      _S_allocate_result(const std::allocator<_Tp>& __a)
      {
	return _Ptr<_Result<_Res>>(new _Result<_Res>);
      }

// Base class for various types of shared state created by an
    // asynchronous provider (such as a std::promise) and shared with one
    // or more associated futures.
    class _State_baseV2
    {
      typedef _Ptr<_Result_base> _Ptr_type;

enum _Status : unsigned {
	__not_ready,
	__ready
      };

_Ptr_type			_M_result;
      __atomic_futex_unsigned<>	_M_status;
      atomic_flag         	_M_retrieved = ATOMIC_FLAG_INIT;
      once_flag			_M_once;

public:
      _State_baseV2() noexcept : _M_result(), _M_status(_Status::__not_ready)
	{ }
      _State_baseV2(const _State_baseV2&) = delete;
      _State_baseV2& operator=(const _State_baseV2&) = delete;
      virtual ~_State_baseV2() = default;

_Result_base&
      wait()
      {
	// Run any deferred function or join any asynchronous thread:
	_M_complete_async();
	// Acquire MO makes sure this synchronizes with the thread that made
	// the future ready.
	_M_status._M_load_when_equal(_Status::__ready, memory_order_acquire);
	return *_M_result;
      }

template<typename _Rep, typename _Period>
        future_status
        wait_for(const chrono::duration<_Rep, _Period>& __rel)
        {
	  // First, check if the future has been made ready.  Use acquire MO
	  // to synchronize with the thread that made it ready.
	  if (_M_status._M_load(memory_order_acquire) == _Status::__ready)
	    return future_status::ready;
	  if (_M_is_deferred_future())
	    return future_status::deferred;
	  if (_M_status._M_load_when_equal_for(_Status::__ready,
	      memory_order_acquire, __rel))
	    {
	      // _GLIBCXX_RESOLVE_LIB_DEFECTS
	      // 2100.  timed waiting functions must also join
	      // This call is a no-op by default except on an async future,
	      // in which case the async thread is joined.  It's also not a
	      // no-op for a deferred future, but such a future will never
	      // reach this point because it returns future_status::deferred
	      // instead of waiting for the future to become ready (see
	      // above).  Async futures synchronize in this call, so we need
	      // no further synchronization here.
	      _M_complete_async();

return future_status::ready;
	    }
	  return future_status::timeout;
	}

template<typename _Clock, typename _Duration>
        future_status
        wait_until(const chrono::time_point<_Clock, _Duration>& __abs)
        {
	  // First, check if the future has been made ready.  Use acquire MO
	  // to synchronize with the thread that made it ready.
	  if (_M_status._M_load(memory_order_acquire) == _Status::__ready)
	    return future_status::ready;
	  if (_M_is_deferred_future())
	    return future_status::deferred;
	  if (_M_status._M_load_when_equal_until(_Status::__ready,
	      memory_order_acquire, __abs))
	    {
	      // _GLIBCXX_RESOLVE_LIB_DEFECTS
	      // 2100.  timed waiting functions must also join
	      // See wait_for(...) above.
	      _M_complete_async();

return future_status::ready;
	    }
	  return future_status::timeout;
	}

// Provide a result to the shared state and make it ready.
      // Calls at most once: _M_result = __res();
      void
      _M_set_result(function<_Ptr_type()> __res, bool __ignore_failure = false)
      {
	bool __did_set = false;
        // all calls to this function are serialized,
        // side-effects of invoking __res only happen once
	call_once(_M_once, &_State_baseV2::_M_do_set, this,
		  std::__addressof(__res), std::__addressof(__did_set));
	if (__did_set)
	  // Use release MO to synchronize with observers of the ready state.
	  _M_status._M_store_notify_all(_Status::__ready,
					memory_order_release);
	else if (!__ignore_failure)
          __throw_future_error(int(future_errc::promise_already_satisfied));
      }

// Provide a result to the shared state but delay making it ready
      // until the calling thread exits.
      // Calls at most once: _M_result = __res();
      void
      _M_set_delayed_result(function<_Ptr_type()> __res,
			    weak_ptr<_State_baseV2> __self)
      {
	bool __did_set = false;
	unique_ptr<_Make_ready> __mr{new _Make_ready};
        // all calls to this function are serialized,
        // side-effects of invoking __res only happen once
	call_once(_M_once, &_State_baseV2::_M_do_set, this,
		  std::__addressof(__res), std::__addressof(__did_set));
	if (!__did_set)
          __throw_future_error(int(future_errc::promise_already_satisfied));
	__mr->_M_shared_state = std::move(__self);
	__mr->_M_set();
	__mr.release();
      }

// Abandon this shared state.
      void
      _M_break_promise(_Ptr_type __res)
      {
	if (static_cast<bool>(__res))
	  {
	    __res->_M_error =
	      make_exception_ptr(future_error(future_errc::broken_promise));
	    // This function is only called when the last asynchronous result
	    // provider is abandoning this shared state, so noone can be
	    // trying to make the shared state ready at the same time, and
	    // we can access _M_result directly instead of through call_once.
	    _M_result.swap(__res);
	    // Use release MO to synchronize with observers of the ready state.
	    _M_status._M_store_notify_all(_Status::__ready,
					  memory_order_release);
	  }
      }

// Called when this object is first passed to a future.
      void
      _M_set_retrieved_flag()
      {
	if (_M_retrieved.test_and_set())
	  __throw_future_error(int(future_errc::future_already_retrieved));
      }

template<typename _Res, typename _Arg>
        struct _Setter;

// set lvalues
      template<typename _Res, typename _Arg>
        struct _Setter<_Res, _Arg&>
        {
          // check this is only used by promise<R>::set_value(const R&)
          // or promise<R&>::set_value(R&)
          static_assert(is_same<_Res, _Arg&>::value  // promise<R&>
              || is_same<const _Res, _Arg>::value,   // promise<R>
              "Invalid specialisation");

// Used by std::promise to copy construct the result.
          typename promise<_Res>::_Ptr_type operator()() const
          {
            _M_promise->_M_storage->_M_set(*_M_arg);
            return std::move(_M_promise->_M_storage);
          }
          promise<_Res>*    _M_promise;
          _Arg*             _M_arg;
        };

// set rvalues
      template<typename _Res>
        struct _Setter<_Res, _Res&&>
        {
	  // Used by std::promise to move construct the result.
          typename promise<_Res>::_Ptr_type operator()() const
          {
            _M_promise->_M_storage->_M_set(std::move(*_M_arg));
            return std::move(_M_promise->_M_storage);
          }
          promise<_Res>*    _M_promise;
          _Res*             _M_arg;
        };

// set void
      template<typename _Res>
	struct _Setter<_Res, void>
	{
	  static_assert(is_void<_Res>::value, "Only used for promise<void>");

typename promise<_Res>::_Ptr_type operator()() const
	  { return std::move(_M_promise->_M_storage); }

promise<_Res>*    _M_promise;
	};

struct __exception_ptr_tag { };

// set exceptions
      template<typename _Res>
        struct _Setter<_Res, __exception_ptr_tag>
        {
	  // Used by std::promise to store an exception as the result.
          typename promise<_Res>::_Ptr_type operator()() const
          {
            _M_promise->_M_storage->_M_error = *_M_ex;
            return std::move(_M_promise->_M_storage);
          }

promise<_Res>*   _M_promise;
          exception_ptr*    _M_ex;
        };

template<typename _Res, typename _Arg>
        static _Setter<_Res, _Arg&&>
        __setter(promise<_Res>* __prom, _Arg&& __arg)
        {
	  _S_check(__prom->_M_future);
          return _Setter<_Res, _Arg&&>{ __prom, std::__addressof(__arg) };
        }

template<typename _Res>
        static _Setter<_Res, __exception_ptr_tag>
        __setter(exception_ptr& __ex, promise<_Res>* __prom)
        {
	  _S_check(__prom->_M_future);
          return _Setter<_Res, __exception_ptr_tag>{ __prom, &__ex };
        }

template<typename _Res>
	static _Setter<_Res, void>
	__setter(promise<_Res>* __prom)
	{
	  _S_check(__prom->_M_future);
	  return _Setter<_Res, void>{ __prom };
	}

template<typename _Tp>
        static void
        _S_check(const shared_ptr<_Tp>& __p)
        {
          if (!static_cast<bool>(__p))
            __throw_future_error((int)future_errc::no_state);
        }

private:
      // The function invoked with std::call_once(_M_once, ...).
      void
      _M_do_set(function<_Ptr_type()>* __f, bool* __did_set)
      {
        _Ptr_type __res = (*__f)();
        // Notify the caller that we did try to set; if we do not throw an
        // exception, the caller will be aware that it did set (e.g., see
        // _M_set_result).
	*__did_set = true;
        _M_result.swap(__res); // nothrow
      }

// Wait for completion of async function.
      virtual void _M_complete_async() { }

// Return true if state corresponds to a deferred function.
      virtual bool _M_is_deferred_future() const { return false; }

struct _Make_ready final : __at_thread_exit_elt
      {
	weak_ptr<_State_baseV2> _M_shared_state;
	static void _S_run(void*);
	void _M_set();
      };
    };

#ifdef _GLIBCXX_ASYNC_ABI_COMPAT
    class _State_base;
    class _Async_state_common;
#else
    using _State_base = _State_baseV2;
    class _Async_state_commonV2;
#endif

template<typename _BoundFn,
	     typename _Res = decltype(std::declval<_BoundFn&>()())>
      class _Deferred_state;

template<typename _BoundFn,
	     typename _Res = decltype(std::declval<_BoundFn&>()())>
      class _Async_state_impl;

template<typename _Signature>
      class _Task_state_base;

template<typename _Fn, typename _Alloc, typename _Signature>
      class _Task_state;

template<typename _BoundFn>
      static std::shared_ptr<_State_base>
      _S_make_deferred_state(_BoundFn&& __fn);

template<typename _BoundFn>
      static std::shared_ptr<_State_base>
      _S_make_async_state(_BoundFn&& __fn);

template<typename _Res_ptr, typename _Fn,
	     typename _Res = typename _Res_ptr::element_type::result_type>
      struct _Task_setter;

template<typename _Res_ptr, typename _BoundFn>
      static _Task_setter<_Res_ptr, _BoundFn>
      _S_task_setter(_Res_ptr& __ptr, _BoundFn& __call)
      {
	return { std::__addressof(__ptr), std::__addressof(__call) };
      }
  };

/// Partial specialization for reference types.
  template<typename _Res>
    struct __future_base::_Result<_Res&> : __future_base::_Result_base
    {
      typedef _Res& result_type;

_Result() noexcept : _M_value_ptr() { }

void
      _M_set(_Res& __res) noexcept
      { _M_value_ptr = std::addressof(__res); }

_Res& _M_get() noexcept { return *_M_value_ptr; }

private:
      _Res* 			_M_value_ptr;

void _M_destroy() { delete this; }
    };

/// Explicit specialization for void.
  template<>
    struct __future_base::_Result<void> : __future_base::_Result_base
    {
      typedef void result_type;

private:
      void _M_destroy() { delete this; }
    };

#ifndef _GLIBCXX_ASYNC_ABI_COMPAT

// Allow _Setter objects to be stored locally in std::function
  template<typename _Res, typename _Arg>
    struct __is_location_invariant
    <__future_base::_State_base::_Setter<_Res, _Arg>>
    : true_type { };

// Allow _Task_setter objects to be stored locally in std::function
  template<typename _Res_ptr, typename _Fn, typename _Res>
    struct __is_location_invariant
    <__future_base::_Task_setter<_Res_ptr, _Fn, _Res>>
    : true_type { };

/// Common implementation for future and shared_future.
  template<typename _Res>
    class __basic_future : public __future_base
    {
    protected:
      typedef shared_ptr<_State_base>		__state_type;
      typedef __future_base::_Result<_Res>&	__result_type;

private:
      __state_type 		_M_state;

public:
      // Disable copying.
      __basic_future(const __basic_future&) = delete;
      __basic_future& operator=(const __basic_future&) = delete;

bool
      valid() const noexcept { return static_cast<bool>(_M_state); }

void
      wait() const
      {
        _State_base::_S_check(_M_state);
        _M_state->wait();
      }

template<typename _Rep, typename _Period>
        future_status
        wait_for(const chrono::duration<_Rep, _Period>& __rel) const
        {
          _State_base::_S_check(_M_state);
          return _M_state->wait_for(__rel);
        }

template<typename _Clock, typename _Duration>
        future_status
        wait_until(const chrono::time_point<_Clock, _Duration>& __abs) const
        {
          _State_base::_S_check(_M_state);
          return _M_state->wait_until(__abs);
        }

protected:
      /// Wait for the state to be ready and rethrow any stored exception
      __result_type
      _M_get_result() const
      {
        _State_base::_S_check(_M_state);
        _Result_base& __res = _M_state->wait();
        if (!(__res._M_error == 0))
          rethrow_exception(__res._M_error);
        return static_cast<__result_type>(__res);
      }

void _M_swap(__basic_future& __that) noexcept
      {
        _M_state.swap(__that._M_state);
      }

// Construction of a future by promise::get_future()
      explicit
      __basic_future(const __state_type& __state) : _M_state(__state)
      {
        _State_base::_S_check(_M_state);
        _M_state->_M_set_retrieved_flag();
      }

// Copy construction from a shared_future
      explicit
      __basic_future(const shared_future<_Res>&) noexcept;

// Move construction from a shared_future
      explicit
      __basic_future(shared_future<_Res>&&) noexcept;

// Move construction from a future
      explicit
      __basic_future(future<_Res>&&) noexcept;

constexpr __basic_future() noexcept : _M_state() { }

struct _Reset
      {
        explicit _Reset(__basic_future& __fut) noexcept : _M_fut(__fut) { }
        ~_Reset() { _M_fut._M_state.reset(); }
        __basic_future& _M_fut;
      };
    };

/// Primary template for future.
  template<typename _Res>
    class future : public __basic_future<_Res>
    {
      friend class promise<_Res>;
      template<typename> friend class packaged_task;
      template<typename _Fn, typename... _Args>
        friend future<__async_result_of<_Fn, _Args...>>
        async(launch, _Fn&&, _Args&&...);

typedef __basic_future<_Res> _Base_type;
      typedef typename _Base_type::__state_type __state_type;

explicit
      future(const __state_type& __state) : _Base_type(__state) { }

public:
      constexpr future() noexcept : _Base_type() { }

/// Move constructor
      future(future&& __uf) noexcept : _Base_type(std::move(__uf)) { }

// Disable copying
      future(const future&) = delete;
      future& operator=(const future&) = delete;

future& operator=(future&& __fut) noexcept
      {
        future(std::move(__fut))._M_swap(*this);
        return *this;
      }

/// Retrieving the value
      _Res
      get()
      {
        typename _Base_type::_Reset __reset(*this);
        return std::move(this->_M_get_result()._M_value());
      }

shared_future<_Res> share() noexcept;
    };

/// Partial specialization for future<R&>
  template<typename _Res>
    class future<_Res&> : public __basic_future<_Res&>
    {
      friend class promise<_Res&>;
      template<typename> friend class packaged_task;
      template<typename _Fn, typename... _Args>
        friend future<__async_result_of<_Fn, _Args...>>
        async(launch, _Fn&&, _Args&&...);

typedef __basic_future<_Res&> _Base_type;
      typedef typename _Base_type::__state_type __state_type;

explicit
      future(const __state_type& __state) : _Base_type(__state) { }

public:
      constexpr future() noexcept : _Base_type() { }

/// Move constructor
      future(future&& __uf) noexcept : _Base_type(std::move(__uf)) { }

// Disable copying
      future(const future&) = delete;
      future& operator=(const future&) = delete;

future& operator=(future&& __fut) noexcept
      {
        future(std::move(__fut))._M_swap(*this);
        return *this;
      }

/// Retrieving the value
      _Res&
      get()
      {
        typename _Base_type::_Reset __reset(*this);
        return this->_M_get_result()._M_get();
      }

shared_future<_Res&> share() noexcept;
    };

/// Explicit specialization for future<void>
  template<>
    class future<void> : public __basic_future<void>
    {
      friend class promise<void>;
      template<typename> friend class packaged_task;
      template<typename _Fn, typename... _Args>
        friend future<__async_result_of<_Fn, _Args...>>
        async(launch, _Fn&&, _Args&&...);

typedef __basic_future<void> _Base_type;
      typedef typename _Base_type::__state_type __state_type;

explicit
      future(const __state_type& __state) : _Base_type(__state) { }

public:
      constexpr future() noexcept : _Base_type() { }

/// Move constructor
      future(future&& __uf) noexcept : _Base_type(std::move(__uf)) { }

// Disable copying
      future(const future&) = delete;
      future& operator=(const future&) = delete;

future& operator=(future&& __fut) noexcept
      {
        future(std::move(__fut))._M_swap(*this);
        return *this;
      }

/// Retrieving the value
      void
      get()
      {
        typename _Base_type::_Reset __reset(*this);
        this->_M_get_result();
      }

shared_future<void> share() noexcept;
    };

/// Primary template for shared_future.
  template<typename _Res>
    class shared_future : public __basic_future<_Res>
    {
      typedef __basic_future<_Res> _Base_type;

public:
      constexpr shared_future() noexcept : _Base_type() { }

/// Copy constructor
      shared_future(const shared_future& __sf) noexcept : _Base_type(__sf) { }

/// Construct from a future rvalue
      shared_future(future<_Res>&& __uf) noexcept
      : _Base_type(std::move(__uf))
      { }

/// Construct from a shared_future rvalue
      shared_future(shared_future&& __sf) noexcept
      : _Base_type(std::move(__sf))
      { }

shared_future& operator=(const shared_future& __sf) noexcept
      {
        shared_future(__sf)._M_swap(*this);
        return *this;
      }

shared_future& operator=(shared_future&& __sf) noexcept
      {
        shared_future(std::move(__sf))._M_swap(*this);
        return *this;
      }

/// Retrieving the value
      const _Res&
      get() const { return this->_M_get_result()._M_value(); }
    };

/// Partial specialization for shared_future<R&>
  template<typename _Res>
    class shared_future<_Res&> : public __basic_future<_Res&>
    {
      typedef __basic_future<_Res&>           _Base_type;

public:
      constexpr shared_future() noexcept : _Base_type() { }

/// Copy constructor
      shared_future(const shared_future& __sf) : _Base_type(__sf) { }

/// Construct from a future rvalue
      shared_future(future<_Res&>&& __uf) noexcept
      : _Base_type(std::move(__uf))
      { }

/// Construct from a shared_future rvalue
      shared_future(shared_future&& __sf) noexcept
      : _Base_type(std::move(__sf))
      { }

shared_future& operator=(const shared_future& __sf)
      {
        shared_future(__sf)._M_swap(*this);
        return *this;
      }

shared_future& operator=(shared_future&& __sf) noexcept
      {
        shared_future(std::move(__sf))._M_swap(*this);
        return *this;
      }

/// Retrieving the value
      _Res&
      get() const { return this->_M_get_result()._M_get(); }
    };

/// Explicit specialization for shared_future<void>
  template<>
    class shared_future<void> : public __basic_future<void>
    {
      typedef __basic_future<void> _Base_type;

public:
      constexpr shared_future() noexcept : _Base_type() { }

/// Copy constructor
      shared_future(const shared_future& __sf) : _Base_type(__sf) { }

/// Construct from a future rvalue
      shared_future(future<void>&& __uf) noexcept
      : _Base_type(std::move(__uf))
      { }

/// Construct from a shared_future rvalue
      shared_future(shared_future&& __sf) noexcept
      : _Base_type(std::move(__sf))
      { }

shared_future& operator=(const shared_future& __sf)
      {
        shared_future(__sf)._M_swap(*this);
        return *this;
      }

shared_future& operator=(shared_future&& __sf) noexcept
      {
        shared_future(std::move(__sf))._M_swap(*this);
        return *this;
      }

// Retrieving the value
      void
      get() const { this->_M_get_result(); }
    };

// Now we can define the protected __basic_future constructors.
  template<typename _Res>
    inline __basic_future<_Res>::
    __basic_future(const shared_future<_Res>& __sf) noexcept
    : _M_state(__sf._M_state)
    { }

template<typename _Res>
    inline __basic_future<_Res>::
    __basic_future(shared_future<_Res>&& __sf) noexcept
    : _M_state(std::move(__sf._M_state))
    { }

template<typename _Res>
    inline __basic_future<_Res>::
    __basic_future(future<_Res>&& __uf) noexcept
    : _M_state(std::move(__uf._M_state))
    { }

// _GLIBCXX_RESOLVE_LIB_DEFECTS
  // 2556. Wide contract for future::share()
  template<typename _Res>
    inline shared_future<_Res>
    future<_Res>::share() noexcept
    { return shared_future<_Res>(std::move(*this)); }

template<typename _Res>
    inline shared_future<_Res&>
    future<_Res&>::share() noexcept
    { return shared_future<_Res&>(std::move(*this)); }

inline shared_future<void>
  future<void>::share() noexcept
  { return shared_future<void>(std::move(*this)); }

/// Primary template for promise
  template<typename _Res>
    class promise
    {
      typedef __future_base::_State_base 	_State;
      typedef __future_base::_Result<_Res>	_Res_type;
      typedef __future_base::_Ptr<_Res_type>	_Ptr_type;
      template<typename, typename> friend class _State::_Setter;
      friend _State;

shared_ptr<_State>                        _M_future;
      _Ptr_type                                 _M_storage;

public:
      promise()
      : _M_future(std::make_shared<_State>()),
	_M_storage(new _Res_type())
      { }

promise(promise&& __rhs) noexcept
      : _M_future(std::move(__rhs._M_future)),
	_M_storage(std::move(__rhs._M_storage))
      { }

template<typename _Allocator>
        promise(allocator_arg_t, const _Allocator& __a)
        : _M_future(std::allocate_shared<_State>(__a)),
	  _M_storage(__future_base::_S_allocate_result<_Res>(__a))
        { }

template<typename _Allocator>
        promise(allocator_arg_t, const _Allocator&, promise&& __rhs)
        : _M_future(std::move(__rhs._M_future)),
	  _M_storage(std::move(__rhs._M_storage))
        { }

promise(const promise&) = delete;

~promise()
      {
        if (static_cast<bool>(_M_future) && !_M_future.unique())
          _M_future->_M_break_promise(std::move(_M_storage));
      }

// Assignment
      promise&
      operator=(promise&& __rhs) noexcept
      {
        promise(std::move(__rhs)).swap(*this);
        return *this;
      }

promise& operator=(const promise&) = delete;

void
      swap(promise& __rhs) noexcept
      {
        _M_future.swap(__rhs._M_future);
        _M_storage.swap(__rhs._M_storage);
      }

// Retrieving the result
      future<_Res>
      get_future()
      { return future<_Res>(_M_future); }

// Setting the result
      void
      set_value(const _Res& __r)
      { _M_future->_M_set_result(_State::__setter(this, __r)); }

void
      set_value(_Res&& __r)
      { _M_future->_M_set_result(_State::__setter(this, std::move(__r))); }

void
      set_exception(exception_ptr __p)
      { _M_future->_M_set_result(_State::__setter(__p, this)); }

void
      set_value_at_thread_exit(const _Res& __r)
      {
	_M_future->_M_set_delayed_result(_State::__setter(this, __r),
					 _M_future);
      }

void
      set_value_at_thread_exit(_Res&& __r)
      {
	_M_future->_M_set_delayed_result(
	    _State::__setter(this, std::move(__r)), _M_future);
      }

void
      set_exception_at_thread_exit(exception_ptr __p)
      {
	_M_future->_M_set_delayed_result(_State::__setter(__p, this),
					 _M_future);
      }
    };

template<typename _Res>
    inline void
    swap(promise<_Res>& __x, promise<_Res>& __y) noexcept
    { __x.swap(__y); }

template<typename _Res, typename _Alloc>
    struct uses_allocator<promise<_Res>, _Alloc>
    : public true_type { };

/// Partial specialization for promise<R&>
  template<typename _Res>
    class promise<_Res&>
    {
      typedef __future_base::_State_base	_State;
      typedef __future_base::_Result<_Res&>	_Res_type;
      typedef __future_base::_Ptr<_Res_type> 	_Ptr_type;
      template<typename, typename> friend class _State::_Setter;
      friend _State;

shared_ptr<_State>                        _M_future;
      _Ptr_type                                 _M_storage;

public:
      promise()
      : _M_future(std::make_shared<_State>()),
	_M_storage(new _Res_type())
      { }

promise(promise&& __rhs) noexcept
      : _M_future(std::move(__rhs._M_future)),
	_M_storage(std::move(__rhs._M_storage))
      { }

promise(const promise&) = delete;

~promise()
      {
        if (static_cast<bool>(_M_future) && !_M_future.unique())
          _M_future->_M_break_promise(std::move(_M_storage));
      }

// Assignment
      promise&
      operator=(promise&& __rhs) noexcept
      {
        promise(std::move(__rhs)).swap(*this);
        return *this;
      }

promise& operator=(const promise&) = delete;

void
      swap(promise& __rhs) noexcept
      {
        _M_future.swap(__rhs._M_future);
        _M_storage.swap(__rhs._M_storage);
      }

// Retrieving the result
      future<_Res&>
      get_future()
      { return future<_Res&>(_M_future); }

// Setting the result
      void
      set_value(_Res& __r)
      { _M_future->_M_set_result(_State::__setter(this, __r)); }

void
      set_exception(exception_ptr __p)
      { _M_future->_M_set_result(_State::__setter(__p, this)); }

void
      set_value_at_thread_exit(_Res& __r)
      {
	_M_future->_M_set_delayed_result(_State::__setter(this, __r),
					 _M_future);
      }

void
      set_exception_at_thread_exit(exception_ptr __p)
      {
	_M_future->_M_set_delayed_result(_State::__setter(__p, this),
					 _M_future);
      }
    };

/// Explicit specialization for promise<void>
  template<>
    class promise<void>
    {
      typedef __future_base::_State_base	_State;
      typedef __future_base::_Result<void>	_Res_type;
      typedef __future_base::_Ptr<_Res_type> 	_Ptr_type;
      template<typename, typename> friend class _State::_Setter;
      friend _State;

shared_ptr<_State>                        _M_future;
      _Ptr_type                                 _M_storage;

public:
      promise()
      : _M_future(std::make_shared<_State>()),
	_M_storage(new _Res_type())
      { }

promise(promise&& __rhs) noexcept
      : _M_future(std::move(__rhs._M_future)),
	_M_storage(std::move(__rhs._M_storage))
      { }

// _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 2095.  missing constructors needed for uses-allocator construction
      template<typename _Allocator>
        promise(allocator_arg_t, const _Allocator&, promise&& __rhs)
        : _M_future(std::move(__rhs._M_future)),
	  _M_storage(std::move(__rhs._M_storage))
        { }

promise(const promise&) = delete;

~promise()
      {
        if (static_cast<bool>(_M_future) && !_M_future.unique())
          _M_future->_M_break_promise(std::move(_M_storage));
      }

// Assignment
      promise&
      operator=(promise&& __rhs) noexcept
      {
        promise(std::move(__rhs)).swap(*this);
        return *this;
      }

promise& operator=(const promise&) = delete;

void
      swap(promise& __rhs) noexcept
      {
        _M_future.swap(__rhs._M_future);
        _M_storage.swap(__rhs._M_storage);
      }

// Retrieving the result
      future<void>
      get_future()
      { return future<void>(_M_future); }

// Setting the result
      void
      set_value()
      { _M_future->_M_set_result(_State::__setter(this)); }

void
      set_exception(exception_ptr __p)
      { _M_future->_M_set_result(_State::__setter(__p, this)); }

void
      set_value_at_thread_exit()
      { _M_future->_M_set_delayed_result(_State::__setter(this), _M_future); }

void
      set_exception_at_thread_exit(exception_ptr __p)
      {
	_M_future->_M_set_delayed_result(_State::__setter(__p, this),
					 _M_future);
      }
    };

template<typename _Ptr_type, typename _Fn, typename _Res>
    struct __future_base::_Task_setter
    {
      // Invoke the function and provide the result to the caller.
      _Ptr_type operator()() const
      {
	__try
	  {
	    (*_M_result)->_M_set((*_M_fn)());
	  }
	__catch(const __cxxabiv1::__forced_unwind&)
	  {
	    __throw_exception_again; // will cause broken_promise
	  }
	__catch(...)
	  {
	    (*_M_result)->_M_error = current_exception();
	  }
	return std::move(*_M_result);
      }
      _Ptr_type*	_M_result;
      _Fn*		_M_fn;
    };

template<typename _Ptr_type, typename _Fn>
    struct __future_base::_Task_setter<_Ptr_type, _Fn, void>
    {
      _Ptr_type operator()() const
      {
	__try
	  {
	    (*_M_fn)();
	  }
	__catch(const __cxxabiv1::__forced_unwind&)
	  {
	    __throw_exception_again; // will cause broken_promise
	  }
	__catch(...)
	  {
	    (*_M_result)->_M_error = current_exception();
	  }
	return std::move(*_M_result);
      }
      _Ptr_type*	_M_result;
      _Fn*		_M_fn;
    };

// Holds storage for a packaged_task's result.
  template<typename _Res, typename... _Args>
    struct __future_base::_Task_state_base<_Res(_Args...)>
    : __future_base::_State_base
    {
      typedef _Res _Res_type;

template<typename _Alloc>
	_Task_state_base(const _Alloc& __a)
	: _M_result(_S_allocate_result<_Res>(__a))
	{ }

// Invoke the stored task and make the state ready.
      virtual void
      _M_run(_Args&&... __args) = 0;

// Invoke the stored task and make the state ready at thread exit.
      virtual void
      _M_run_delayed(_Args&&... __args, weak_ptr<_State_base>) = 0;

virtual shared_ptr<_Task_state_base>
      _M_reset() = 0;

typedef __future_base::_Ptr<_Result<_Res>> _Ptr_type;
      _Ptr_type _M_result;
    };

// Holds a packaged_task's stored task.
  template<typename _Fn, typename _Alloc, typename _Res, typename... _Args>
    struct __future_base::_Task_state<_Fn, _Alloc, _Res(_Args...)> final
    : __future_base::_Task_state_base<_Res(_Args...)>
    {
      template<typename _Fn2>
	_Task_state(_Fn2&& __fn, const _Alloc& __a)
	: _Task_state_base<_Res(_Args...)>(__a),
	  _M_impl(std::forward<_Fn2>(__fn), __a)
	{ }

private:
      virtual void
      _M_run(_Args&&... __args)
      {
	auto __boundfn = [&] () -> typename result_of<_Fn&(_Args&&...)>::type {
	    return std::__invoke(_M_impl._M_fn, std::forward<_Args>(__args)...);
	};
	this->_M_set_result(_S_task_setter(this->_M_result, __boundfn));
      }

virtual void
      _M_run_delayed(_Args&&... __args, weak_ptr<_State_base> __self)
      {
	auto __boundfn = [&] () -> typename result_of<_Fn&(_Args&&...)>::type {
	    return std::__invoke(_M_impl._M_fn, std::forward<_Args>(__args)...);
	};
	this->_M_set_delayed_result(_S_task_setter(this->_M_result, __boundfn),
				    std::move(__self));
      }

virtual shared_ptr<_Task_state_base<_Res(_Args...)>>
      _M_reset();

struct _Impl : _Alloc
      {
	template<typename _Fn2>
	  _Impl(_Fn2&& __fn, const _Alloc& __a)
	  : _Alloc(__a), _M_fn(std::forward<_Fn2>(__fn)) { }
	_Fn _M_fn;
      } _M_impl;
    };

template<typename _Signature, typename _Fn, typename _Alloc>
    static shared_ptr<__future_base::_Task_state_base<_Signature>>
    __create_task_state(_Fn&& __fn, const _Alloc& __a)
    {
      typedef typename decay<_Fn>::type _Fn2;
      typedef __future_base::_Task_state<_Fn2, _Alloc, _Signature> _State;
      return std::allocate_shared<_State>(__a, std::forward<_Fn>(__fn), __a);
    }

template<typename _Fn, typename _Alloc, typename _Res, typename... _Args>
    shared_ptr<__future_base::_Task_state_base<_Res(_Args...)>>
    __future_base::_Task_state<_Fn, _Alloc, _Res(_Args...)>::_M_reset()
    {
      return __create_task_state<_Res(_Args...)>(std::move(_M_impl._M_fn),
						 static_cast<_Alloc&>(_M_impl));
    }

template<typename _Task, typename _Fn, bool
	   = is_same<_Task, typename decay<_Fn>::type>::value>
    struct __constrain_pkgdtask
    { typedef void __type; };

template<typename _Task, typename _Fn>
    struct __constrain_pkgdtask<_Task, _Fn, true>
    { };

/// packaged_task
  template<typename _Res, typename... _ArgTypes>
    class packaged_task<_Res(_ArgTypes...)>
    {
      typedef __future_base::_Task_state_base<_Res(_ArgTypes...)> _State_type;
      shared_ptr<_State_type>                   _M_state;

public:
      // Construction and destruction
      packaged_task() noexcept { }

// _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 2095.  missing constructors needed for uses-allocator construction
      template<typename _Allocator>
	packaged_task(allocator_arg_t, const _Allocator& __a) noexcept
	{ }

template<typename _Fn, typename = typename
	       __constrain_pkgdtask<packaged_task, _Fn>::__type>
	explicit
	packaged_task(_Fn&& __fn)
	: packaged_task(allocator_arg, std::allocator<int>(),
			std::forward<_Fn>(__fn))
	{ }

// _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 2097.  packaged_task constructors should be constrained
      // 2407. [this constructor should not be] explicit
      template<typename _Fn, typename _Alloc, typename = typename
	       __constrain_pkgdtask<packaged_task, _Fn>::__type>
	packaged_task(allocator_arg_t, const _Alloc& __a, _Fn&& __fn)
	: _M_state(__create_task_state<_Res(_ArgTypes...)>(
		    std::forward<_Fn>(__fn), __a))
	{ }

~packaged_task()
      {
        if (static_cast<bool>(_M_state) && !_M_state.unique())
	  _M_state->_M_break_promise(std::move(_M_state->_M_result));
      }

// No copy
      packaged_task(const packaged_task&) = delete;
      packaged_task& operator=(const packaged_task&) = delete;

template<typename _Allocator>
	packaged_task(allocator_arg_t, const _Allocator&,
		      const packaged_task&) = delete;

// Move support
      packaged_task(packaged_task&& __other) noexcept
      { this->swap(__other); }

template<typename _Allocator>
	packaged_task(allocator_arg_t, const _Allocator&,
		      packaged_task&& __other) noexcept
	{ this->swap(__other); }

packaged_task& operator=(packaged_task&& __other) noexcept
      {
	packaged_task(std::move(__other)).swap(*this);
	return *this;
      }

void
      swap(packaged_task& __other) noexcept
      { _M_state.swap(__other._M_state); }

bool
      valid() const noexcept
      { return static_cast<bool>(_M_state); }

// Result retrieval
      future<_Res>
      get_future()
      { return future<_Res>(_M_state); }

// Execution
      void
      operator()(_ArgTypes... __args)
      {
	__future_base::_State_base::_S_check(_M_state);
	_M_state->_M_run(std::forward<_ArgTypes>(__args)...);
      }

void
      make_ready_at_thread_exit(_ArgTypes... __args)
      {
	__future_base::_State_base::_S_check(_M_state);
	_M_state->_M_run_delayed(std::forward<_ArgTypes>(__args)..., _M_state);
      }

void
      reset()
      {
	__future_base::_State_base::_S_check(_M_state);
	packaged_task __tmp;
	__tmp._M_state = _M_state;
	_M_state = _M_state->_M_reset();
      }
    };

/// swap
  template<typename _Res, typename... _ArgTypes>
    inline void
    swap(packaged_task<_Res(_ArgTypes...)>& __x,
	 packaged_task<_Res(_ArgTypes...)>& __y) noexcept
    { __x.swap(__y); }

template<typename _Res, typename _Alloc>
    struct uses_allocator<packaged_task<_Res>, _Alloc>
    : public true_type { };

// Shared state created by std::async().
  // Holds a deferred function and storage for its result.
  template<typename _BoundFn, typename _Res>
    class __future_base::_Deferred_state final
    : public __future_base::_State_base
    {
    public:
      explicit
      _Deferred_state(_BoundFn&& __fn)
      : _M_result(new _Result<_Res>()), _M_fn(std::move(__fn))
      { }

private:
      typedef __future_base::_Ptr<_Result<_Res>> _Ptr_type;
      _Ptr_type _M_result;
      _BoundFn _M_fn;

// Run the deferred function.
      virtual void
      _M_complete_async()
      {
	// Multiple threads can call a waiting function on the future and
	// reach this point at the same time. The call_once in _M_set_result
	// ensures only the first one run the deferred function, stores the
	// result in _M_result, swaps that with the base _M_result and makes
	// the state ready. Tell _M_set_result to ignore failure so all later
	// calls do nothing.
        _M_set_result(_S_task_setter(_M_result, _M_fn), true);
      }

// Caller should check whether the state is ready first, because this
      // function will return true even after the deferred function has run.
      virtual bool _M_is_deferred_future() const { return true; }
    };

// Common functionality hoisted out of the _Async_state_impl template.
  class __future_base::_Async_state_commonV2
    : public __future_base::_State_base
  {
  protected:
    ~_Async_state_commonV2() = default;

// Make waiting functions block until the thread completes, as if joined.
    //
    // This function is used by wait() to satisfy the first requirement below
    // and by wait_for() / wait_until() to satisfy the second.
    //
    // [futures.async]:
    //
    // — a call to a waiting function on an asynchronous return object that
    // shares the shared state created by this async call shall block until
    // the associated thread has completed, as if joined, or else time out.
    //
    // — the associated thread completion synchronizes with the return from
    // the first function that successfully detects the ready status of the
    // shared state or with the return from the last function that releases
    // the shared state, whichever happens first.
    virtual void _M_complete_async() { _M_join(); }

void _M_join() { std::call_once(_M_once, &thread::join, &_M_thread); }

thread _M_thread;
    once_flag _M_once;
  };

// Shared state created by std::async().
  // Starts a new thread that runs a function and makes the shared state ready.
  template<typename _BoundFn, typename _Res>
    class __future_base::_Async_state_impl final
    : public __future_base::_Async_state_commonV2
    {
    public:
      explicit
      _Async_state_impl(_BoundFn&& __fn)
      : _M_result(new _Result<_Res>()), _M_fn(std::move(__fn))
      {
	_M_thread = std::thread{ [this] {
	    __try
	      {
		_M_set_result(_S_task_setter(_M_result, _M_fn));
	      }
	    __catch (const __cxxabiv1::__forced_unwind&)
	      {
		// make the shared state ready on thread cancellation
		if (static_cast<bool>(_M_result))
		  this->_M_break_promise(std::move(_M_result));
		__throw_exception_again;
	      }
        } };
      }

// Must not destroy _M_result and _M_fn until the thread finishes.
      // Call join() directly rather than through _M_join() because no other
      // thread can be referring to this state if it is being destroyed.
      ~_Async_state_impl() { if (_M_thread.joinable()) _M_thread.join(); }

private:
      typedef __future_base::_Ptr<_Result<_Res>> _Ptr_type;
      _Ptr_type _M_result;
      _BoundFn _M_fn;
    };

template<typename _BoundFn>
    inline std::shared_ptr<__future_base::_State_base>
    __future_base::_S_make_deferred_state(_BoundFn&& __fn)
    {
      typedef typename remove_reference<_BoundFn>::type __fn_type;
      typedef _Deferred_state<__fn_type> __state_type;
      return std::make_shared<__state_type>(std::move(__fn));
    }

template<typename _BoundFn>
    inline std::shared_ptr<__future_base::_State_base>
    __future_base::_S_make_async_state(_BoundFn&& __fn)
    {
      typedef typename remove_reference<_BoundFn>::type __fn_type;
      typedef _Async_state_impl<__fn_type> __state_type;
      return std::make_shared<__state_type>(std::move(__fn));
    }

/// async
  template<typename _Fn, typename... _Args>
    future<__async_result_of<_Fn, _Args...>>
    async(launch __policy, _Fn&& __fn, _Args&&... __args)
    {
      std::shared_ptr<__future_base::_State_base> __state;
      if ((__policy & launch::async) == launch::async)
	{
	  __try
	    {
	      __state = __future_base::_S_make_async_state(
		  std::thread::__make_invoker(std::forward<_Fn>(__fn),
					      std::forward<_Args>(__args)...)
		  );
	    }
#if __cpp_exceptions
	  catch(const system_error& __e)
	    {
	      if (__e.code() != errc::resource_unavailable_try_again
		  || (__policy & launch::deferred) != launch::deferred)
		throw;
	    }
#endif
	}
      if (!__state)
	{
	  __state = __future_base::_S_make_deferred_state(
	      std::thread::__make_invoker(std::forward<_Fn>(__fn),
					  std::forward<_Args>(__args)...));
	}
      return future<__async_result_of<_Fn, _Args...>>(__state);
    }

/// async, potential overload
  template<typename _Fn, typename... _Args>
    inline future<__async_result_of<_Fn, _Args...>>
    async(_Fn&& __fn, _Args&&... __args)
    {
      return std::async(launch::async|launch::deferred,
			std::forward<_Fn>(__fn),
			std::forward<_Args>(__args)...);
    }

#endif // _GLIBCXX_ASYNC_ABI_COMPAT
#endif // _GLIBCXX_HAS_GTHREADS && _GLIBCXX_USE_C99_STDINT_TR1

// @} group futures
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#endif // C++11

#endif // _GLIBCXX_FUTURE

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