future
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// <future> -*- C++ -*-
// Copyright (C) 2009-2021 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> // call_once
#include <condition_variable> // __at_thread_exit_elt
#include <system_error>
#include <atomic>
#include <bits/allocated_ptr.h>
#include <bits/atomic_futex.h>
#include <bits/invoke.h>
#include <bits/unique_ptr.h>
#include <bits/shared_ptr.h>
#include <bits/std_function.h>
#include <bits/std_thread.h>
#include <bits/uses_allocator.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 __invoke_result<
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)
/// 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;
// Don't wait unless the relative time is greater than zero.
if (__rel > __rel.zero()
&& _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)
{
#if __cplusplus > 201703L
static_assert(chrono::is_clock_v<_Clock>);
#endif
// 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>
__attribute__((__always_inline__))
static _Setter<_Res, _Arg&&>
__setter(promise<_Res>* __prom, _Arg&& __arg) noexcept
{
return _Setter<_Res, _Arg&&>{ __prom, std::__addressof(__arg) };
}
template<typename _Res>
__attribute__((__always_inline__))
static _Setter<_Res, __exception_ptr_tag>
__setter(exception_ptr& __ex, promise<_Res>* __prom) noexcept
{
return _Setter<_Res, __exception_ptr_tag>{ __prom, &__ex };
}
template<typename _Res>
__attribute__((__always_inline__))
static _Setter<_Res, void>
__setter(promise<_Res>* __prom) noexcept
{
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 _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 == nullptr))
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>
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3458. Is shared_future intended to work with arrays or function types?
static_assert(!is_array<_Res>{}, "result type must not be an array");
static_assert(!is_function<_Res>{}, "result type must not be a function");
static_assert(is_destructible<_Res>{},
"result type must be destructible");
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>
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3458. Is shared_future intended to work with arrays or function types?
static_assert(!is_array<_Res>{}, "result type must not be an array");
static_assert(!is_function<_Res>{}, "result type must not be a function");
static_assert(is_destructible<_Res>{},
"result type must be destructible");
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
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3466: Specify the requirements for promise/future/[...] consistently
static_assert(!is_array<_Res>{}, "result type must not be an array");
static_assert(!is_function<_Res>{}, "result type must not be a function");
static_assert(is_destructible<_Res>{},
"result type must be destructible");
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 struct _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_state()._M_set_result(_State::__setter(this, __r)); }
void
set_value(_Res&& __r)
{ _M_state()._M_set_result(_State::__setter(this, std::move(__r))); }
void
set_exception(exception_ptr __p)
{ _M_state()._M_set_result(_State::__setter(__p, this)); }
void
set_value_at_thread_exit(const _Res& __r)
{
_M_state()._M_set_delayed_result(_State::__setter(this, __r),
_M_future);
}
void
set_value_at_thread_exit(_Res&& __r)
{
_M_state()._M_set_delayed_result(
_State::__setter(this, std::move(__r)), _M_future);
}
void
set_exception_at_thread_exit(exception_ptr __p)
{
_M_state()._M_set_delayed_result(_State::__setter(__p, this),
_M_future);
}
private:
_State&
_M_state()
{
__future_base::_State_base::_S_check(_M_future);
return *_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 struct _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_state()._M_set_result(_State::__setter(this, __r)); }
void
set_exception(exception_ptr __p)
{ _M_state()._M_set_result(_State::__setter(__p, this)); }
void
set_value_at_thread_exit(_Res& __r)
{
_M_state()._M_set_delayed_result(_State::__setter(this, __r),
_M_future);
}
void
set_exception_at_thread_exit(exception_ptr __p)
{
_M_state()._M_set_delayed_result(_State::__setter(__p, this),
_M_future);
}
private:
_State&
_M_state()
{
__future_base::_State_base::_S_check(_M_future);
return *_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 struct _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_state()._M_set_result(_State::__setter(this)); }
void
set_exception(exception_ptr __p)
{ _M_state()._M_set_result(_State::__setter(__p, this)); }
void
set_value_at_thread_exit()
{ _M_state()._M_set_delayed_result(_State::__setter(this), _M_future); }
void
set_exception_at_thread_exit(exception_ptr __p)
{
_M_state()._M_set_delayed_result(_State::__setter(__p, this),
_M_future);
}
private:
_State&
_M_state()
{
__future_base::_State_base::_S_check(_M_future);
return *_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 = [&] () -> _Res {
return std::__invoke_r<_Res>(_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 = [&] () -> _Res {
return std::__invoke_r<_Res>(_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 = std::allocator<int>>
static shared_ptr<__future_base::_Task_state_base<_Signature>>
__create_task_state(_Fn&& __fn, const _Alloc& __a = _Alloc())
{
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));
}
/// 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;
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3039. Unnecessary decay in thread and packaged_task
template<typename _Fn, typename _Fn2 = __remove_cvref_t<_Fn>>
using __not_same
= typename enable_if<!is_same<packaged_task, _Fn2>::value>::type;
public:
// Construction and destruction
packaged_task() noexcept { }
template<typename _Fn, typename = __not_same<_Fn>>
explicit
packaged_task(_Fn&& __fn)
: _M_state(
__create_task_state<_Res(_ArgTypes...)>(std::forward<_Fn>(__fn)))
{ }
#if __cplusplus < 201703L
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2097. packaged_task constructors should be constrained
// 2407. [this constructor should not be] explicit
// 2921. packaged_task and type-erased allocators
template<typename _Fn, typename _Alloc, typename = __not_same<_Fn>>
packaged_task(allocator_arg_t, const _Alloc& __a, _Fn&& __fn)
: _M_state(__create_task_state<_Res(_ArgTypes...)>(
std::forward<_Fn>(__fn), __a))
{ }
// _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 _Allocator>
packaged_task(allocator_arg_t, const _Allocator&,
const packaged_task&) = delete;
template<typename _Allocator>
packaged_task(allocator_arg_t, const _Allocator&,
packaged_task&& __other) noexcept
{ this->swap(__other); }
#endif
~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;
// Move support
packaged_task(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); }
#if __cplusplus < 201703L
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2976. Dangling uses_allocator specialization for packaged_task
template<typename _Res, typename _Alloc>
struct uses_allocator<packaged_task<_Res>, _Alloc>
: public true_type { };
#endif
// 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:
template<typename... _Args>
explicit
_Deferred_state(_Args&&... __args)
: _M_result(new _Result<_Res>()),
_M_fn{{std::forward<_Args>(__args)...}}
{ }
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:
template<typename... _Args>
explicit
_Async_state_impl(_Args&&... __args)
: _M_result(new _Result<_Res>()),
_M_fn{{std::forward<_Args>(__args)...}}
{
_M_thread = std::thread{&_Async_state_impl::_M_run, this};
}
// 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:
void
_M_run()
{
__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;
}
}
typedef __future_base::_Ptr<_Result<_Res>> _Ptr_type;
_Ptr_type _M_result;
_BoundFn _M_fn;
};
/// async
template<typename _Fn, typename... _Args>
_GLIBCXX_NODISCARD future<__async_result_of<_Fn, _Args...>>
async(launch __policy, _Fn&& __fn, _Args&&... __args)
{
using _Wr = std::thread::_Call_wrapper<_Fn, _Args...>;
using _As = __future_base::_Async_state_impl<_Wr>;
using _Ds = __future_base::_Deferred_state<_Wr>;
std::shared_ptr<__future_base::_State_base> __state;
if ((__policy & launch::async) == launch::async)
{
__try
{
__state = std::make_shared<_As>(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 = std::make_shared<_Ds>(std::forward<_Fn>(__fn),
std::forward<_Args>(__args)...);
}
return future<__async_result_of<_Fn, _Args...>>(std::move(__state));
}
/// async, potential overload
template<typename _Fn, typename... _Args>
_GLIBCXX_NODISCARD 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
/// @} group futures
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif // C++11
#endif // _GLIBCXX_FUTURE