llvm-project/libcxx/include/future

// -*- C++ -*-
//===--------------------------- future -----------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP_FUTURE
#define _LIBCPP_FUTURE

/*
    future synopsis

namespace std
{

enum class future_errc
{
    broken_promise,
    future_already_retrieved,
    promise_already_satisfied,
    no_state
};

enum class launch
{
    any,
    async,
    sync
};

enum class future_status
{
    ready,
    timeout,
    deferred
};

template <> struct is_error_code_enum<future_errc> : public true_type { };
error_code make_error_code(future_errc e);
error_condition make_error_condition(future_errc e);

const error_category& future_category();

class future_error
    : public logic_error
{
public:
    future_error(error_code ec);  // exposition only

    const error_code& code() const throw();
    const char*       what() const throw();
};

template <class R>
class promise
{
public:
    promise();
    template <class Allocator>
        promise(allocator_arg_t, const Allocator& a);
    promise(promise&& rhs);
    promise(const promise& rhs) = delete;
    ~promise();

    // assignment
    promise& operator=(promise&& rhs);
    promise& operator=(const promise& rhs) = delete;
    void swap(promise& other);

    // retrieving the result
    future<R> get_future();

    // setting the result
    void set_value(const R& r);
    void set_value(R&& r);
    void set_exception(exception_ptr p);

    // setting the result with deferred notification
    void set_value_at_thread_exit(const R& r);
    void set_value_at_thread_exit(R&& r);
    void set_exception_at_thread_exit(exception_ptr p);
};

template <class R>
class promise<R&>
{
public:
    promise();
    template <class Allocator>
        promise(allocator_arg_t, const Allocator& a);
    promise(promise&& rhs);
    promise(const promise& rhs) = delete;
    ~promise();

    // assignment
    promise& operator=(promise&& rhs);
    promise& operator=(const promise& rhs) = delete;
    void swap(promise& other);

    // retrieving the result
    future<R&> get_future();

    // setting the result
    void set_value(R& r);
    void set_exception(exception_ptr p);

    // setting the result with deferred notification
    void set_value_at_thread_exit(R&);
    void set_exception_at_thread_exit(exception_ptr p);
};

template <>
class promise<void>
{
public:
    promise();
    template <class Allocator>
        promise(allocator_arg_t, const Allocator& a);
    promise(promise&& rhs);
    promise(const promise& rhs) = delete;
    ~promise();

    // assignment
    promise& operator=(promise&& rhs);
    promise& operator=(const promise& rhs) = delete;
    void swap(promise& other);

    // retrieving the result
    future<void> get_future();

    // setting the result
    void set_value();
    void set_exception(exception_ptr p);

    // setting the result with deferred notification
    void set_value_at_thread_exit();
    void set_exception_at_thread_exit(exception_ptr p);
};

template <class R> void swap(promise<R>& x, promise<R>& y);

template <class R, class Alloc>
    struct uses_allocator<promise<R>, Alloc> : public true_type {};

template <class R>
class future
{
public:
    future();
    future(future&&);
    future(const future& rhs) = delete;
    ~future();
    future& operator=(const future& rhs) = delete;
    future& operator=(future&&);

    // retrieving the value
    R get();

    // functions to check state
    bool valid() const;

    void wait() const;
    template <class Rep, class Period>
        future_status
        wait_for(const chrono::duration<Rep, Period>& rel_time) const;
    template <class Clock, class Duration>
        future_status
        wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;
};

template <class R>
class future<R&>
{
public:
    future();
    future(future&&);
    future(const future& rhs) = delete;
    ~future();
    future& operator=(const future& rhs) = delete;
    future& operator=(future&&);

    // retrieving the value
    R& get();

    // functions to check state
    bool valid() const;

    void wait() const;
    template <class Rep, class Period>
        future_status
        wait_for(const chrono::duration<Rep, Period>& rel_time) const;
    template <class Clock, class Duration>
        future_status
        wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;
};

template <>
class future<void>
{
public:
    future();
    future(future&&);
    future(const future& rhs) = delete;
    ~future();
    future& operator=(const future& rhs) = delete;
    future& operator=(future&&);

    // retrieving the value
    void get();

    // functions to check state
    bool valid() const;

    void wait() const;
    template <class Rep, class Period>
        future_status
        wait_for(const chrono::duration<Rep, Period>& rel_time) const;
    template <class Clock, class Duration>
        future_status
        wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;
};

template <class R>
class shared_future
{
public:
    shared_future();
    shared_future(const shared_future& rhs);
    shared_future(future<R>&&);
    shared_future(shared_future&& rhs);
    ~shared_future();
    shared_future& operator=(const shared_future& rhs);
    shared_future& operator=(shared_future&& rhs);

    // retrieving the value
    const R& get() const;

    // functions to check state
    bool valid() const;

    void wait() const;
    template <class Rep, class Period>
        future_status
        wait_for(const chrono::duration<Rep, Period>& rel_time) const;
    template <class Clock, class Duration>
        future_status
        wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;
};

template <class R>
class shared_future<R&>
{
public:
    shared_future();
    shared_future(const shared_future& rhs);
    shared_future(future<R>&&);
    shared_future(shared_future&& rhs);
    ~shared_future();
    shared_future& operator=(const shared_future& rhs);
    shared_future& operator=(shared_future&& rhs);

    // retrieving the value
    R& get() const;

    // functions to check state
    bool valid() const;

    void wait() const;
    template <class Rep, class Period>
        future_status
        wait_for(const chrono::duration<Rep, Period>& rel_time) const;
    template <class Clock, class Duration>
        future_status
        wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;
};

template <>
class shared_future<void>
{
public:
    shared_future();
    shared_future(const shared_future& rhs);
    shared_future(future<R>&&);
    shared_future(shared_future&& rhs);
    ~shared_future();
    shared_future& operator=(const shared_future& rhs);
    shared_future& operator=(shared_future&& rhs);

    // retrieving the value
    void get() const;

    // functions to check state
    bool valid() const;

    void wait() const;
    template <class Rep, class Period>
        future_status
        wait_for(const chrono::duration<Rep, Period>& rel_time) const;
    template <class Clock, class Duration>
        future_status
        wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;
};

template <class R>
class atomic_future
{
public:
    atomic_future();
    atomic_future(const atomic_future& rhs);
    atomic_future(future<R>&&);
    ~atomic_future();
    atomic_future& operator=(const atomic_future& rhs);

    // retrieving the value
    const R& get() const;

    // functions to check state
    bool valid() const;

    void wait() const;
    template <class Rep, class Period>
        future_status
        wait_for(const chrono::duration<Rep, Period>& rel_time) const;
    template <class Clock, class Duration>
        future_status
        wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;
};

template <class R>
class atomic_future<R&>
{
public:
    atomic_future();
    atomic_future(const atomic_future& rhs);
    atomic_future(future<R>&&);
    ~atomic_future();
    atomic_future& operator=(const atomic_future& rhs);

    // retrieving the value
    R& get() const;

    // functions to check state
    bool valid() const;

    void wait() const;
    template <class Rep, class Period>
        future_status
        wait_for(const chrono::duration<Rep, Period>& rel_time) const;
    template <class Clock, class Duration>
        future_status
        wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;
};

template <>
class atomic_future<void>
{
public:
    atomic_future();
    atomic_future(const atomic_future& rhs);
    atomic_future(future<R>&&);
    ~atomic_future();
    atomic_future& operator=(const atomic_future& rhs);

    // retrieving the value
    void get() const;

    // functions to check state
    bool valid() const;

    void wait() const;
    template <class Rep, class Period>
        future_status
        wait_for(const chrono::duration<Rep, Period>& rel_time) const;
    template <class Clock, class Duration>
        future_status
        wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;
};

template <class F, class... Args>
  future<typename result_of<F(Args...)>::type>
  async(F&& f, Args&&... args);

template <class F, class... Args>
  future<typename result_of<F(Args...)>::type>
  async(launch policy, F&& f, Args&&... args);

template <class> class packaged_task; // undefined

template <class R, class... ArgTypes>
class packaged_task<R(ArgTypes...)>
{
public:
    typedef R result_type;

    // construction and destruction
    packaged_task();
    template <class F>
        explicit packaged_task(F f);
    template <class F, class Allocator>
        explicit packaged_task(allocator_arg_t, const Allocator& a, F f);
    explicit packaged_task(R(*f)(ArgTypes...));
    template <class F>
        explicit packaged_task(F&& f);
    template <class F, class Allocator>
        explicit packaged_task(allocator_arg_t, const Allocator& a, F&& f);
    ~packaged_task();

    // no copy
    packaged_task(packaged_task&) = delete;
    packaged_task& operator=(packaged_task&) = delete;

    // move support
    packaged_task(packaged_task&& other);
    packaged_task& operator=(packaged_task&& other);
    void swap(packaged_task& other);

    explicit operator bool() const;

    // result retrieval
    future<R> get_future();

    // execution
    void operator()(ArgTypes... );
    void make_ready_at_thread_exit(ArgTypes...);

    void reset();
};

template <class R>
  void swap(packaged_task<R(ArgTypes...)&, packaged_task<R(ArgTypes...)>&);

template <class R, class Alloc> struct uses_allocator<packaged_task<R>, Alloc>;

}  // std

*/

#include <__config>
#include <system_error>
#include <memory>
#include <chrono>
#include <exception>
#include <__mutex_base>
#include <thread>

#pragma GCC system_header

_LIBCPP_BEGIN_NAMESPACE_STD

//enum class future_errc
struct future_errc
{
enum _ {
    broken_promise,
    future_already_retrieved,
    promise_already_satisfied,
    no_state
};

    _ __v_;

    future_errc(_ __v) : __v_(__v) {}
    operator int() const {return __v_;}

};

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

//enum class launch
struct launch
{
enum _ {
    any,
    async,
    sync
};

    _ __v_;

    launch(_ __v) : __v_(__v) {}
    operator int() const {return __v_;}

};

//enum class future_status
struct future_status
{
enum _ {
    ready,
    timeout,
    deferred
};

    _ __v_;

    future_status(_ __v) : __v_(__v) {}
    operator int() const {return __v_;}

};

const error_category& future_category();

inline _LIBCPP_INLINE_VISIBILITY
error_code
make_error_code(future_errc __e)
{
    return error_code(static_cast<int>(__e), future_category());
}

inline _LIBCPP_INLINE_VISIBILITY
error_condition
make_error_condition(future_errc __e)
{
    return error_condition(static_cast<int>(__e), future_category());
}

class future_error
    : public logic_error
{
    error_code __ec_;
public:
    future_error(error_code __ec);

    const error_code& code() const throw() {return __ec_;}
};

class __assoc_sub_state
    : public __shared_count
{
protected:
    exception_ptr __exception_;
    mutable mutex __mut_;
    mutable condition_variable __cv_;
    unsigned __state_;

    virtual void __on_zero_shared();

public:
    enum
    {
        __constructed = 1,
        __future_attached = 2,
        ready = 4,
        deferred = 8
    };

    __assoc_sub_state() : __state_(0) {}

    bool __has_value() const
        {return (__state_ & __constructed) || (__exception_ != nullptr);}

    void __set_future_attached() {__state_ |= __future_attached;}
    bool __has_future_attached() const {return __state_ & __future_attached;}

    void __make_ready();
    bool __is_ready() const {return __state_ & ready;}

    void set_value();
    void set_value_at_thread_exit();

    void set_exception(exception_ptr __p);
    void set_exception_at_thread_exit(exception_ptr __p);

    void copy();

    void wait() const;
    template <class _Rep, class _Period>
        future_status
        wait_for(const chrono::duration<_Rep, _Period>& __rel_time) const;
    template <class _Clock, class _Duration>
        future_status
        wait_until(const chrono::time_point<_Clock, _Duration>& __abs_time) const;
};

template <class _Clock, class _Duration>
future_status
__assoc_sub_state::wait_until(const chrono::time_point<_Clock, _Duration>& __abs_time) const
{
    unique_lock<mutex> __lk(__mut_);
    while (!(__state_ & (ready | deferred)) && _Clock::now() < __abs_time)
        __cv_.wait_until(__lk, __abs_time);
    if (__state_ & ready)
        return future_status::ready;
    if (__state_ & deferred)
        return future_status::deferred;
    return future_status::timeout;
}

template <class _Rep, class _Period>
inline _LIBCPP_INLINE_VISIBILITY
future_status
__assoc_sub_state::wait_for(const chrono::duration<_Rep, _Period>& __rel_time) const
{
    return wait_until(chrono::monotonic_clock::now() + __rel_time);
}

template <class _R>
class __assoc_state
    : public __assoc_sub_state
{
    typedef __assoc_sub_state base;
    typedef typename aligned_storage<sizeof(_R), alignment_of<_R>::value>::type _U;
protected:
    _U __value_;

    virtual void __on_zero_shared();
public:

    template <class _Arg>
#ifdef _LIBCPP_MOVE
        void set_value(_Arg&& __arg);
#else
        void set_value(_Arg& __arg);
#endif

    template <class _Arg>
#ifdef _LIBCPP_MOVE
        void set_value_at_thread_exit(_Arg&& __arg);
#else
        void set_value_at_thread_exit(_Arg& __arg);
#endif

    _R move();
    typename add_lvalue_reference<_R>::type copy();
};

template <class _R>
void
__assoc_state<_R>::__on_zero_shared()
{
    if (this->__state_ & base::__constructed)
        reinterpret_cast<_R*>(&__value_)->~_R();
    delete this;
}

template <class _R>
template <class _Arg>
void
#ifdef _LIBCPP_MOVE
__assoc_state<_R>::set_value(_Arg&& __arg)
#else
__assoc_state<_R>::set_value(_Arg& __arg)
#endif
{
    unique_lock<mutex> __lk(this->__mut_);
    if (this->__has_value())
        throw future_error(make_error_code(future_errc::promise_already_satisfied));
    ::new(&__value_) _R(_STD::forward<_Arg>(__arg));
    this->__state_ |= base::__constructed | base::ready;
    __lk.unlock();
    __cv_.notify_all();
}

template <class _R>
template <class _Arg>
void
#ifdef _LIBCPP_MOVE
__assoc_state<_R>::set_value_at_thread_exit(_Arg&& __arg)
#else
__assoc_state<_R>::set_value_at_thread_exit(_Arg& __arg)
#endif
{
    unique_lock<mutex> __lk(this->__mut_);
    if (this->__has_value())
        throw future_error(make_error_code(future_errc::promise_already_satisfied));
    ::new(&__value_) _R(_STD::forward<_Arg>(__arg));
    this->__state_ |= base::__constructed;
    __thread_local_data->__make_ready_at_thread_exit(this);
    __lk.unlock();
}

template <class _R>
_R
__assoc_state<_R>::move()
{
    unique_lock<mutex> __lk(this->__mut_);
    while (!this->__is_ready())
        this->__cv_.wait(__lk);
    if (this->__exception_ != nullptr)
        rethrow_exception(this->__exception_);
    return _STD::move(*reinterpret_cast<_R*>(&__value_));
}

template <class _R>
typename add_lvalue_reference<_R>::type
__assoc_state<_R>::copy()
{
    unique_lock<mutex> __lk(this->__mut_);
    while (!this->__is_ready())
        this->__cv_.wait(__lk);
    if (this->__exception_ != nullptr)
        rethrow_exception(this->__exception_);
    return *reinterpret_cast<_R*>(&__value_);
}

template <class _R>
class __assoc_state<_R&>
    : public __assoc_sub_state
{
    typedef __assoc_sub_state base;
    typedef _R* _U;
protected:
    _U __value_;

    virtual void __on_zero_shared();
public:

    void set_value(_R& __arg);
    void set_value_at_thread_exit(_R& __arg);

    _R& copy();
};

template <class _R>
void
__assoc_state<_R&>::__on_zero_shared()
{
    delete this;
}

template <class _R>
void
__assoc_state<_R&>::set_value(_R& __arg)
{
    unique_lock<mutex> __lk(this->__mut_);
    if (this->__has_value())
        throw future_error(make_error_code(future_errc::promise_already_satisfied));
    __value_ = &__arg;
    this->__state_ |= base::__constructed | base::ready;
    __lk.unlock();
    __cv_.notify_all();
}

template <class _R>
void
__assoc_state<_R&>::set_value_at_thread_exit(_R& __arg)
{
    unique_lock<mutex> __lk(this->__mut_);
    if (this->__has_value())
        throw future_error(make_error_code(future_errc::promise_already_satisfied));
    __value_ = &__arg;
    this->__state_ |= base::__constructed;
    __thread_local_data->__make_ready_at_thread_exit(this);
    __lk.unlock();
}

template <class _R>
_R&
__assoc_state<_R&>::copy()
{
    unique_lock<mutex> __lk(this->__mut_);
    while (!this->__is_ready())
        this->__cv_.wait(__lk);
    if (this->__exception_ != nullptr)
        rethrow_exception(this->__exception_);
    return *__value_;
}

template <class _R, class _Alloc>
class __assoc_state_alloc
    : public __assoc_state<_R>
{
    typedef __assoc_state<_R> base;
    _Alloc __alloc_;

    virtual void __on_zero_shared();
public:
    explicit __assoc_state_alloc(const _Alloc& __a)
        : __alloc_(__a) {}
};

template <class _R, class _Alloc>
void
__assoc_state_alloc<_R, _Alloc>::__on_zero_shared()
{
    if (this->__state_ & base::__constructed)
        reinterpret_cast<_R*>(&this->__value_)->~_R();
    typename _Alloc::template rebind<__assoc_state_alloc>::other __a(__alloc_);
    this->~__assoc_state_alloc();
    __a.deallocate(this, 1);
}

template <class _R, class _Alloc>
class __assoc_state_alloc<_R&, _Alloc>
    : public __assoc_state<_R&>
{
    typedef __assoc_state<_R&> base;
    _Alloc __alloc_;

    virtual void __on_zero_shared();
public:
    explicit __assoc_state_alloc(const _Alloc& __a)
        : __alloc_(__a) {}
};

template <class _R, class _Alloc>
void
__assoc_state_alloc<_R&, _Alloc>::__on_zero_shared()
{
    typename _Alloc::template rebind<__assoc_state_alloc>::other __a(__alloc_);
    this->~__assoc_state_alloc();
    __a.deallocate(this, 1);
}

template <class _Alloc>
class __assoc_sub_state_alloc
    : public __assoc_sub_state
{
    typedef __assoc_sub_state base;
    _Alloc __alloc_;

    virtual void __on_zero_shared();
public:
    explicit __assoc_sub_state_alloc(const _Alloc& __a)
        : __alloc_(__a) {}
};

template <class _Alloc>
void
__assoc_sub_state_alloc<_Alloc>::__on_zero_shared()
{
    this->~base();
    typename _Alloc::template rebind<__assoc_sub_state_alloc>::other __a(__alloc_);
    this->~__assoc_sub_state_alloc();
    __a.deallocate(this, 1);
}

template <class> class promise;

// future

template <class _R>
class future
{
    __assoc_state<_R>* __state_;

    explicit future(__assoc_state<_R>* __state);

    template <class> friend class promise;
public:
    future() : __state_(nullptr) {}
#ifdef _LIBCPP_MOVE
    future(future&& __rhs)
        : __state_(__rhs.__state_) {__rhs.__state_ = nullptr;}
    future(const future&) = delete;
    future& operator=(const future&) = delete;
    future& operator=(future&& __rhs)
        {
            future(std::move(__rhs)).swap(*this);
            return *this;
        }
#else  // _LIBCPP_MOVE
private:
    future(const future&);
    future& operator=(const future&);
public:
#endif  // _LIBCPP_MOVE
    ~future();

    // retrieving the value
    _R get();

    void swap(future& __rhs) {_STD::swap(__state_, __rhs.__state_);}

    // functions to check state
    bool valid() const {return __state_ != nullptr;}

    void wait() const {__state_->wait();}
    template <class _Rep, class _Period>
        future_status
        wait_for(const chrono::duration<_Rep, _Period>& __rel_time) const
            {return __state_->wait_for(__rel_time);}
    template <class _Clock, class _Duration>
        future_status
        wait_until(const chrono::time_point<_Clock, _Duration>& __abs_time) const
            {return __state_->wait_until(__abs_time);}
};

template <class _R>
future<_R>::future(__assoc_state<_R>* __state)
    : __state_(__state)
{
    if (__state_->__has_future_attached())
        throw future_error(make_error_code(future_errc::future_already_retrieved));
    __state_->__add_shared();
}

template <class _R>
future<_R>::~future()
{
    if (__state_)
        __state_->__release_shared();
}

template <class _R>
_R
future<_R>::get()
{
    __assoc_state<_R>* __s = __state_;
    __state_ = nullptr;
    return __s->move();
}

template <class _R>
class future<_R&>
{
    __assoc_state<_R&>* __state_;

    explicit future(__assoc_state<_R&>* __state);

    template <class> friend class promise;
public:
    future() : __state_(nullptr) {}
#ifdef _LIBCPP_MOVE
    future(future&& __rhs)
        : __state_(__rhs.__state_) {__rhs.__state_ = nullptr;}
    future(const future&) = delete;
    future& operator=(const future&) = delete;
    future& operator=(future&& __rhs)
        {
            future(std::move(__rhs)).swap(*this);
            return *this;
        }
#else  // _LIBCPP_MOVE
private:
    future(const future&);
    future& operator=(const future&);
public:
#endif  // _LIBCPP_MOVE
    ~future();

    // retrieving the value
    _R& get();

    void swap(future& __rhs) {_STD::swap(__state_, __rhs.__state_);}

    // functions to check state
    bool valid() const {return __state_ != nullptr;}

    void wait() const {__state_->wait();}
    template <class _Rep, class _Period>
        future_status
        wait_for(const chrono::duration<_Rep, _Period>& __rel_time) const
            {return __state_->wait_for(__rel_time);}
    template <class _Clock, class _Duration>
        future_status
        wait_until(const chrono::time_point<_Clock, _Duration>& __abs_time) const
            {return __state_->wait_until(__abs_time);}
};

template <class _R>
future<_R&>::future(__assoc_state<_R&>* __state)
    : __state_(__state)
{
    if (__state_->__has_future_attached())
        throw future_error(make_error_code(future_errc::future_already_retrieved));
    __state_->__add_shared();
}

template <class _R>
future<_R&>::~future()
{
    if (__state_)
        __state_->__release_shared();
}

template <class _R>
_R&
future<_R&>::get()
{
    __assoc_state<_R&>* __s = __state_;
    __state_ = nullptr;
    return __s->copy();
}

template <>
class future<void>
{
    __assoc_sub_state* __state_;

    explicit future(__assoc_sub_state* __state);

    template <class> friend class promise;
public:
    future() : __state_(nullptr) {}
#ifdef _LIBCPP_MOVE
    future(future&& __rhs)
        : __state_(__rhs.__state_) {__rhs.__state_ = nullptr;}
    future(const future&) = delete;
    future& operator=(const future&) = delete;
    future& operator=(future&& __rhs)
        {
            future(std::move(__rhs)).swap(*this);
            return *this;
        }
#else  // _LIBCPP_MOVE
private:
    future(const future&);
    future& operator=(const future&);
public:
#endif  // _LIBCPP_MOVE
    ~future();

    // retrieving the value
    void get();

    void swap(future& __rhs) {_STD::swap(__state_, __rhs.__state_);}

    // functions to check state
    bool valid() const {return __state_ != nullptr;}

    void wait() const {__state_->wait();}
    template <class _Rep, class _Period>
        future_status
        wait_for(const chrono::duration<_Rep, _Period>& __rel_time) const
            {return __state_->wait_for(__rel_time);}
    template <class _Clock, class _Duration>
        future_status
        wait_until(const chrono::time_point<_Clock, _Duration>& __abs_time) const
            {return __state_->wait_until(__abs_time);}
};

// promise<R>

template <class _R>
class promise
{
    __assoc_state<_R>* __state_;
public:
    promise();
    template <class _Alloc>
        promise(allocator_arg_t, const _Alloc& __a);
#ifdef _LIBCPP_MOVE
    promise(promise&& __rhs)
        : __state_(__rhs.__state_) {__rhs.__state_ = nullptr;}
    promise(const promise& __rhs) = delete;
#else  // _LIBCPP_MOVE
private:
    promise(const promise& __rhs);
public:
#endif  // _LIBCPP_MOVE
    ~promise();

    // assignment
#ifdef _LIBCPP_MOVE
    promise& operator=(promise&& __rhs)
        {
            promise(std::move(__rhs)).swap(*this);
            return *this;
        }
    promise& operator=(const promise& __rhs) = delete;
#else  // _LIBCPP_MOVE
private:
    promise& operator=(const promise& __rhs);
public:
#endif  // _LIBCPP_MOVE
    void swap(promise& __rhs) {_STD::swap(__state_, __rhs.__state_);}

    // retrieving the result
    future<_R> get_future();

    // setting the result
    void set_value(const _R& __r);
#ifdef _LIBCPP_MOVE
    void set_value(_R&& __r);
#endif
    void set_exception(exception_ptr __p);

    // setting the result with deferred notification
    void set_value_at_thread_exit(const _R& __r);
#ifdef _LIBCPP_MOVE
    void set_value_at_thread_exit(_R&& __r);
#endif
    void set_exception_at_thread_exit(exception_ptr __p);
};

template <class _R>
promise<_R>::promise()
    : __state_(new __assoc_state<_R>)
{
}

template <class _R>
template <class _Alloc>
promise<_R>::promise(allocator_arg_t, const _Alloc& __a0)
{
    typedef typename _Alloc::template rebind<__assoc_state_alloc<_R, _Alloc> >::other _A2;
    typedef __allocator_destructor<_A2> _D2;
    _A2 __a(__a0);
    unique_ptr<__assoc_state_alloc<_R, _Alloc>, _D2> __hold(__a.allocate(1), _D2(__a, 1));
    ::new(__hold.get()) __assoc_state_alloc<_R, _Alloc>(__a0);
    __state_ = __hold.release();
}

template <class _R>
promise<_R>::~promise()
{
    if (__state_)
    {
        if (!__state_->__has_value() && __state_->use_count() > 1)
            __state_->set_exception(make_exception_ptr(
                      future_error(make_error_code(future_errc::broken_promise))
                                                      ));
        __state_->__release_shared();
    }
}

template <class _R>
future<_R>
promise<_R>::get_future()
{
    if (__state_ == nullptr)
        throw future_error(make_error_code(future_errc::no_state));
    return future<_R>(__state_);
}

template <class _R>
void
promise<_R>::set_value(const _R& __r)
{
    if (__state_ == nullptr)
        throw future_error(make_error_code(future_errc::no_state));
    __state_->set_value(__r);
}

#ifdef _LIBCPP_MOVE

template <class _R>
void
promise<_R>::set_value(_R&& __r)
{
    if (__state_ == nullptr)
        throw future_error(make_error_code(future_errc::no_state));
    __state_->set_value(_STD::move(__r));
}

#endif  // _LIBCPP_MOVE

template <class _R>
void
promise<_R>::set_exception(exception_ptr __p)
{
    if (__state_ == nullptr)
        throw future_error(make_error_code(future_errc::no_state));
    __state_->set_exception(__p);
}

template <class _R>
void
promise<_R>::set_value_at_thread_exit(const _R& __r)
{
    if (__state_ == nullptr)
        throw future_error(make_error_code(future_errc::no_state));
    __state_->set_value_at_thread_exit(__r);
}

#ifdef _LIBCPP_MOVE

template <class _R>
void
promise<_R>::set_value_at_thread_exit(_R&& __r)
{
    if (__state_ == nullptr)
        throw future_error(make_error_code(future_errc::no_state));
    __state_->set_value_at_thread_exit(_STD::move(__r));
}

#endif  // _LIBCPP_MOVE

template <class _R>
void
promise<_R>::set_exception_at_thread_exit(exception_ptr __p)
{
    if (__state_ == nullptr)
        throw future_error(make_error_code(future_errc::no_state));
    __state_->set_exception_at_thread_exit(__p);
}

// promise<R&>

template <class _R>
class promise<_R&>
{
    __assoc_state<_R&>* __state_;
public:
    promise();
    template <class _Allocator>
        promise(allocator_arg_t, const _Allocator& __a);
#ifdef _LIBCPP_MOVE
    promise(promise&& __rhs)
        : __state_(__rhs.__state_) {__rhs.__state_ = nullptr;}
    promise(const promise& __rhs) = delete;
#else  // _LIBCPP_MOVE
private:
    promise(const promise& __rhs);
public:
#endif  // _LIBCPP_MOVE
    ~promise();

    // assignment
#ifdef _LIBCPP_MOVE
    promise& operator=(promise&& __rhs)
        {
            promise(std::move(__rhs)).swap(*this);
            return *this;
        }
    promise& operator=(const promise& __rhs) = delete;
#else  // _LIBCPP_MOVE
private:
    promise& operator=(const promise& __rhs);
public:
#endif  // _LIBCPP_MOVE
    void swap(promise& __rhs) {_STD::swap(__state_, __rhs.__state_);}

    // retrieving the result
    future<_R&> get_future();

    // setting the result
    void set_value(_R& __r);
    void set_exception(exception_ptr __p);

    // setting the result with deferred notification
    void set_value_at_thread_exit(_R&);
    void set_exception_at_thread_exit(exception_ptr __p);
};

template <class _R>
promise<_R&>::promise()
    : __state_(new __assoc_state<_R&>)
{
}

template <class _R>
template <class _Alloc>
promise<_R&>::promise(allocator_arg_t, const _Alloc& __a0)
{
    typedef typename _Alloc::template rebind<__assoc_state_alloc<_R&, _Alloc> >::other _A2;
    typedef __allocator_destructor<_A2> _D2;
    _A2 __a(__a0);
    unique_ptr<__assoc_state_alloc<_R&, _Alloc>, _D2> __hold(__a.allocate(1), _D2(__a, 1));
    ::new(__hold.get()) __assoc_state_alloc<_R&, _Alloc>(__a0);
    __state_ = __hold.release();
}

template <class _R>
promise<_R&>::~promise()
{
    if (__state_)
    {
        if (!__state_->__has_value() && __state_->use_count() > 1)
            __state_->set_exception(make_exception_ptr(
                      future_error(make_error_code(future_errc::broken_promise))
                                                      ));
        __state_->__release_shared();
    }
}

template <class _R>
future<_R&>
promise<_R&>::get_future()
{
    if (__state_ == nullptr)
        throw future_error(make_error_code(future_errc::no_state));
    return future<_R&>(__state_);
}

template <class _R>
void
promise<_R&>::set_value(_R& __r)
{
    if (__state_ == nullptr)
        throw future_error(make_error_code(future_errc::no_state));
    __state_->set_value(__r);
}

template <class _R>
void
promise<_R&>::set_exception(exception_ptr __p)
{
    if (__state_ == nullptr)
        throw future_error(make_error_code(future_errc::no_state));
    __state_->set_exception(__p);
}

template <class _R>
void
promise<_R&>::set_value_at_thread_exit(_R& __r)
{
    if (__state_ == nullptr)
        throw future_error(make_error_code(future_errc::no_state));
    __state_->set_value_at_thread_exit(__r);
}

template <class _R>
void
promise<_R&>::set_exception_at_thread_exit(exception_ptr __p)
{
    if (__state_ == nullptr)
        throw future_error(make_error_code(future_errc::no_state));
    __state_->set_exception_at_thread_exit(__p);
}

// promise<void>

template <>
class promise<void>
{
    __assoc_sub_state* __state_;
public:
    promise();
    template <class _Allocator>
        promise(allocator_arg_t, const _Allocator& __a);
#ifdef _LIBCPP_MOVE
    promise(promise&& __rhs)
        : __state_(__rhs.__state_) {__rhs.__state_ = nullptr;}
    promise(const promise& __rhs) = delete;
#else  // _LIBCPP_MOVE
private:
    promise(const promise& __rhs);
public:
#endif  // _LIBCPP_MOVE
    ~promise();

    // assignment
#ifdef _LIBCPP_MOVE
    promise& operator=(promise&& __rhs)
        {
            promise(std::move(__rhs)).swap(*this);
            return *this;
        }
    promise& operator=(const promise& __rhs) = delete;
#else  // _LIBCPP_MOVE
private:
    promise& operator=(const promise& __rhs);
public:
#endif  // _LIBCPP_MOVE
    void swap(promise& __rhs) {_STD::swap(__state_, __rhs.__state_);}

    // retrieving the result
    future<void> get_future();

    // setting the result
    void set_value();
    void set_exception(exception_ptr __p);

    // setting the result with deferred notification
    void set_value_at_thread_exit();
    void set_exception_at_thread_exit(exception_ptr __p);
};

template <class _Alloc>
promise<void>::promise(allocator_arg_t, const _Alloc& __a0)
{
    typedef typename _Alloc::template rebind<__assoc_sub_state_alloc<_Alloc> >::other _A2;
    typedef __allocator_destructor<_A2> _D2;
    _A2 __a(__a0);
    unique_ptr<__assoc_sub_state_alloc<_Alloc>, _D2> __hold(__a.allocate(1), _D2(__a, 1));
    ::new(__hold.get()) __assoc_sub_state_alloc<_Alloc>(__a0);
    __state_ = __hold.release();
}

template <class _R>
inline _LIBCPP_INLINE_VISIBILITY
void
swap(promise<_R>& __x, promise<_R>& __y)
{
    __x.swap(__y);
}

template <class _R, class _Alloc>
    struct uses_allocator<promise<_R>, _Alloc> : public true_type {};

_LIBCPP_END_NAMESPACE_STD

#endif  // _LIBCPP_FUTURE