llvm-project/libcxx/include/future

// -*- C++ -*-
//===--------------------------- future -----------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. 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
{
    async = 1,
    deferred = 2,
    any = async | deferred
};

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<void>&&);
    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);
    ~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>
#include <thread>

#pragma GCC system_header

_LIBCPP_BEGIN_NAMESPACE_STD

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

    _ __v_;

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

};

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

//enum class launch
struct _LIBCPP_VISIBLE launch
{
enum _ {
    async = 1,
    deferred = 2,
    any = async | deferred
};

    _ __v_;

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

};

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

    _ __v_;

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

};

_LIBCPP_VISIBLE
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 _LIBCPP_EXCEPTION_ABI future_error
    : public logic_error
{
    error_code __ec_;
public:
    future_error(error_code __ec);

    _LIBCPP_INLINE_VISIBILITY
    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();
    void __sub_wait(unique_lock<mutex>& __lk);
public:
    enum
    {
        __constructed = 1,
        __future_attached = 2,
        ready = 4,
        deferred = 8
    };

    _LIBCPP_INLINE_VISIBILITY
    __assoc_sub_state() : __state_(0) {}

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

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

    _LIBCPP_INLINE_VISIBILITY
    void __set_deferred() {__state_ |= deferred;}

    void __make_ready();
    _LIBCPP_INLINE_VISIBILITY
    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();
    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;

    virtual void __execute();
};

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_);
    if (__state_ & deferred)
        return future_status::deferred;
    while (!(__state_ & ready) && _Clock::now() < __abs_time)
        __cv_.wait_until(__lk, __abs_time);
    if (__state_ & ready)
        return future_status::ready;
    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::steady_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>
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
        void set_value(_Arg&& __arg);
#else
        void set_value(_Arg& __arg);
#endif

    template <class _Arg>
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
        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
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
__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
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
__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_);
    this->__sub_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_);
    this->__sub_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_);
    this->__sub_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:
    _LIBCPP_INLINE_VISIBILITY
    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:
    _LIBCPP_INLINE_VISIBILITY
    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:
    _LIBCPP_INLINE_VISIBILITY
    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 _R, class _F>
class __deferred_assoc_state
    : public __assoc_state<_R>
{
    typedef __assoc_state<_R> base;

    _F __func_;

public:
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    explicit __deferred_assoc_state(_F&& __f);
#endif

    virtual void __execute();
};

#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES

template <class _R, class _F>
inline _LIBCPP_INLINE_VISIBILITY
__deferred_assoc_state<_R, _F>::__deferred_assoc_state(_F&& __f)
    : __func_(_STD::forward<_F>(__f))
{
    this->__set_deferred();
}

#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES

template <class _R, class _F>
void
__deferred_assoc_state<_R, _F>::__execute()
{
#ifndef _LIBCPP_NO_EXCEPTIONS
    try
    {
#endif  // _LIBCPP_NO_EXCEPTIONS
        this->set_value(__func_());
#ifndef _LIBCPP_NO_EXCEPTIONS
    }
    catch (...)
    {
        this->set_exception(current_exception());
    }
#endif  // _LIBCPP_NO_EXCEPTIONS
}

template <class _F>
class __deferred_assoc_state<void, _F>
    : public __assoc_sub_state
{
    typedef __assoc_sub_state base;

    _F __func_;

public:
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    explicit __deferred_assoc_state(_F&& __f);
#endif

    virtual void __execute();
};

#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES

template <class _F>
inline _LIBCPP_INLINE_VISIBILITY
__deferred_assoc_state<void, _F>::__deferred_assoc_state(_F&& __f)
    : __func_(_STD::forward<_F>(__f))
{
    this->__set_deferred();
}

#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES

template <class _F>
void
__deferred_assoc_state<void, _F>::__execute()
{
#ifndef _LIBCPP_NO_EXCEPTIONS
    try
    {
#endif  // _LIBCPP_NO_EXCEPTIONS
        __func_();
        this->set_value();
#ifndef _LIBCPP_NO_EXCEPTIONS
    }
    catch (...)
    {
        this->set_exception(current_exception());
    }
#endif  // _LIBCPP_NO_EXCEPTIONS
}

template <class> class promise;
template <class> class shared_future;
template <class> class atomic_future;

// future

template <class _R> class future;

template <class _R, class _F>
future<_R>
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
__make_deferred_assoc_state(_F&& __f);
#else
__make_deferred_assoc_state(_F __f);
#endif

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

    explicit future(__assoc_state<_R>* __state);

    template <class> friend class promise;
    template <class> friend class shared_future;
    template <class> friend class atomic_future;

    template <class _R1, class _F>
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
        friend future<_R1> __make_deferred_assoc_state(_F&& __f);
#else
        friend future<_R1> __make_deferred_assoc_state(_F __f);
#endif

public:
    _LIBCPP_INLINE_VISIBILITY
    future() : __state_(nullptr) {}
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    future(future&& __rhs)
        : __state_(__rhs.__state_) {__rhs.__state_ = nullptr;}
    future(const future&) = delete;
    future& operator=(const future&) = delete;
    _LIBCPP_INLINE_VISIBILITY
    future& operator=(future&& __rhs)
        {
            future(std::move(__rhs)).swap(*this);
            return *this;
        }
#else  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
private:
    future(const future&);
    future& operator=(const future&);
public:
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    ~future();

    // retrieving the value
    _R get();

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

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

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

struct __release_shared_count
{
    void operator()(__shared_count* p) {p->__release_shared();}
};

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

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

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

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

    template <class> friend class promise;
    template <class> friend class shared_future;
    template <class> friend class atomic_future;

    template <class _R1, class _F>
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
        friend future<_R1> __make_deferred_assoc_state(_F&& __f);
#else
        friend future<_R1> __make_deferred_assoc_state(_F __f);
#endif

public:
    _LIBCPP_INLINE_VISIBILITY
    future() : __state_(nullptr) {}
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    future(future&& __rhs)
        : __state_(__rhs.__state_) {__rhs.__state_ = nullptr;}
    future(const future&) = delete;
    future& operator=(const future&) = delete;
    _LIBCPP_INLINE_VISIBILITY
    future& operator=(future&& __rhs)
        {
            future(std::move(__rhs)).swap(*this);
            return *this;
        }
#else  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
private:
    future(const future&);
    future& operator=(const future&);
public:
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    ~future();

    // retrieving the value
    _R& get();

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

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

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

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

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

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

    explicit future(__assoc_sub_state* __state);

    template <class> friend class promise;
    template <class> friend class shared_future;
    template <class> friend class atomic_future;

    template <class _R1, class _F>
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
        friend future<_R1> __make_deferred_assoc_state(_F&& __f);
#else
        friend future<_R1> __make_deferred_assoc_state(_F __f);
#endif

public:
    _LIBCPP_INLINE_VISIBILITY
    future() : __state_(nullptr) {}
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    future(future&& __rhs)
        : __state_(__rhs.__state_) {__rhs.__state_ = nullptr;}
    future(const future&) = delete;
    future& operator=(const future&) = delete;
    _LIBCPP_INLINE_VISIBILITY
    future& operator=(future&& __rhs)
        {
            future(std::move(__rhs)).swap(*this);
            return *this;
        }
#else  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
private:
    future(const future&);
    future& operator=(const future&);
public:
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    ~future();

    // retrieving the value
    void get();

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

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

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

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

// promise<R>

template <class> class packaged_task;

template <class _R>
class _LIBCPP_VISIBLE promise
{
    __assoc_state<_R>* __state_;

    _LIBCPP_INLINE_VISIBILITY
    explicit promise(nullptr_t) : __state_(nullptr) {}

    template <class> friend class packaged_task;
public:
    promise();
    template <class _Alloc>
        promise(allocator_arg_t, const _Alloc& __a);
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    promise(promise&& __rhs)
        : __state_(__rhs.__state_) {__rhs.__state_ = nullptr;}
    promise(const promise& __rhs) = delete;
#else  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
private:
    promise(const promise& __rhs);
public:
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    ~promise();

    // assignment
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    promise& operator=(promise&& __rhs)
        {
            promise(std::move(__rhs)).swap(*this);
            return *this;
        }
    promise& operator=(const promise& __rhs) = delete;
#else  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
private:
    promise& operator=(const promise& __rhs);
public:
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    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);
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    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);
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    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);
}

#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES

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_HAS_NO_RVALUE_REFERENCES

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);
}

#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES

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_HAS_NO_RVALUE_REFERENCES

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 _LIBCPP_VISIBLE promise<_R&>
{
    __assoc_state<_R&>* __state_;

    _LIBCPP_INLINE_VISIBILITY
    explicit promise(nullptr_t) : __state_(nullptr) {}

    template <class> friend class packaged_task;

public:
    promise();
    template <class _Allocator>
        promise(allocator_arg_t, const _Allocator& __a);
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    promise(promise&& __rhs)
        : __state_(__rhs.__state_) {__rhs.__state_ = nullptr;}
    promise(const promise& __rhs) = delete;
#else  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
private:
    promise(const promise& __rhs);
public:
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    ~promise();

    // assignment
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    promise& operator=(promise&& __rhs)
        {
            promise(std::move(__rhs)).swap(*this);
            return *this;
        }
    promise& operator=(const promise& __rhs) = delete;
#else  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
private:
    promise& operator=(const promise& __rhs);
public:
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    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 _LIBCPP_VISIBLE promise<void>
{
    __assoc_sub_state* __state_;

    _LIBCPP_INLINE_VISIBILITY
    explicit promise(nullptr_t) : __state_(nullptr) {}

    template <class> friend class packaged_task;

public:
    promise();
    template <class _Allocator>
        promise(allocator_arg_t, const _Allocator& __a);
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    promise(promise&& __rhs)
        : __state_(__rhs.__state_) {__rhs.__state_ = nullptr;}
    promise(const promise& __rhs) = delete;
#else  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
private:
    promise(const promise& __rhs);
public:
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    ~promise();

    // assignment
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    promise& operator=(promise&& __rhs)
        {
            promise(std::move(__rhs)).swap(*this);
            return *this;
        }
    promise& operator=(const promise& __rhs) = delete;
#else  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
private:
    promise& operator=(const promise& __rhs);
public:
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    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 _LIBCPP_VISIBLE uses_allocator<promise<_R>, _Alloc>
        : public true_type {};

#ifndef _LIBCPP_HAS_NO_VARIADICS

// packaged_task

template<class _Fp> class __packaged_task_base;

template<class _R, class ..._ArgTypes>
class __packaged_task_base<_R(_ArgTypes...)>
{
    __packaged_task_base(const __packaged_task_base&);
    __packaged_task_base& operator=(const __packaged_task_base&);
public:
    _LIBCPP_INLINE_VISIBILITY
    __packaged_task_base() {}
    _LIBCPP_INLINE_VISIBILITY
    virtual ~__packaged_task_base() {}
    virtual void __move_to(__packaged_task_base*) = 0;
    virtual void destroy() = 0;
    virtual void destroy_deallocate() = 0;
    virtual _R operator()(_ArgTypes&& ...) = 0;
};

template<class _FD, class _Alloc, class _FB> class __packaged_task_func;

template<class _F, class _Alloc, class _R, class ..._ArgTypes>
class __packaged_task_func<_F, _Alloc, _R(_ArgTypes...)>
    : public  __packaged_task_base<_R(_ArgTypes...)>
{
    __compressed_pair<_F, _Alloc> __f_;
public:
    _LIBCPP_INLINE_VISIBILITY
    explicit __packaged_task_func(const _F& __f) : __f_(__f) {}
    _LIBCPP_INLINE_VISIBILITY
    explicit __packaged_task_func(_F&& __f) : __f_(_STD::move(__f)) {}
    _LIBCPP_INLINE_VISIBILITY
    __packaged_task_func(const _F& __f, const _Alloc& __a)
        : __f_(__f, __a) {}
    _LIBCPP_INLINE_VISIBILITY
    __packaged_task_func(_F&& __f, const _Alloc& __a)
        : __f_(_STD::move(__f), __a) {}
    virtual void __move_to(__packaged_task_base<_R(_ArgTypes...)>*);
    virtual void destroy();
    virtual void destroy_deallocate();
    virtual _R operator()(_ArgTypes&& ... __args);
};

template<class _F, class _Alloc, class _R, class ..._ArgTypes>
void
__packaged_task_func<_F, _Alloc, _R(_ArgTypes...)>::__move_to(
                              __packaged_task_base<_R(_ArgTypes...)>* __p)
{
    ::new (__p) __packaged_task_func(_STD::move(__f_.first()), _STD::move(__f_.second()));
}

template<class _F, class _Alloc, class _R, class ..._ArgTypes>
void
__packaged_task_func<_F, _Alloc, _R(_ArgTypes...)>::destroy()
{
    __f_.~__compressed_pair<_F, _Alloc>();
}

template<class _F, class _Alloc, class _R, class ..._ArgTypes>
void
__packaged_task_func<_F, _Alloc, _R(_ArgTypes...)>::destroy_deallocate()
{
    typedef typename _Alloc::template rebind<__packaged_task_func>::other _A;
    _A __a(__f_.second());
    __f_.~__compressed_pair<_F, _Alloc>();
    __a.deallocate(this, 1);
}

template<class _F, class _Alloc, class _R, class ..._ArgTypes>
_R
__packaged_task_func<_F, _Alloc, _R(_ArgTypes...)>::operator()(_ArgTypes&& ... __arg)
{
    return __invoke(__f_.first(), _STD::forward<_ArgTypes>(__arg)...);
}

template <class> class __packaged_task_function;

template<class _R, class ..._ArgTypes>
class __packaged_task_function<_R(_ArgTypes...)>
{
    typedef __packaged_task_base<_R(_ArgTypes...)> __base;
    aligned_storage<3*sizeof(void*)>::type __buf_;
    __base* __f_;

public:
    typedef _R result_type;

    // construct/copy/destroy:
    _LIBCPP_INLINE_VISIBILITY
    __packaged_task_function() : __f_(nullptr) {}
    template<class _F>
      __packaged_task_function(_F&& __f);
    template<class _F, class _Alloc>
      __packaged_task_function(allocator_arg_t, const _Alloc& __a, _F&& __f);

    __packaged_task_function(__packaged_task_function&&);
    __packaged_task_function& operator=(__packaged_task_function&&);

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

    ~__packaged_task_function();

    void swap(__packaged_task_function&);

    _R operator()(_ArgTypes...) const;
};

template<class _R, class ..._ArgTypes>
__packaged_task_function<_R(_ArgTypes...)>::__packaged_task_function(__packaged_task_function&& __f)
{
    if (__f.__f_ == nullptr)
        __f_ = nullptr;
    else if (__f.__f_ == (__base*)&__f.__buf_)
    {
        __f_ = (__base*)&__buf_;
        __f.__f_->__move_to(__f_);
    }
    else
    {
        __f_ = __f.__f_;
        __f.__f_ = nullptr;
    }
}

template<class _R, class ..._ArgTypes>
template <class _F>
__packaged_task_function<_R(_ArgTypes...)>::__packaged_task_function(_F&& __f)
    : __f_(nullptr)
{
    typedef typename remove_reference<_F>::type _FR;
    typedef __packaged_task_func<_FR, allocator<_FR>, _R(_ArgTypes...)> _FF;
    if (sizeof(_FF) <= sizeof(__buf_))
    {
        __f_ = (__base*)&__buf_;
        ::new (__f_) _FF(_STD::forward<_F>(__f));
    }
    else
    {
        typedef allocator<_FF> _A;
        _A __a;
        typedef __allocator_destructor<_A> _D;
        unique_ptr<__base, _D> __hold(__a.allocate(1), _D(__a, 1));
        ::new (__hold.get()) _FF(_STD::forward<_F>(__f), allocator<_FR>(__a));
        __f_ = __hold.release();
    }
}

template<class _R, class ..._ArgTypes>
template <class _F, class _Alloc>
__packaged_task_function<_R(_ArgTypes...)>::__packaged_task_function(
                                  allocator_arg_t, const _Alloc& __a0, _F&& __f)
    : __f_(nullptr)
{
    typedef allocator_traits<_Alloc> __alloc_traits;
    typedef typename remove_reference<_F>::type _FR;
    typedef __packaged_task_func<_FR, _Alloc, _R(_ArgTypes...)> _FF;
    if (sizeof(_FF) <= sizeof(__buf_))
    {
        __f_ = (__base*)&__buf_;
        ::new (__f_) _FF(_STD::forward<_F>(__f));
    }
    else
    {
        typedef typename __alloc_traits::template
#ifndef _LIBCPP_HAS_NO_TEMPLATE_ALIASES
            rebind_alloc<_FF>
#else
            rebind_alloc<_FF>::other
#endif
                                                     _A;
        _A __a(__a0);
        typedef __allocator_destructor<_A> _D;
        unique_ptr<__base, _D> __hold(__a.allocate(1), _D(__a, 1));
        ::new (__hold.get()) _FF(_STD::forward<_F>(__f), _Alloc(__a));
        __f_ = __hold.release();
    }
}

template<class _R, class ..._ArgTypes>
__packaged_task_function<_R(_ArgTypes...)>&
__packaged_task_function<_R(_ArgTypes...)>::operator=(__packaged_task_function&& __f)
{
    if (__f_ == (__base*)&__buf_)
        __f_->destroy();
    else if (__f_)
        __f_->destroy_deallocate();
    __f_ = nullptr;
    if (__f.__f_ == nullptr)
        __f_ = nullptr;
    else if (__f.__f_ == (__base*)&__f.__buf_)
    {
        __f_ = (__base*)&__buf_;
        __f.__f_->__move_to(__f_);
    }
    else
    {
        __f_ = __f.__f_;
        __f.__f_ = nullptr;
    }
}

template<class _R, class ..._ArgTypes>
__packaged_task_function<_R(_ArgTypes...)>::~__packaged_task_function()
{
    if (__f_ == (__base*)&__buf_)
        __f_->destroy();
    else if (__f_)
        __f_->destroy_deallocate();
}

template<class _R, class ..._ArgTypes>
void
__packaged_task_function<_R(_ArgTypes...)>::swap(__packaged_task_function& __f)
{
    if (__f_ == (__base*)&__buf_ && __f.__f_ == (__base*)&__f.__buf_)
    {
        typename aligned_storage<sizeof(__buf_)>::type __tempbuf;
        __base* __t = (__base*)&__tempbuf;
        __f_->__move_to(__t);
        __f_->destroy();
        __f_ = nullptr;
        __f.__f_->__move_to((__base*)&__buf_);
        __f.__f_->destroy();
        __f.__f_ = nullptr;
        __f_ = (__base*)&__buf_;
        __t->__move_to((__base*)&__f.__buf_);
        __t->destroy();
        __f.__f_ = (__base*)&__f.__buf_;
    }
    else if (__f_ == (__base*)&__buf_)
    {
        __f_->__move_to((__base*)&__f.__buf_);
        __f_->destroy();
        __f_ = __f.__f_;
        __f.__f_ = (__base*)&__f.__buf_;
    }
    else if (__f.__f_ == (__base*)&__f.__buf_)
    {
        __f.__f_->__move_to((__base*)&__buf_);
        __f.__f_->destroy();
        __f.__f_ = __f_;
        __f_ = (__base*)&__buf_;
    }
    else
        _STD::swap(__f_, __f.__f_);
}

template<class _R, class ..._ArgTypes>
inline _LIBCPP_INLINE_VISIBILITY
_R
__packaged_task_function<_R(_ArgTypes...)>::operator()(_ArgTypes... __arg) const
{
    return (*__f_)(_STD::forward<_ArgTypes>(__arg)...);
}

template<class _R, class ..._ArgTypes>
class _LIBCPP_VISIBLE packaged_task<_R(_ArgTypes...)>
{
public:
    typedef _R result_type;

private:
    __packaged_task_function<result_type(_ArgTypes...)> __f_;
    promise<result_type>                                __p_;

public:
    // construction and destruction
    _LIBCPP_INLINE_VISIBILITY
    packaged_task() : __p_(nullptr) {}
    template <class _F>
        _LIBCPP_INLINE_VISIBILITY
        explicit packaged_task(_F&& __f) : __f_(_STD::forward<_F>(__f)) {}
    template <class _F, class _Allocator>
        _LIBCPP_INLINE_VISIBILITY
        explicit packaged_task(allocator_arg_t, const _Allocator& __a, _F&& __f)
             : __f_(allocator_arg, __a, _STD::forward<_F>(__f)),
               __p_(allocator_arg, __a) {}
    // ~packaged_task() = default;

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

    // move support
    _LIBCPP_INLINE_VISIBILITY
    packaged_task(packaged_task&& __other)
        : __f_(_STD::move(__other.__f_)), __p_(_STD::move(__other.__p_)) {}
    _LIBCPP_INLINE_VISIBILITY
    packaged_task& operator=(packaged_task&& __other)
    {
        __f_ = _STD::move(__other.__f_);
        __p_ = _STD::move(__other.__p_);
        return *this;
    }
    _LIBCPP_INLINE_VISIBILITY
    void swap(packaged_task& __other)
    {
        __f_.swap(__other.__f_);
        __p_.swap(__other.__p_);
    }

    _LIBCPP_INLINE_VISIBILITY
    //explicit
        operator bool() const {return __p_.__state_ != nullptr;}

    // result retrieval
    _LIBCPP_INLINE_VISIBILITY
    future<result_type> get_future() {return __p_.get_future();}

    // execution
    void operator()(_ArgTypes... __args);
    void make_ready_at_thread_exit(_ArgTypes... __args);

    void reset();
};

template<class _R, class ..._ArgTypes>
void
packaged_task<_R(_ArgTypes...)>::operator()(_ArgTypes... __args)
{
#ifndef _LIBCPP_NO_EXCEPTIONS
    if (__p_.__state_ == nullptr)
        throw future_error(make_error_code(future_errc::no_state));
    if (__p_.__state_->__has_value())
        throw future_error(make_error_code(future_errc::promise_already_satisfied));
    try
    {
#endif  // _LIBCPP_NO_EXCEPTIONS
        __p_.set_value(__f_(_STD::forward<_ArgTypes>(__args)...));
#ifndef _LIBCPP_NO_EXCEPTIONS
    }
    catch (...)
    {
        __p_.set_exception(current_exception());
    }
#endif  // _LIBCPP_NO_EXCEPTIONS
}

template<class _R, class ..._ArgTypes>
void
packaged_task<_R(_ArgTypes...)>::make_ready_at_thread_exit(_ArgTypes... __args)
{
#ifndef _LIBCPP_NO_EXCEPTIONS
    if (__p_.__state_ == nullptr)
        throw future_error(make_error_code(future_errc::no_state));
    if (__p_.__state_->__has_value())
        throw future_error(make_error_code(future_errc::promise_already_satisfied));
    try
    {
#endif  // _LIBCPP_NO_EXCEPTIONS
        __p_.set_value_at_thread_exit(__f_(_STD::forward<_ArgTypes>(__args)...));
#ifndef _LIBCPP_NO_EXCEPTIONS
    }
    catch (...)
    {
        __p_.set_exception_at_thread_exit(current_exception());
    }
#endif  // _LIBCPP_NO_EXCEPTIONS
}

template<class _R, class ..._ArgTypes>
void
packaged_task<_R(_ArgTypes...)>::reset()
{
#ifndef _LIBCPP_NO_EXCEPTIONS
    if (!(*this))
        throw future_error(make_error_code(future_errc::no_state));
#endif  // _LIBCPP_NO_EXCEPTIONS
    __p_ = promise<result_type>();
}

template<class ..._ArgTypes>
class _LIBCPP_VISIBLE packaged_task<void(_ArgTypes...)>
{
public:
    typedef void result_type;

private:
    __packaged_task_function<result_type(_ArgTypes...)> __f_;
    promise<result_type>                                __p_;

public:
    // construction and destruction
    _LIBCPP_INLINE_VISIBILITY
    packaged_task() : __p_(nullptr) {}
    template <class _F>
        _LIBCPP_INLINE_VISIBILITY
        explicit packaged_task(_F&& __f) : __f_(_STD::forward<_F>(__f)) {}
    template <class _F, class _Allocator>
        _LIBCPP_INLINE_VISIBILITY
        explicit packaged_task(allocator_arg_t, const _Allocator& __a, _F&& __f)
             : __f_(allocator_arg, __a, _STD::forward<_F>(__f)),
               __p_(allocator_arg, __a) {}
    // ~packaged_task() = default;

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

    // move support
    _LIBCPP_INLINE_VISIBILITY
    packaged_task(packaged_task&& __other)
        : __f_(_STD::move(__other.__f_)), __p_(_STD::move(__other.__p_)) {}
    _LIBCPP_INLINE_VISIBILITY
    packaged_task& operator=(packaged_task&& __other)
    {
        __f_ = _STD::move(__other.__f_);
        __p_ = _STD::move(__other.__p_);
        return *this;
    }
    _LIBCPP_INLINE_VISIBILITY
    void swap(packaged_task& __other)
    {
        __f_.swap(__other.__f_);
        __p_.swap(__other.__p_);
    }

    _LIBCPP_INLINE_VISIBILITY
    //explicit
        operator bool() const {return __p_.__state_ != nullptr;}

    // result retrieval
    _LIBCPP_INLINE_VISIBILITY
    future<result_type> get_future() {return __p_.get_future();}

    // execution
    void operator()(_ArgTypes... __args);
    void make_ready_at_thread_exit(_ArgTypes... __args);

    void reset();
};

template<class ..._ArgTypes>
void
packaged_task<void(_ArgTypes...)>::operator()(_ArgTypes... __args)
{
#ifndef _LIBCPP_NO_EXCEPTIONS
    if (__p_.__state_ == nullptr)
        throw future_error(make_error_code(future_errc::no_state));
    if (__p_.__state_->__has_value())
        throw future_error(make_error_code(future_errc::promise_already_satisfied));
    try
    {
#endif  // _LIBCPP_NO_EXCEPTIONS
        __f_(_STD::forward<_ArgTypes>(__args)...);
        __p_.set_value();
#ifndef _LIBCPP_NO_EXCEPTIONS
    }
    catch (...)
    {
        __p_.set_exception(current_exception());
    }
#endif  // _LIBCPP_NO_EXCEPTIONS
}

template<class ..._ArgTypes>
void
packaged_task<void(_ArgTypes...)>::make_ready_at_thread_exit(_ArgTypes... __args)
{
#ifndef _LIBCPP_NO_EXCEPTIONS
    if (__p_.__state_ == nullptr)
        throw future_error(make_error_code(future_errc::no_state));
    if (__p_.__state_->__has_value())
        throw future_error(make_error_code(future_errc::promise_already_satisfied));
    try
    {
#endif  // _LIBCPP_NO_EXCEPTIONS
        __f_(_STD::forward<_ArgTypes>(__args)...);
        __p_.set_value_at_thread_exit();
#ifndef _LIBCPP_NO_EXCEPTIONS
    }
    catch (...)
    {
        __p_.set_exception_at_thread_exit(current_exception());
    }
#endif  // _LIBCPP_NO_EXCEPTIONS
}

template<class ..._ArgTypes>
void
packaged_task<void(_ArgTypes...)>::reset()
{
#ifndef _LIBCPP_NO_EXCEPTIONS
    if (!(*this))
        throw future_error(make_error_code(future_errc::no_state));
#endif  // _LIBCPP_NO_EXCEPTIONS
    __p_ = promise<result_type>();
}

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

template <class _Callable, class _Alloc>
struct _LIBCPP_VISIBLE uses_allocator<packaged_task<_Callable>, _Alloc>
    : public true_type {};

template <class _R, class _F>
future<_R>
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
__make_deferred_assoc_state(_F&& __f)
#else
__make_deferred_assoc_state(_F __f)
#endif
{
    unique_ptr<__deferred_assoc_state<_R, _F>, __release_shared_count>
        __h(new __deferred_assoc_state<_R, _F>(_STD::forward<_F>(__f)));
    return future<_R>(__h.get());
}

template <class _F, class... _Args>
future<typename result_of<_F(_Args...)>::type>
async(launch __policy, _F&& __f, _Args&&... __args)
{
    typedef typename result_of<_F(_Args...)>::type _R;
    future<_R> __r;
    if (__policy & launch::async)
    {
        packaged_task<_R()> __pk(bind(_STD::forward<_F>(__f),
                                      _STD::forward<_Args>(__args)...));
        __r = __pk.get_future();
        thread(_STD::move(__pk)).detach();
    }
    else if (__policy & launch::deferred)
        __r = _STD::__make_deferred_assoc_state<_R>(bind(_STD::forward<_F>(__f),
                                              _STD::forward<_Args>(__args)...));
    return __r;
}

template <class _F, class... _Args>
inline _LIBCPP_INLINE_VISIBILITY
typename enable_if
<
    !is_same<typename decay<_F>::type, launch>::value,
    future<typename result_of<_F(_Args...)>::type>
>::type
async(_F&& __f, _Args&&... __args)
{
    return async(launch::any, _STD::forward<_F>(__f),
                              _STD::forward<_Args>(__args)...);
}

#endif  // _LIBCPP_HAS_NO_VARIADICS

// shared_future

template <class _R>
class _LIBCPP_VISIBLE shared_future
{
    __assoc_state<_R>* __state_;

public:
    _LIBCPP_INLINE_VISIBILITY
    shared_future() : __state_(nullptr) {}
    _LIBCPP_INLINE_VISIBILITY
    shared_future(const shared_future& __rhs) : __state_(__rhs.__state_)
        {if (__state_) __state_->__add_shared();}
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    shared_future(future<_R>&& __f) : __state_(__f.__state_)
        {__f.__state_ = nullptr;}
    _LIBCPP_INLINE_VISIBILITY
    shared_future(shared_future&& __rhs) : __state_(__rhs.__state_)
        {__rhs.__state_ = nullptr;}
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    ~shared_future();
    shared_future& operator=(const shared_future& __rhs);
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    shared_future& operator=(shared_future&& __rhs)
        {
            shared_future(std::move(__rhs)).swap(*this);
            return *this;
        }
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES

    // retrieving the value
    _LIBCPP_INLINE_VISIBILITY
    const _R& get() const {return __state_->copy();}

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

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

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

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

template <class _R>
shared_future<_R>&
shared_future<_R>::operator=(const shared_future& __rhs)
{
    if (__rhs.__state_)
        __rhs.__state_->__add_shared();
    if (__state_)
        __state_->__release_shared();
    __state_ = __rhs.__state_;
    return *this;
}

template <class _R>
class _LIBCPP_VISIBLE shared_future<_R&>
{
    __assoc_state<_R&>* __state_;

public:
    _LIBCPP_INLINE_VISIBILITY
    shared_future() : __state_(nullptr) {}
    _LIBCPP_INLINE_VISIBILITY
    shared_future(const shared_future& __rhs) : __state_(__rhs.__state_)
        {if (__state_) __state_->__add_shared();}
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    shared_future(future<_R&>&& __f) : __state_(__f.__state_)
        {__f.__state_ = nullptr;}
    _LIBCPP_INLINE_VISIBILITY
    shared_future(shared_future&& __rhs) : __state_(__rhs.__state_)
        {__rhs.__state_ = nullptr;}
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    ~shared_future();
    shared_future& operator=(const shared_future& __rhs);
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    shared_future& operator=(shared_future&& __rhs)
        {
            shared_future(std::move(__rhs)).swap(*this);
            return *this;
        }
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES

    // retrieving the value
    _LIBCPP_INLINE_VISIBILITY
    _R& get() const {return __state_->copy();}

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

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

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

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

template <class _R>
shared_future<_R&>&
shared_future<_R&>::operator=(const shared_future& __rhs)
{
    if (__rhs.__state_)
        __rhs.__state_->__add_shared();
    if (__state_)
        __state_->__release_shared();
    __state_ = __rhs.__state_;
    return *this;
}

template <>
class _LIBCPP_VISIBLE shared_future<void>
{
    __assoc_sub_state* __state_;

public:
    _LIBCPP_INLINE_VISIBILITY
    shared_future() : __state_(nullptr) {}
    _LIBCPP_INLINE_VISIBILITY
    shared_future(const shared_future& __rhs) : __state_(__rhs.__state_)
        {if (__state_) __state_->__add_shared();}
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    shared_future(future<void>&& __f) : __state_(__f.__state_)
        {__f.__state_ = nullptr;}
    _LIBCPP_INLINE_VISIBILITY
    shared_future(shared_future&& __rhs) : __state_(__rhs.__state_)
        {__rhs.__state_ = nullptr;}
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    ~shared_future();
    shared_future& operator=(const shared_future& __rhs);
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    shared_future& operator=(shared_future&& __rhs)
        {
            shared_future(std::move(__rhs)).swap(*this);
            return *this;
        }
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES

    // retrieving the value
    _LIBCPP_INLINE_VISIBILITY
    void get() const {__state_->copy();}

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

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

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

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

// atomic_future

template <class _R>
class _LIBCPP_VISIBLE atomic_future
{
    __assoc_state<_R>* __state_;
    mutable mutex __mut_;

public:
    _LIBCPP_INLINE_VISIBILITY
    atomic_future() : __state_(nullptr) {}
    _LIBCPP_INLINE_VISIBILITY
    atomic_future(const atomic_future& __rhs) : __state_(__rhs.__state_)
        {if (__state_) __state_->__add_shared();}
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    atomic_future(future<_R>&& __f) : __state_(__f.__state_)
        {__f.__state_ = nullptr;}
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    ~atomic_future();
    atomic_future& operator=(const atomic_future& __rhs);

    // retrieving the value
    _LIBCPP_INLINE_VISIBILITY
    const _R& get() const {return __state_->copy();}

    void swap(atomic_future& __rhs);

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

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

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

template <class _R>
atomic_future<_R>&
atomic_future<_R>::operator=(const atomic_future& __rhs)
{
    if (this != &__rhs)
    {
        unique_lock<mutex> __this(__mut_, defer_lock);
        unique_lock<mutex> __that(__rhs.__mut_, defer_lock);
        _STD::lock(__this, __that);
        if (__rhs.__state_)
            __rhs.__state_->__add_shared();
        if (__state_)
            __state_->__release_shared();
        __state_ = __rhs.__state_;
    }
    return *this;
}

template <class _R>
void
atomic_future<_R>::swap(atomic_future& __rhs)
{
    if (this != &__rhs)
    {
        unique_lock<mutex> __this(__mut_, defer_lock);
        unique_lock<mutex> __that(__rhs.__mut_, defer_lock);
        _STD::lock(__this, __that);
        _STD::swap(__state_, __rhs.__state_);
    }
}

template <class _R>
class _LIBCPP_VISIBLE atomic_future<_R&>
{
    __assoc_state<_R&>* __state_;
    mutable mutex __mut_;

public:
    _LIBCPP_INLINE_VISIBILITY
    atomic_future() : __state_(nullptr) {}
    _LIBCPP_INLINE_VISIBILITY
    atomic_future(const atomic_future& __rhs) : __state_(__rhs.__state_)
        {if (__state_) __state_->__add_shared();}
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    atomic_future(future<_R&>&& __f) : __state_(__f.__state_)
        {__f.__state_ = nullptr;}
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    ~atomic_future();
    atomic_future& operator=(const atomic_future& __rhs);

    // retrieving the value
    _LIBCPP_INLINE_VISIBILITY
    _R& get() const {return __state_->copy();}

    void swap(atomic_future& __rhs);

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

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

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

template <class _R>
atomic_future<_R&>&
atomic_future<_R&>::operator=(const atomic_future& __rhs)
{
    if (this != &__rhs)
    {
        unique_lock<mutex> __this(__mut_, defer_lock);
        unique_lock<mutex> __that(__rhs.__mut_, defer_lock);
        _STD::lock(__this, __that);
        if (__rhs.__state_)
            __rhs.__state_->__add_shared();
        if (__state_)
            __state_->__release_shared();
        __state_ = __rhs.__state_;
    }
    return *this;
}

template <class _R>
void
atomic_future<_R&>::swap(atomic_future& __rhs)
{
    if (this != &__rhs)
    {
        unique_lock<mutex> __this(__mut_, defer_lock);
        unique_lock<mutex> __that(__rhs.__mut_, defer_lock);
        _STD::lock(__this, __that);
        _STD::swap(__state_, __rhs.__state_);
    }
}

template <>
class _LIBCPP_VISIBLE atomic_future<void>
{
    __assoc_sub_state* __state_;
    mutable mutex __mut_;

public:
    _LIBCPP_INLINE_VISIBILITY
    atomic_future() : __state_(nullptr) {}
    _LIBCPP_INLINE_VISIBILITY
    atomic_future(const atomic_future& __rhs) : __state_(__rhs.__state_)
        {if (__state_) __state_->__add_shared();}
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    _LIBCPP_INLINE_VISIBILITY
    atomic_future(future<void>&& __f) : __state_(__f.__state_)
        {__f.__state_ = nullptr;}
#endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    ~atomic_future();
    atomic_future& operator=(const atomic_future& __rhs);

    // retrieving the value
    _LIBCPP_INLINE_VISIBILITY
    void get() const {__state_->copy();}

    void swap(atomic_future& __rhs);

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

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

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

_LIBCPP_END_NAMESPACE_STD

#endif  // _LIBCPP_FUTURE