dpp::basic_promise< T > Class Template Reference

Generic promise class, represents the owning potion of an asynchronous value. More...

#include <awaitable.h>

Inheritance diagram for dpp::basic_promise< T >:

Collaboration diagram for dpp::basic_promise< T >:

Public Member Functions
template<bool Notify = true, typename... Args> requires (std::constructible_from<T, Args...>)
void	emplace_value (Args &&... args)
	Construct the result in place by forwarding the arguments, and by default resume any awaiter. More...
template<bool Notify = true, typename U = T> requires (std::convertible_to<U&&, T>)
void	set_value (U &&v)
	Construct the result by forwarding reference, and resume any awaiter. More...
template<bool Notify = true> requires (std::is_void_v<T>)
void	set_value ()
	Construct a void result, and resume any awaiter. More...
template<bool Notify = true>
void	set_exception (std::exception_ptr ptr)
	Set this promise to an exception and resume any awaiter. More...
void	notify_awaiter ()
	Notify a currently awaiting coroutine that the result is ready. More...
awaitable< T >	get_awaitable ()
	Get an awaitable object for this promise. More...

Protected Types
using	storage_type = result_t< T >
	Variant representing one of either 3 states of the result value : empty, result, exception. More...

Protected Member Functions
void	throw_if_not_empty ()
	Check if the result is empty, throws otherwise. More...
std_coroutine::coroutine_handle	release_awaiter ()
	Unlinks this promise from its currently linked awaiter and returns it. More...

Protected Attributes
storage_type	value = std::monostate{}
	State of the result value. More...
std::atomic< uint8_t >	state = sf_none
	State of the awaitable tied to this promise. More...
std_coroutine::coroutine_handle	awaiter = nullptr
	Coroutine handle currently awaiting the completion of this promise. More...

Detailed Description

template<typename T>
class dpp::basic_promise< T >

Generic promise class, represents the owning potion of an asynchronous value.

This class is roughly equivalent to std::promise, with the crucial distinction that the promise IS the shared state. As such, the promise needs to be kept alive for the entire time a value can be retrieved.

Template Parameters

T	Type of the asynchronous value

See also

awaitable

Member Typedef Documentation

storage_type

template<typename T >

using dpp::detail::promise::promise_base< T >::storage_type = result_t<T>

protectedinherited

Variant representing one of either 3 states of the result value : empty, result, exception.

Member Function Documentation

emplace_value()

template<typename T >

template<bool Notify = true, typename... Args>
requires (std::constructible_from<T, Args...>)

void dpp::basic_promise< T >::emplace_value ( Args &&...  args )

inline

Construct the result in place by forwarding the arguments, and by default resume any awaiter.

Template Parameters

Notify

Whether to resume any awaiter or not.

Exceptions

dpp::logic_exception

if the promise is not empty.

get_awaitable()

template<typename T >

awaitable< T > dpp::detail::promise::promise_base< T >::get_awaitable ( )

inlineinherited

Get an awaitable object for this promise.

Exceptions

dpp::logic_exception

if get_awaitable has already been called on this object.

Returns

awaitable<T> An object that can be co_await-ed to retrieve the value of this promise.

notify_awaiter()

template<typename T >

void dpp::detail::promise::promise_base< T >::notify_awaiter ( )

inlineinherited

Notify a currently awaiting coroutine that the result is ready.

Note

This may resume the coroutine on the current thread.

Exceptions

?	Any exception thrown by the coroutine if resumed will propagate

release_awaiter()

template<typename T >

std_coroutine::coroutine_handle dpp::detail::promise::promise_base< T >::release_awaiter ( )

inlineprotectedinherited

Unlinks this promise from its currently linked awaiter and returns it.

At the time of writing this is only used in the case of a serious internal error in dpp::task. Avoid using this as this will crash if the promise is used after this.

set_exception()

template<typename T >

template<bool Notify = true>

void dpp::detail::promise::promise_base< T >::set_exception ( std::exception_ptr  ptr )

inlineinherited

Set this promise to an exception and resume any awaiter.

Template Parameters

Notify

Whether to resume any awaiter or not.

Exceptions

dpp::logic_exception	if the promise is not empty.
?	Any exception thrown by the coroutine if resumed will propagate

set_value() [1/2]

template<typename T >

template<bool Notify = true>
requires (std::is_void_v<T>)

void dpp::basic_promise< T >::set_value ( )

inline

Construct a void result, and resume any awaiter.

Template Parameters

Notify

Whether to resume any awaiter or not.

Exceptions

dpp::logic_exception

if the promise is not empty.

set_value() [2/2]

template<typename T >

template<bool Notify = true, typename U = T>
requires (std::convertible_to<U&&, T>)

void dpp::basic_promise< T >::set_value ( U &&  v )

inline

Construct the result by forwarding reference, and resume any awaiter.

Template Parameters

Notify

Whether to resume any awaiter or not.

Exceptions

dpp::logic_exception

if the promise is not empty.

throw_if_not_empty()

template<typename T >

void dpp::detail::promise::promise_base< T >::throw_if_not_empty ( )

inlineprotectedinherited

Check if the result is empty, throws otherwise.

Exceptions

dpp::logic_exception

if the result isn't empty.

Member Data Documentation

awaiter

template<typename T >

std_coroutine::coroutine_handle dpp::detail::promise::promise_base< T >::awaiter = nullptr

protectedinherited

Coroutine handle currently awaiting the completion of this promise.

state

template<typename T >

std::atomic<uint8_t> dpp::detail::promise::promise_base< T >::state = sf_none

protectedinherited

State of the awaitable tied to this promise.

value

template<typename T >

storage_type dpp::detail::promise::promise_base< T >::value = std::monostate{}

protectedinherited

State of the result value.

See also

storage_type

Note

use .index() instead of std::holds_alternative to support promise_base<std::exception_ptr> and promise_base<std::monostate> :)