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dpp::basic_promise< T > Class Template Reference

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

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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_tstate = 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
TType 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

◆ 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_exceptionif 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.

◆ requires() [1/3]

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

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

Template Parameters
NotifyWhether to resume any awaiter or not.
Exceptions
dpp::logic_exceptionif the promise is not empty.

◆ requires() [2/3]

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

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

Template Parameters
NotifyWhether to resume any awaiter or not.
Exceptions
dpp::logic_exceptionif the promise is not empty.

◆ requires() [3/3]

template<typename T >
template<bool Notify = true>
dpp::basic_promise< T >::requires ( std::is_void_v< T >  )
inline

Construct a void result, and resume any awaiter.

Template Parameters
NotifyWhether to resume any awaiter or not.
Exceptions
dpp::logic_exceptionif the promise is not empty.

◆ 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
NotifyWhether to resume any awaiter or not.
Exceptions
dpp::logic_exceptionif the promise is not empty.
?Any exception thrown by the coroutine if resumed will propagate

◆ 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_exceptionif 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> :)
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