4.1 KiB
[exec.recv.concepts]
33 Execution control library [exec]
33.7 Receivers [exec.recv]
33.7.1 Receiver concepts [exec.recv.concepts]
A receiver represents the continuation of an asynchronous operation.
The receiver concept defines the requirements for a receiver type ([exec.async.ops]).
The receiver_of concept defines the requirements for a receiver type that is usable as the first argument of a set of completion operations corresponding to a set of completion signatures.
The get_env customization point object is used to access a receiver's associated environment.
namespace std::execution {templateconcept receiver =derived_from<typename remove_cvref_t::receiver_concept, receiver_t> &&requires(const remove_cvref_t& rcvr) {{ get_env(rcvr) } -> queryable; } &&move_constructible<remove_cvref_t> && // rvalues are movable, andconstructible_from<remove_cvref_t, Rcvr>; // lvalues are copyabletemplate<class Signature, class Rcvr>concept valid-completion-for = // exposition onlyrequires (Signature* sig) {[]<class Tag, class... Args>(Tag()(Args...))requires callable<Tag, remove_cvref_t, Args...>{}(sig); }; template<class Rcvr, class Completions>concept has-completions = // exposition onlyrequires (Completions completions) {[]<valid-completion-for...Sigs>(completion_signatures<Sigs...>*){}(completions); }; template<class Rcvr, class Completions>concept receiver_of =receiver && has-completions<Rcvr, Completions>;}
Class types that are marked final do not model the receiver concept.
Let rcvr be a receiver and let op_state be an operation state associated with an asynchronous operation created by connecting rcvr with a sender.
Let token be a stop token equal toget_stop_token(get_env(rcvr)).
token shall remain valid for the duration of the asynchronous operation's lifetime ([exec.async.ops]).
[Note 1:
This means that, unless it knows about further guarantees provided by the type of rcvr, the implementation of op_state cannot use token after it executes a completion operation.
This also implies that any stop callbacks registered on token must be destroyed before the invocation of the completion operation.
â end note]