33 Execution control library [exec]

33.4 Header <execution> synopsis [execution.syn]

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namespace std { // [execpol.type], execution policy type trait template<class T> struct is_execution_policy; template<class T> constexpr bool is_execution_policy_v = is_execution_policy<T>::value; } namespace std::execution { // [execpol.seq], sequenced execution policy class sequenced_policy; // [execpol.par], parallel execution policy class parallel_policy; // [execpol.parunseq], parallel and unsequenced execution policy class parallel_unsequenced_policy; // [execpol.unseq], unsequenced execution policy class unsequenced_policy; // [execpol.objects], execution policy objects inline constexpr sequenced_policy seq{ unspecified }; inline constexpr parallel_policy par{ unspecified }; inline constexpr parallel_unsequenced_policy par_unseq{ unspecified }; inline constexpr unsequenced_policy unseq{ unspecified }; } namespace std { // [exec.general], helper concepts template<class T> concept movable-value = see below; // exposition only template<class From, class To> concept decays-to = same_as<decay_t<From>, To>; // exposition only template<class T> concept class-type = decays-to<T, T> && is_class_v<T>; // exposition only // [exec.queryable], queryable objects template<class T> concept queryable = see below; // exposition only // [exec.queries], queries struct forwarding_query_t { unspecified }; struct get_allocator_t { unspecified }; struct get_stop_token_t { unspecified }; inline constexpr forwarding_query_t forwarding_query{}; inline constexpr get_allocator_t get_allocator{}; inline constexpr get_stop_token_t get_stop_token{}; template<class T> using stop_token_of_t = remove_cvref_t<decltype(get_stop_token(declval<T>()))>; template<class T> concept forwarding-query = forwarding_query(T{}); // exposition only } namespace std::execution { // [exec.queries], queries struct get_domain_t { unspecified }; struct get_scheduler_t { unspecified }; struct get_delegation_scheduler_t { unspecified }; struct get_forward_progress_guarantee_t { unspecified }; template<class CPO> struct get_completion_scheduler_t { unspecified }; inline constexpr get_domain_t get_domain{}; inline constexpr get_scheduler_t get_scheduler{}; inline constexpr get_delegation_scheduler_t get_delegation_scheduler{}; enum class forward_progress_guarantee; inline constexpr get_forward_progress_guarantee_t get_forward_progress_guarantee{}; template<class CPO> constexpr get_completion_scheduler_t<CPO> get_completion_scheduler{}; struct empty_env {}; struct get_env_t { unspecified }; inline constexpr get_env_t get_env{}; template<class T> using env_of_t = decltype(get_env(declval<T>())); // [exec.domain.default], execution domains struct default_domain; // [exec.sched], schedulers struct scheduler_t {}; template<class Sch> concept scheduler = see below; // [exec.recv], receivers struct receiver_t {}; template<class Rcvr> concept receiver = see below; template<class Rcvr, class Completions> concept receiver_of = see below; struct set_value_t { unspecified }; struct set_error_t { unspecified }; struct set_stopped_t { unspecified }; inline constexpr set_value_t set_value{}; inline constexpr set_error_t set_error{}; inline constexpr set_stopped_t set_stopped{}; // [exec.opstate], operation states struct operation_state_t {}; template<class O> concept operation_state = see below; struct start_t; inline constexpr start_t start{}; // [exec.snd], senders struct sender_t {}; template<class Sndr> concept sender = see below; template<class Sndr, class Env = empty_env> concept sender_in = see below; template<class Sndr, class Rcvr> concept sender_to = see below; template<class... Ts> struct type-list; // exposition only // [exec.getcomplsigs], completion signatures struct get_completion_signatures_t; inline constexpr get_completion_signatures_t get_completion_signatures {}; template<class Sndr, class Env = empty_env> requires sender_in<Sndr, Env> using completion_signatures_of_t = call-result-t<get_completion_signatures_t, Sndr, Env>; template<class... Ts> using decayed-tuple = tuple<decay_t<Ts>...>; // exposition only template<class... Ts> using variant-or-empty = see below; // exposition only template<class Sndr, class Env = empty_env, template<class...> class Tuple = decayed-tuple, template<class...> class Variant = variant-or-empty> requires sender_in<Sndr, Env> using value_types_of_t = see below; template<class Sndr, class Env = empty_env, template<class...> class Variant = variant-or-empty> requires sender_in<Sndr, Env> using error_types_of_t = see below; template<class Sndr, class Env = empty_env> requires sender_in<Sndr, Env> constexpr bool sends_stopped = see below; template<class Sndr, class Env> using single-sender-value-type = see below; // exposition only template<class Sndr, class Env> concept single-sender = see below; // exposition only template<sender Sndr> using tag_of_t = see below; // [exec.snd.transform], sender transformations template<class Domain, sender Sndr, queryable... Env> requires (sizeof...(Env) <= 1) constexpr sender decltype(auto) transform_sender( Domain dom, Sndr&& sndr, const Env&... env) noexcept(see below); // [exec.snd.transform.env], environment transformations template<class Domain, sender Sndr, queryable Env> constexpr queryable decltype(auto) transform_env( Domain dom, Sndr&& sndr, Env&& env) noexcept; // [exec.snd.apply], sender algorithm application template<class Domain, class Tag, sender Sndr, class... Args> constexpr decltype(auto) apply_sender( Domain dom, Tag, Sndr&& sndr, Args&&... args) noexcept(see below); // [exec.connect], the connect sender algorithm struct connect_t; inline constexpr connect_t connect{}; template<class Sndr, class Rcvr> using connect_result_t = decltype(connect(declval<Sndr>(), declval<Rcvr>())); // [exec.factories], sender factories struct just_t { unspecified }; struct just_error_t { unspecified }; struct just_stopped_t { unspecified }; struct schedule_t { unspecified }; inline constexpr just_t just{}; inline constexpr just_error_t just_error{}; inline constexpr just_stopped_t just_stopped{}; inline constexpr schedule_t schedule{}; inline constexpr unspecified read_env{}; template<scheduler Sndr> using schedule_result_t = decltype(schedule(declval<Sndr>())); // [exec.adapt], sender adaptors template<class-type D> struct sender_adaptor_closure { }; struct starts_on_t { unspecified }; struct continues_on_t { unspecified }; struct on_t { unspecified }; struct schedule_from_t { unspecified }; struct then_t { unspecified }; struct upon_error_t { unspecified }; struct upon_stopped_t { unspecified }; struct let_value_t { unspecified }; struct let_error_t { unspecified }; struct let_stopped_t { unspecified }; struct bulk_t { unspecified }; struct split_t { unspecified }; struct when_all_t { unspecified }; struct when_all_with_variant_t { unspecified }; struct into_variant_t { unspecified }; struct stopped_as_optional_t { unspecified }; struct stopped_as_error_t { unspecified }; inline constexpr starts_on_t starts_on{}; inline constexpr continues_on_t continues_on{}; inline constexpr on_t on{}; inline constexpr schedule_from_t schedule_from{}; inline constexpr then_t then{}; inline constexpr upon_error_t upon_error{}; inline constexpr upon_stopped_t upon_stopped{}; inline constexpr let_value_t let_value{}; inline constexpr let_error_t let_error{}; inline constexpr let_stopped_t let_stopped{}; inline constexpr bulk_t bulk{}; inline constexpr split_t split{}; inline constexpr when_all_t when_all{}; inline constexpr when_all_with_variant_t when_all_with_variant{}; inline constexpr into_variant_t into_variant{}; inline constexpr stopped_as_optional_t stopped_as_optional{}; inline constexpr stopped_as_error_t stopped_as_error{}; // [exec.util], sender and receiver utilities // [exec.util.cmplsig] template<class Fn> concept completion-signature = see below; // exposition only template<completion-signature... Fns> struct completion_signatures {}; template<class Sigs> concept valid-completion-signatures = see below; // exposition only // [exec.util.cmplsig.trans] template< valid-completion-signatures InputSignatures, valid-completion-signatures AdditionalSignatures = completion_signatures<>, template<class...> class SetValue = see below, template<class> class SetError = see below, valid-completion-signatures SetStopped = completion_signatures<set_stopped_t()>> using transform_completion_signatures = completion_signatures<see below>; template< sender Sndr, class Env = empty_env, valid-completion-signatures AdditionalSignatures = completion_signatures<>, template<class...> class SetValue = see below, template<class> class SetError = see below, valid-completion-signatures SetStopped = completion_signatures<set_stopped_t()>> requires sender_in<Sndr, Env> using transform_completion_signatures_of = transform_completion_signatures< completion_signatures_of_t<Sndr, Env>, AdditionalSignatures, SetValue, SetError, SetStopped>; // [exec.run.loop], run_loop class run_loop; } namespace std::this_thread { // [exec.consumers], consumers struct sync_wait_t { unspecified }; struct sync_wait_with_variant_t { unspecified }; inline constexpr sync_wait_t sync_wait{}; inline constexpr sync_wait_with_variant_t sync_wait_with_variant{}; } namespace std::execution { // [exec.as.awaitable] struct as_awaitable_t { unspecified }; inline constexpr as_awaitable_t as_awaitable{}; // [exec.with.awaitable.senders] template<class-type Promise> struct with_awaitable_senders; }
1
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The exposition-only type variant-or-empty<Ts...> is defined as follows:
  • (1.1)
    If sizeof...(Ts) is greater than zero, variant-or-empty<Ts...> denotes variant<Us...> where Us... is the pack decay_t<Ts>... with duplicate types removed.
  • (1.2)
    Otherwise, variant-or-empty<Ts...> denotes the exposition-only class type: namespace std::execution { struct empty-variant { // exposition only empty-variant() = delete; }; }
2
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For types Sndr and Env, single-sender-value-type<Sndr, Env> is an alias for:
  • (2.1)
    value_types_of_t<Sndr, Env, decay_t, type_identity_t> if that type is well-formed,
  • (2.2)
    Otherwise, void if value_types_of_t<Sndr, Env, tuple, variant> is variant<tuple<>> or variant<>,
  • (2.3)
    Otherwise, value_types_of_t<Sndr, Env, decayed-tuple, type_identity_t> if that type is well-formed,
  • (2.4)
    Otherwise, single-sender-value-type<Sndr, Env> is ill-formed.
3
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The exposition-only concept single-sender is defined as follows: namespace std::execution { template<class Sndr, class Env> concept single-sender = sender_in<Sndr, Env> && requires { typename single-sender-value-type<Sndr, Env>; }; }