[exec.queries]

# 33 Execution control library [[exec]](./#exec)

## 33.5 Queries [exec.queries]

### [33.5.1](#exec.fwd.env) forwarding_query [[exec.fwd.env]](exec.fwd.env)

[1](#exec.fwd.env-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L837)

forwarding_query asks a query object
whether it should be forwarded through queryable adaptors[.](#exec.fwd.env-1.sentence-1)

[2](#exec.fwd.env-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L841)

The name forwarding_query denotes a query object[.](#exec.fwd.env-2.sentence-1)

For some query object q of type Q,forwarding_query(q) is expression-equivalent to:

- [(2.1)](#exec.fwd.env-2.1)

  *MANDATE-NOTHROW*(q.query(forwarding_query)) if that expression is well-formed[.](#exec.fwd.env-2.1.sentence-1)
  *Mandates*: The expression above has type bool and
is a core constant expression if q is a core constant expression[.](#exec.fwd.env-2.1.sentence-2)

- [(2.2)](#exec.fwd.env-2.2)

  Otherwise, true if [derived_from](concept.derived#concept:derived_from "18.4.3 Concept derived_­from [concept.derived]")<Q, forwarding_query_t> is true[.](#exec.fwd.env-2.2.sentence-1)

- [(2.3)](#exec.fwd.env-2.3)

  Otherwise, false[.](#exec.fwd.env-2.3.sentence-1)

### [33.5.2](#exec.get.allocator) get_allocator [[exec.get.allocator]](exec.get.allocator)

[1](#exec.get.allocator-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L861)

get_allocator asks a queryable object for its associated allocator[.](#exec.get.allocator-1.sentence-1)

[2](#exec.get.allocator-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L864)

The name get_allocator denotes a query object[.](#exec.get.allocator-2.sentence-1)

For a subexpression env,get_allocator(env) is expression-equivalent to*MANDATE-NOTHROW*(*AS-CONST*(env).query(get_allocator))[.](#exec.get.allocator-2.sentence-2)

*Mandates*: If the expression above is well-formed,
its type satisfies[*simple-allocator*](allocator.requirements.general#concept:simple-allocator "16.4.4.6.1 General [allocator.requirements.general]") ([[allocator.requirements.general]](allocator.requirements.general "16.4.4.6.1 General"))[.](#exec.get.allocator-2.sentence-3)

[3](#exec.get.allocator-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L875)

forwarding_query(get_allocator) is a core constant expression and
has value true[.](#exec.get.allocator-3.sentence-1)

### [33.5.3](#exec.get.stop.token) get_stop_token [[exec.get.stop.token]](exec.get.stop.token)

[1](#exec.get.stop.token-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L881)

get_stop_token asks a queryable object for an associated stop token[.](#exec.get.stop.token-1.sentence-1)

[2](#exec.get.stop.token-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L884)

The name get_stop_token denotes a query object[.](#exec.get.stop.token-2.sentence-1)

For a subexpression env,get_stop_token(env) is expression-equivalent to:

- [(2.1)](#exec.get.stop.token-2.1)

  *MANDATE-NOTHROW*(*AS-CONST*(env).query(get_stop_token)) if that expression is well-formed[.](#exec.get.stop.token-2.1.sentence-1)
  *Mandates*: The type of the expression above satisfies [stoppable_token](stoptoken.concepts#concept:stoppable_token "32.3.3 Stop token concepts [stoptoken.concepts]")[.](#exec.get.stop.token-2.1.sentence-2)

- [(2.2)](#exec.get.stop.token-2.2)

  Otherwise, never_stop_token{}[.](#exec.get.stop.token-2.2.sentence-1)

[3](#exec.get.stop.token-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L900)

forwarding_query(get_stop_token) is a core constant expression and
has value true[.](#exec.get.stop.token-3.sentence-1)

### [33.5.4](#exec.get.env) execution​::​get_env [[exec.get.env]](exec.get.env)

[1](#exec.get.env-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L906)

execution​::​get_env is a customization point object[.](#exec.get.env-1.sentence-1)

For a subexpression o,execution​::​get_env(o) is expression-equivalent to:

- [(1.1)](#exec.get.env-1.1)

  *MANDATE-NOTHROW*(*AS-CONST*(o).get_env()) if that expression is well-formed[.](#exec.get.env-1.1.sentence-1)
  *Mandates*: The type of the expression above satisfies[*queryable*](exec.queryable.concept#concept:queryable "33.2.2 queryable concept [exec.queryable.concept]") ([[exec.queryable]](exec.queryable "33.2 Queries and queryables"))[.](#exec.get.env-1.1.sentence-2)

- [(1.2)](#exec.get.env-1.2)

  Otherwise, env<>{}[.](#exec.get.env-1.2.sentence-1)

[2](#exec.get.env-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L922)

The value of get_env(o) shall be valid while o is valid[.](#exec.get.env-2.sentence-1)

[3](#exec.get.env-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L925)

[*Note [1](#exec.get.env-note-1)*:

When passed a sender object,get_env returns the sender's associated attributes[.](#exec.get.env-3.sentence-1)

When passed a receiver,get_env returns the receiver's associated execution environment[.](#exec.get.env-3.sentence-2)

â *end note*]

### [33.5.5](#exec.get.domain) execution​::​get_domain [[exec.get.domain]](exec.get.domain)

[1](#exec.get.domain-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L935)

get_domain asks a queryable object
for its associated execution domain tag[.](#exec.get.domain-1.sentence-1)

[2](#exec.get.domain-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L939)

The name get_domain denotes a query object[.](#exec.get.domain-2.sentence-1)

For a subexpression env,get_domain(env) is expression-equivalent to*MANDATE-NOTHROW*(*AS-CONST*(env).query(get_domain))[.](#exec.get.domain-2.sentence-2)

[3](#exec.get.domain-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L945)

forwarding_query(execution​::​get_domain) is
a core constant expression and has value true[.](#exec.get.domain-3.sentence-1)

### [33.5.6](#exec.get.scheduler) execution​::​get_scheduler [[exec.get.scheduler]](exec.get.scheduler)

[1](#exec.get.scheduler-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L951)

get_scheduler asks a queryable object for its associated scheduler[.](#exec.get.scheduler-1.sentence-1)

[2](#exec.get.scheduler-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L954)

The name get_scheduler denotes a query object[.](#exec.get.scheduler-2.sentence-1)

For a subexpression env,get_scheduler(env) is expression-equivalent to*MANDATE-NOTHROW*(*AS-CONST*(env).query(get_scheduler))[.](#exec.get.scheduler-2.sentence-2)

*Mandates*: If the expression above is well-formed,
its type satisfies [scheduler](exec.sched#concept:scheduler "33.6 Schedulers [exec.sched]")[.](#exec.get.scheduler-2.sentence-3)

[3](#exec.get.scheduler-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L964)

forwarding_query(execution​::​get_scheduler) is
a core constant expression and has value true[.](#exec.get.scheduler-3.sentence-1)

### [33.5.7](#exec.get.delegation.scheduler) execution​::​get_delegation_scheduler [[exec.get.delegation.scheduler]](exec.get.delegation.scheduler)

[1](#exec.get.delegation.scheduler-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L970)

get_delegation_scheduler asks a queryable object for a scheduler
that can be used to delegate work to
for the purpose of forward progress delegation ([[intro.progress]](intro.progress "6.10.2.3 Forward progress"))[.](#exec.get.delegation.scheduler-1.sentence-1)

[2](#exec.get.delegation.scheduler-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L975)

The name get_delegation_scheduler denotes a query object[.](#exec.get.delegation.scheduler-2.sentence-1)

For a subexpression env,get_delegation_scheduler(env) is expression-equivalent to*MANDATE-NOTHROW*(*AS-CONST*(env).query(get_delegation_scheduler))[.](#exec.get.delegation.scheduler-2.sentence-2)

*Mandates*: If the expression above is well-formed,
its type satisfies [scheduler](exec.sched#concept:scheduler "33.6 Schedulers [exec.sched]")[.](#exec.get.delegation.scheduler-2.sentence-3)

[3](#exec.get.delegation.scheduler-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L985)

forwarding_query(execution​::​get_delegation_scheduler) is
a core constant expression and has value true[.](#exec.get.delegation.scheduler-3.sentence-1)

### [33.5.8](#exec.get.fwd.progress) execution​::​get_forward_progress_guarantee [[exec.get.fwd.progress]](exec.get.fwd.progress)

namespace std::execution {enum class [forward_progress_guarantee](#lib:forward_progress_guarantee "33.5.8 execution​::​get_­forward_­progress_­guarantee [exec.get.fwd.progress]") { concurrent,
 parallel,
 weakly_parallel };}

[1](#exec.get.fwd.progress-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L1001)

get_forward_progress_guarantee asks a scheduler about
the forward progress guarantee of execution agents
created by that scheduler's associated execution resource ([[intro.progress]](intro.progress "6.10.2.3 Forward progress"))[.](#exec.get.fwd.progress-1.sentence-1)

[2](#exec.get.fwd.progress-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L1006)

The name get_forward_progress_guarantee denotes a query object[.](#exec.get.fwd.progress-2.sentence-1)

For a subexpression sch, let Sch be decltype((sch))[.](#exec.get.fwd.progress-2.sentence-2)

If Sch does not satisfy [scheduler](exec.sched#concept:scheduler "33.6 Schedulers [exec.sched]"),get_forward_progress_guarantee is ill-formed[.](#exec.get.fwd.progress-2.sentence-3)

Otherwise,get_forward_progress_guarantee(sch) is expression-equivalent to:

- [(2.1)](#exec.get.fwd.progress-2.1)

  *MANDATE-NOTHROW*(*AS-CONST*(sch).query(get_forward_progress_guarantee)),
if that expression is well-formed[.](#exec.get.fwd.progress-2.1.sentence-1)
  *Mandates*: The type of the expression above is forward_progress_guarantee[.](#exec.get.fwd.progress-2.1.sentence-2)

- [(2.2)](#exec.get.fwd.progress-2.2)

  Otherwise, forward_progress_guarantee​::​weakly_parallel[.](#exec.get.fwd.progress-2.2.sentence-1)

[3](#exec.get.fwd.progress-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L1024)

If get_forward_progress_guarantee(sch) for some scheduler sch returns forward_progress_guarantee​::​concurrent,
all execution agents created by that scheduler's associated execution resource
shall provide the concurrent forward progress guarantee[.](#exec.get.fwd.progress-3.sentence-1)

If it returns forward_progress_guarantee​::​parallel,
all such execution agents
shall provide at least the parallel forward progress guarantee[.](#exec.get.fwd.progress-3.sentence-2)

### [33.5.9](#exec.get.compl.sched) execution​::​get_completion_scheduler [[exec.get.compl.sched]](exec.get.compl.sched)

[1](#exec.get.compl.sched-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L1035)

get_completion_scheduler<*completion-tag>* obtains
the completion scheduler associated with a completion tag
from a sender's attributes[.](#exec.get.compl.sched-1.sentence-1)

[2](#exec.get.compl.sched-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L1040)

The name get_completion_scheduler denotes a query object template[.](#exec.get.compl.sched-2.sentence-1)

For a subexpression q,
the expression get_completion_scheduler<*completion-tag*>(q) is ill-formed if *completion-tag* is not one ofset_value_t, set_error_t, or set_stopped_t[.](#exec.get.compl.sched-2.sentence-2)

Otherwise, get_completion_scheduler<*completion-tag*>(q) is expression-equivalent to*MANDATE-NOTHROW*(*AS-CONST*(q).query(get_completion_scheduler<*completion-tag*>))*Mandates*: If the expression above is well-formed,
its type satisfies [scheduler](exec.sched#concept:scheduler "33.6 Schedulers [exec.sched]")[.](#exec.get.compl.sched-2.sentence-3)

[3](#exec.get.compl.sched-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L1055)

Let *completion-fn* be a completion function ([[exec.async.ops]](exec.async.ops "33.3 Asynchronous operations"));
let *completion-tag* be
the associated completion tag of *completion-fn*;
let args be a pack of subexpressions; and
let sndr be a subexpression
such that [sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]")<decltype((sndr))> is true andget_completion_scheduler<*completion-tag*>(get_env(sndr)) is well-formed and denotes a scheduler sch[.](#exec.get.compl.sched-3.sentence-1)

If an asynchronous operation
created by connecting sndr with a receiver rcvr causes the evaluation of *completion-fn*(rcvr, args...),
the behavior is undefined
unless the evaluation happens on an execution agent
that belongs to sch's associated execution resource[.](#exec.get.compl.sched-3.sentence-2)

[4](#exec.get.compl.sched-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L1071)

The expressionforwarding_query(get_completion_scheduler<*completion-tag*>) is a core constant expression and has value true[.](#exec.get.compl.sched-4.sentence-1)

### [33.5.10](#exec.get.await.adapt) execution​::​get_await_completion_adaptor [[exec.get.await.adapt]](exec.get.await.adapt)

[1](#exec.get.await.adapt-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L1078)

get_await_completion_adaptor asks a queryable object for
its associated awaitable completion adaptor[.](#exec.get.await.adapt-1.sentence-1)

[2](#exec.get.await.adapt-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L1082)

The name get_await_completion_adaptor denotes a query object[.](#exec.get.await.adapt-2.sentence-1)

For a subexpression env,get_await_completion_adaptor(env) is expression-equivalent to*MANDATE-NOTHROW*(*AS-CONST*(env).query(get_await_completion_adaptor))

[3](#exec.get.await.adapt-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L1093)

forwarding_query(execution​::​get_await_completion_adaptor) is a core constant expression and has value true[.](#exec.get.await.adapt-3.sentence-1)
