[exec.task.scheduler]

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

## 33.13 Coroutine utilities [[exec.coro.util]](exec.coro.util#exec.task.scheduler)

### 33.13.5 execution​::​task_scheduler [exec.task.scheduler]

namespace std::execution {class [task_scheduler](#lib:task_scheduler "33.13.5 execution​::​task_­scheduler [exec.task.scheduler]") {class *ts-sender*; // *exposition only*template<[receiver](exec.recv.concepts#concept:receiver "33.7.1 Receiver concepts [exec.recv.concepts]") R>class *state*; // *exposition only*public:using scheduler_concept = scheduler_t; template<class Sch, class Allocator = allocator<void>>requires (![same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<task_scheduler, remove_cvref_t<Sch>>)&& [scheduler](exec.sched#concept:scheduler "33.6 Schedulers [exec.sched]")<Sch>explicit task_scheduler(Sch&& sch, Allocator alloc = {}); *ts-sender* schedule(); friend bool operator==(const task_scheduler& lhs, const task_scheduler& rhs)noexcept; template<class Sch>requires (![same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<task_scheduler, Sch>)&& [scheduler](exec.sched#concept:scheduler "33.6 Schedulers [exec.sched]")<Sch>friend bool operator==(const task_scheduler& lhs, const Sch& rhs) noexcept; private: shared_ptr<void> *sch_*; // *exposition only*};}

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L7028)

task_scheduler is a class that models[scheduler](exec.sched#concept:scheduler "33.6 Schedulers [exec.sched]") ([[exec.sched]](exec.sched "33.6 Schedulers"))[.](#1.sentence-1)

Given an object s of type task_scheduler, let*SCHED*(s) be the object owned by s.*sch_*[.](#1.sentence-2)

[ð](#lib:task_scheduler,constructor)

`template<class Sch, class Allocator = allocator<void>>
  requires(![same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<task_scheduler, remove_cvref_t<Sch>>) && [scheduler](exec.sched#concept:scheduler "33.6 Schedulers [exec.sched]")<Sch>
explicit task_scheduler(Sch&& sch, Allocator alloc = {});
`

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L7041)

*Effects*: Initialize *sch_* withallocate_shared<remove_cvref_t<Sch>>(alloc,​ std​::​forward<Sch>​(sch))[.](#2.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L7046)

*Recommended practice*: Implementations should avoid the use of dynamically
allocated memory for small scheduler objects[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L7051)

*Remarks*: Any allocations performed by construction of *ts-sender* or*state* objects resulting from calls on *this are
performed using a copy of alloc[.](#4.sentence-1)

[ð](#lib:scheduler,task_scheduler)

`ts-sender schedule();
`

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L7063)

*Effects*: Returns an object of type *ts-sender* containing a sender
initialized with schedule(​*SCHED*​(*this))[.](#5.sentence-1)

[ð](#lib:operator==,task_scheduler)

`bool operator==(const task_scheduler& lhs, const task_scheduler& rhs) noexcept;
`

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L7074)

*Effects*: Equivalent to: return lhs == *SCHED*(rhs);

[ð](#lib:operator==,task_scheduler_)

`template<class Sch>
  requires (![same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<task_scheduler, Sch>)
        && [scheduler](exec.sched#concept:scheduler "33.6 Schedulers [exec.sched]")<Sch>
bool operator==(const task_scheduler& lhs, const Sch& rhs) noexcept;
`

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L7087)

*Returns*: false if the type of *SCHED*(lhs) is not Sch,
otherwise *SCHED*(lhs) == rhs[.](#7.sentence-1)

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L7093)

namespace std::execution {class task_scheduler::*ts-sender* { // *exposition only*public:using sender_concept = sender_t; template<[receiver](exec.recv.concepts#concept:receiver "33.7.1 Receiver concepts [exec.recv.concepts]") Rcvr>*state*<Rcvr> connect(Rcvr&& rcvr); };}*ts-sender* is an exposition-only class that models[sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]") ([[exec.snd]](exec.snd "33.9 Senders")) and for whichcompletion_signatures_of_t<*ts-sender*> denotes:completion_signatures< set_value_t(),
 set_error_t(error_code),
 set_error_t(exception_ptr),
 set_stopped_t()>

[9](#9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L7116)

Let *sch* be an object of type task_scheduler and let sndr be an object of type *ts-sender* obtained
from schedule(*sch*)[.](#9.sentence-1)

Then get_completion_scheduler<set_value_t>(get_env(sndr)) == *sch* is true[.](#9.sentence-2)

The object *SENDER*(sndr) is the sender object contained bysndr or an object move constructed from it[.](#9.sentence-3)

[ð](#lib:connect,task_scheduler::ts-sender)

`template<[receiver](exec.recv.concepts#concept:receiver "33.7.1 Receiver concepts [exec.recv.concepts]") Rcvr>
  state<Rcvr> connect(Rcvr&& rcvr);
`

[10](#10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L7131)

*Effects*: Let *r* be an object of a type that models [receiver](exec.recv.concepts#concept:receiver "33.7.1 Receiver concepts [exec.recv.concepts]") and whose completion handlers result in invoking the corresponding
completion handlers of rcvr or copy thereof[.](#10.sentence-1)

Returns an object of type *state*<Rcvr> containing
an operation state object initialized with connect(*SENDER*(*this),
std​::​move(*r*))[.](#10.sentence-2)

[11](#11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L7141)

namespace std::execution {template<[receiver](exec.recv.concepts#concept:receiver "33.7.1 Receiver concepts [exec.recv.concepts]") R>class task_scheduler::*state* { // *exposition only*public:using operation_state_concept = operation_state_t; void start() & noexcept; };}*state* is an exposition-only class template whose
specializations model [operation_state](exec.opstate.general#concept:operation_state "33.8.1 General [exec.opstate.general]") ([[exec.opstate]](exec.opstate "33.8 Operation states"))[.](#11.sentence-1)

[ð](#lib:start,task_scheduler::state)

`void start() & noexcept;
`

[12](#12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L7161)

*Effects*: Equivalent to start(st) where st is the operation
state object contained by *this[.](#12.sentence-1)
