[exec.scope.simple.counting]

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

## 33.14 Execution scope utilities [[exec.scope]](exec.scope#simple.counting)

### 33.14.2 Counting Scopes [[exec.counting.scopes]](exec.counting.scopes#exec.scope.simple.counting)

#### 33.14.2.2 Simple Counting Scope [exec.scope.simple.counting]

#### [33.14.2.2.1](#general) General [[exec.scope.simple.counting.general]](exec.scope.simple.counting.general)

[🔗](#lib:execution::simple_counting_scope)

namespace std::execution {class simple_counting_scope {public:// [[exec.simple.counting.token]](#exec.simple.counting.token "33.14.2.2.4 Token"), tokenstruct token; static constexpr size_t max_associations = *implementation-defined*; // [[exec.simple.counting.ctor]](#exec.simple.counting.ctor "33.14.2.2.2 Constructor and Destructor"), constructor and destructor simple_counting_scope() noexcept;
 simple_counting_scope(simple_counting_scope&&) = delete; ~simple_counting_scope(); // [[exec.simple.counting.mem]](#exec.simple.counting.mem "33.14.2.2.3 Members"), members token get_token() noexcept; void close() noexcept; [sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]") auto join() noexcept; private: size_t *count*; // *exposition only**scope-state-type* *state*; // *exposition only*bool *try-associate*() noexcept; // *exposition only*void *disassociate*() noexcept; // *exposition only*template<class State>bool *start-join-sender*(State& state) noexcept; // *exposition only*};}

[1](#general-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L7971)

For purposes of determining the existence of a data race,get_token,close,join,*try-associate*,*disassociate*, and*start-join-sender* behave as atomic operations ([[intro.multithread]](intro.multithread "6.10.2 Multi-threaded executions and data races"))[.](#general-1.sentence-1)

These operations on a single object of
type simple_counting_scope appear to occur in a single total order[.](#general-1.sentence-2)

#### [33.14.2.2.2](#exec.simple.counting.ctor) Constructor and Destructor [[exec.simple.counting.ctor]](exec.simple.counting.ctor)

[🔗](#lib:execution::simple_counting_scope,constructor)

`simple_counting_scope() noexcept;
`

[1](#exec.simple.counting.ctor-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L7991)

*Postconditions*: *count* is 0 and *state* is *unused*[.](#exec.simple.counting.ctor-1.sentence-1)

[🔗](#lib:execution::simple_counting_scope,destructor)

`~simple_counting_scope();
`

[2](#exec.simple.counting.ctor-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L8002)

*Effects*: If *state* is not one of*joined*, *unused*, or *unused-and-closed*,
invokes terminate ([[except.terminate]](except.terminate "14.6.2 The std​::​terminate function"))[.](#exec.simple.counting.ctor-2.sentence-1)

Otherwise, has no effects[.](#exec.simple.counting.ctor-2.sentence-2)

#### [33.14.2.2.3](#exec.simple.counting.mem) Members [[exec.simple.counting.mem]](exec.simple.counting.mem)

[🔗](#lib:get_token,execution::simple_counting_scope)

`token get_token() noexcept;
`

[1](#exec.simple.counting.mem-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L8018)

*Returns*: An object t of type simple_counting_scope​::​token such thatt.*scope* == this is true[.](#exec.simple.counting.mem-1.sentence-1)

[🔗](#lib:close,execution::simple_counting_scope)

`void close() noexcept;
`

[2](#exec.simple.counting.mem-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L8030)

*Effects*: If *state* is

- [(2.1)](#exec.simple.counting.mem-2.1)

*unused*, then changes *state* to *unused-and-closed*;

- [(2.2)](#exec.simple.counting.mem-2.2)

*open*, then changes *state* to *closed*;

- [(2.3)](#exec.simple.counting.mem-2.3)

*open-and-joining*,
then changes *state* to *closed-and-joining*;

- [(2.4)](#exec.simple.counting.mem-2.4)

otherwise, no effects[.](#exec.simple.counting.mem-2.sentence-1)

[3](#exec.simple.counting.mem-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L8045)

*Postconditions*: Any subsequent call to *try-associate*() on *this returns false[.](#exec.simple.counting.mem-3.sentence-1)

[🔗](#lib:join,execution::simple_counting_scope)

`[sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]") auto join() noexcept;
`

[4](#exec.simple.counting.mem-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L8057)

*Returns*: *make-sender*(*scope-join-t*(), this)[.](#exec.simple.counting.mem-4.sentence-1)

[🔗](#lib:try-associate,execution::simple_counting_scope)

`bool try-associate() noexcept;
`

[5](#exec.simple.counting.mem-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L8068)

*Effects*: If *count* is equal to max_associations, then no effects[.](#exec.simple.counting.mem-5.sentence-1)

Otherwise, if *state* is

- [(5.1)](#exec.simple.counting.mem-5.1)

*unused*,
then increments *count* and changes *state* to *open*;

- [(5.2)](#exec.simple.counting.mem-5.2)

*open* or *open-and-joining*,
then increments *count*;

- [(5.3)](#exec.simple.counting.mem-5.3)

otherwise, no effects[.](#exec.simple.counting.mem-5.sentence-2)

[6](#exec.simple.counting.mem-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L8083)

*Returns*: true if *count* was incremented, false otherwise[.](#exec.simple.counting.mem-6.sentence-1)

[🔗](#lib:disassociate,execution::simple_counting_scope)

`void disassociate() noexcept;
`

[7](#exec.simple.counting.mem-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L8094)

*Preconditions*: *count* is greater than zero[.](#exec.simple.counting.mem-7.sentence-1)

[8](#exec.simple.counting.mem-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L8098)

*Effects*: Decrements *count*[.](#exec.simple.counting.mem-8.sentence-1)

If *count* is zero after decrementing and*state* is *open-and-joining* or *closed-and-joining*,
changes *state* to *joined* and
calls *complete*() on all objects registered with *this[.](#exec.simple.counting.mem-8.sentence-2)

[*Note [1](#exec.simple.counting.mem-note-1)*:

Calling *complete*() on any registered object
can cause *this to be destroyed[.](#exec.simple.counting.mem-8.sentence-3)

— *end note*]

[🔗](#lib:start-join-sender,execution::simple_counting_scope)

`template<class State>
  bool start-join-sender(State& st) noexcept;
`

[9](#exec.simple.counting.mem-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L8118)

*Effects*: If *state* is

- [(9.1)](#exec.simple.counting.mem-9.1)

*unused*, *unused-and-closed*, or *joined*, then
changes *state* to *joined* and returns true;

- [(9.2)](#exec.simple.counting.mem-9.2)

*open* or *open-and-joining*, then
changes *state* to *open-and-joining*,
registers st with *this and returns false;

- [(9.3)](#exec.simple.counting.mem-9.3)

*closed* or *closed-and-joining*, then
changes *state* to *closed-and-joining*,
registers st with *this and returns false[.](#exec.simple.counting.mem-9.sentence-1)

#### [33.14.2.2.4](#exec.simple.counting.token) Token [[exec.simple.counting.token]](exec.simple.counting.token)

[🔗](#lib:execution::simple_counting_scope::token)

namespace std::execution {struct simple_counting_scope::token {template<[sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]") Sender> Sender&& wrap(Sender&& snd) const noexcept; bool try_associate() const noexcept; void disassociate() const noexcept; private: simple_counting_scope* *scope*; // *exposition only*};}

[🔗](#lib:wrap,execution::simple_counting_scope::token)

`template<[sender](exec.snd.concepts#concept:sender "33.9.3 Sender concepts [exec.snd.concepts]") Sender>
  Sender&& wrap(Sender&& snd) const noexcept;
`

[1](#exec.simple.counting.token-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L8160)

*Returns*: std​::​forward<Sender>(snd)[.](#exec.simple.counting.token-1.sentence-1)

[🔗](#lib:try_associate,execution::simple_counting_scope::token)

`bool try_associate() const noexcept;
`

[2](#exec.simple.counting.token-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L8171)

*Effects*: Equivalent to: return *scope*->*try-associate*();

[🔗](#lib:disassociate,execution::simple_counting_scope::token)

`void disassociate() const noexcept;
`

[3](#exec.simple.counting.token-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L8182)

*Effects*: Equivalent to *scope*->*disassociate*()[.](#exec.simple.counting.token-3.sentence-1)