[stopcallback.cons]

# 32 Concurrency support library [[thread]](./#thread)

## 32.3 Stop tokens [[thread.stoptoken]](thread.stoptoken#stopcallback.cons)

### 32.3.6 Class template stop_callback [[stopcallback]](stopcallback#cons)

#### 32.3.6.2 Constructors and destructor [stopcallback.cons]

[🔗](#lib:stop_callback,constructor)

`template<class Initializer>
  explicit stop_callback(const stop_token& st, Initializer&& init)
    noexcept(is_nothrow_constructible_v<CallbackFn, Initializer>);

template<class Initializer>
  explicit stop_callback(stop_token&& st, Initializer&& init)
    noexcept(is_nothrow_constructible_v<CallbackFn, Initializer>);
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L1103)

*Constraints*: CallbackFn and Initializer satisfy[constructible_from](concept.constructible#concept:constructible_from "18.4.11 Concept constructible_­from [concept.constructible]")<CallbackFn, Initializer>[.](#1.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L1108)

*Effects*: Initializes *callback-fn* with std​::​forward<Initializer>(init) and executes a stoppable callback registration ([[stoptoken.concepts]](stoptoken.concepts "32.3.3 Stop token concepts"))[.](#2.sentence-1)

If a callback is registered with st's shared stop state,
then *this acquires shared ownership of that stop state[.](#2.sentence-2)

[🔗](#lib:stop_callback,destructor)

`~stop_callback();
`

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L1122)

*Effects*: Executes a stoppable callback deregistration ([[stoptoken.concepts]](stoptoken.concepts "32.3.3 Stop token concepts")) and
releases ownership of the stop state, if any[.](#3.sentence-1)