32 Thread support library [thread]

32.3 Stop tokens [thread.stoptoken]

32.3.3 Class stop_token [stoptoken]

The class stop_token provides an interface for querying whether a stop request has been made (stop_requested) or can ever be made (stop_possible) using an associated stop_source object ([stopsource]).

A stop_token can also be passed to a stop_callback ([stopcallback]) constructor to register a callback to be called when a stop request has been made from an associated stop_source.

namespace std {
  class stop_token {
  public:
    // [stoptoken.cons], constructors, copy, and assignment
    stop_token() noexcept;

    stop_token(const stop_token&) noexcept;
    stop_token(stop_token&&) noexcept;
    stop_token& operator=(const stop_token&) noexcept;
    stop_token& operator=(stop_token&&) noexcept;
    ~stop_token();
    void swap(stop_token&) noexcept;

    // [stoptoken.mem], stop handling
    [[nodiscard]] bool stop_requested() const noexcept;
    [[nodiscard]] bool stop_possible() const noexcept;

    [[nodiscard]] friend bool operator==(const stop_token& lhs, const stop_token& rhs) noexcept;
    friend void swap(stop_token& lhs, stop_token& rhs) noexcept;
  };
}

32.3.3.1 Constructors, copy, and assignment [stoptoken.cons]

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stop_token() noexcept;

Postconditions: stop_possible() is false and stop_requested() is false.

[Note

Because the created stop_token object can never receive a stop request, no resources are allocated for a stop state.

— end note

]

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stop_token(const stop_token& rhs) noexcept;

Postconditions: *this == rhs is true.

[Note

*this and rhs share the ownership of the same stop state, if any.

— end note

]

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stop_token(stop_token&& rhs) noexcept;

Postconditions: *this contains the value of rhs prior to the start of construction and rhs.stop_possible() is false.

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~stop_token();

Effects: Releases ownership of the stop state, if any.

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stop_token& operator=(const stop_token& rhs) noexcept;

Effects: Equivalent to: stop_token(rhs).swap(*this).

Returns: *this.

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stop_token& operator=(stop_token&& rhs) noexcept;

Effects: Equivalent to: stop_token(std::move(rhs)).swap(*this).

Returns: *this.

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void swap(stop_token& rhs) noexcept;

Effects: Exchanges the values of *this and rhs.

32.3.3.2 Members [stoptoken.mem]

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[[nodiscard]] bool stop_requested() const noexcept;

Returns: true if *this has ownership of a stop state that has received a stop request; otherwise, false.

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[[nodiscard]] bool stop_possible() const noexcept;

Returns: false if:

(2.1)
*this does not have ownership of a stop state, or
(2.2)
a stop request was not made and there are no associated stop_source objects;

otherwise, true.

32.3.3.3 Non-member functions [stoptoken.nonmembers]

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[[nodiscard]] bool operator==(const stop_token& lhs, const stop_token& rhs) noexcept;

Returns: true if lhs and rhs have ownership of the same stop state or if both lhs and rhs do not have ownership of a stop state; otherwise false.

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friend void swap(stop_token& x, stop_token& y) noexcept;