cancellation_callback and cancellation_observer

cancellation_callback registers a callback that will be invoked when cancellation occurs.

cancellation_observer checks for cancellation, potentially invoking the handler and returns whether cancellation occured.

Prototype

template <typename F>
struct cancellation_callback {
	cancellation_callback(cancellation_token ct, F functor = {}); // (1)

	cancellation_callback(const cancellation_callback &) = delete;
	cancellation_callback(cancellation_callback &&) = delete;

	cancellation_callback &operator=(const cancellation_callback &) = delete;
	cancellation_callback &operator=(cancellation_callback &&) = delete;

	void unbind(); // (2)
};

template <typename F>
struct cancellation_observer {
	cancellation_observer(F functor = {}); // (3)

	cancellation_observer(const cancellation_observer &) = delete;
	cancellation_observer(cancellation_observer &&) = delete;

	cancellation_observer &operator=(const cancellation_observer &) = delete;
	cancellation_observer &operator=(cancellation_observer &&) = delete;

	bool try_set(cancellation_token ct); // (4)

	bool try_reset(); // (5)
};

1. Constructs and attaches the cancellation callback to the given token.
2. Detaches the cancellation callback.
3. Constructs a cancellation observer.
4. Attaches the cancellation observer to the given token and checks for cancellation without invoking the functor.
5. Checks for cancellation, potentially invoking the functor, and detaches the cancellation observer.

Requirements

F is a functor that takes no arguments.

Arguments

• ct - the cancellation token to attach to.
• functor - the functor to call on cancellation.

Return values

1. N/A
2. This method doesn't return any value.
3. N/A
4. Returns false if cancellation was already requested and the observer hasn't been attached, true otherwise.
5. Same as (4).