# std::stop_source::request_stop

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< cpp‎ | thread‎ | stop source

bool request_stop() noexcept; |  | (since C++20)

Issues a stop request to the stop-state, if the `stop_source` object has a stop-state and it has not yet already had stop requested.

The determination is made atomically, and if stop was requested, the stop-state is atomically updated to avoid race conditions, such that:

- stop_requested() and stop_possible() can be concurrently invoked on other `stop_token`s and `stop_source`s of the same stop-state;
- request_stop() can be concurrently invoked on other `stop_source` objects, and only one will actually perform the stop request.

However, see the Notes section.

### Parameters

(none)

### Return value

true if the `stop_source` object has a stop-state and this invocation made a stop request, otherwise false.

### Postconditions

stop_possible() is false or stop_requested() is true.

### Notes

If the request_stop() does issue a stop request (i.e., returns true), then any `stop_callback`s registered for the same associated stop-state will be invoked synchronously, on the same thread request_stop() is issued on. If an invocation of a callback exits via an exception, std::terminate is called.

If the `stop_source` object has a stop-state but a stop request has already been made, this function returns false. However there is no guarantee that another `stop_source` object which has just (successfully) requested stop is not still in the middle of invoking a `stop_callback` function.

If the request_stop() does issue a stop request (i.e., returns true), then all condition variables of base type std::condition_variable_any registered with an interruptible wait for `stop_token`s associated with the `stop_source`'s stop-state will be notified.

### Example

| This section is incomplete Reason: no example

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