#### cancel_after (5 of 6 overloads)

Adapt a completion token to cancel an operation if not complete before the specified relative timeout has elapsed.

    template<
        typename Clock,
        typename WaitTraits,
        typename Executor,
        typename Rep,
        typename Period,
        typename CompletionToken>
    cancel_after_timer< decay_t< CompletionToken >, Clock, WaitTraits, Executor > cancel_after(
        basic_waitable_timer< Clock, WaitTraits, Executor > & timer,
        const chrono::duration< Rep, Period > & timeout,
        CompletionToken && completion_token);

###### Thread Safety

When an asynchronous operation is used with cancel_after, a timer async_wait operation is performed in parallel to the main operation. If this parallel async_wait completes first, a cancellation request is emitted to cancel the main operation. Consequently, the application must ensure that the asynchronous operation is performed within an implicit or explicit strand.