#### cancel_after (1 of 6 overloads)

Create a partial completion token adapter that cancels an operation if not complete before the specified relative timeout has elapsed.

    template<
        typename Rep,
        typename Period>
    partial_cancel_after< chrono::steady_clock > cancel_after(
        const chrono::duration< Rep, Period > & timeout,
        cancellation_type_t cancel_type = cancellation_type::terminal);

###### 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.