Line data    Source code

       1              : //
       2              : // Copyright (c) 2025 Vinnie Falco (vinnie dot falco at gmail dot com)
       3              : //
       4              : // Distributed under the Boost Software License, Version 1.0. (See accompanying
       5              : // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
       6              : //
       7              : // Official repository: https://github.com/cppalliance/capy
       8              : //
       9              : 
      10              : #ifndef BOOST_CAPY_EX_GET_STOP_TOKEN_HPP
      11              : #define BOOST_CAPY_EX_GET_STOP_TOKEN_HPP
      12              : 
      13              : #include <boost/capy/detail/config.hpp>
      14              : 
      15              : namespace boost {
      16              : namespace capy {
      17              : 
      18              : /** Tag type for coroutine stop token retrieval.
      19              : 
      20              :     This tag is returned by @ref get_stop_token and intercepted by a
      21              :     promise type's `await_transform` to yield the coroutine's current
      22              :     stop token. The tag itself carries no data; it serves only as a
      23              :     sentinel for compile-time dispatch.
      24              : 
      25              :     @see get_stop_token
      26              :     @see stop_token_support
      27              : */
      28              : struct get_stop_token_tag {};
      29              : 
      30              : /** Return a tag that yields the current stop token when awaited.
      31              : 
      32              :     Use `co_await get_stop_token()` inside a coroutine whose promise
      33              :     type supports stop token access (e.g., inherits from
      34              :     @ref stop_token_support). The returned stop token reflects whatever
      35              :     token was passed to this coroutine when it was awaited.
      36              : 
      37              :     @par Example
      38              :     @code
      39              :     task<void> cancellable_work()
      40              :     {
      41              :         auto token = co_await get_stop_token();
      42              :         for (int i = 0; i < 1000; ++i)
      43              :         {
      44              :             if (token.stop_requested())
      45              :                 co_return;  // Exit gracefully on cancellation
      46              :             co_await process_chunk(i);
      47              :         }
      48              :     }
      49              :     @endcode
      50              : 
      51              :     @par Behavior
      52              :     @li If no stop token was propagated, returns a default-constructed
      53              :         `std::stop_token` (where `stop_possible()` returns `false`).
      54              :     @li The returned token remains valid for the coroutine's lifetime.
      55              :     @li This operation never suspends; `await_ready()` always returns `true`.
      56              : 
      57              :     @return A tag that `await_transform` intercepts to return the stop token.
      58              : 
      59              :     @see get_stop_token_tag
      60              :     @see stop_token_support
      61              : */
      62           14 : inline get_stop_token_tag get_stop_token() noexcept
      63              : {
      64           14 :     return {};
      65              : }
      66              : 
      67              : } // namespace capy
      68              : } // namespace boost
      69              : 
      70              : #endif