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       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              : #if BOOST_CAPY_HAS_STOP_TOKEN
      19              : 
      20              : /** Tag type for coroutine stop token retrieval.
      21              : 
      22              :     This tag is returned by @ref get_stop_token and intercepted by a
      23              :     promise type's `await_transform` to yield the coroutine's current
      24              :     stop token. The tag itself carries no data; it serves only as a
      25              :     sentinel for compile-time dispatch.
      26              : 
      27              :     @see get_stop_token
      28              :     @see stop_token_support
      29              : */
      30              : struct get_stop_token_tag {};
      31              : 
      32              : /** Return a tag that yields the current stop token when awaited.
      33              : 
      34              :     Use `co_await get_stop_token()` inside a coroutine whose promise
      35              :     type supports stop token access (e.g., inherits from
      36              :     @ref stop_token_support). The returned stop token reflects whatever
      37              :     token was passed to this coroutine when it was awaited.
      38              : 
      39              :     @par Example
      40              :     @code
      41              :     task<void> cancellable_work()
      42              :     {
      43              :         auto token = co_await get_stop_token();
      44              :         for (int i = 0; i < 1000; ++i)
      45              :         {
      46              :             if (token.stop_requested())
      47              :                 co_return;  // Exit gracefully on cancellation
      48              :             co_await process_chunk(i);
      49              :         }
      50              :     }
      51              :     @endcode
      52              : 
      53              :     @par Behavior
      54              :     @li If no stop token was propagated, returns a default-constructed
      55              :         `std::stop_token` (where `stop_possible()` returns `false`).
      56              :     @li The returned token remains valid for the coroutine's lifetime.
      57              :     @li This operation never suspends; `await_ready()` always returns `true`.
      58              : 
      59              :     @return A tag that `await_transform` intercepts to return the stop token.
      60              : 
      61              :     @see get_stop_token_tag
      62              :     @see stop_token_support
      63              : */
      64           15 : inline get_stop_token_tag get_stop_token() noexcept
      65              : {
      66           15 :     return {};
      67              : }
      68              : 
      69              : #endif // BOOST_CAPY_HAS_STOP_TOKEN
      70              : 
      71              : } // namespace capy
      72              : } // namespace boost
      73              : 
      74              : #endif