| Line | Branch | Exec | Source |
|---|---|---|---|
| 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_STOP_TOKEN_SUPPORT_HPP | ||
| 11 | #define BOOST_CAPY_EX_STOP_TOKEN_SUPPORT_HPP | ||
| 12 | |||
| 13 | #include <boost/capy/detail/config.hpp> | ||
| 14 | #include <boost/capy/ex/any_coro.hpp> | ||
| 15 | #include <boost/capy/ex/get_stop_token.hpp> | ||
| 16 | |||
| 17 | #include <coroutine> | ||
| 18 | #if BOOST_CAPY_HAS_STOP_TOKEN | ||
| 19 | #include <stop_token> | ||
| 20 | #endif | ||
| 21 | #include <type_traits> | ||
| 22 | |||
| 23 | namespace boost { | ||
| 24 | namespace capy { | ||
| 25 | |||
| 26 | #if BOOST_CAPY_HAS_STOP_TOKEN | ||
| 27 | |||
| 28 | /** CRTP mixin that adds stop token support to a promise type. | ||
| 29 | |||
| 30 | Inherit from this class to enable two capabilities in your coroutine: | ||
| 31 | |||
| 32 | 1. **Stop token storage** — The mixin stores the `std::stop_token` | ||
| 33 | that was passed when your coroutine was awaited. | ||
| 34 | |||
| 35 | 2. **Stop token access** — Coroutine code can retrieve the token via | ||
| 36 | `co_await get_stop_token()`. | ||
| 37 | |||
| 38 | @tparam Derived The derived promise type (CRTP pattern). | ||
| 39 | |||
| 40 | @par Basic Usage | ||
| 41 | |||
| 42 | For coroutines that only need to access their stop token: | ||
| 43 | |||
| 44 | @code | ||
| 45 | struct my_task | ||
| 46 | { | ||
| 47 | struct promise_type : stop_token_support<promise_type> | ||
| 48 | { | ||
| 49 | my_task get_return_object(); | ||
| 50 | std::suspend_always initial_suspend() noexcept; | ||
| 51 | std::suspend_always final_suspend() noexcept; | ||
| 52 | void return_void(); | ||
| 53 | void unhandled_exception(); | ||
| 54 | }; | ||
| 55 | |||
| 56 | // ... awaitable interface ... | ||
| 57 | }; | ||
| 58 | |||
| 59 | my_task example() | ||
| 60 | { | ||
| 61 | auto token = co_await get_stop_token(); | ||
| 62 | // Use token... | ||
| 63 | } | ||
| 64 | @endcode | ||
| 65 | |||
| 66 | @par Custom Awaitable Transformation | ||
| 67 | |||
| 68 | If your promise needs to transform awaitables (e.g., for affinity or | ||
| 69 | logging), override `transform_awaitable` instead of `await_transform`: | ||
| 70 | |||
| 71 | @code | ||
| 72 | struct promise_type : stop_token_support<promise_type> | ||
| 73 | { | ||
| 74 | any_executor_ref ex_; | ||
| 75 | |||
| 76 | template<typename A> | ||
| 77 | auto transform_awaitable(A&& a) | ||
| 78 | { | ||
| 79 | // Your custom transformation logic | ||
| 80 | return make_affine(std::forward<A>(a), ex_); | ||
| 81 | } | ||
| 82 | }; | ||
| 83 | @endcode | ||
| 84 | |||
| 85 | The mixin's `await_transform` intercepts @ref get_stop_token_tag and | ||
| 86 | delegates all other awaitables to your `transform_awaitable`. | ||
| 87 | |||
| 88 | @par Making Your Coroutine Stoppable | ||
| 89 | |||
| 90 | The mixin handles the "inside the coroutine" part—accessing the token. | ||
| 91 | To receive a token when your coroutine is awaited (satisfying | ||
| 92 | @ref IoAwaitable), implement the stoppable `await_suspend` | ||
| 93 | overload on your coroutine return type: | ||
| 94 | |||
| 95 | @code | ||
| 96 | struct my_task | ||
| 97 | { | ||
| 98 | struct promise_type : stop_token_support<promise_type> { ... }; | ||
| 99 | |||
| 100 | std::coroutine_handle<promise_type> h_; | ||
| 101 | |||
| 102 | // Stoppable await_suspend receives and stores the token | ||
| 103 | template<class Ex> | ||
| 104 | any_coro await_suspend(any_coro cont, Ex const& ex, std::stop_token token) | ||
| 105 | { | ||
| 106 | h_.promise().set_stop_token(token); // Store via mixin API | ||
| 107 | // ... rest of suspend logic ... | ||
| 108 | } | ||
| 109 | }; | ||
| 110 | @endcode | ||
| 111 | |||
| 112 | @par Thread Safety | ||
| 113 | The stop token is stored during `await_suspend` and read during | ||
| 114 | `co_await get_stop_token()`. These occur on the same logical thread | ||
| 115 | of execution, so no synchronization is required. | ||
| 116 | |||
| 117 | @see get_stop_token | ||
| 118 | @see get_stop_token_tag | ||
| 119 | @see IoAwaitable | ||
| 120 | */ | ||
| 121 | template<typename Derived> | ||
| 122 | class stop_token_support | ||
| 123 | { | ||
| 124 | std::stop_token stop_token_; | ||
| 125 | |||
| 126 | public: | ||
| 127 | /** Store a stop token for later retrieval. | ||
| 128 | |||
| 129 | Call this from your coroutine type's stoppable `await_suspend` | ||
| 130 | overload to make the token available via `co_await get_stop_token()`. | ||
| 131 | |||
| 132 | @param token The stop token to store. | ||
| 133 | */ | ||
| 134 | 368 | void set_stop_token(std::stop_token token) noexcept | |
| 135 | { | ||
| 136 | 368 | stop_token_ = token; | |
| 137 | 368 | } | |
| 138 | |||
| 139 | /** Return the stored stop token. | ||
| 140 | |||
| 141 | @return The stop token, or a default-constructed token if none was set. | ||
| 142 | */ | ||
| 143 | 199 | std::stop_token const& stop_token() const noexcept | |
| 144 | { | ||
| 145 | 199 | return stop_token_; | |
| 146 | } | ||
| 147 | |||
| 148 | /** Transform an awaitable before co_await. | ||
| 149 | |||
| 150 | Override this in your derived promise type to customize how | ||
| 151 | awaitables are transformed. The default implementation passes | ||
| 152 | the awaitable through unchanged. | ||
| 153 | |||
| 154 | @param a The awaitable expression from `co_await a`. | ||
| 155 | |||
| 156 | @return The transformed awaitable. | ||
| 157 | */ | ||
| 158 | template<typename A> | ||
| 159 | decltype(auto) transform_awaitable(A&& a) | ||
| 160 | { | ||
| 161 | return std::forward<A>(a); | ||
| 162 | } | ||
| 163 | |||
| 164 | /** Intercept co_await expressions. | ||
| 165 | |||
| 166 | This function handles @ref get_stop_token_tag specially, returning | ||
| 167 | an awaiter that yields the stored stop token. All other awaitables | ||
| 168 | are delegated to @ref transform_awaitable. | ||
| 169 | |||
| 170 | @param t The awaited expression. | ||
| 171 | |||
| 172 | @return An awaiter for the expression. | ||
| 173 | */ | ||
| 174 | template<typename T> | ||
| 175 | 114 | auto await_transform(T&& t) | |
| 176 | { | ||
| 177 | if constexpr (std::is_same_v<std::decay_t<T>, get_stop_token_tag>) | ||
| 178 | { | ||
| 179 | struct awaiter | ||
| 180 | { | ||
| 181 | std::stop_token token_; | ||
| 182 | |||
| 183 | 13 | bool await_ready() const noexcept | |
| 184 | { | ||
| 185 | 13 | return true; | |
| 186 | } | ||
| 187 | |||
| 188 | 1 | void await_suspend(any_coro) const noexcept | |
| 189 | { | ||
| 190 | 1 | } | |
| 191 | |||
| 192 | 12 | std::stop_token await_resume() const noexcept | |
| 193 | { | ||
| 194 | 12 | return token_; | |
| 195 | } | ||
| 196 | }; | ||
| 197 | 14 | return awaiter{stop_token_}; | |
| 198 | } | ||
| 199 | else | ||
| 200 | { | ||
| 201 | 25 | return static_cast<Derived*>(this)->transform_awaitable( | |
| 202 | 100 | std::forward<T>(t)); | |
| 203 | } | ||
| 204 | } | ||
| 205 | }; | ||
| 206 | |||
| 207 | #endif // BOOST_CAPY_HAS_STOP_TOKEN | ||
| 208 | |||
| 209 | } // namespace capy | ||
| 210 | } // namespace boost | ||
| 211 | |||
| 212 | #endif | ||
| 213 |