libs/capy/include/boost/capy/task.hpp
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libs/capy/include/boost/capy/task.hpp
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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/corosio | ||
| 8 | // | ||
| 9 | |||
| 10 | #ifndef BOOST_CAPY_TASK_HPP | ||
| 11 | #define BOOST_CAPY_TASK_HPP | ||
| 12 | |||
| 13 | #include <boost/capy/detail/config.hpp> | ||
| 14 | #include <boost/capy/concept/executor.hpp> | ||
| 15 | #include <boost/capy/concept/io_awaitable.hpp> | ||
| 16 | #include <boost/capy/ex/io_awaitable_support.hpp> | ||
| 17 | #include <boost/capy/ex/executor_ref.hpp> | ||
| 18 | #include <boost/capy/ex/frame_allocator.hpp> | ||
| 19 | |||
| 20 | #include <exception> | ||
| 21 | #include <optional> | ||
| 22 | #include <type_traits> | ||
| 23 | #include <utility> | ||
| 24 | #include <variant> | ||
| 25 | |||
| 26 | namespace boost { | ||
| 27 | namespace capy { | ||
| 28 | |||
| 29 | namespace detail { | ||
| 30 | |||
| 31 | // Helper base for result storage and return_void/return_value | ||
| 32 | template<typename T> | ||
| 33 | struct task_return_base | ||
| 34 | { | ||
| 35 | std::optional<T> result_; | ||
| 36 | |||
| 37 | 835 | void return_value(T value) | |
| 38 | { | ||
| 39 | 835 | result_ = std::move(value); | |
| 40 | 835 | } | |
| 41 | |||
| 42 | 62 | T&& result() noexcept | |
| 43 | { | ||
| 44 | 62 | return std::move(*result_); | |
| 45 | } | ||
| 46 | }; | ||
| 47 | |||
| 48 | template<> | ||
| 49 | struct task_return_base<void> | ||
| 50 | { | ||
| 51 | 957 | void return_void() | |
| 52 | { | ||
| 53 | 957 | } | |
| 54 | }; | ||
| 55 | |||
| 56 | } // namespace detail | ||
| 57 | |||
| 58 | /** A coroutine task type implementing the affine awaitable protocol. | ||
| 59 | |||
| 60 | This task type represents an asynchronous operation that can be awaited. | ||
| 61 | It implements the affine awaitable protocol where `await_suspend` receives | ||
| 62 | the caller's executor, enabling proper completion dispatch across executor | ||
| 63 | boundaries. | ||
| 64 | |||
| 65 | @tparam T The return type of the task. Defaults to void. | ||
| 66 | |||
| 67 | Key features: | ||
| 68 | @li Lazy execution - the coroutine does not start until awaited | ||
| 69 | @li Symmetric transfer - uses coroutine handle returns for efficient | ||
| 70 | resumption | ||
| 71 | @li Executor inheritance - inherits caller's executor unless explicitly | ||
| 72 | bound | ||
| 73 | |||
| 74 | The task uses `[[clang::coro_await_elidable]]` (when available) to enable | ||
| 75 | heap allocation elision optimization (HALO) for nested coroutine calls. | ||
| 76 | |||
| 77 | @see executor_ref | ||
| 78 | */ | ||
| 79 | template<typename T = void> | ||
| 80 | struct [[nodiscard]] BOOST_CAPY_CORO_AWAIT_ELIDABLE | ||
| 81 | task | ||
| 82 | { | ||
| 83 | struct promise_type | ||
| 84 | : io_awaitable_support<promise_type> | ||
| 85 | , detail::task_return_base<T> | ||
| 86 | { | ||
| 87 | std::exception_ptr ep_; | ||
| 88 | |||
| 89 | 2204 | std::exception_ptr exception() const noexcept | |
| 90 | { | ||
| 91 | 2204 | return ep_; | |
| 92 | } | ||
| 93 | |||
| 94 | 2869 | task get_return_object() | |
| 95 | { | ||
| 96 | 2869 | return task{std::coroutine_handle<promise_type>::from_promise(*this)}; | |
| 97 | } | ||
| 98 | |||
| 99 | 2869 | auto initial_suspend() noexcept | |
| 100 | { | ||
| 101 | struct awaiter | ||
| 102 | { | ||
| 103 | promise_type* p_; | ||
| 104 | |||
| 105 | 279 | bool await_ready() const noexcept | |
| 106 | { | ||
| 107 | 279 | return false; | |
| 108 | } | ||
| 109 | |||
| 110 | 279 | void await_suspend(coro) const noexcept | |
| 111 | { | ||
| 112 | // Capture TLS allocator while it's still valid | ||
| 113 | 279 | p_->set_frame_allocator(current_frame_allocator()); | |
| 114 | 279 | } | |
| 115 | |||
| 116 | 279 | void await_resume() const noexcept | |
| 117 | { | ||
| 118 | // Restore TLS when body starts executing | ||
| 119 |
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279 | if(p_->frame_allocator()) |
| 120 | 255 | current_frame_allocator() = p_->frame_allocator(); | |
| 121 | 279 | } | |
| 122 | }; | ||
| 123 | 2869 | return awaiter{this}; | |
| 124 | } | ||
| 125 | |||
| 126 | 2866 | auto final_suspend() noexcept | |
| 127 | { | ||
| 128 | struct awaiter | ||
| 129 | { | ||
| 130 | promise_type* p_; | ||
| 131 | |||
| 132 | 279 | bool await_ready() const noexcept | |
| 133 | { | ||
| 134 | 279 | return false; | |
| 135 | } | ||
| 136 | |||
| 137 | 279 | coro await_suspend(coro) const noexcept | |
| 138 | { | ||
| 139 | 279 | return p_->complete(); | |
| 140 | } | ||
| 141 | |||
| 142 | ✗ | void await_resume() const noexcept | |
| 143 | { | ||
| 144 | ✗ | } | |
| 145 | }; | ||
| 146 | 2866 | return awaiter{this}; | |
| 147 | } | ||
| 148 | |||
| 149 | 1074 | void unhandled_exception() | |
| 150 | { | ||
| 151 | 1074 | ep_ = std::current_exception(); | |
| 152 | 1074 | } | |
| 153 | |||
| 154 | template<class Awaitable> | ||
| 155 | struct transform_awaiter | ||
| 156 | { | ||
| 157 | std::decay_t<Awaitable> a_; | ||
| 158 | promise_type* p_; | ||
| 159 | |||
| 160 | 6845 | bool await_ready() | |
| 161 | { | ||
| 162 | 6845 | return a_.await_ready(); | |
| 163 | } | ||
| 164 | |||
| 165 | 6844 | decltype(auto) await_resume() | |
| 166 | { | ||
| 167 | // Restore TLS before body resumes | ||
| 168 |
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6844 | if(p_->frame_allocator()) |
| 169 | 6780 | current_frame_allocator() = p_->frame_allocator(); | |
| 170 | 6844 | return a_.await_resume(); | |
| 171 | } | ||
| 172 | |||
| 173 | template<class Promise> | ||
| 174 | 1813 | auto await_suspend(std::coroutine_handle<Promise> h) | |
| 175 | { | ||
| 176 |
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1813 | return a_.await_suspend(h, p_->executor(), p_->stop_token()); |
| 177 | } | ||
| 178 | }; | ||
| 179 | |||
| 180 | template<class Awaitable> | ||
| 181 | 6845 | auto transform_awaitable(Awaitable&& a) | |
| 182 | { | ||
| 183 | using A = std::decay_t<Awaitable>; | ||
| 184 | if constexpr (IoAwaitable<A>) | ||
| 185 | { | ||
| 186 | return transform_awaiter<Awaitable>{ | ||
| 187 | 8085 | std::forward<Awaitable>(a), this}; | |
| 188 | } | ||
| 189 | else | ||
| 190 | { | ||
| 191 | static_assert(sizeof(A) == 0, "requires IoAwaitable"); | ||
| 192 | } | ||
| 193 | 1240 | } | |
| 194 | }; | ||
| 195 | |||
| 196 | std::coroutine_handle<promise_type> h_; | ||
| 197 | |||
| 198 | 5675 | ~task() | |
| 199 | { | ||
| 200 |
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5675 | if(h_) |
| 201 | 1230 | h_.destroy(); | |
| 202 | 5675 | } | |
| 203 | |||
| 204 | 1103 | bool await_ready() const noexcept | |
| 205 | { | ||
| 206 | 1103 | return false; | |
| 207 | } | ||
| 208 | |||
| 209 | 1228 | auto await_resume() | |
| 210 | { | ||
| 211 |
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1228 | if(h_.promise().ep_) |
| 212 | 462 | std::rethrow_exception(h_.promise().ep_); | |
| 213 | if constexpr (! std::is_void_v<T>) | ||
| 214 | 756 | return std::move(*h_.promise().result_); | |
| 215 | else | ||
| 216 | 10 | return; | |
| 217 | } | ||
| 218 | |||
| 219 | // IoAwaitable: receive caller's executor and stop_token for completion dispatch | ||
| 220 | 1216 | coro await_suspend(coro cont, executor_ref caller_ex, std::stop_token token) | |
| 221 | { | ||
| 222 | 1216 | h_.promise().set_continuation(cont, caller_ex); | |
| 223 | 1216 | h_.promise().set_executor(caller_ex); | |
| 224 | 1216 | h_.promise().set_stop_token(token); | |
| 225 | 1216 | return h_; | |
| 226 | } | ||
| 227 | |||
| 228 | /** Return the coroutine handle. | ||
| 229 | |||
| 230 | @return The coroutine handle. | ||
| 231 | */ | ||
| 232 | 1654 | std::coroutine_handle<promise_type> handle() const noexcept | |
| 233 | { | ||
| 234 | 1654 | return h_; | |
| 235 | } | ||
| 236 | |||
| 237 | /** Release ownership of the coroutine handle. | ||
| 238 | |||
| 239 | After calling this, the task no longer owns the handle and will | ||
| 240 | not destroy it. The caller is responsible for the handle's lifetime. | ||
| 241 | */ | ||
| 242 | 1639 | void release() noexcept | |
| 243 | { | ||
| 244 | 1639 | h_ = nullptr; | |
| 245 | 1639 | } | |
| 246 | |||
| 247 | // Non-copyable | ||
| 248 | task(task const&) = delete; | ||
| 249 | task& operator=(task const&) = delete; | ||
| 250 | |||
| 251 | // Movable | ||
| 252 | 2806 | task(task&& other) noexcept | |
| 253 | 2806 | : h_(std::exchange(other.h_, nullptr)) | |
| 254 | { | ||
| 255 | 2806 | } | |
| 256 | |||
| 257 | task& operator=(task&& other) noexcept | ||
| 258 | { | ||
| 259 | if(this != &other) | ||
| 260 | { | ||
| 261 | if(h_) | ||
| 262 | h_.destroy(); | ||
| 263 | h_ = std::exchange(other.h_, nullptr); | ||
| 264 | } | ||
| 265 | return *this; | ||
| 266 | } | ||
| 267 | |||
| 268 | private: | ||
| 269 | 2869 | explicit task(std::coroutine_handle<promise_type> h) | |
| 270 | 2869 | : h_(h) | |
| 271 | { | ||
| 272 | 2869 | } | |
| 273 | }; | ||
| 274 | |||
| 275 | } // namespace capy | ||
| 276 | } // namespace boost | ||
| 277 | |||
| 278 | #endif | ||
| 279 |