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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/ex/any_dispatcher.hpp> | ||
| 15 | #include <boost/capy/concept/affine_awaitable.hpp> | ||
| 16 | #include <boost/capy/concept/stoppable_awaitable.hpp> | ||
| 17 | #include <boost/capy/ex/frame_allocator.hpp> | ||
| 18 | #include <boost/capy/ex/get_stop_token.hpp> | ||
| 19 | #include <boost/capy/ex/make_affine.hpp> | ||
| 20 | #include <boost/capy/ex/stop_token_support.hpp> | ||
| 21 | |||
| 22 | #include <exception> | ||
| 23 | #include <optional> | ||
| 24 | #include <type_traits> | ||
| 25 | #include <utility> | ||
| 26 | #include <variant> | ||
| 27 | |||
| 28 | namespace boost { | ||
| 29 | namespace capy { | ||
| 30 | |||
| 31 | namespace detail { | ||
| 32 | |||
| 33 | // Helper base for result storage and return_void/return_value | ||
| 34 | template<typename T> | ||
| 35 | struct task_return_base | ||
| 36 | { | ||
| 37 | std::optional<T> result_; | ||
| 38 | |||
| 39 | 298 | void return_value(T value) | |
| 40 | { | ||
| 41 | 298 | result_ = std::move(value); | |
| 42 | 298 | } | |
| 43 | }; | ||
| 44 | |||
| 45 | template<> | ||
| 46 | struct task_return_base<void> | ||
| 47 | { | ||
| 48 | 37 | void return_void() | |
| 49 | { | ||
| 50 | 37 | } | |
| 51 | }; | ||
| 52 | |||
| 53 | } // namespace detail | ||
| 54 | |||
| 55 | /** A coroutine task type implementing the affine awaitable protocol. | ||
| 56 | |||
| 57 | This task type represents an asynchronous operation that can be awaited. | ||
| 58 | It implements the affine awaitable protocol where `await_suspend` receives | ||
| 59 | the caller's executor, enabling proper completion dispatch across executor | ||
| 60 | boundaries. | ||
| 61 | |||
| 62 | @tparam T The return type of the task. Defaults to void. | ||
| 63 | |||
| 64 | Key features: | ||
| 65 | @li Lazy execution - the coroutine does not start until awaited | ||
| 66 | @li Symmetric transfer - uses coroutine handle returns for efficient | ||
| 67 | resumption | ||
| 68 | @li Executor inheritance - inherits caller's executor unless explicitly | ||
| 69 | bound | ||
| 70 | |||
| 71 | The task uses `[[clang::coro_await_elidable]]` (when available) to enable | ||
| 72 | heap allocation elision optimization (HALO) for nested coroutine calls. | ||
| 73 | |||
| 74 | @see any_dispatcher | ||
| 75 | */ | ||
| 76 | template<typename T = void> | ||
| 77 | struct [[nodiscard]] BOOST_CAPY_CORO_AWAIT_ELIDABLE | ||
| 78 | task | ||
| 79 | { | ||
| 80 | struct promise_type | ||
| 81 | : frame_allocating_base | ||
| 82 | #if BOOST_CAPY_HAS_STOP_TOKEN | ||
| 83 | , stop_token_support<promise_type> | ||
| 84 | #endif | ||
| 85 | , detail::task_return_base<T> | ||
| 86 | { | ||
| 87 | any_dispatcher ex_; | ||
| 88 | any_dispatcher caller_ex_; | ||
| 89 | any_coro continuation_; | ||
| 90 | std::exception_ptr ep_; | ||
| 91 | detail::frame_allocator_base* alloc_ = nullptr; | ||
| 92 | bool needs_dispatch_ = false; | ||
| 93 | |||
| 94 | 448 | task get_return_object() | |
| 95 | { | ||
| 96 | 448 | return task{std::coroutine_handle<promise_type>::from_promise(*this)}; | |
| 97 | } | ||
| 98 | |||
| 99 | 448 | auto initial_suspend() noexcept | |
| 100 | { | ||
| 101 | struct awaiter | ||
| 102 | { | ||
| 103 | promise_type* p_; | ||
| 104 | |||
| 105 | 224 | bool await_ready() const noexcept | |
| 106 | { | ||
| 107 | 224 | return false; | |
| 108 | } | ||
| 109 | |||
| 110 | 224 | void await_suspend(any_coro) const noexcept | |
| 111 | { | ||
| 112 | // Capture TLS allocator while it's still valid | ||
| 113 | 224 | p_->alloc_ = get_frame_allocator(); | |
| 114 | 224 | } | |
| 115 | |||
| 116 | 223 | void await_resume() const noexcept | |
| 117 | { | ||
| 118 | // Restore TLS when body starts executing | ||
| 119 | 223 | if(p_->alloc_) | |
| 120 | ✗ | set_frame_allocator(*p_->alloc_); | |
| 121 | 223 | } | |
| 122 | }; | ||
| 123 | 448 | return awaiter{this}; | |
| 124 | } | ||
| 125 | |||
| 126 | 446 | auto final_suspend() noexcept | |
| 127 | { | ||
| 128 | struct awaiter | ||
| 129 | { | ||
| 130 | promise_type* p_; | ||
| 131 | |||
| 132 | 223 | bool await_ready() const noexcept | |
| 133 | { | ||
| 134 | 223 | return false; | |
| 135 | } | ||
| 136 | |||
| 137 | 223 | any_coro await_suspend(any_coro) const noexcept | |
| 138 | { | ||
| 139 | 223 | if(p_->continuation_) | |
| 140 | { | ||
| 141 | // Same dispatcher: true symmetric transfer | ||
| 142 | 205 | if(!p_->needs_dispatch_) | |
| 143 | 205 | return p_->continuation_; | |
| 144 | ✗ | return p_->caller_ex_(p_->continuation_); | |
| 145 | } | ||
| 146 | 18 | return std::noop_coroutine(); | |
| 147 | } | ||
| 148 | |||
| 149 | ✗ | void await_resume() const noexcept | |
| 150 | { | ||
| 151 | ✗ | } | |
| 152 | }; | ||
| 153 | 446 | return awaiter{this}; | |
| 154 | } | ||
| 155 | |||
| 156 | // return_void() or return_value() inherited from task_return_base | ||
| 157 | |||
| 158 | 74 | void unhandled_exception() | |
| 159 | { | ||
| 160 | 74 | ep_ = std::current_exception(); | |
| 161 | 74 | } | |
| 162 | |||
| 163 | template<class Awaitable> | ||
| 164 | struct transform_awaiter | ||
| 165 | { | ||
| 166 | std::decay_t<Awaitable> a_; | ||
| 167 | promise_type* p_; | ||
| 168 | |||
| 169 | 197 | bool await_ready() | |
| 170 | { | ||
| 171 | 197 | return a_.await_ready(); | |
| 172 | } | ||
| 173 | |||
| 174 | 197 | auto await_resume() | |
| 175 | { | ||
| 176 | // Restore TLS before body resumes | ||
| 177 |
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197 | if(p_->alloc_) |
| 178 | ✗ | set_frame_allocator(*p_->alloc_); | |
| 179 | 197 | return a_.await_resume(); | |
| 180 | } | ||
| 181 | |||
| 182 | template<class Promise> | ||
| 183 | 197 | auto await_suspend(std::coroutine_handle<Promise> h) | |
| 184 | { | ||
| 185 | #if BOOST_CAPY_HAS_STOP_TOKEN | ||
| 186 | using A = std::decay_t<Awaitable>; | ||
| 187 | if constexpr (stoppable_awaitable<A, any_dispatcher>) | ||
| 188 |
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149 | return a_.await_suspend(h, p_->ex_, p_->stop_token()); |
| 189 | else | ||
| 190 | #endif | ||
| 191 | 48 | return a_.await_suspend(h, p_->ex_); | |
| 192 | } | ||
| 193 | }; | ||
| 194 | |||
| 195 | template<class Awaitable> | ||
| 196 | 197 | auto transform_awaitable(Awaitable&& a) | |
| 197 | { | ||
| 198 | using A = std::decay_t<Awaitable>; | ||
| 199 | if constexpr (affine_awaitable<A, any_dispatcher>) | ||
| 200 | { | ||
| 201 | // Zero-overhead path for affine awaitables | ||
| 202 | return transform_awaiter<Awaitable>{ | ||
| 203 | 346 | std::forward<Awaitable>(a), this}; | |
| 204 | } | ||
| 205 | else | ||
| 206 | { | ||
| 207 | // Trampoline fallback for legacy awaitables | ||
| 208 | return make_affine(std::forward<Awaitable>(a), ex_); | ||
| 209 | } | ||
| 210 | 149 | } | |
| 211 | |||
| 212 | #if !BOOST_CAPY_HAS_STOP_TOKEN | ||
| 213 | // Without stop token support, provide await_transform directly | ||
| 214 | template<class Awaitable> | ||
| 215 | auto await_transform(Awaitable&& a) | ||
| 216 | { | ||
| 217 | return transform_awaitable(std::forward<Awaitable>(a)); | ||
| 218 | } | ||
| 219 | #endif | ||
| 220 | }; | ||
| 221 | |||
| 222 | std::coroutine_handle<promise_type> h_; | ||
| 223 | |||
| 224 | 1180 | ~task() | |
| 225 | { | ||
| 226 |
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1180 | if(h_) |
| 227 | 226 | h_.destroy(); | |
| 228 | 1180 | } | |
| 229 | |||
| 230 | 225 | bool await_ready() const noexcept | |
| 231 | { | ||
| 232 | 225 | return false; | |
| 233 | } | ||
| 234 | |||
| 235 | 223 | auto await_resume() | |
| 236 | { | ||
| 237 |
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223 | if(h_.promise().ep_) |
| 238 | 32 | std::rethrow_exception(h_.promise().ep_); | |
| 239 | if constexpr (! std::is_void_v<T>) | ||
| 240 | 157 | return std::move(*h_.promise().result_); | |
| 241 | else | ||
| 242 | 34 | return; | |
| 243 | } | ||
| 244 | |||
| 245 | // Affine awaitable: receive caller's dispatcher for completion dispatch | ||
| 246 | template<dispatcher D> | ||
| 247 | any_coro await_suspend(any_coro continuation, D const& caller_ex) | ||
| 248 | { | ||
| 249 | h_.promise().caller_ex_ = caller_ex; | ||
| 250 | h_.promise().continuation_ = continuation; | ||
| 251 | h_.promise().ex_ = caller_ex; | ||
| 252 | h_.promise().needs_dispatch_ = false; | ||
| 253 | return h_; | ||
| 254 | } | ||
| 255 | |||
| 256 | #if BOOST_CAPY_HAS_STOP_TOKEN | ||
| 257 | // Stoppable awaitable: receive caller's dispatcher and stop_token | ||
| 258 | template<dispatcher D> | ||
| 259 | 223 | any_coro await_suspend(any_coro continuation, D const& caller_ex, std::stop_token token) | |
| 260 | { | ||
| 261 | 223 | h_.promise().caller_ex_ = caller_ex; | |
| 262 | 223 | h_.promise().continuation_ = continuation; | |
| 263 | 223 | h_.promise().ex_ = caller_ex; | |
| 264 | 223 | h_.promise().set_stop_token(token); | |
| 265 | 223 | h_.promise().needs_dispatch_ = false; | |
| 266 | 223 | return h_; | |
| 267 | } | ||
| 268 | #endif | ||
| 269 | |||
| 270 | /** Release ownership of the coroutine handle. | ||
| 271 | |||
| 272 | After calling this, the task no longer owns the handle and will | ||
| 273 | not destroy it. The caller is responsible for the handle's lifetime. | ||
| 274 | |||
| 275 | @return The coroutine handle, or nullptr if already released. | ||
| 276 | */ | ||
| 277 | 228 | auto release() noexcept -> | |
| 278 | std::coroutine_handle<promise_type> | ||
| 279 | { | ||
| 280 | 228 | return std::exchange(h_, nullptr); | |
| 281 | } | ||
| 282 | |||
| 283 | // Non-copyable | ||
| 284 | task(task const&) = delete; | ||
| 285 | task& operator=(task const&) = delete; | ||
| 286 | |||
| 287 | // Movable | ||
| 288 | 731 | task(task&& other) noexcept | |
| 289 | 731 | : h_(std::exchange(other.h_, nullptr)) | |
| 290 | { | ||
| 291 | 731 | } | |
| 292 | |||
| 293 | task& operator=(task&& other) noexcept | ||
| 294 | { | ||
| 295 | if(this != &other) | ||
| 296 | { | ||
| 297 | if(h_) | ||
| 298 | h_.destroy(); | ||
| 299 | h_ = std::exchange(other.h_, nullptr); | ||
| 300 | } | ||
| 301 | return *this; | ||
| 302 | } | ||
| 303 | |||
| 304 | private: | ||
| 305 | 448 | explicit task(std::coroutine_handle<promise_type> h) | |
| 306 | 448 | : h_(h) | |
| 307 | { | ||
| 308 | 448 | } | |
| 309 | }; | ||
| 310 | |||
| 311 | } // namespace capy | ||
| 312 | } // namespace boost | ||
| 313 | |||
| 314 | #endif | ||
| 315 |