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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/make_affine.hpp> | ||
| 19 | |||
| 20 | #include <exception> | ||
| 21 | #include <optional> | ||
| 22 | #include <stop_token> | ||
| 23 | #include <type_traits> | ||
| 24 | #include <utility> | ||
| 25 | #include <variant> | ||
| 26 | |||
| 27 | namespace boost { | ||
| 28 | namespace capy { | ||
| 29 | |||
| 30 | namespace detail { | ||
| 31 | |||
| 32 | // Helper base for result storage and return_void/return_value | ||
| 33 | template<typename T> | ||
| 34 | struct task_return_base | ||
| 35 | { | ||
| 36 | std::optional<T> result_; | ||
| 37 | |||
| 38 | 270 | void return_value(T value) | |
| 39 | { | ||
| 40 | 270 | result_ = std::move(value); | |
| 41 | 270 | } | |
| 42 | }; | ||
| 43 | |||
| 44 | template<> | ||
| 45 | struct task_return_base<void> | ||
| 46 | { | ||
| 47 | 33 | void return_void() | |
| 48 | { | ||
| 49 | 33 | } | |
| 50 | }; | ||
| 51 | |||
| 52 | } // namespace detail | ||
| 53 | |||
| 54 | /** A coroutine task type implementing the affine awaitable protocol. | ||
| 55 | |||
| 56 | This task type represents an asynchronous operation that can be awaited. | ||
| 57 | It implements the affine awaitable protocol where `await_suspend` receives | ||
| 58 | the caller's executor, enabling proper completion dispatch across executor | ||
| 59 | boundaries. | ||
| 60 | |||
| 61 | @tparam T The return type of the task. Defaults to void. | ||
| 62 | |||
| 63 | Key features: | ||
| 64 | @li Lazy execution - the coroutine does not start until awaited | ||
| 65 | @li Symmetric transfer - uses coroutine handle returns for efficient | ||
| 66 | resumption | ||
| 67 | @li Executor inheritance - inherits caller's executor unless explicitly | ||
| 68 | bound | ||
| 69 | |||
| 70 | The task uses `[[clang::coro_await_elidable]]` (when available) to enable | ||
| 71 | heap allocation elision optimization (HALO) for nested coroutine calls. | ||
| 72 | |||
| 73 | @see any_dispatcher | ||
| 74 | */ | ||
| 75 | template<typename T = void> | ||
| 76 | struct [[nodiscard]] BOOST_CAPY_CORO_AWAIT_ELIDABLE | ||
| 77 | task | ||
| 78 | { | ||
| 79 | struct promise_type | ||
| 80 | : frame_allocating_base | ||
| 81 | , detail::task_return_base<T> | ||
| 82 | { | ||
| 83 | any_dispatcher ex_; | ||
| 84 | any_dispatcher caller_ex_; | ||
| 85 | any_coro continuation_; | ||
| 86 | std::exception_ptr ep_; | ||
| 87 | #if BOOST_CAPY_HAS_STOP_TOKEN | ||
| 88 | std::stop_token stop_token_; | ||
| 89 | #endif | ||
| 90 | detail::frame_allocator_base* alloc_ = nullptr; | ||
| 91 | bool needs_dispatch_ = false; | ||
| 92 | |||
| 93 | 410 | task get_return_object() | |
| 94 | { | ||
| 95 | 410 | return task{std::coroutine_handle<promise_type>::from_promise(*this)}; | |
| 96 | } | ||
| 97 | |||
| 98 | 410 | auto initial_suspend() noexcept | |
| 99 | { | ||
| 100 | struct awaiter | ||
| 101 | { | ||
| 102 | promise_type* p_; | ||
| 103 | |||
| 104 | 205 | bool await_ready() const noexcept | |
| 105 | { | ||
| 106 | 205 | return false; | |
| 107 | } | ||
| 108 | |||
| 109 | 205 | void await_suspend(any_coro) const noexcept | |
| 110 | { | ||
| 111 | // Capture TLS allocator while it's still valid | ||
| 112 | 205 | p_->alloc_ = get_frame_allocator(); | |
| 113 | 205 | } | |
| 114 | |||
| 115 | 204 | void await_resume() const noexcept | |
| 116 | { | ||
| 117 | // Restore TLS when body starts executing | ||
| 118 | 204 | if(p_->alloc_) | |
| 119 | 175 | set_frame_allocator(*p_->alloc_); | |
| 120 | 204 | } | |
| 121 | }; | ||
| 122 | 410 | return awaiter{this}; | |
| 123 | } | ||
| 124 | |||
| 125 | 408 | auto final_suspend() noexcept | |
| 126 | { | ||
| 127 | struct awaiter | ||
| 128 | { | ||
| 129 | promise_type* p_; | ||
| 130 | |||
| 131 | 204 | bool await_ready() const noexcept | |
| 132 | { | ||
| 133 | 204 | return false; | |
| 134 | } | ||
| 135 | |||
| 136 | 204 | any_coro await_suspend(any_coro) const noexcept | |
| 137 | { | ||
| 138 | 204 | if(p_->continuation_) | |
| 139 | { | ||
| 140 | // Same dispatcher: true symmetric transfer | ||
| 141 | 187 | if(!p_->needs_dispatch_) | |
| 142 | 187 | return p_->continuation_; | |
| 143 | ✗ | return p_->caller_ex_(p_->continuation_); | |
| 144 | } | ||
| 145 | 17 | return std::noop_coroutine(); | |
| 146 | } | ||
| 147 | |||
| 148 | ✗ | void await_resume() const noexcept | |
| 149 | { | ||
| 150 | ✗ | } | |
| 151 | }; | ||
| 152 | 408 | return awaiter{this}; | |
| 153 | } | ||
| 154 | |||
| 155 | // return_void() or return_value() inherited from task_return_base | ||
| 156 | |||
| 157 | 72 | void unhandled_exception() | |
| 158 | { | ||
| 159 | 72 | ep_ = std::current_exception(); | |
| 160 | 72 | } | |
| 161 | |||
| 162 | template<class Awaitable> | ||
| 163 | struct transform_awaiter | ||
| 164 | { | ||
| 165 | std::decay_t<Awaitable> a_; | ||
| 166 | promise_type* p_; | ||
| 167 | |||
| 168 | 246 | bool await_ready() | |
| 169 | { | ||
| 170 | 246 | return a_.await_ready(); | |
| 171 | } | ||
| 172 | |||
| 173 | 246 | auto await_resume() | |
| 174 | { | ||
| 175 | // Restore TLS before body resumes | ||
| 176 |
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246 | if(p_->alloc_) |
| 177 | 222 | set_frame_allocator(*p_->alloc_); | |
| 178 | 246 | return a_.await_resume(); | |
| 179 | } | ||
| 180 | |||
| 181 | template<class Promise> | ||
| 182 | 246 | auto await_suspend(std::coroutine_handle<Promise> h) | |
| 183 | { | ||
| 184 | #if BOOST_CAPY_HAS_STOP_TOKEN | ||
| 185 | using A = std::decay_t<Awaitable>; | ||
| 186 | if constexpr (stoppable_awaitable<A, any_dispatcher>) | ||
| 187 |
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178 | return a_.await_suspend(h, p_->ex_, p_->stop_token_); |
| 188 | else | ||
| 189 | #endif | ||
| 190 | 68 | return a_.await_suspend(h, p_->ex_); | |
| 191 | } | ||
| 192 | }; | ||
| 193 | |||
| 194 | template<class Awaitable> | ||
| 195 | 246 | auto await_transform(Awaitable&& a) | |
| 196 | { | ||
| 197 | using A = std::decay_t<Awaitable>; | ||
| 198 | if constexpr (affine_awaitable<A, any_dispatcher>) | ||
| 199 | { | ||
| 200 | // Zero-overhead path for affine awaitables | ||
| 201 | return transform_awaiter<Awaitable>{ | ||
| 202 | 444 | std::forward<Awaitable>(a), this}; | |
| 203 | } | ||
| 204 | else | ||
| 205 | { | ||
| 206 | // Trampoline fallback for legacy awaitables | ||
| 207 | return make_affine(std::forward<Awaitable>(a), ex_); | ||
| 208 | } | ||
| 209 | 198 | } | |
| 210 | }; | ||
| 211 | |||
| 212 | std::coroutine_handle<promise_type> h_; | ||
| 213 | |||
| 214 | 1276 | ~task() | |
| 215 | { | ||
| 216 |
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1276 | if(h_) |
| 217 | 254 | h_.destroy(); | |
| 218 | 1276 | } | |
| 219 | |||
| 220 | 254 | bool await_ready() const noexcept | |
| 221 | { | ||
| 222 | 254 | return false; | |
| 223 | } | ||
| 224 | |||
| 225 | 252 | auto await_resume() | |
| 226 | { | ||
| 227 |
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252 | if(h_.promise().ep_) |
| 228 | 42 | std::rethrow_exception(h_.promise().ep_); | |
| 229 | if constexpr (! std::is_void_v<T>) | ||
| 230 | 182 | return std::move(*h_.promise().result_); | |
| 231 | else | ||
| 232 | 28 | return; | |
| 233 | } | ||
| 234 | |||
| 235 | // Affine awaitable: receive caller's dispatcher for completion dispatch | ||
| 236 | template<dispatcher D> | ||
| 237 | any_coro await_suspend(any_coro continuation, D const& caller_ex) | ||
| 238 | { | ||
| 239 | h_.promise().caller_ex_ = caller_ex; | ||
| 240 | h_.promise().continuation_ = continuation; | ||
| 241 | h_.promise().ex_ = caller_ex; | ||
| 242 | h_.promise().needs_dispatch_ = false; | ||
| 243 | return h_; | ||
| 244 | } | ||
| 245 | |||
| 246 | #if BOOST_CAPY_HAS_STOP_TOKEN | ||
| 247 | // Stoppable awaitable: receive caller's dispatcher and stop_token | ||
| 248 | template<dispatcher D> | ||
| 249 | 252 | any_coro await_suspend(any_coro continuation, D const& caller_ex, std::stop_token token) | |
| 250 | { | ||
| 251 | 252 | h_.promise().caller_ex_ = caller_ex; | |
| 252 | 252 | h_.promise().continuation_ = continuation; | |
| 253 | 252 | h_.promise().ex_ = caller_ex; | |
| 254 | 252 | h_.promise().stop_token_ = token; | |
| 255 | 252 | h_.promise().needs_dispatch_ = false; | |
| 256 | 252 | return h_; | |
| 257 | } | ||
| 258 | #endif | ||
| 259 | |||
| 260 | /** Release ownership of the coroutine handle. | ||
| 261 | |||
| 262 | After calling this, the task no longer owns the handle and will | ||
| 263 | not destroy it. The caller is responsible for the handle's lifetime. | ||
| 264 | |||
| 265 | @return The coroutine handle, or nullptr if already released. | ||
| 266 | */ | ||
| 267 | 162 | auto release() noexcept -> | |
| 268 | std::coroutine_handle<promise_type> | ||
| 269 | { | ||
| 270 | 162 | return std::exchange(h_, nullptr); | |
| 271 | } | ||
| 272 | |||
| 273 | // Non-copyable | ||
| 274 | task(task const&) = delete; | ||
| 275 | task& operator=(task const&) = delete; | ||
| 276 | |||
| 277 | // Movable | ||
| 278 | 866 | task(task&& other) noexcept | |
| 279 | 866 | : h_(std::exchange(other.h_, nullptr)) | |
| 280 | { | ||
| 281 | 866 | } | |
| 282 | |||
| 283 | task& operator=(task&& other) noexcept | ||
| 284 | { | ||
| 285 | if(this != &other) | ||
| 286 | { | ||
| 287 | if(h_) | ||
| 288 | h_.destroy(); | ||
| 289 | h_ = std::exchange(other.h_, nullptr); | ||
| 290 | } | ||
| 291 | return *this; | ||
| 292 | } | ||
| 293 | |||
| 294 | private: | ||
| 295 | 410 | explicit task(std::coroutine_handle<promise_type> h) | |
| 296 | 410 | : h_(h) | |
| 297 | { | ||
| 298 | 410 | } | |
| 299 | }; | ||
| 300 | |||
| 301 | } // namespace capy | ||
| 302 | } // namespace boost | ||
| 303 | |||
| 304 | #endif | ||
| 305 |