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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/any_executor_ref.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 | 268 | void return_value(T value) | |
| 40 | { | ||
| 41 | 268 | result_ = std::move(value); | |
| 42 | 268 | } | |
| 43 | }; | ||
| 44 | |||
| 45 | template<> | ||
| 46 | struct task_return_base<void> | ||
| 47 | { | ||
| 48 | 28 | void return_void() | |
| 49 | { | ||
| 50 | 28 | } | |
| 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_executor_ref | ||
| 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 | , stop_token_support<promise_type> | ||
| 83 | , detail::task_return_base<T> | ||
| 84 | { | ||
| 85 | any_executor_ref ex_; | ||
| 86 | any_executor_ref caller_ex_; | ||
| 87 | any_coro continuation_; | ||
| 88 | std::exception_ptr ep_; | ||
| 89 | detail::frame_allocator_base* alloc_ = nullptr; | ||
| 90 | bool needs_dispatch_ = false; | ||
| 91 | |||
| 92 | 400 | task get_return_object() | |
| 93 | { | ||
| 94 | 400 | return task{std::coroutine_handle<promise_type>::from_promise(*this)}; | |
| 95 | } | ||
| 96 | |||
| 97 | 400 | auto initial_suspend() noexcept | |
| 98 | { | ||
| 99 | struct awaiter | ||
| 100 | { | ||
| 101 | promise_type* p_; | ||
| 102 | |||
| 103 | 200 | bool await_ready() const noexcept | |
| 104 | { | ||
| 105 | 200 | return false; | |
| 106 | } | ||
| 107 | |||
| 108 | 200 | void await_suspend(any_coro) const noexcept | |
| 109 | { | ||
| 110 | // Capture TLS allocator while it's still valid | ||
| 111 | 200 | p_->alloc_ = get_frame_allocator(); | |
| 112 | 200 | } | |
| 113 | |||
| 114 | 199 | void await_resume() const noexcept | |
| 115 | { | ||
| 116 | // Restore TLS when body starts executing | ||
| 117 | 199 | if(p_->alloc_) | |
| 118 | ✗ | set_frame_allocator(*p_->alloc_); | |
| 119 | 199 | } | |
| 120 | }; | ||
| 121 | 400 | return awaiter{this}; | |
| 122 | } | ||
| 123 | |||
| 124 | 398 | auto final_suspend() noexcept | |
| 125 | { | ||
| 126 | struct awaiter | ||
| 127 | { | ||
| 128 | promise_type* p_; | ||
| 129 | |||
| 130 | 199 | bool await_ready() const noexcept | |
| 131 | { | ||
| 132 | 199 | return false; | |
| 133 | } | ||
| 134 | |||
| 135 | 199 | any_coro await_suspend(any_coro) const noexcept | |
| 136 | { | ||
| 137 | 199 | if(p_->continuation_) | |
| 138 | { | ||
| 139 | // Same executor: true symmetric transfer | ||
| 140 | 182 | if(!p_->needs_dispatch_) | |
| 141 | 182 | return p_->continuation_; | |
| 142 | ✗ | return p_->caller_ex_.dispatch(p_->continuation_); | |
| 143 | } | ||
| 144 | 17 | return std::noop_coroutine(); | |
| 145 | } | ||
| 146 | |||
| 147 | ✗ | void await_resume() const noexcept | |
| 148 | { | ||
| 149 | ✗ | } | |
| 150 | }; | ||
| 151 | 398 | return awaiter{this}; | |
| 152 | } | ||
| 153 | |||
| 154 | // return_void() or return_value() inherited from task_return_base | ||
| 155 | |||
| 156 | 74 | void unhandled_exception() | |
| 157 | { | ||
| 158 | 74 | ep_ = std::current_exception(); | |
| 159 | 74 | } | |
| 160 | |||
| 161 | template<class Awaitable> | ||
| 162 | struct transform_awaiter | ||
| 163 | { | ||
| 164 | std::decay_t<Awaitable> a_; | ||
| 165 | promise_type* p_; | ||
| 166 | |||
| 167 | 127 | bool await_ready() | |
| 168 | { | ||
| 169 | 127 | return a_.await_ready(); | |
| 170 | } | ||
| 171 | |||
| 172 | 127 | auto await_resume() | |
| 173 | { | ||
| 174 | // Restore TLS before body resumes | ||
| 175 |
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127 | if(p_->alloc_) |
| 176 | ✗ | set_frame_allocator(*p_->alloc_); | |
| 177 | 127 | return a_.await_resume(); | |
| 178 | } | ||
| 179 | |||
| 180 | template<class Promise> | ||
| 181 | 127 | auto await_suspend(std::coroutine_handle<Promise> h) | |
| 182 | { | ||
| 183 |
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127 | return a_.await_suspend(h, p_->ex_, p_->stop_token()); |
| 184 | } | ||
| 185 | }; | ||
| 186 | |||
| 187 | template<class Awaitable> | ||
| 188 | 127 | auto transform_awaitable(Awaitable&& a) | |
| 189 | { | ||
| 190 | using A = std::decay_t<Awaitable>; | ||
| 191 | if constexpr (IoAwaitable<A, any_executor_ref>) | ||
| 192 | { | ||
| 193 | // Zero-overhead path for I/O awaitables | ||
| 194 | return transform_awaiter<Awaitable>{ | ||
| 195 | 206 | std::forward<Awaitable>(a), this}; | |
| 196 | } | ||
| 197 | else | ||
| 198 | { | ||
| 199 | static_assert("legacy tasks not supported"); | ||
| 200 | #if 0 | ||
| 201 | // Trampoline fallback for legacy awaitables | ||
| 202 | return make_affine(std::forward<Awaitable>(a), ex_); | ||
| 203 | #endif | ||
| 204 | } | ||
| 205 | 79 | } | |
| 206 | }; | ||
| 207 | |||
| 208 | std::coroutine_handle<promise_type> h_; | ||
| 209 | |||
| 210 | 1110 | ~task() | |
| 211 | { | ||
| 212 |
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1110 | if(h_) |
| 213 | 204 | h_.destroy(); | |
| 214 | 1110 | } | |
| 215 | |||
| 216 | 203 | bool await_ready() const noexcept | |
| 217 | { | ||
| 218 | 203 | return false; | |
| 219 | } | ||
| 220 | |||
| 221 | 201 | auto await_resume() | |
| 222 | { | ||
| 223 |
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201 | if(h_.promise().ep_) |
| 224 | 32 | std::rethrow_exception(h_.promise().ep_); | |
| 225 | if constexpr (! std::is_void_v<T>) | ||
| 226 | 143 | return std::move(*h_.promise().result_); | |
| 227 | else | ||
| 228 | 26 | return; | |
| 229 | } | ||
| 230 | |||
| 231 | // IoAwaitable: receive caller's executor and stop_token for completion dispatch | ||
| 232 | template<typename Ex> | ||
| 233 | 201 | any_coro await_suspend(any_coro continuation, Ex const& caller_ex, std::stop_token token) | |
| 234 | { | ||
| 235 | 201 | h_.promise().caller_ex_ = caller_ex; | |
| 236 | 201 | h_.promise().continuation_ = continuation; | |
| 237 | 201 | h_.promise().ex_ = caller_ex; | |
| 238 | 201 | h_.promise().set_stop_token(token); | |
| 239 | 201 | h_.promise().needs_dispatch_ = false; | |
| 240 | 201 | return h_; | |
| 241 | } | ||
| 242 | |||
| 243 | /** Release ownership of the coroutine handle. | ||
| 244 | |||
| 245 | After calling this, the task no longer owns the handle and will | ||
| 246 | not destroy it. The caller is responsible for the handle's lifetime. | ||
| 247 | |||
| 248 | @return The coroutine handle, or nullptr if already released. | ||
| 249 | */ | ||
| 250 | 202 | auto release() noexcept -> | |
| 251 | std::coroutine_handle<promise_type> | ||
| 252 | { | ||
| 253 | 202 | return std::exchange(h_, nullptr); | |
| 254 | } | ||
| 255 | |||
| 256 | // Non-copyable | ||
| 257 | task(task const&) = delete; | ||
| 258 | task& operator=(task const&) = delete; | ||
| 259 | |||
| 260 | // Movable | ||
| 261 | 709 | task(task&& other) noexcept | |
| 262 | 709 | : h_(std::exchange(other.h_, nullptr)) | |
| 263 | { | ||
| 264 | 709 | } | |
| 265 | |||
| 266 | task& operator=(task&& other) noexcept | ||
| 267 | { | ||
| 268 | if(this != &other) | ||
| 269 | { | ||
| 270 | if(h_) | ||
| 271 | h_.destroy(); | ||
| 272 | h_ = std::exchange(other.h_, nullptr); | ||
| 273 | } | ||
| 274 | return *this; | ||
| 275 | } | ||
| 276 | |||
| 277 | private: | ||
| 278 | 400 | explicit task(std::coroutine_handle<promise_type> h) | |
| 279 | 400 | : h_(h) | |
| 280 | { | ||
| 281 | 400 | } | |
| 282 | }; | ||
| 283 | |||
| 284 | } // namespace capy | ||
| 285 | } // namespace boost | ||
| 286 | |||
| 287 | #endif | ||
| 288 |