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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/io_awaitable.hpp> | ||
| 16 | #include <boost/capy/ex/executor_ref.hpp> | ||
| 17 | #include <boost/capy/ex/frame_allocator.hpp> | ||
| 18 | |||
| 19 | #include <exception> | ||
| 20 | #include <optional> | ||
| 21 | #include <type_traits> | ||
| 22 | #include <utility> | ||
| 23 | #include <variant> | ||
| 24 | |||
| 25 | namespace boost { | ||
| 26 | namespace capy { | ||
| 27 | |||
| 28 | namespace detail { | ||
| 29 | |||
| 30 | // Helper base for result storage and return_void/return_value | ||
| 31 | template<typename T> | ||
| 32 | struct task_return_base | ||
| 33 | { | ||
| 34 | std::optional<T> result_; | ||
| 35 | |||
| 36 | 163 | void return_value(T value) | |
| 37 | { | ||
| 38 | 163 | result_ = std::move(value); | |
| 39 | 163 | } | |
| 40 | |||
| 41 | 102 | T&& result() noexcept | |
| 42 | { | ||
| 43 | 102 | return std::move(*result_); | |
| 44 | } | ||
| 45 | }; | ||
| 46 | |||
| 47 | template<> | ||
| 48 | struct task_return_base<void> | ||
| 49 | { | ||
| 50 | 26 | void return_void() | |
| 51 | { | ||
| 52 | 26 | } | |
| 53 | }; | ||
| 54 | |||
| 55 | } // namespace detail | ||
| 56 | |||
| 57 | /** A coroutine task type implementing the affine awaitable protocol. | ||
| 58 | |||
| 59 | This task type represents an asynchronous operation that can be awaited. | ||
| 60 | It implements the affine awaitable protocol where `await_suspend` receives | ||
| 61 | the caller's executor, enabling proper completion dispatch across executor | ||
| 62 | boundaries. | ||
| 63 | |||
| 64 | @tparam T The return type of the task. Defaults to void. | ||
| 65 | |||
| 66 | Key features: | ||
| 67 | @li Lazy execution - the coroutine does not start until awaited | ||
| 68 | @li Symmetric transfer - uses coroutine handle returns for efficient | ||
| 69 | resumption | ||
| 70 | @li Executor inheritance - inherits caller's executor unless explicitly | ||
| 71 | bound | ||
| 72 | |||
| 73 | The task uses `[[clang::coro_await_elidable]]` (when available) to enable | ||
| 74 | heap allocation elision optimization (HALO) for nested coroutine calls. | ||
| 75 | |||
| 76 | @see executor_ref | ||
| 77 | */ | ||
| 78 | template<typename T = void> | ||
| 79 | struct [[nodiscard]] BOOST_CAPY_CORO_AWAIT_ELIDABLE | ||
| 80 | task | ||
| 81 | { | ||
| 82 | struct promise_type | ||
| 83 | : frame_allocating_base | ||
| 84 | , io_awaitable_support<promise_type> | ||
| 85 | , detail::task_return_base<T> | ||
| 86 | { | ||
| 87 | std::exception_ptr ep_; | ||
| 88 | detail::frame_allocator_base* alloc_ = nullptr; | ||
| 89 | |||
| 90 | 185 | std::exception_ptr exception() const noexcept | |
| 91 | { | ||
| 92 | 185 | return ep_; | |
| 93 | } | ||
| 94 | |||
| 95 | 266 | task get_return_object() | |
| 96 | { | ||
| 97 | 266 | return task{std::coroutine_handle<promise_type>::from_promise(*this)}; | |
| 98 | } | ||
| 99 | |||
| 100 | 266 | auto initial_suspend() noexcept | |
| 101 | { | ||
| 102 | struct awaiter | ||
| 103 | { | ||
| 104 | promise_type* p_; | ||
| 105 | |||
| 106 | 133 | bool await_ready() const noexcept | |
| 107 | { | ||
| 108 | 133 | return false; | |
| 109 | } | ||
| 110 | |||
| 111 | 133 | void await_suspend(coro) const noexcept | |
| 112 | { | ||
| 113 | // Capture TLS allocator while it's still valid | ||
| 114 | 133 | p_->alloc_ = get_frame_allocator(); | |
| 115 | 133 | } | |
| 116 | |||
| 117 | 131 | void await_resume() const noexcept | |
| 118 | { | ||
| 119 | // Restore TLS when body starts executing | ||
| 120 | 131 | if(p_->alloc_) | |
| 121 | ✗ | set_frame_allocator(*p_->alloc_); | |
| 122 | 131 | } | |
| 123 | }; | ||
| 124 | 266 | return awaiter{this}; | |
| 125 | } | ||
| 126 | |||
| 127 | 260 | auto final_suspend() noexcept | |
| 128 | { | ||
| 129 | struct awaiter | ||
| 130 | { | ||
| 131 | promise_type* p_; | ||
| 132 | |||
| 133 | 130 | bool await_ready() const noexcept | |
| 134 | { | ||
| 135 | 130 | return false; | |
| 136 | } | ||
| 137 | |||
| 138 | 130 | coro await_suspend(coro) const noexcept | |
| 139 | { | ||
| 140 | 130 | return p_->complete(); | |
| 141 | } | ||
| 142 | |||
| 143 | ✗ | void await_resume() const noexcept | |
| 144 | { | ||
| 145 | ✗ | } | |
| 146 | }; | ||
| 147 | 260 | return awaiter{this}; | |
| 148 | } | ||
| 149 | |||
| 150 | // return_void() or return_value() inherited from task_return_base | ||
| 151 | |||
| 152 | 44 | void unhandled_exception() | |
| 153 | { | ||
| 154 | 44 | ep_ = std::current_exception(); | |
| 155 | 44 | } | |
| 156 | |||
| 157 | template<class Awaitable> | ||
| 158 | struct transform_awaiter | ||
| 159 | { | ||
| 160 | std::decay_t<Awaitable> a_; | ||
| 161 | promise_type* p_; | ||
| 162 | |||
| 163 | 74 | bool await_ready() | |
| 164 | { | ||
| 165 | 74 | return a_.await_ready(); | |
| 166 | } | ||
| 167 | |||
| 168 | 72 | auto await_resume() | |
| 169 | { | ||
| 170 | // Restore TLS before body resumes | ||
| 171 |
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72 | if(p_->alloc_) |
| 172 | ✗ | set_frame_allocator(*p_->alloc_); | |
| 173 | 72 | return a_.await_resume(); | |
| 174 | } | ||
| 175 | |||
| 176 | template<class Promise> | ||
| 177 | 74 | auto await_suspend(std::coroutine_handle<Promise> h) | |
| 178 | { | ||
| 179 |
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74 | return a_.await_suspend(h, p_->executor(), p_->stop_token()); |
| 180 | } | ||
| 181 | }; | ||
| 182 | |||
| 183 | template<class Awaitable> | ||
| 184 | 74 | auto transform_awaitable(Awaitable&& a) | |
| 185 | { | ||
| 186 | using A = std::decay_t<Awaitable>; | ||
| 187 | if constexpr (IoAwaitable<A>) | ||
| 188 | { | ||
| 189 | // Zero-overhead path for I/O awaitables | ||
| 190 | return transform_awaiter<Awaitable>{ | ||
| 191 | 144 | std::forward<Awaitable>(a), this}; | |
| 192 | } | ||
| 193 | else | ||
| 194 | { | ||
| 195 | static_assert(sizeof(A) == 0, "requires IoAwaitable"); | ||
| 196 | } | ||
| 197 | 70 | } | |
| 198 | }; | ||
| 199 | |||
| 200 | std::coroutine_handle<promise_type> h_; | ||
| 201 | |||
| 202 | 430 | ~task() | |
| 203 | { | ||
| 204 |
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430 | if(h_) |
| 205 | 72 | h_.destroy(); | |
| 206 | 430 | } | |
| 207 | |||
| 208 | 68 | bool await_ready() const noexcept | |
| 209 | { | ||
| 210 | 68 | return false; | |
| 211 | } | ||
| 212 | |||
| 213 | 66 | auto await_resume() | |
| 214 | { | ||
| 215 |
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66 | if(h_.promise().ep_) |
| 216 | 8 | std::rethrow_exception(h_.promise().ep_); | |
| 217 | if constexpr (! std::is_void_v<T>) | ||
| 218 | 42 | return std::move(*h_.promise().result_); | |
| 219 | else | ||
| 220 | 16 | return; | |
| 221 | } | ||
| 222 | |||
| 223 | // IoAwaitable: receive caller's executor and stop_token for completion dispatch | ||
| 224 | template<typename Ex> | ||
| 225 | 66 | coro await_suspend(coro cont, Ex const& caller_ex, std::stop_token token) | |
| 226 | { | ||
| 227 | 66 | h_.promise().set_continuation(cont, caller_ex); | |
| 228 | 66 | h_.promise().set_executor(caller_ex); | |
| 229 | 66 | h_.promise().set_stop_token(token); | |
| 230 | 66 | return h_; | |
| 231 | } | ||
| 232 | |||
| 233 | /** Return the coroutine handle. | ||
| 234 | |||
| 235 | @return The coroutine handle. | ||
| 236 | */ | ||
| 237 | 199 | std::coroutine_handle<promise_type> handle() const noexcept | |
| 238 | { | ||
| 239 | 199 | return h_; | |
| 240 | } | ||
| 241 | |||
| 242 | /** Release ownership of the coroutine handle. | ||
| 243 | |||
| 244 | After calling this, the task no longer owns the handle and will | ||
| 245 | not destroy it. The caller is responsible for the handle's lifetime. | ||
| 246 | */ | ||
| 247 | 193 | void release() noexcept | |
| 248 | { | ||
| 249 | 193 | h_ = nullptr; | |
| 250 | 193 | } | |
| 251 | |||
| 252 | // Non-copyable | ||
| 253 | task(task const&) = delete; | ||
| 254 | task& operator=(task const&) = delete; | ||
| 255 | |||
| 256 | // Movable | ||
| 257 | 163 | task(task&& other) noexcept | |
| 258 | 163 | : h_(std::exchange(other.h_, nullptr)) | |
| 259 | { | ||
| 260 | 163 | } | |
| 261 | |||
| 262 | task& operator=(task&& other) noexcept | ||
| 263 | { | ||
| 264 | if(this != &other) | ||
| 265 | { | ||
| 266 | if(h_) | ||
| 267 | h_.destroy(); | ||
| 268 | h_ = std::exchange(other.h_, nullptr); | ||
| 269 | } | ||
| 270 | return *this; | ||
| 271 | } | ||
| 272 | |||
| 273 | private: | ||
| 274 | 266 | explicit task(std::coroutine_handle<promise_type> h) | |
| 275 | 266 | : h_(h) | |
| 276 | { | ||
| 277 | 266 | } | |
| 278 | }; | ||
| 279 | |||
| 280 | } // namespace capy | ||
| 281 | } // namespace boost | ||
| 282 | |||
| 283 | #endif | ||
| 284 |