ex/any_executor.hpp
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ex/any_executor.hpp
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|---|---|---|---|
| 1 | // | ||
| 2 | // Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.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/capy | ||
| 8 | // | ||
| 9 | |||
| 10 | #ifndef BOOST_CAPY_ANY_EXECUTOR_HPP | ||
| 11 | #define BOOST_CAPY_ANY_EXECUTOR_HPP | ||
| 12 | |||
| 13 | #include <boost/capy/detail/config.hpp> | ||
| 14 | #include <concepts> | ||
| 15 | #include <coroutine> | ||
| 16 | #include <memory> | ||
| 17 | #include <type_traits> | ||
| 18 | #include <typeinfo> | ||
| 19 | |||
| 20 | namespace boost { | ||
| 21 | namespace capy { | ||
| 22 | |||
| 23 | class execution_context; | ||
| 24 | template<typename> class strand; | ||
| 25 | |||
| 26 | namespace detail { | ||
| 27 | |||
| 28 | template<typename T> | ||
| 29 | struct is_strand_type : std::false_type {}; | ||
| 30 | |||
| 31 | template<typename E> | ||
| 32 | struct is_strand_type<strand<E>> : std::true_type {}; | ||
| 33 | |||
| 34 | } // detail | ||
| 35 | |||
| 36 | /** A type-erased wrapper for executor objects. | ||
| 37 | |||
| 38 | This class provides type erasure for any executor type, enabling | ||
| 39 | runtime polymorphism with automatic memory management via shared | ||
| 40 | ownership. It stores a shared pointer to a polymorphic wrapper, | ||
| 41 | allowing executors of different types to be stored uniformly | ||
| 42 | while satisfying the full `Executor` concept. | ||
| 43 | |||
| 44 | @par Value Semantics | ||
| 45 | |||
| 46 | This class has value semantics with shared ownership. Copy and | ||
| 47 | move operations are cheap, simply copying the internal shared | ||
| 48 | pointer. Multiple `any_executor` instances may share the same | ||
| 49 | underlying executor. Move operations do not invalidate the | ||
| 50 | source; there is no moved-from state. | ||
| 51 | |||
| 52 | @par Default State | ||
| 53 | |||
| 54 | A default-constructed `any_executor` holds no executor. Calling | ||
| 55 | executor operations on a default-constructed instance results | ||
| 56 | in undefined behavior. Use `operator bool()` to check validity. | ||
| 57 | |||
| 58 | @par Thread Safety | ||
| 59 | |||
| 60 | The `any_executor` itself is thread-safe for concurrent reads. | ||
| 61 | Concurrent modification requires external synchronization. | ||
| 62 | Executor operations are safe to call concurrently if the | ||
| 63 | underlying executor supports it. | ||
| 64 | |||
| 65 | @par Executor Concept | ||
| 66 | |||
| 67 | This class satisfies the `Executor` concept, making it usable | ||
| 68 | anywhere a concrete executor is expected. | ||
| 69 | |||
| 70 | @par Example | ||
| 71 | @code | ||
| 72 | any_executor exec = ctx.get_executor(); | ||
| 73 | if(exec) | ||
| 74 | { | ||
| 75 | auto& context = exec.context(); | ||
| 76 | exec.post(my_coroutine); | ||
| 77 | } | ||
| 78 | @endcode | ||
| 79 | |||
| 80 | @see executor_ref, Executor | ||
| 81 | */ | ||
| 82 | class any_executor | ||
| 83 | { | ||
| 84 | struct impl_base; | ||
| 85 | |||
| 86 | std::shared_ptr<impl_base> p_; | ||
| 87 | |||
| 88 | struct impl_base | ||
| 89 | { | ||
| 90 | 16 | virtual ~impl_base() = default; | |
| 91 | virtual execution_context& context() const noexcept = 0; | ||
| 92 | virtual void on_work_started() const noexcept = 0; | ||
| 93 | virtual void on_work_finished() const noexcept = 0; | ||
| 94 | virtual std::coroutine_handle<> dispatch(std::coroutine_handle<>) const = 0; | ||
| 95 | virtual void post(std::coroutine_handle<>) const = 0; | ||
| 96 | virtual bool equals(impl_base const*) const noexcept = 0; | ||
| 97 | virtual std::type_info const& target_type() const noexcept = 0; | ||
| 98 | }; | ||
| 99 | |||
| 100 | template<class Ex> | ||
| 101 | struct impl final : impl_base | ||
| 102 | { | ||
| 103 | Ex ex_; | ||
| 104 | |||
| 105 | template<class Ex1> | ||
| 106 | 16 | explicit impl(Ex1&& ex) | |
| 107 | 16 | : ex_(std::forward<Ex1>(ex)) | |
| 108 | { | ||
| 109 | 16 | } | |
| 110 | |||
| 111 | 5 | execution_context& context() const noexcept override | |
| 112 | { | ||
| 113 | 5 | return const_cast<Ex&>(ex_).context(); | |
| 114 | } | ||
| 115 | |||
| 116 | ✗ | void on_work_started() const noexcept override | |
| 117 | { | ||
| 118 | ✗ | ex_.on_work_started(); | |
| 119 | ✗ | } | |
| 120 | |||
| 121 | ✗ | void on_work_finished() const noexcept override | |
| 122 | { | ||
| 123 | ✗ | ex_.on_work_finished(); | |
| 124 | ✗ | } | |
| 125 | |||
| 126 | 1 | std::coroutine_handle<> dispatch(std::coroutine_handle<> h) const override | |
| 127 | { | ||
| 128 | 1 | return ex_.dispatch(h); | |
| 129 | } | ||
| 130 | |||
| 131 | 15 | void post(std::coroutine_handle<> h) const override | |
| 132 | { | ||
| 133 | 15 | ex_.post(h); | |
| 134 | 15 | } | |
| 135 | |||
| 136 | 8 | bool equals(impl_base const* other) const noexcept override | |
| 137 | { | ||
| 138 |
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8 | if(target_type() != other->target_type()) |
| 139 | ✗ | return false; | |
| 140 | 8 | return ex_ == static_cast<impl const*>(other)->ex_; | |
| 141 | } | ||
| 142 | |||
| 143 | 17 | std::type_info const& target_type() const noexcept override | |
| 144 | { | ||
| 145 | 17 | return typeid(Ex); | |
| 146 | } | ||
| 147 | }; | ||
| 148 | |||
| 149 | public: | ||
| 150 | /** Default constructor. | ||
| 151 | |||
| 152 | Constructs an empty `any_executor`. Calling any executor | ||
| 153 | operations on a default-constructed instance results in | ||
| 154 | undefined behavior. | ||
| 155 | |||
| 156 | @par Postconditions | ||
| 157 | @li `!*this` | ||
| 158 | */ | ||
| 159 | any_executor() = default; | ||
| 160 | |||
| 161 | /** Copy constructor. | ||
| 162 | |||
| 163 | Creates a new `any_executor` sharing ownership of the | ||
| 164 | underlying executor with `other`. | ||
| 165 | |||
| 166 | @par Postconditions | ||
| 167 | @li `*this == other` | ||
| 168 | */ | ||
| 169 | 9 | any_executor(any_executor const&) = default; | |
| 170 | |||
| 171 | /** Copy assignment operator. | ||
| 172 | |||
| 173 | Shares ownership of the underlying executor with `other`. | ||
| 174 | |||
| 175 | @par Postconditions | ||
| 176 | @li `*this == other` | ||
| 177 | */ | ||
| 178 | 2 | any_executor& operator=(any_executor const&) = default; | |
| 179 | |||
| 180 | /** Constructs from any executor type. | ||
| 181 | |||
| 182 | Allocates storage for a copy of the given executor and | ||
| 183 | stores it internally. The executor must satisfy the | ||
| 184 | `Executor` concept. | ||
| 185 | |||
| 186 | @param ex The executor to wrap. A copy is stored internally. | ||
| 187 | |||
| 188 | @par Postconditions | ||
| 189 | @li `*this` is valid | ||
| 190 | */ | ||
| 191 | template<class Ex> | ||
| 192 | requires ( | ||
| 193 | !std::same_as<std::decay_t<Ex>, any_executor> && | ||
| 194 | !detail::is_strand_type<std::decay_t<Ex>>::value && | ||
| 195 | std::copy_constructible<std::decay_t<Ex>>) | ||
| 196 | 16 | any_executor(Ex&& ex) | |
| 197 |
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16 | : p_(std::make_shared<impl<std::decay_t<Ex>>>(std::forward<Ex>(ex))) |
| 198 | { | ||
| 199 | 16 | } | |
| 200 | |||
| 201 | /** Returns true if this instance holds a valid executor. | ||
| 202 | |||
| 203 | @return `true` if constructed with an executor, `false` if | ||
| 204 | default-constructed. | ||
| 205 | */ | ||
| 206 | 6 | explicit operator bool() const noexcept | |
| 207 | { | ||
| 208 | 6 | return p_ != nullptr; | |
| 209 | } | ||
| 210 | |||
| 211 | /** Returns a reference to the associated execution context. | ||
| 212 | |||
| 213 | @return A reference to the execution context. | ||
| 214 | |||
| 215 | @pre This instance holds a valid executor. | ||
| 216 | */ | ||
| 217 | 5 | execution_context& context() const noexcept | |
| 218 | { | ||
| 219 | 5 | return p_->context(); | |
| 220 | } | ||
| 221 | |||
| 222 | /** Informs the executor that work is beginning. | ||
| 223 | |||
| 224 | Must be paired with a subsequent call to `on_work_finished()`. | ||
| 225 | |||
| 226 | @pre This instance holds a valid executor. | ||
| 227 | */ | ||
| 228 | ✗ | void on_work_started() const noexcept | |
| 229 | { | ||
| 230 | ✗ | p_->on_work_started(); | |
| 231 | ✗ | } | |
| 232 | |||
| 233 | /** Informs the executor that work has completed. | ||
| 234 | |||
| 235 | @pre A preceding call to `on_work_started()` was made. | ||
| 236 | @pre This instance holds a valid executor. | ||
| 237 | */ | ||
| 238 | ✗ | void on_work_finished() const noexcept | |
| 239 | { | ||
| 240 | ✗ | p_->on_work_finished(); | |
| 241 | ✗ | } | |
| 242 | |||
| 243 | /** Dispatches a coroutine handle through the wrapped executor. | ||
| 244 | |||
| 245 | Returns a handle for symmetric transfer. If running in the | ||
| 246 | executor's thread, returns `h`. Otherwise, posts the coroutine | ||
| 247 | for later execution and returns `std::noop_coroutine()`. | ||
| 248 | |||
| 249 | @param h The coroutine handle to dispatch for resumption. | ||
| 250 | |||
| 251 | @return A handle for symmetric transfer or `std::noop_coroutine()`. | ||
| 252 | |||
| 253 | @pre This instance holds a valid executor. | ||
| 254 | */ | ||
| 255 | 1 | std::coroutine_handle<> dispatch(std::coroutine_handle<> h) const | |
| 256 | { | ||
| 257 | 1 | return p_->dispatch(h); | |
| 258 | } | ||
| 259 | |||
| 260 | /** Posts a coroutine handle to the wrapped executor. | ||
| 261 | |||
| 262 | Posts the coroutine handle to the executor for later execution | ||
| 263 | and returns. The caller should transfer to `std::noop_coroutine()` | ||
| 264 | after calling this. | ||
| 265 | |||
| 266 | @param h The coroutine handle to post for resumption. | ||
| 267 | |||
| 268 | @pre This instance holds a valid executor. | ||
| 269 | */ | ||
| 270 | 15 | void post(std::coroutine_handle<> h) const | |
| 271 | { | ||
| 272 | 15 | p_->post(h); | |
| 273 | 15 | } | |
| 274 | |||
| 275 | /** Compares two executor wrappers for equality. | ||
| 276 | |||
| 277 | Two `any_executor` instances are equal if they both hold | ||
| 278 | executors of the same type that compare equal, or if both | ||
| 279 | are empty. | ||
| 280 | |||
| 281 | @param other The executor to compare against. | ||
| 282 | |||
| 283 | @return `true` if both wrap equal executors of the same type, | ||
| 284 | or both are empty. | ||
| 285 | */ | ||
| 286 | 10 | bool operator==(any_executor const& other) const noexcept | |
| 287 | { | ||
| 288 |
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10 | if(!p_ && !other.p_) |
| 289 | 1 | return true; | |
| 290 |
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9 | if(!p_ || !other.p_) |
| 291 | 1 | return false; | |
| 292 | 8 | return p_->equals(other.p_.get()); | |
| 293 | } | ||
| 294 | |||
| 295 | /** Returns the type_info of the wrapped executor. | ||
| 296 | |||
| 297 | @return The `std::type_info` of the stored executor type, | ||
| 298 | or `typeid(void)` if empty. | ||
| 299 | */ | ||
| 300 | 2 | std::type_info const& target_type() const noexcept | |
| 301 | { | ||
| 302 |
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2 | if(!p_) |
| 303 | 1 | return typeid(void); | |
| 304 | 1 | return p_->target_type(); | |
| 305 | } | ||
| 306 | }; | ||
| 307 | |||
| 308 | } // capy | ||
| 309 | } // boost | ||
| 310 | |||
| 311 | #endif | ||
| 312 |