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