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libs/capy/include/boost/capy/ex/executor_ref.hpp

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libs/capy/include/boost/capy/ex/executor_ref.hpp
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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_EXECUTOR_REF_HPP
11 #define BOOST_CAPY_EXECUTOR_REF_HPP
12
13 #include <boost/capy/detail/config.hpp>
14 #include <boost/capy/coro.hpp>
15
16 #include <concepts>
17 #include <coroutine>
18 #include <type_traits>
19 #include <utility>
20
21 namespace boost {
22 namespace capy {
23
24 class execution_context;
25
26 namespace detail {
27
28 /** Virtual function table for type-erased executor operations. */
29 struct executor_vtable
30 {
31 execution_context& (*context)(void const*) noexcept;
32 void (*on_work_started)(void const*) noexcept;
33 void (*on_work_finished)(void const*) noexcept;
34 void (*post)(void const*, std::coroutine_handle<>);
35 std::coroutine_handle<> (*dispatch)(void const*, std::coroutine_handle<>);
36 bool (*equals)(void const*, void const*) noexcept;
37 };
38
39 /** Vtable instance for a specific executor type. */
40 template<class Ex>
41 inline constexpr executor_vtable vtable_for = {
42 // context
43 ✗ [](void const* p) noexcept -> execution_context& {
44 ✗ return const_cast<Ex*>(static_cast<Ex const*>(p))->context();
45 },
46 // on_work_started
47 ✗ [](void const* p) noexcept {
48 ✗ const_cast<Ex*>(static_cast<Ex const*>(p))->on_work_started();
49 },
50 // on_work_finished
51 ✗ [](void const* p) noexcept {
52 ✗ const_cast<Ex*>(static_cast<Ex const*>(p))->on_work_finished();
53 },
54 // post
55 36 [](void const* p, std::coroutine_handle<> h) {
56 18 static_cast<Ex const*>(p)->post(h);
57 },
58 // dispatch
59 7 [](void const* p, std::coroutine_handle<> h) -> std::coroutine_handle<> {
60 7 return static_cast<Ex const*>(p)->dispatch(h);
61 },
62 // equals
63 9 [](void const* a, void const* b) noexcept -> bool {
64 9 return *static_cast<Ex const*>(a) == *static_cast<Ex const*>(b);
65 }
66 };
67
68 } // detail
69
70 /** A type-erased reference wrapper for executor objects.
71
72 This class provides type erasure for any executor type, enabling
73 runtime polymorphism without virtual functions or allocation.
74 It stores a pointer to the original executor and a pointer to a
75 static vtable, allowing executors of different types to be stored
76 uniformly while satisfying the full `Executor` concept.
77
78 @par Reference Semantics
79 This class has reference semantics: it does not allocate or own
80 the wrapped executor. Copy operations simply copy the internal
81 pointers. The caller must ensure the referenced executor outlives
82 all `executor_ref` instances that wrap it.
83
84 @par Thread Safety
85 The `executor_ref` itself is not thread-safe for concurrent
86 modification, but its executor operations are safe to call
87 concurrently if the underlying executor supports it.
88
89 @par Executor Concept
90 This class satisfies the `Executor` concept, making it usable
91 anywhere a concrete executor is expected.
92 */
93 class executor_ref
94 {
95 void const* ex_ = nullptr;
96 detail::executor_vtable const* vt_ = nullptr;
97
98 public:
99 /** Default constructor.
100
101 Constructs an empty `executor_ref`. Calling any executor
102 operations on a default-constructed instance results in
103 undefined behavior.
104 */
105 5790 executor_ref() = default;
106
107 /** Copy constructor.
108
109 Copies the internal pointers, preserving identity.
110 This enables the same-executor optimization when passing
111 executor_ref through coroutine chains.
112 */
113 executor_ref(executor_ref const&) = default;
114
115 /** Copy assignment operator. */
116 executor_ref& operator=(executor_ref const&) = default;
117
118 /** Constructs from any executor type.
119
120 Captures a reference to the given executor and stores a pointer
121 to the type-specific vtable. The executor must remain valid for
122 the lifetime of this `executor_ref` instance.
123
124 @param ex The executor to wrap. Must satisfy the `Executor`
125 concept. A pointer to this object is stored
126 internally; the executor must outlive this wrapper.
127 */
128 #if defined(__GNUC__) && !defined(__clang__)
129 // GCC constraint satisfaction caching bug workaround
130 template<class Ex,
131 std::enable_if_t<!std::is_same_v<
132 std::decay_t<Ex>, executor_ref>, int> = 0>
133 #else
134 template<class Ex>
135 requires (!std::same_as<std::decay_t<Ex>, executor_ref>)
136 #endif
137 3545 executor_ref(Ex const& ex) noexcept
138 3545 : ex_(&ex)
139 3545 , vt_(&detail::vtable_for<Ex>)
140 {
141 3545 }
142
143 /** Returns true if this instance holds a valid executor.
144
145 @return `true` if constructed with an executor, `false` if
146 default-constructed.
147 */
148 22 explicit operator bool() const noexcept
149 {
150 22 return ex_ != nullptr;
151 }
152
153 /** Returns a reference to the associated execution context.
154
155 @return A reference to the execution context.
156
157 @pre This instance was constructed with a valid executor.
158 */
159 execution_context& context() const noexcept
160 {
161 return vt_->context(ex_);
162 }
163
164 /** Informs the executor that work is beginning.
165
166 Must be paired with a subsequent call to `on_work_finished()`.
167
168 @pre This instance was constructed with a valid executor.
169 */
170 void on_work_started() const noexcept
171 {
172 vt_->on_work_started(ex_);
173 }
174
175 /** Informs the executor that work has completed.
176
177 @pre A preceding call to `on_work_started()` was made.
178 @pre This instance was constructed with a valid executor.
179 */
180 void on_work_finished() const noexcept
181 {
182 vt_->on_work_finished(ex_);
183 }
184
185 /** Dispatches a coroutine handle through the wrapped executor.
186
187 Invokes the executor's `dispatch()` operation with the given
188 coroutine handle, returning a handle suitable for symmetric
189 transfer.
190
191 @param h The coroutine handle to dispatch for resumption.
192
193 @return A coroutine handle that the caller may use for symmetric
194 transfer, or `std::noop_coroutine()` if the executor
195 posted the work for later execution.
196
197 @pre This instance was constructed with a valid executor.
198 */
199 7 coro dispatch(coro h) const
200 {
201 7 return vt_->dispatch(ex_, h);
202 }
203
204 /** Posts a coroutine handle to the wrapped executor.
205
206 Posts the coroutine handle to the executor for later execution
207 and returns. The caller should transfer to `std::noop_coroutine()`
208 after calling this.
209
210 @param h The coroutine handle to post for resumption.
211
212 @pre This instance was constructed with a valid executor.
213 */
214 18 void post(coro h) const
215 {
216 18 vt_->post(ex_, h);
217 18 }
218
219 /** Compares two executor references for equality.
220
221 Two `executor_ref` instances are equal if they wrap
222 executors of the same type that compare equal.
223
224 @param other The executor reference to compare against.
225
226 @return `true` if both wrap equal executors of the same type.
227 */
228 2834 bool operator==(executor_ref const& other) const noexcept
229 {
230
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231 2825 return true;
232
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 9 if (vt_ != other.vt_)
233 ✗ return false;
234 9 return vt_->equals(ex_, other.ex_);
235 }
236 };
237
238 } // capy
239 } // boost
240
241 #endif
242