1   
//
1   
//
2   
// Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com)
2   
// Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com)
3   
//
3   
//
4   
// Distributed under the Boost Software License, Version 1.0. (See accompanying
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)
5   
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6   
//
6   
//
7   
// Official repository: https://github.com/cppalliance/capy
7   
// Official repository: https://github.com/cppalliance/capy
8   
//
8   
//
9  
9  
10   
#ifndef BOOST_CAPY_EXECUTION_CONTEXT_HPP
10   
#ifndef BOOST_CAPY_EXECUTION_CONTEXT_HPP
11   
#define BOOST_CAPY_EXECUTION_CONTEXT_HPP
11   
#define BOOST_CAPY_EXECUTION_CONTEXT_HPP
12  
12  
13   
#include <boost/capy/detail/config.hpp>
13   
#include <boost/capy/detail/config.hpp>
14   
#include <boost/capy/detail/frame_memory_resource.hpp>
14   
#include <boost/capy/detail/frame_memory_resource.hpp>
15   
#include <boost/capy/detail/type_id.hpp>
15   
#include <boost/capy/detail/type_id.hpp>
16   
#include <boost/capy/concept/executor.hpp>
16   
#include <boost/capy/concept/executor.hpp>
17   
#include <concepts>
17   
#include <concepts>
18   
#include <memory>
18   
#include <memory>
19   
#include <memory_resource>
19   
#include <memory_resource>
20   
#include <mutex>
20   
#include <mutex>
21   
#include <tuple>
21   
#include <tuple>
22   
#include <type_traits>
22   
#include <type_traits>
23   
#include <utility>
23   
#include <utility>
24  
24  
25   
namespace boost {
25   
namespace boost {
26   
namespace capy {
26   
namespace capy {
27  
27  
28   
/** Base class for I/O object containers providing service management.
28   
/** Base class for I/O object containers providing service management.
29  
29  
30   
    An execution context represents a place where function objects are
30   
    An execution context represents a place where function objects are
31   
    executed. It provides a service registry where polymorphic services
31   
    executed. It provides a service registry where polymorphic services
32   
    can be stored and retrieved by type. Each service type may be stored
32   
    can be stored and retrieved by type. Each service type may be stored
33   
    at most once. Services may specify a nested `key_type` to enable
33   
    at most once. Services may specify a nested `key_type` to enable
34   
    lookup by a base class type.
34   
    lookup by a base class type.
35  
35  
36   
    Derived classes such as `io_context` extend this to provide
36   
    Derived classes such as `io_context` extend this to provide
37   
    execution facilities like event loops and thread pools. Derived
37   
    execution facilities like event loops and thread pools. Derived
38   
    class destructors must call `shutdown()` and `destroy()` to ensure
38   
    class destructors must call `shutdown()` and `destroy()` to ensure
39   
    proper service cleanup before member destruction.
39   
    proper service cleanup before member destruction.
40  
40  
41   
    @par Service Lifecycle
41   
    @par Service Lifecycle
42   
    Services are created on first use via `use_service()` or explicitly
42   
    Services are created on first use via `use_service()` or explicitly
43   
    via `make_service()`. During destruction, `shutdown()` is called on
43   
    via `make_service()`. During destruction, `shutdown()` is called on
44   
    each service in reverse order of creation, then `destroy()` deletes
44   
    each service in reverse order of creation, then `destroy()` deletes
45   
    them. Both functions are idempotent.
45   
    them. Both functions are idempotent.
46  
46  
47   
    @par Thread Safety
47   
    @par Thread Safety
48   
    Service registration and lookup functions are thread-safe.
48   
    Service registration and lookup functions are thread-safe.
49   
    The `shutdown()` and `destroy()` functions are not thread-safe
49   
    The `shutdown()` and `destroy()` functions are not thread-safe
50   
    and must only be called during destruction.
50   
    and must only be called during destruction.
51  
51  
52   
    @par Example
52   
    @par Example
53   
    @code
53   
    @code
54   
    struct file_service : execution_context::service
54   
    struct file_service : execution_context::service
55   
    {
55   
    {
56   
    protected:
56   
    protected:
57   
        void shutdown() override {}
57   
        void shutdown() override {}
58   
    };
58   
    };
59  
59  
60   
    struct posix_file_service : file_service
60   
    struct posix_file_service : file_service
61   
    {
61   
    {
62   
        using key_type = file_service;
62   
        using key_type = file_service;
63  
63  
64   
        explicit posix_file_service(execution_context&) {}
64   
        explicit posix_file_service(execution_context&) {}
65   
    };
65   
    };
66  
66  
67   
    class io_context : public execution_context
67   
    class io_context : public execution_context
68   
    {
68   
    {
69   
    public:
69   
    public:
70   
        ~io_context()
70   
        ~io_context()
71   
        {
71   
        {
72   
            shutdown();
72   
            shutdown();
73   
            destroy();
73   
            destroy();
74   
        }
74   
        }
75   
    };
75   
    };
76  
76  
77   
    io_context ctx;
77   
    io_context ctx;
78   
    ctx.make_service<posix_file_service>();
78   
    ctx.make_service<posix_file_service>();
79   
    ctx.find_service<file_service>();       // returns posix_file_service*
79   
    ctx.find_service<file_service>();       // returns posix_file_service*
80   
    ctx.find_service<posix_file_service>(); // also works
80   
    ctx.find_service<posix_file_service>(); // also works
81   
    @endcode
81   
    @endcode
82  
82  
83   
    @see service, is_execution_context
83   
    @see service, is_execution_context
84   
*/
84   
*/
85   
class BOOST_CAPY_DECL
85   
class BOOST_CAPY_DECL
86   
    execution_context
86   
    execution_context
87   
{
87   
{
88   
    detail::type_info const* ti_ = nullptr;
88   
    detail::type_info const* ti_ = nullptr;
89  
89  
90   
    template<class T, class = void>
90   
    template<class T, class = void>
91   
    struct get_key : std::false_type
91   
    struct get_key : std::false_type
92   
    {};
92   
    {};
93  
93  
94   
    template<class T>
94   
    template<class T>
95   
    struct get_key<T, std::void_t<typename T::key_type>> : std::true_type
95   
    struct get_key<T, std::void_t<typename T::key_type>> : std::true_type
96   
    {
96   
    {
97   
        using type = typename T::key_type;
97   
        using type = typename T::key_type;
98   
    };
98   
    };
99   
protected:
99   
protected:
100   
    template< typename Derived >
100   
    template< typename Derived >
101   
    explicit execution_context( Derived* ) noexcept;
101   
    explicit execution_context( Derived* ) noexcept;
102  
102  
103   
public:
103   
public:
104   
    //------------------------------------------------
104   
    //------------------------------------------------
105  
105  
106   
    /** Abstract base class for services owned by an execution context.
106   
    /** Abstract base class for services owned by an execution context.
107  
107  
108   
        Services provide extensible functionality to an execution context.
108   
        Services provide extensible functionality to an execution context.
109   
        Each service type can be registered at most once. Services are
109   
        Each service type can be registered at most once. Services are
110   
        created via `use_service()` or `make_service()` and are owned by
110   
        created via `use_service()` or `make_service()` and are owned by
111   
        the execution context for their lifetime.
111   
        the execution context for their lifetime.
112  
112  
113   
        Derived classes must implement the pure virtual `shutdown()` member
113   
        Derived classes must implement the pure virtual `shutdown()` member
114   
        function, which is called when the owning execution context is
114   
        function, which is called when the owning execution context is
115   
        being destroyed. The `shutdown()` function should release resources
115   
        being destroyed. The `shutdown()` function should release resources
116   
        and cancel outstanding operations without blocking.
116   
        and cancel outstanding operations without blocking.
117  
117  
118   
        @par Deriving from service
118   
        @par Deriving from service
119   
        @li Implement `shutdown()` to perform cleanup.
119   
        @li Implement `shutdown()` to perform cleanup.
120   
        @li Accept `execution_context&` as the first constructor parameter.
120   
        @li Accept `execution_context&` as the first constructor parameter.
121   
        @li Optionally define `key_type` to enable base-class lookup.
121   
        @li Optionally define `key_type` to enable base-class lookup.
122  
122  
123   
        @par Example
123   
        @par Example
124   
        @code
124   
        @code
125   
        struct my_service : execution_context::service
125   
        struct my_service : execution_context::service
126   
        {
126   
        {
127   
            explicit my_service(execution_context&) {}
127   
            explicit my_service(execution_context&) {}
128  
128  
129   
        protected:
129   
        protected:
130   
            void shutdown() override
130   
            void shutdown() override
131   
            {
131   
            {
132   
                // Cancel pending operations, release resources
132   
                // Cancel pending operations, release resources
133   
            }
133   
            }
134   
        };
134   
        };
135   
        @endcode
135   
        @endcode
136  
136  
137   
        @see execution_context
137   
        @see execution_context
138   
    */
138   
    */
139   
    class BOOST_CAPY_DECL
139   
    class BOOST_CAPY_DECL
140   
        service
140   
        service
141   
    {
141   
    {
142   
    public:
142   
    public:
143   
        virtual ~service() = default;
143   
        virtual ~service() = default;
144  
144  
145   
    protected:
145   
    protected:
146   
        service() = default;
146   
        service() = default;
147  
147  
148   
        /** Called when the owning execution context shuts down.
148   
        /** Called when the owning execution context shuts down.
149  
149  
150   
            Implementations should release resources and cancel any
150   
            Implementations should release resources and cancel any
151   
            outstanding asynchronous operations. This function must
151   
            outstanding asynchronous operations. This function must
152   
            not block and must not throw exceptions. Services are
152   
            not block and must not throw exceptions. Services are
153   
            shut down in reverse order of creation.
153   
            shut down in reverse order of creation.
154  
154  
155   
            @par Exception Safety
155   
            @par Exception Safety
156   
            No-throw guarantee.
156   
            No-throw guarantee.
157   
        */
157   
        */
158   
        virtual void shutdown() = 0;
158   
        virtual void shutdown() = 0;
159  
159  
160   
    private:
160   
    private:
161   
        friend class execution_context;
161   
        friend class execution_context;
162  
162  
163   
        service* next_ = nullptr;
163   
        service* next_ = nullptr;
164  
164  
165   
// warning C4251: 'std::type_index' needs to have dll-interface
165   
// warning C4251: 'std::type_index' needs to have dll-interface
166 - 
#ifdef _MSC_VER
166 + 
        BOOST_CAPY_MSVC_WARNING_PUSH
167 - 
# pragma warning(push)
167 + 
        BOOST_CAPY_MSVC_WARNING_DISABLE(4251)
168 - 
# pragma warning(disable: 4251)
 
169 - 
#endif
 
170   
        detail::type_index t0_{detail::type_id<void>()};
168   
        detail::type_index t0_{detail::type_id<void>()};
171   
        detail::type_index t1_{detail::type_id<void>()};
169   
        detail::type_index t1_{detail::type_id<void>()};
172 - 
#ifdef _MSC_VER
170 + 
        BOOST_CAPY_MSVC_WARNING_POP
173 - 
# pragma warning(pop)
 
174 - 
#endif
 
175   
    };
171   
    };
176  
172  
177   
    //------------------------------------------------
173   
    //------------------------------------------------
178  
174  
179   
    execution_context(execution_context const&) = delete;
175   
    execution_context(execution_context const&) = delete;
180  
176  
181   
    execution_context& operator=(execution_context const&) = delete;
177   
    execution_context& operator=(execution_context const&) = delete;
182  
178  
183   
    /** Destructor.
179   
    /** Destructor.
184  
180  
185   
        Calls `shutdown()` then `destroy()` to clean up all services.
181   
        Calls `shutdown()` then `destroy()` to clean up all services.
186  
182  
187   
        @par Effects
183   
        @par Effects
188   
        All services are shut down and deleted in reverse order
184   
        All services are shut down and deleted in reverse order
189   
        of creation.
185   
        of creation.
190  
186  
191   
        @par Exception Safety
187   
        @par Exception Safety
192   
        No-throw guarantee.
188   
        No-throw guarantee.
193   
    */
189   
    */
194   
    ~execution_context();
190   
    ~execution_context();
195  
191  
196   
    /** Construct a default instance.
192   
    /** Construct a default instance.
197  
193  
198   
        @par Exception Safety
194   
        @par Exception Safety
199   
        Strong guarantee.
195   
        Strong guarantee.
200   
    */
196   
    */
201   
    execution_context();
197   
    execution_context();
202  
198  
203   
    /** Return true if a service of type T exists.
199   
    /** Return true if a service of type T exists.
204  
200  
205   
        @par Thread Safety
201   
        @par Thread Safety
206   
        Thread-safe.
202   
        Thread-safe.
207  
203  
208   
        @tparam T The type of service to check.
204   
        @tparam T The type of service to check.
209  
205  
210   
        @return `true` if the service exists.
206   
        @return `true` if the service exists.
211   
    */
207   
    */
212   
    template<class T>
208   
    template<class T>
213   
    bool has_service() const noexcept
209   
    bool has_service() const noexcept
214   
    {
210   
    {
215   
        return find_service<T>() != nullptr;
211   
        return find_service<T>() != nullptr;
216   
    }
212   
    }
217  
213  
218   
    /** Return a pointer to the service of type T, or nullptr.
214   
    /** Return a pointer to the service of type T, or nullptr.
219  
215  
220   
        @par Thread Safety
216   
        @par Thread Safety
221   
        Thread-safe.
217   
        Thread-safe.
222  
218  
223   
        @tparam T The type of service to find.
219   
        @tparam T The type of service to find.
224  
220  
225   
        @return A pointer to the service, or `nullptr` if not present.
221   
        @return A pointer to the service, or `nullptr` if not present.
226   
    */
222   
    */
227   
    template<class T>
223   
    template<class T>
228   
    T* find_service() const noexcept
224   
    T* find_service() const noexcept
229   
    {
225   
    {
230   
        std::lock_guard<std::mutex> lock(mutex_);
226   
        std::lock_guard<std::mutex> lock(mutex_);
231   
        return static_cast<T*>(find_impl(detail::type_id<T>()));
227   
        return static_cast<T*>(find_impl(detail::type_id<T>()));
232   
    }
228   
    }
233  
229  
234   
    /** Return a reference to the service of type T, creating it if needed.
230   
    /** Return a reference to the service of type T, creating it if needed.
235  
231  
236   
        If no service of type T exists, one is created by calling
232   
        If no service of type T exists, one is created by calling
237   
        `T(execution_context&)`. If T has a nested `key_type`, the
233   
        `T(execution_context&)`. If T has a nested `key_type`, the
238   
        service is also indexed under that type.
234   
        service is also indexed under that type.
239  
235  
240   
        @par Constraints
236   
        @par Constraints
241   
        @li `T` must derive from `service`.
237   
        @li `T` must derive from `service`.
242   
        @li `T` must be constructible from `execution_context&`.
238   
        @li `T` must be constructible from `execution_context&`.
243  
239  
244   
        @par Exception Safety
240   
        @par Exception Safety
245   
        Strong guarantee. If service creation throws, the container
241   
        Strong guarantee. If service creation throws, the container
246   
        is unchanged.
242   
        is unchanged.
247  
243  
248   
        @par Thread Safety
244   
        @par Thread Safety
249   
        Thread-safe.
245   
        Thread-safe.
250  
246  
251   
        @tparam T The type of service to retrieve or create.
247   
        @tparam T The type of service to retrieve or create.
252  
248  
253   
        @return A reference to the service.
249   
        @return A reference to the service.
254   
    */
250   
    */
255   
    template<class T>
251   
    template<class T>
256   
    T& use_service()
252   
    T& use_service()
257   
    {
253   
    {
258   
        static_assert(std::is_base_of<service, T>::value,
254   
        static_assert(std::is_base_of<service, T>::value,
259   
            "T must derive from service");
255   
            "T must derive from service");
260   
        static_assert(std::is_constructible<T, execution_context&>::value,
256   
        static_assert(std::is_constructible<T, execution_context&>::value,
261   
            "T must be constructible from execution_context&");
257   
            "T must be constructible from execution_context&");
262  
258  
263   
        struct impl : factory
259   
        struct impl : factory
264   
        {
260   
        {
265   
            impl()
261   
            impl()
266   
                : factory(
262   
                : factory(
267   
                    detail::type_id<T>(),
263   
                    detail::type_id<T>(),
268   
                    get_key<T>::value
264   
                    get_key<T>::value
269   
                        ? detail::type_id<typename get_key<T>::type>()
265   
                        ? detail::type_id<typename get_key<T>::type>()
270   
                        : detail::type_id<T>())
266   
                        : detail::type_id<T>())
271   
            {
267   
            {
272   
            }
268   
            }
273  
269  
274   
            service* create(execution_context& ctx) override
270   
            service* create(execution_context& ctx) override
275   
            {
271   
            {
276   
                return new T(ctx);
272   
                return new T(ctx);
277   
            }
273   
            }
278   
        };
274   
        };
279  
275  
280   
        impl f;
276   
        impl f;
281   
        return static_cast<T&>(use_service_impl(f));
277   
        return static_cast<T&>(use_service_impl(f));
282   
    }
278   
    }
283  
279  
284   
    /** Construct and add a service.
280   
    /** Construct and add a service.
285  
281  
286   
        A new service of type T is constructed using the provided
282   
        A new service of type T is constructed using the provided
287   
        arguments and added to the container. If T has a nested
283   
        arguments and added to the container. If T has a nested
288   
        `key_type`, the service is also indexed under that type.
284   
        `key_type`, the service is also indexed under that type.
289  
285  
290   
        @par Constraints
286   
        @par Constraints
291   
        @li `T` must derive from `service`.
287   
        @li `T` must derive from `service`.
292   
        @li `T` must be constructible from `execution_context&, Args...`.
288   
        @li `T` must be constructible from `execution_context&, Args...`.
293   
        @li If `T::key_type` exists, `T&` must be convertible to `key_type&`.
289   
        @li If `T::key_type` exists, `T&` must be convertible to `key_type&`.
294  
290  
295   
        @par Exception Safety
291   
        @par Exception Safety
296   
        Strong guarantee. If service creation throws, the container
292   
        Strong guarantee. If service creation throws, the container
297   
        is unchanged.
293   
        is unchanged.
298  
294  
299   
        @par Thread Safety
295   
        @par Thread Safety
300   
        Thread-safe.
296   
        Thread-safe.
301  
297  
302   
        @throws std::invalid_argument if a service of the same type
298   
        @throws std::invalid_argument if a service of the same type
303   
            or `key_type` already exists.
299   
            or `key_type` already exists.
304  
300  
305   
        @tparam T The type of service to create.
301   
        @tparam T The type of service to create.
306  
302  
307   
        @param args Arguments forwarded to the constructor of T.
303   
        @param args Arguments forwarded to the constructor of T.
308  
304  
309   
        @return A reference to the created service.
305   
        @return A reference to the created service.
310   
    */
306   
    */
311   
    template<class T, class... Args>
307   
    template<class T, class... Args>
312   
    T& make_service(Args&&... args)
308   
    T& make_service(Args&&... args)
313   
    {
309   
    {
314   
        static_assert(std::is_base_of<service, T>::value,
310   
        static_assert(std::is_base_of<service, T>::value,
315   
            "T must derive from service");
311   
            "T must derive from service");
316   
        if constexpr(get_key<T>::value)
312   
        if constexpr(get_key<T>::value)
317   
        {
313   
        {
318   
            static_assert(
314   
            static_assert(
319   
                std::is_convertible<T&, typename get_key<T>::type&>::value,
315   
                std::is_convertible<T&, typename get_key<T>::type&>::value,
320   
                "T& must be convertible to key_type&");
316   
                "T& must be convertible to key_type&");
321   
        }
317   
        }
322  
318  
323   
        struct impl : factory
319   
        struct impl : factory
324   
        {
320   
        {
325   
            std::tuple<Args&&...> args_;
321   
            std::tuple<Args&&...> args_;
326  
322  
327   
            explicit impl(Args&&... a)
323   
            explicit impl(Args&&... a)
328   
                : factory(
324   
                : factory(
329   
                    detail::type_id<T>(),
325   
                    detail::type_id<T>(),
330   
                    get_key<T>::value
326   
                    get_key<T>::value
331   
                        ? detail::type_id<typename get_key<T>::type>()
327   
                        ? detail::type_id<typename get_key<T>::type>()
332   
                        : detail::type_id<T>())
328   
                        : detail::type_id<T>())
333   
                , args_(std::forward<Args>(a)...)
329   
                , args_(std::forward<Args>(a)...)
334   
            {
330   
            {
335   
            }
331   
            }
336  
332  
337   
            service* create(execution_context& ctx) override
333   
            service* create(execution_context& ctx) override
338   
            {
334   
            {
339   
                return std::apply([&ctx](auto&&... a) {
335   
                return std::apply([&ctx](auto&&... a) {
340   
                    return new T(ctx, std::forward<decltype(a)>(a)...);
336   
                    return new T(ctx, std::forward<decltype(a)>(a)...);
341   
                }, std::move(args_));
337   
                }, std::move(args_));
342   
            }
338   
            }
343   
        };
339   
        };
344  
340  
345   
        impl f(std::forward<Args>(args)...);
341   
        impl f(std::forward<Args>(args)...);
346   
        return static_cast<T&>(make_service_impl(f));
342   
        return static_cast<T&>(make_service_impl(f));
347   
    }
343   
    }
348  
344  
349   
    //------------------------------------------------
345   
    //------------------------------------------------
350  
346  
351   
    /** Return the memory resource used for coroutine frame allocation.
347   
    /** Return the memory resource used for coroutine frame allocation.
352  
348  
353   
        The returned pointer is valid for the lifetime of this context.
349   
        The returned pointer is valid for the lifetime of this context.
354   
        By default, this returns a pointer to the recycling memory
350   
        By default, this returns a pointer to the recycling memory
355   
        resource which pools frame allocations for reuse.
351   
        resource which pools frame allocations for reuse.
356  
352  
357   
        @return Pointer to the frame allocator.
353   
        @return Pointer to the frame allocator.
358  
354  
359   
        @see set_frame_allocator
355   
        @see set_frame_allocator
360   
    */
356   
    */
361   
    std::pmr::memory_resource*
357   
    std::pmr::memory_resource*
362   
    get_frame_allocator() const noexcept
358   
    get_frame_allocator() const noexcept
363   
    {
359   
    {
364   
        return frame_alloc_;
360   
        return frame_alloc_;
365   
    }
361   
    }
366  
362  
367   
    /** Set the memory resource used for coroutine frame allocation.
363   
    /** Set the memory resource used for coroutine frame allocation.
368  
364  
369   
        The caller is responsible for ensuring the memory resource
365   
        The caller is responsible for ensuring the memory resource
370   
        remains valid for the lifetime of all coroutines launched
366   
        remains valid for the lifetime of all coroutines launched
371   
        using this context's executor.
367   
        using this context's executor.
372  
368  
373   
        @par Thread Safety
369   
        @par Thread Safety
374   
        Not thread-safe. Must not be called while any thread may
370   
        Not thread-safe. Must not be called while any thread may
375   
        be referencing this execution context or its executor.
371   
        be referencing this execution context or its executor.
376  
372  
377   
        @param mr Pointer to the memory resource.
373   
        @param mr Pointer to the memory resource.
378  
374  
379   
        @see get_frame_allocator
375   
        @see get_frame_allocator
380   
    */
376   
    */
381   
    void
377   
    void
382   
    set_frame_allocator(std::pmr::memory_resource* mr) noexcept
378   
    set_frame_allocator(std::pmr::memory_resource* mr) noexcept
383   
    {
379   
    {
384   
        owned_.reset();
380   
        owned_.reset();
385   
        frame_alloc_ = mr;
381   
        frame_alloc_ = mr;
386   
    }
382   
    }
387  
383  
388   
    /** Set the frame allocator from a standard Allocator.
384   
    /** Set the frame allocator from a standard Allocator.
389  
385  
390   
        The allocator is wrapped in an internal memory resource
386   
        The allocator is wrapped in an internal memory resource
391   
        adapter owned by this context. The wrapper remains valid
387   
        adapter owned by this context. The wrapper remains valid
392   
        for the lifetime of this context or until a subsequent
388   
        for the lifetime of this context or until a subsequent
393   
        call to set_frame_allocator.
389   
        call to set_frame_allocator.
394  
390  
395   
        @par Thread Safety
391   
        @par Thread Safety
396   
        Not thread-safe. Must not be called while any thread may
392   
        Not thread-safe. Must not be called while any thread may
397   
        be referencing this execution context or its executor.
393   
        be referencing this execution context or its executor.
398  
394  
399   
        @tparam Allocator The allocator type satisfying the
395   
        @tparam Allocator The allocator type satisfying the
400   
            standard Allocator requirements.
396   
            standard Allocator requirements.
401  
397  
402   
        @param a The allocator to use.
398   
        @param a The allocator to use.
403  
399  
404   
        @see get_frame_allocator
400   
        @see get_frame_allocator
405   
    */
401   
    */
406   
    template<class Allocator>
402   
    template<class Allocator>
407   
        requires (!std::is_pointer_v<Allocator>)
403   
        requires (!std::is_pointer_v<Allocator>)
408   
    void
404   
    void
409   
    set_frame_allocator(Allocator const& a)
405   
    set_frame_allocator(Allocator const& a)
410   
    {
406   
    {
411   
        static_assert(
407   
        static_assert(
412   
            requires { typename std::allocator_traits<Allocator>::value_type; },
408   
            requires { typename std::allocator_traits<Allocator>::value_type; },
413   
            "Allocator must satisfy allocator requirements");
409   
            "Allocator must satisfy allocator requirements");
414   
        static_assert(
410   
        static_assert(
415   
            std::is_copy_constructible_v<Allocator>,
411   
            std::is_copy_constructible_v<Allocator>,
416   
            "Allocator must be copy constructible");
412   
            "Allocator must be copy constructible");
417  
413  
418   
        auto p = std::make_shared<
414   
        auto p = std::make_shared<
419   
            detail::frame_memory_resource<Allocator>>(a);
415   
            detail::frame_memory_resource<Allocator>>(a);
420   
        frame_alloc_ = p.get();
416   
        frame_alloc_ = p.get();
421   
        owned_ = std::move(p);
417   
        owned_ = std::move(p);
422   
    }
418   
    }
423  
419  
424   
    /** Return a pointer to this context if it matches the
420   
    /** Return a pointer to this context if it matches the
425   
        requested type.
421   
        requested type.
426  
422  
427   
        Performs a type check and downcasts `this` when the
423   
        Performs a type check and downcasts `this` when the
428   
        types match, or returns `nullptr` otherwise. Analogous
424   
        types match, or returns `nullptr` otherwise. Analogous
429   
        to `std::any_cast< ExecutionContext >( &a )`.
425   
        to `std::any_cast< ExecutionContext >( &a )`.
430  
426  
431   
        @tparam ExecutionContext The derived context type to
427   
        @tparam ExecutionContext The derived context type to
432   
            retrieve.
428   
            retrieve.
433  
429  
434   
        @return A pointer to this context as the requested
430   
        @return A pointer to this context as the requested
435   
            type, or `nullptr` if the type does not match.
431   
            type, or `nullptr` if the type does not match.
436   
    */
432   
    */
437   
    template< typename ExecutionContext >
433   
    template< typename ExecutionContext >
438   
    const ExecutionContext* target() const
434   
    const ExecutionContext* target() const
439   
    {
435   
    {
440   
        if ( ti_ && *ti_ == detail::type_id< ExecutionContext >() )
436   
        if ( ti_ && *ti_ == detail::type_id< ExecutionContext >() )
441   
           return static_cast< ExecutionContext const* >( this );
437   
           return static_cast< ExecutionContext const* >( this );
442   
        return nullptr;
438   
        return nullptr;
443   
    }
439   
    }
444  
440  
445   
    /// @copydoc target() const
441   
    /// @copydoc target() const
446   
    template< typename ExecutionContext >
442   
    template< typename ExecutionContext >
447   
    ExecutionContext* target()
443   
    ExecutionContext* target()
448   
    {
444   
    {
449   
        if ( ti_ && *ti_ == detail::type_id< ExecutionContext >() )
445   
        if ( ti_ && *ti_ == detail::type_id< ExecutionContext >() )
450   
           return static_cast< ExecutionContext* >( this );
446   
           return static_cast< ExecutionContext* >( this );
451   
        return nullptr;
447   
        return nullptr;
452   
    }
448   
    }
453  
449  
454   
protected:
450   
protected:
455   
    /** Shut down all services.
451   
    /** Shut down all services.
456  
452  
457   
        Calls `shutdown()` on each service in reverse order of creation.
453   
        Calls `shutdown()` on each service in reverse order of creation.
458   
        After this call, services remain allocated but are in a stopped
454   
        After this call, services remain allocated but are in a stopped
459   
        state. Derived classes should call this in their destructor
455   
        state. Derived classes should call this in their destructor
460   
        before any members are destroyed. This function is idempotent;
456   
        before any members are destroyed. This function is idempotent;
461   
        subsequent calls have no effect.
457   
        subsequent calls have no effect.
462  
458  
463   
        @par Effects
459   
        @par Effects
464   
        Each service's `shutdown()` member function is invoked once.
460   
        Each service's `shutdown()` member function is invoked once.
465  
461  
466   
        @par Postconditions
462   
        @par Postconditions
467   
        @li All services are in a stopped state.
463   
        @li All services are in a stopped state.
468  
464  
469   
        @par Exception Safety
465   
        @par Exception Safety
470   
        No-throw guarantee.
466   
        No-throw guarantee.
471  
467  
472   
        @par Thread Safety
468   
        @par Thread Safety
473   
        Not thread-safe. Must not be called concurrently with other
469   
        Not thread-safe. Must not be called concurrently with other
474   
        operations on this execution_context.
470   
        operations on this execution_context.
475   
    */
471   
    */
476   
    void shutdown() noexcept;
472   
    void shutdown() noexcept;
477  
473  
478   
    /** Destroy all services.
474   
    /** Destroy all services.
479  
475  
480   
        Deletes all services in reverse order of creation. Derived
476   
        Deletes all services in reverse order of creation. Derived
481   
        classes should call this as the final step of destruction.
477   
        classes should call this as the final step of destruction.
482   
        This function is idempotent; subsequent calls have no effect.
478   
        This function is idempotent; subsequent calls have no effect.
483  
479  
484   
        @par Preconditions
480   
        @par Preconditions
485   
        @li `shutdown()` has been called.
481   
        @li `shutdown()` has been called.
486  
482  
487   
        @par Effects
483   
        @par Effects
488   
        All services are deleted and removed from the container.
484   
        All services are deleted and removed from the container.
489  
485  
490   
        @par Postconditions
486   
        @par Postconditions
491   
        @li The service container is empty.
487   
        @li The service container is empty.
492  
488  
493   
        @par Exception Safety
489   
        @par Exception Safety
494   
        No-throw guarantee.
490   
        No-throw guarantee.
495  
491  
496   
        @par Thread Safety
492   
        @par Thread Safety
497   
        Not thread-safe. Must not be called concurrently with other
493   
        Not thread-safe. Must not be called concurrently with other
498   
        operations on this execution_context.
494   
        operations on this execution_context.
499   
    */
495   
    */
500   
    void destroy() noexcept;
496   
    void destroy() noexcept;
501  
497  
502   
private:
498   
private:
503   
    struct BOOST_CAPY_DECL
499   
    struct BOOST_CAPY_DECL
504   
        factory
500   
        factory
505 - 
#ifdef _MSC_VER
 
506 - 
# pragma warning(push)
 
507 - 
# pragma warning(disable: 4251)
 
508 - 
#endif
 
509   
    {
501   
    {
510   
// warning C4251: 'std::type_index' needs to have dll-interface
502   
// warning C4251: 'std::type_index' needs to have dll-interface
 
503 + 
        BOOST_CAPY_MSVC_WARNING_PUSH
 
504 + 
        BOOST_CAPY_MSVC_WARNING_DISABLE(4251)
511   
        detail::type_index t0;
505   
        detail::type_index t0;
512   
        detail::type_index t1;
506   
        detail::type_index t1;
513 - 
#ifdef _MSC_VER
507 + 
        BOOST_CAPY_MSVC_WARNING_POP
514 - 
# pragma warning(pop)
 
515 - 
#endif
 
516  
508  
517   
        factory(
509   
        factory(
518   
            detail::type_info const& t0_,
510   
            detail::type_info const& t0_,
519   
            detail::type_info const& t1_)
511   
            detail::type_info const& t1_)
520   
            : t0(t0_), t1(t1_)
512   
            : t0(t0_), t1(t1_)
521   
        {
513   
        {
522   
        }
514   
        }
523  
515  
524   
        virtual service* create(execution_context&) = 0;
516   
        virtual service* create(execution_context&) = 0;
525  
517  
526   
    protected:
518   
    protected:
527   
        ~factory() = default;
519   
        ~factory() = default;
528   
    };
520   
    };
529  
521  
530   
    service* find_impl(detail::type_index ti) const noexcept;
522   
    service* find_impl(detail::type_index ti) const noexcept;
531   
    service& use_service_impl(factory& f);
523   
    service& use_service_impl(factory& f);
532   
    service& make_service_impl(factory& f);
524   
    service& make_service_impl(factory& f);
533  
525  
534 - 
#ifdef _MSC_VER
526 + 
// warning C4251: std::mutex, std::shared_ptr need dll-interface
535 - 
# pragma warning(push)
527 + 
    BOOST_CAPY_MSVC_WARNING_PUSH
536 - 
# pragma warning(disable: 4251)
528 + 
    BOOST_CAPY_MSVC_WARNING_DISABLE(4251)
537 - 
#endif
 
538 - 
// warning C4251: 'std::type_index' needs to have dll-interface
 
539   
    mutable std::mutex mutex_;
529   
    mutable std::mutex mutex_;
540   
    std::shared_ptr<void> owned_;
530   
    std::shared_ptr<void> owned_;
541 - 
#ifdef _MSC_VER
531 + 
    BOOST_CAPY_MSVC_WARNING_POP
542 - 
# pragma warning(pop)
 
543 - 
#endif
 
544   
    std::pmr::memory_resource* frame_alloc_ = nullptr;
532   
    std::pmr::memory_resource* frame_alloc_ = nullptr;
545   
    service* head_ = nullptr;
533   
    service* head_ = nullptr;
546   
    bool shutdown_ = false;
534   
    bool shutdown_ = false;
547   
};
535   
};
548  
536  
549   
template< typename Derived >
537   
template< typename Derived >
550   
execution_context::
538   
execution_context::
551   
execution_context( Derived* ) noexcept
539   
execution_context( Derived* ) noexcept
552   
    : execution_context()
540   
    : execution_context()
553   
{
541   
{
554   
    ti_ = &detail::type_id< Derived >();
542   
    ti_ = &detail::type_id< Derived >();
555   
}
543   
}
556  
544  
557   
} // namespace capy
545   
} // namespace capy
558   
} // namespace boost
546   
} // namespace boost
559  
547  
560   
#endif
548   
#endif