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Diffstat (limited to 'lib/asio/execution_context.hpp')
| -rw-r--r-- | lib/asio/execution_context.hpp | 411 |
1 files changed, 411 insertions, 0 deletions
diff --git a/lib/asio/execution_context.hpp b/lib/asio/execution_context.hpp new file mode 100644 index 0000000..1476d19 --- /dev/null +++ b/lib/asio/execution_context.hpp @@ -0,0 +1,411 @@ +// +// execution_context.hpp +// ~~~~~~~~~~~~~~~~~~~~~ +// +// Copyright (c) 2003-2018 Christopher M. Kohlhoff (chris at kohlhoff dot com) +// +// Distributed under the Boost Software License, Version 1.0. (See accompanying +// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) +// + +#ifndef ASIO_EXECUTION_CONTEXT_HPP +#define ASIO_EXECUTION_CONTEXT_HPP + +#if defined(_MSC_VER) && (_MSC_VER >= 1200) +# pragma once +#endif // defined(_MSC_VER) && (_MSC_VER >= 1200) + +#include "asio/detail/config.hpp" +#include <cstddef> +#include <stdexcept> +#include <typeinfo> +#include "asio/detail/noncopyable.hpp" +#include "asio/detail/variadic_templates.hpp" + +#include "asio/detail/push_options.hpp" + +namespace asio { + +class execution_context; +class io_context; + +#if !defined(GENERATING_DOCUMENTATION) +template <typename Service> Service& use_service(execution_context&); +template <typename Service> Service& use_service(io_context&); +template <typename Service> void add_service(execution_context&, Service*); +template <typename Service> bool has_service(execution_context&); +#endif // !defined(GENERATING_DOCUMENTATION) + +namespace detail { class service_registry; } + +/// A context for function object execution. +/** + * An execution context represents a place where function objects will be + * executed. An @c io_context is an example of an execution context. + * + * @par The execution_context class and services + * + * Class execution_context implements an extensible, type-safe, polymorphic set + * of services, indexed by service type. + * + * Services exist to manage the resources that are shared across an execution + * context. For example, timers may be implemented in terms of a single timer + * queue, and this queue would be stored in a service. + * + * Access to the services of an execution_context is via three function + * templates, use_service(), add_service() and has_service(). + * + * In a call to @c use_service<Service>(), the type argument chooses a service, + * making available all members of the named type. If @c Service is not present + * in an execution_context, an object of type @c Service is created and added + * to the execution_context. A C++ program can check if an execution_context + * implements a particular service with the function template @c + * has_service<Service>(). + * + * Service objects may be explicitly added to an execution_context using the + * function template @c add_service<Service>(). If the @c Service is already + * present, the service_already_exists exception is thrown. If the owner of the + * service is not the same object as the execution_context parameter, the + * invalid_service_owner exception is thrown. + * + * Once a service reference is obtained from an execution_context object by + * calling use_service(), that reference remains usable as long as the owning + * execution_context object exists. + * + * All service implementations have execution_context::service as a public base + * class. Custom services may be implemented by deriving from this class and + * then added to an execution_context using the facilities described above. + * + * @par The execution_context as a base class + * + * Class execution_context may be used only as a base class for concrete + * execution context types. The @c io_context is an example of such a derived + * type. + * + * On destruction, a class that is derived from execution_context must perform + * <tt>execution_context::shutdown()</tt> followed by + * <tt>execution_context::destroy()</tt>. + * + * This destruction sequence permits programs to simplify their resource + * management by using @c shared_ptr<>. Where an object's lifetime is tied to + * the lifetime of a connection (or some other sequence of asynchronous + * operations), a @c shared_ptr to the object would be bound into the handlers + * for all asynchronous operations associated with it. This works as follows: + * + * @li When a single connection ends, all associated asynchronous operations + * complete. The corresponding handler objects are destroyed, and all @c + * shared_ptr references to the objects are destroyed. + * + * @li To shut down the whole program, the io_context function stop() is called + * to terminate any run() calls as soon as possible. The io_context destructor + * calls @c shutdown() and @c destroy() to destroy all pending handlers, + * causing all @c shared_ptr references to all connection objects to be + * destroyed. + */ +class execution_context + : private noncopyable +{ +public: + class id; + class service; + +protected: + /// Constructor. + ASIO_DECL execution_context(); + + /// Destructor. + ASIO_DECL ~execution_context(); + + /// Shuts down all services in the context. + /** + * This function is implemented as follows: + * + * @li For each service object @c svc in the execution_context set, in + * reverse order of the beginning of service object lifetime, performs @c + * svc->shutdown(). + */ + ASIO_DECL void shutdown(); + + /// Destroys all services in the context. + /** + * This function is implemented as follows: + * + * @li For each service object @c svc in the execution_context set, in + * reverse order * of the beginning of service object lifetime, performs + * <tt>delete static_cast<execution_context::service*>(svc)</tt>. + */ + ASIO_DECL void destroy(); + +public: + /// Fork-related event notifications. + enum fork_event + { + /// Notify the context that the process is about to fork. + fork_prepare, + + /// Notify the context that the process has forked and is the parent. + fork_parent, + + /// Notify the context that the process has forked and is the child. + fork_child + }; + + /// Notify the execution_context of a fork-related event. + /** + * This function is used to inform the execution_context that the process is + * about to fork, or has just forked. This allows the execution_context, and + * the services it contains, to perform any necessary housekeeping to ensure + * correct operation following a fork. + * + * This function must not be called while any other execution_context + * function, or any function associated with the execution_context's derived + * class, is being called in another thread. It is, however, safe to call + * this function from within a completion handler, provided no other thread + * is accessing the execution_context or its derived class. + * + * @param event A fork-related event. + * + * @throws asio::system_error Thrown on failure. If the notification + * fails the execution_context object should no longer be used and should be + * destroyed. + * + * @par Example + * The following code illustrates how to incorporate the notify_fork() + * function: + * @code my_execution_context.notify_fork(execution_context::fork_prepare); + * if (fork() == 0) + * { + * // This is the child process. + * my_execution_context.notify_fork(execution_context::fork_child); + * } + * else + * { + * // This is the parent process. + * my_execution_context.notify_fork(execution_context::fork_parent); + * } @endcode + * + * @note For each service object @c svc in the execution_context set, + * performs <tt>svc->notify_fork();</tt>. When processing the fork_prepare + * event, services are visited in reverse order of the beginning of service + * object lifetime. Otherwise, services are visited in order of the beginning + * of service object lifetime. + */ + ASIO_DECL void notify_fork(fork_event event); + + /// Obtain the service object corresponding to the given type. + /** + * This function is used to locate a service object that corresponds to the + * given service type. If there is no existing implementation of the service, + * then the execution_context will create a new instance of the service. + * + * @param e The execution_context object that owns the service. + * + * @return The service interface implementing the specified service type. + * Ownership of the service interface is not transferred to the caller. + */ + template <typename Service> + friend Service& use_service(execution_context& e); + + /// Obtain the service object corresponding to the given type. + /** + * This function is used to locate a service object that corresponds to the + * given service type. If there is no existing implementation of the service, + * then the io_context will create a new instance of the service. + * + * @param ioc The io_context object that owns the service. + * + * @return The service interface implementing the specified service type. + * Ownership of the service interface is not transferred to the caller. + * + * @note This overload is preserved for backwards compatibility with services + * that inherit from io_context::service. + */ + template <typename Service> + friend Service& use_service(io_context& ioc); + +#if defined(GENERATING_DOCUMENTATION) + + /// Creates a service object and adds it to the execution_context. + /** + * This function is used to add a service to the execution_context. + * + * @param e The execution_context object that owns the service. + * + * @param args Zero or more arguments to be passed to the service + * constructor. + * + * @throws asio::service_already_exists Thrown if a service of the + * given type is already present in the execution_context. + */ + template <typename Service, typename... Args> + friend Service& make_service(execution_context& e, Args&&... args); + +#elif defined(ASIO_HAS_VARIADIC_TEMPLATES) + + template <typename Service, typename... Args> + friend Service& make_service(execution_context& e, + ASIO_MOVE_ARG(Args)... args); + +#else // defined(ASIO_HAS_VARIADIC_TEMPLATES) + + template <typename Service> + friend Service& make_service(execution_context& e); + +#define ASIO_PRIVATE_MAKE_SERVICE_DEF(n) \ + template <typename Service, ASIO_VARIADIC_TPARAMS(n)> \ + friend Service& make_service(execution_context& e, \ + ASIO_VARIADIC_MOVE_PARAMS(n)); \ + /**/ + ASIO_VARIADIC_GENERATE(ASIO_PRIVATE_MAKE_SERVICE_DEF) +#undef ASIO_PRIVATE_MAKE_SERVICE_DEF + +#endif // defined(ASIO_HAS_VARIADIC_TEMPLATES) + + /// (Deprecated: Use make_service().) Add a service object to the + /// execution_context. + /** + * This function is used to add a service to the execution_context. + * + * @param e The execution_context object that owns the service. + * + * @param svc The service object. On success, ownership of the service object + * is transferred to the execution_context. When the execution_context object + * is destroyed, it will destroy the service object by performing: @code + * delete static_cast<execution_context::service*>(svc) @endcode + * + * @throws asio::service_already_exists Thrown if a service of the + * given type is already present in the execution_context. + * + * @throws asio::invalid_service_owner Thrown if the service's owning + * execution_context is not the execution_context object specified by the + * @c e parameter. + */ + template <typename Service> + friend void add_service(execution_context& e, Service* svc); + + /// Determine if an execution_context contains a specified service type. + /** + * This function is used to determine whether the execution_context contains a + * service object corresponding to the given service type. + * + * @param e The execution_context object that owns the service. + * + * @return A boolean indicating whether the execution_context contains the + * service. + */ + template <typename Service> + friend bool has_service(execution_context& e); + +private: + // The service registry. + asio::detail::service_registry* service_registry_; +}; + +/// Class used to uniquely identify a service. +class execution_context::id + : private noncopyable +{ +public: + /// Constructor. + id() {} +}; + +/// Base class for all io_context services. +class execution_context::service + : private noncopyable +{ +public: + /// Get the context object that owns the service. + execution_context& context(); + +protected: + /// Constructor. + /** + * @param owner The execution_context object that owns the service. + */ + ASIO_DECL service(execution_context& owner); + + /// Destructor. + ASIO_DECL virtual ~service(); + +private: + /// Destroy all user-defined handler objects owned by the service. + virtual void shutdown() = 0; + + /// Handle notification of a fork-related event to perform any necessary + /// housekeeping. + /** + * This function is not a pure virtual so that services only have to + * implement it if necessary. The default implementation does nothing. + */ + ASIO_DECL virtual void notify_fork( + execution_context::fork_event event); + + friend class asio::detail::service_registry; + struct key + { + key() : type_info_(0), id_(0) {} + const std::type_info* type_info_; + const execution_context::id* id_; + } key_; + + execution_context& owner_; + service* next_; +}; + +/// Exception thrown when trying to add a duplicate service to an +/// execution_context. +class service_already_exists + : public std::logic_error +{ +public: + ASIO_DECL service_already_exists(); +}; + +/// Exception thrown when trying to add a service object to an +/// execution_context where the service has a different owner. +class invalid_service_owner + : public std::logic_error +{ +public: + ASIO_DECL invalid_service_owner(); +}; + +namespace detail { + +// Special derived service id type to keep classes header-file only. +template <typename Type> +class service_id + : public execution_context::id +{ +}; + +// Special service base class to keep classes header-file only. +template <typename Type> +class execution_context_service_base + : public execution_context::service +{ +public: + static service_id<Type> id; + + // Constructor. + execution_context_service_base(execution_context& e) + : execution_context::service(e) + { + } +}; + +template <typename Type> +service_id<Type> execution_context_service_base<Type>::id; + +} // namespace detail +} // namespace asio + +#include "asio/detail/pop_options.hpp" + +#include "asio/impl/execution_context.hpp" +#if defined(ASIO_HEADER_ONLY) +# include "asio/impl/execution_context.ipp" +#endif // defined(ASIO_HEADER_ONLY) + +#endif // ASIO_EXECUTION_CONTEXT_HPP |