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-//
-// 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