boost/asio/io_service.hpp

//
// io_service.hpp
// ~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2008 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 BOOST_ASIO_IO_SERVICE_HPP
#define BOOST_ASIO_IO_SERVICE_HPP

#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)

#include <boost/asio/detail/push_options.hpp>

#include <boost/asio/detail/push_options.hpp>
#include <cstddef>
#include <stdexcept>
#include <typeinfo>
#include <boost/config.hpp>
#include <boost/throw_exception.hpp>
#include <boost/system/error_code.hpp>
#include <boost/asio/detail/pop_options.hpp>

#include <boost/asio/detail/dev_poll_reactor_fwd.hpp>
#include <boost/asio/detail/epoll_reactor_fwd.hpp>
#include <boost/asio/detail/kqueue_reactor_fwd.hpp>
#include <boost/asio/detail/noncopyable.hpp>
#include <boost/asio/detail/select_reactor_fwd.hpp>
#include <boost/asio/detail/service_registry_fwd.hpp>
#include <boost/asio/detail/signal_init.hpp>
#include <boost/asio/detail/task_io_service_fwd.hpp>
#include <boost/asio/detail/win_iocp_io_service_fwd.hpp>
#include <boost/asio/detail/winsock_init.hpp>
#include <boost/asio/detail/wrapped_handler.hpp>

namespace boost {
namespace asio {

class io_service;
template <typename Service> Service& use_service(io_service& ios);
template <typename Service> void add_service(io_service& ios, Service* svc);
template <typename Service> bool has_service(io_service& ios);

/// Provides core I/O functionality.
/**
 * The io_service class provides the core I/O functionality for users of the
 * asynchronous I/O objects, including:
 *
 * @li boost::asio::ip::tcp::socket
 * @li boost::asio::ip::tcp::acceptor
 * @li boost::asio::ip::udp::socket
 * @li boost::asio::deadline_timer.
 *
 * The io_service class also includes facilities intended for developers of
 * custom asynchronous services.
 *
 * @par Thread Safety
 * @e Distinct @e objects: Safe.@n
 * @e Shared @e objects: Safe, with the exception that calling reset() while
 * there are unfinished run(), run_one(), poll() or poll_one() calls results in
 * undefined behaviour.
 *
 * @par Concepts:
 * Dispatcher.
 *
 * @par Synchronous and asynchronous operations
 *
 * Synchronous operations on I/O objects implicitly run the io_service object
 * for an individual operation. The io_service functions run(), run_one(),
 * poll() or poll_one() must be called for the io_service to perform
 * asynchronous operations on behalf of a C++ program. Notification that an
 * asynchronous operation has completed is delivered by invocation of the
 * associated handler. Handlers are invoked only by a thread that is currently
 * calling any overload of run(), run_one(), poll() or poll_one() for the
 * io_service.
 *
 * @par Effect of exceptions thrown from handlers
 *
 * If an exception is thrown from a handler, the exception is allowed to
 * propagate through the throwing thread's invocation of run(), run_one(),
 * poll() or poll_one(). No other threads that are calling any of these
 * functions are affected. It is then the responsibility of the application to
 * catch the exception.
 *
 * After the exception has been caught, the run(), run_one(), poll() or
 * poll_one() call may be restarted @em without the need for an intervening
 * call to reset(). This allows the thread to rejoin the io_service object's
 * thread pool without impacting any other threads in the pool.
 *
 * For example:
 *
 * @code
 * boost::asio::io_service io_service;
 * ...
 * for (;;)
 * {
 *   try
 *   {
 *     io_service.run();
 *     break; // run() exited normally
 *   }
 *   catch (my_exception& e)
 *   {
 *     // Deal with exception as appropriate.
 *   }
 * }
 * @endcode
 *
 * @par Stopping the io_service from running out of work
 *
 * Some applications may need to prevent an io_service object's run() call from
 * returning when there is no more work to do. For example, the io_service may
 * be being run in a background thread that is launched prior to the
 * application's asynchronous operations. The run() call may be kept running by
 * creating an object of type boost::asio::io_service::work:
 *
 * @code boost::asio::io_service io_service;
 * boost::asio::io_service::work work(io_service);
 * ... @endcode
 *
 * To effect a shutdown, the application will then need to call the io_service
 * object's stop() member function. This will cause the io_service run() call
 * to return as soon as possible, abandoning unfinished operations and without
 * permitting ready handlers to be dispatched.
 *
 * Alternatively, if the application requires that all operations and handlers
 * be allowed to finish normally, the work object may be explicitly destroyed.
 *
 * @code boost::asio::io_service io_service;
 * auto_ptr<boost::asio::io_service::work> work(
 *     new boost::asio::io_service::work(io_service));
 * ...
 * work.reset(); // Allow run() to exit. @endcode
 *
 * @par The io_service class and I/O services
 *
 * Class io_service implements an extensible, type-safe, polymorphic set of I/O
 * services, indexed by service type. An object of class io_service must be
 * initialised before I/O objects such as sockets, resolvers and timers can be
 * used. These I/O objects are distinguished by having constructors that accept
 * an @c io_service& parameter.
 *
 * I/O services exist to manage the logical interface to the operating system on
 * behalf of the I/O objects. In particular, there are resources that are shared
 * across a class of I/O objects. For example, timers may be implemented in
 * terms of a single timer queue. The I/O services manage these shared
 * resources.
 *
 * Access to the services of an io_service 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 io_service, an object of type @c Service is created and added to the
 * io_service. A C++ program can check if an io_service implements a
 * particular service with the function template @c has_service<Service>().
 *
 * Service objects may be explicitly added to an io_service 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 io_service parameter, the invalid_service_owner
 * exception is thrown.
 *
 * Once a service reference is obtained from an io_service object by calling
 * use_service(), that reference remains usable as long as the owning io_service
 * object exists.
 *
 * All I/O service implementations have io_service::service as a public base
 * class. Custom I/O services may be implemented by deriving from this class and
 * then added to an io_service using the facilities described above.
 */
class io_service
  : private noncopyable
{
private:
  // The type of the platform-specific implementation.
#if defined(BOOST_ASIO_HAS_IOCP)
  typedef detail::win_iocp_io_service impl_type;
  friend class detail::win_iocp_overlapped_ptr;
#elif defined(BOOST_ASIO_HAS_EPOLL)
  typedef detail::task_io_service<detail::epoll_reactor<false> > impl_type;
#elif defined(BOOST_ASIO_HAS_KQUEUE)
  typedef detail::task_io_service<detail::kqueue_reactor<false> > impl_type;
#elif defined(BOOST_ASIO_HAS_DEV_POLL)
  typedef detail::task_io_service<detail::dev_poll_reactor<false> > impl_type;
#else
  typedef detail::task_io_service<detail::select_reactor<false> > impl_type;
#endif

public:
  class work;
  friend class work;

  class id;

  class service;

  class strand;

  /// Constructor.
  io_service();

  /// Constructor.
  /**
   * Construct with a hint about the required level of concurrency.
   *
   * @param concurrency_hint A suggestion to the implementation on how many
   * threads it should allow to run simultaneously.
   */
  explicit io_service(std::size_t concurrency_hint);

  /// Destructor.
  /**
   * On destruction, the io_service performs the following sequence of
   * operations:
   *
   * @li For each service object @c svc in the io_service set, in reverse order
   * of the beginning of service object lifetime, performs
   * @c svc->shutdown_service().
   *
   * @li Uninvoked handler objects that were scheduled for deferred invocation
   * on the io_service, or any associated strand, are destroyed.
   *
   * @li For each service object @c svc in the io_service set, in reverse order
   * of the beginning of service object lifetime, performs
   * <tt>delete static_cast<io_service::service*>(svc)</tt>.
   *
   * @note The destruction sequence described above 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_service function stop() is
   * called to terminate any run() calls as soon as possible. The io_service
   * destructor defined above destroys all handlers, causing all @c shared_ptr
   * references to all connection objects to be destroyed.
   */
  ~io_service();

  /// Run the io_service object's event processing loop.
  /**
   * The run() function blocks until all work has finished and there are no
   * more handlers to be dispatched, or until the io_service has been stopped.
   *
   * Multiple threads may call the run() function to set up a pool of threads
   * from which the io_service may execute handlers. All threads that are
   * waiting in the pool are equivalent and the io_service may choose any one
   * of them to invoke a handler.
   *
   * The run() function may be safely called again once it has completed only
   * after a call to reset().
   *
   * @return The number of handlers that were executed.
   *
   * @throws boost::system::system_error Thrown on failure.
   *
   * @note The run() function must not be called from a thread that is currently
   * calling one of run(), run_one(), poll() or poll_one() on the same
   * io_service object.
   *
   * The poll() function may also be used to dispatch ready handlers, but
   * without blocking.
   */
  std::size_t run();

  /// Run the io_service object's event processing loop.
  /**
   * The run() function blocks until all work has finished and there are no
   * more handlers to be dispatched, or until the io_service has been stopped.
   *
   * Multiple threads may call the run() function to set up a pool of threads
   * from which the io_service may execute handlers. All threads that are
   * waiting in the pool are equivalent and the io_service may choose any one
   * of them to invoke a handler.
   *
   * The run() function may be safely called again once it has completed only
   * after a call to reset().
   *
   * @param ec Set to indicate what error occurred, if any.
   *
   * @return The number of handlers that were executed.
   *
   * @note The run() function must not be called from a thread that is currently
   * calling one of run(), run_one(), poll() or poll_one() on the same
   * io_service object.
   *
   * The poll() function may also be used to dispatch ready handlers, but
   * without blocking.
   */
  std::size_t run(boost::system::error_code& ec);

  /// Run the io_service object's event processing loop to execute at most one
  /// handler.
  /**
   * The run_one() function blocks until one handler has been dispatched, or
   * until the io_service has been stopped.
   *
   * @return The number of handlers that were executed.
   *
   * @throws boost::system::system_error Thrown on failure.
   */
  std::size_t run_one();

  /// Run the io_service object's event processing loop to execute at most one
  /// handler.
  /**
   * The run_one() function blocks until one handler has been dispatched, or
   * until the io_service has been stopped.
   *
   * @param ec Set to indicate what error occurred, if any.
   *
   * @return The number of handlers that were executed.
   */
  std::size_t run_one(boost::system::error_code& ec);

  /// Run the io_service object's event processing loop to execute ready
  /// handlers.
  /**
   * The poll() function runs handlers that are ready to run, without blocking,
   * until the io_service has been stopped or there are no more ready handlers.
   *
   * @return The number of handlers that were executed.
   *
   * @throws boost::system::system_error Thrown on failure.
   */
  std::size_t poll();

  /// Run the io_service object's event processing loop to execute ready
  /// handlers.
  /**
   * The poll() function runs handlers that are ready to run, without blocking,
   * until the io_service has been stopped or there are no more ready handlers.
   *
   * @param ec Set to indicate what error occurred, if any.
   *
   * @return The number of handlers that were executed.
   */
  std::size_t poll(boost::system::error_code& ec);

  /// Run the io_service object's event processing loop to execute one ready
  /// handler.
  /**
   * The poll_one() function runs at most one handler that is ready to run,
   * without blocking.
   *
   * @return The number of handlers that were executed.
   *
   * @throws boost::system::system_error Thrown on failure.
   */
  std::size_t poll_one();

  /// Run the io_service object's event processing loop to execute one ready
  /// handler.
  /**
   * The poll_one() function runs at most one handler that is ready to run,
   * without blocking.
   *
   * @param ec Set to indicate what error occurred, if any.
   *
   * @return The number of handlers that were executed.
   */
  std::size_t poll_one(boost::system::error_code& ec);

  /// Stop the io_service object's event processing loop.
  /**
   * This function does not block, but instead simply signals the io_service to
   * stop. All invocations of its run() or run_one() member functions should
   * return as soon as possible. Subsequent calls to run(), run_one(), poll()
   * or poll_one() will return immediately until reset() is called.
   */
  void stop();

  /// Reset the io_service in preparation for a subsequent run() invocation.
  /**
   * This function must be called prior to any second or later set of
   * invocations of the run(), run_one(), poll() or poll_one() functions when a
   * previous invocation of these functions returned due to the io_service
   * being stopped or running out of work. This function allows the io_service
   * to reset any internal state, such as a "stopped" flag.
   *
   * This function must not be called while there are any unfinished calls to
   * the run(), run_one(), poll() or poll_one() functions.
   */
  void reset();

  /// Request the io_service to invoke the given handler.
  /**
   * This function is used to ask the io_service to execute the given handler.
   *
   * The io_service guarantees that the handler will only be called in a thread
   * in which the run(), run_one(), poll() or poll_one() member functions is
   * currently being invoked. The handler may be executed inside this function
   * if the guarantee can be met.
   *
   * @param handler The handler to be called. The io_service will make
   * a copy of the handler object as required. The function signature of the
   * handler must be: @code void handler(); @endcode
   */
  template <typename CompletionHandler>
  void dispatch(CompletionHandler handler);

  /// Request the io_service to invoke the given handler and return immediately.
  /**
   * This function is used to ask the io_service to execute the given handler,
   * but without allowing the io_service to call the handler from inside this
   * function.
   *
   * The io_service guarantees that the handler will only be called in a thread
   * in which the run(), run_one(), poll() or poll_one() member functions is
   * currently being invoked.
   *
   * @param handler The handler to be called. The io_service will make
   * a copy of the handler object as required. The function signature of the
   * handler must be: @code void handler(); @endcode
   */
  template <typename CompletionHandler>
  void post(CompletionHandler handler);

  /// Create a new handler that automatically dispatches the wrapped handler
  /// on the io_service.
  /**
   * This function is used to create a new handler function object that, when
   * invoked, will automatically pass the wrapped handler to the io_service
   * object's dispatch function.
   *
   * @param handler The handler to be wrapped. The io_service will make a copy
   * of the handler object as required. The function signature of the handler
   * must be: @code void handler(A1 a1, ... An an); @endcode
   *
   * @return A function object that, when invoked, passes the wrapped handler to
   * the io_service object's dispatch function. Given a function object with the
   * signature:
   * @code R f(A1 a1, ... An an); @endcode
   * If this function object is passed to the wrap function like so:
   * @code io_service.wrap(f); @endcode
   * then the return value is a function object with the signature
   * @code void g(A1 a1, ... An an); @endcode
   * that, when invoked, executes code equivalent to:
   * @code io_service.dispatch(boost::bind(f, a1, ... an)); @endcode
   */
  template <typename Handler>
#if defined(GENERATING_DOCUMENTATION)
  unspecified
#else
  detail::wrapped_handler<io_service&, Handler>
#endif
  wrap(Handler handler);

  /// 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_service will create a new instance of the service.
   *
   * @param ios The io_service 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(io_service& ios);

  /// Add a service object to the io_service.
  /**
   * This function is used to add a service to the io_service.
   *
   * @param ios The io_service object that owns the service.
   *
   * @param svc The service object. On success, ownership of the service object
   * is transferred to the io_service. When the io_service object is destroyed,
   * it will destroy the service object by performing:
   * @code delete static_cast<io_service::service*>(svc) @endcode
   *
   * @throws boost::asio::service_already_exists Thrown if a service of the
   * given type is already present in the io_service.
   *
   * @throws boost::asio::invalid_service_owner Thrown if the service's owning
   * io_service is not the io_service object specified by the ios parameter.
   */
  template <typename Service>
  friend void add_service(io_service& ios, Service* svc);

  /// Determine if an io_service contains a specified service type.
  /**
   * This function is used to determine whether the io_service contains a
   * service object corresponding to the given service type.
   *
   * @param ios The io_service object that owns the service.
   *
   * @return A boolean indicating whether the io_service contains the service.
   */
  template <typename Service>
  friend bool has_service(io_service& ios);

private:
#if defined(BOOST_WINDOWS) || defined(__CYGWIN__)
  detail::winsock_init<> init_;
#elif defined(__sun) || defined(__QNX__) || defined(__hpux) || defined(_AIX) \
  || defined(__osf__)
  detail::signal_init<> init_;
#endif

  // The service registry.
  boost::asio::detail::service_registry* service_registry_;

  // The implementation.
  impl_type& impl_;
};

/// Class to inform the io_service when it has work to do.
/**
 * The work class is used to inform the io_service when work starts and
 * finishes. This ensures that the io_service object's run() function will not
 * exit while work is underway, and that it does exit when there is no
 * unfinished work remaining.
 *
 * The work class is copy-constructible so that it may be used as a data member
 * in a handler class. It is not assignable.
 */
class io_service::work
{
public:
  /// Constructor notifies the io_service that work is starting.
  /**
   * The constructor is used to inform the io_service that some work has begun.
   * This ensures that the io_service object's run() function will not exit
   * while the work is underway.
   */
  explicit work(boost::asio::io_service& io_service);

  /// Copy constructor notifies the io_service that work is starting.
  /**
   * The constructor is used to inform the io_service that some work has begun.
   * This ensures that the io_service object's run() function will not exit
   * while the work is underway.
   */
  work(const work& other);

  /// Destructor notifies the io_service that the work is complete.
  /**
   * The destructor is used to inform the io_service that some work has
   * finished. Once the count of unfinished work reaches zero, the io_service
   * object's run() function is permitted to exit.
   */
  ~work();

  /// (Deprecated: use get_io_service().) Get the io_service associated with the
  /// work.
  boost::asio::io_service& io_service();

  /// Get the io_service associated with the work.
  boost::asio::io_service& get_io_service();

private:
  // Prevent assignment.
  void operator=(const work& other);

  // The io_service.
  boost::asio::io_service& io_service_;
};

/// Class used to uniquely identify a service.
class io_service::id
  : private noncopyable
{
public:
  /// Constructor.
  id() {}
};

/// Base class for all io_service services.
class io_service::service
  : private noncopyable
{
public:
  /// (Deprecated: use get_io_service().) Get the io_service object that owns
  /// the service.
  boost::asio::io_service& io_service();

  /// Get the io_service object that owns the service.
  boost::asio::io_service& get_io_service();

protected:
  /// Constructor.
  /**
   * @param owner The io_service object that owns the service.
   */
  service(boost::asio::io_service& owner);

  /// Destructor.
  virtual ~service();

private:
  /// Destroy all user-defined handler objects owned by the service.
  virtual void shutdown_service() = 0;

  friend class boost::asio::detail::service_registry;
  boost::asio::io_service& owner_;
  const std::type_info* type_info_;
  const boost::asio::io_service::id* id_;
  service* next_;
};

/// Exception thrown when trying to add a duplicate service to an io_service.
class service_already_exists
  : public std::logic_error
{
public:
  service_already_exists()
    : std::logic_error("Service already exists.")
  {
  }
};

/// Exception thrown when trying to add a service object to an io_service where
/// the service has a different owner.
class invalid_service_owner
  : public std::logic_error
{
public:
  invalid_service_owner()
    : std::logic_error("Invalid service owner.")
  {
  }
};

} // namespace asio
} // namespace boost

#include <boost/asio/impl/io_service.ipp>

#include <boost/asio/detail/pop_options.hpp>

#endif // BOOST_ASIO_IO_SERVICE_HPP