[software/eventxx.git] / eventxx

#ifndef _EVENTXX_HPP_
#define _EVENTXX_HPP_

#include <sys/types.h> // timeval
#include <stdexcept>   // std::exception, std::invalid_argument,
                       // std::runtime_error, std::bad_alloc

/** @mainpage
 *
 * @section Introduction
 *
 * @libevent is a popular API that provides a mechanism to execute a callback
 * function when a specific event occurs on a file descriptor or after a
 * timeout has been reached. Furthermore, @libevent also support callbacks due
 * to signals or regular timeouts.
 *
 * @eventxx is a simple, direct, one-header inline C++ wrapper for @libevent.
 * Yes, it's just one header file, so if you want to use it you can just copy
 * the file to your project and you are set (well, you'll need to link to
 * @libevent too ;). I know @eventxx will work with @libevent 1.1 and 1.2 if you
 * use the @c event_base_free() fix (see \ref Status section for more details).
 *
 * It's designed to be as close to use to @libevent (without compromising
 * modern C++ programming techniques) and efficient (since all implementation
 * is trivial and inline, theoretically, it imposes no overhead at all) as
 * possible.
 *
 * Please, visit the @eventxx website for the latest version of this
 * documentation.
 *
 * You can always get the <a
 * href="http://www.llucax.com.ar/~luca/eventxx/releases/eventxx.tar.gz">current
 * release</a> from the
 * <a href="http://www.llucax.com.ar/~luca/eventxx/releases/">release
 * directory</a> or grab the
 * <a href="http://www.llucax.com.ar/~luca/repos/eventxx/">most up to date
 * sources</a> from the <a href="http://www.darcs.net/">darcs</a> repository.
 *
 * You can also take a look the the <a
 * href="http://auriga.wearlab.de/~alb/darcsweb/">darcsweb</a> interface to see
 * the <a href="http://www.llucax.com.ar/~luca/repos/darcsweb/?r=eventxx">latest
 * changes online</a> or subscribe to its
 * <a href="http://www.llucax.com.ar/~luca/repos/darcsweb/?r=eventxx;a=rss">RSS
 * feed</a> to follow the development.
 *
 *
 * @section Usage
 *
 * You probably should read @libevent documentation to get started or at least
 * just for reference, although @eventxx is pretty simple so you can jump right
 * into the \ref Example section (or the example list) and write a working
 * program without much trouble.
 *
 * This wrapper was designed to be used just like @libevent, but with C++ style
 * syntax sugar (or poison, depends on your point of view ;) and goodies. The
 * main difference to libevent is you always have to instance a
 * eventxx::dispatcher to get an event loop. There is no implicit global event
 * loop. This adds just an extra line of code for single threaded applications
 * and makes things much more simpler, so I hope nobody complains about it ;).
 * See eventxx::dispatcher documentation for more details.
 *
 * You can use use the same plain functions callbacks @libevent use or the other
 * kind of function objects (see @ref events section for details on event
 * types).
 *
 * @eventxx uses @ref exceptions to report errors. All functions have exception
 * specifications, so it's easy to find out what to expect. See @ref exceptions
 * section for more detail.
 *
 * A @c timespec abstraction is provided as eventxx::time for convenient
 * argument passing. Even more, it's a @c timespec itself, with some convenient
 * methods for accessing the attributes with pritier names. And even more,
 * @eventxx is such a direct mapping that all eventxx::event's are @libevent
 * event structs too, so theoretically you can pass a eventxx::event to
 * @libevent C functions without much trouble. eventxx::dispatcher is the only
 * class that is not derived from @libevent struct (@c event_base) because this
 * struct it's not defined on the libevent header (just declared).
 *
 * Maybe you shouldn't know this implementation details to keep the abstraction,
 * but this is a basic design goal of this wrapper so there is not much chance
 * that this changes in the future (but use this knowledge with care, you have
 * been  warned ;).
 *
 *
 * @section Example
 *
 * @code
 * #include <eventxx>
 * #include <iostream>
 * #include <csignal>
 *
 * struct handler
 * {
 *      eventxx::dispatcher& d;
 *      int i;
 *      handler(eventxx::dispatcher& d): d(d), i(0) {}
 *      void operator() (int signum, eventxx::type event)
 *      {
 *              if (i < 5) std::cout << "keep going...\n";
 *              else
 *              {
 *                      std::cout << "done!\n";
 *                      d.exit();
 *              }
 *      }
 * };
 *
 * void sighandler(int signum, short event, void* data)
 * {
 *      int& i = *static_cast< int* >(data);
 *      std::cout << ++i << " interrupts, ";
 * }
 *
 * int main()
 * {
 *      eventxx::dispatcher d;
 *      handler h(d);
 *      eventxx::csignal sigev(SIGINT, sighandler, &h.i);
 *      eventxx::signal< handler > e(SIGINT, h);
 *      d.add(sigev);
 *      d.add(e);
 *      d.dispatch();
 *      return 0;
 * }
 * @endcode
 *
 * You can see more examples on the test directory of the distribution or on the
 * examples related page.
 *
 *
 * @section Status
 *
 * This library has not been widely used yet, so it lacks proper testing.
 * Because templates are not even compiled when they are not used, don't be
 * surprised if you catch a piece of code that doesn't compile. The library
 * has no support for buffered events yet. It doesn't support the HTTP stuff,
 * and probably never will because that has nothing to do with event handling.
 *
 * If you notice that when using @eventxx your program leaks some memory, don't
 * blame me, blame @libevent :) @libevent has a known bug on @c event_base_free()
 * that makes it assert always, so @c event_base_free() is unusable, unless you
 * patch your libevent (for example, using this <a
 * href="http://monkeymail.org/archives/libevent-users/2006-April/000141.html">patch</a>
 * written by Mark D. Anderson, and who knows why it's not still applied). If
 * you do so, you can compile your programs with @c -DEVENT_BASE_FREE_FIX so
 * @c event_base_free() gets called in the eventxx::dispatcher @link
 * eventxx::dispatcher::~dispatcher() destructor @endlink.
 *
 * That said, I think it's still pretty usable anyways. If something is broken
 * it would be really easy to fix because @eventxx is just a simple wrapper
 * around @libevent. So, please try it out, and if you have any problems,
 * <a href="mailto:llucax+eventxx@gmail.com">drop me an
 * e-mail</a> and and I'll fix it ASAP (or provide a patch and you will be my
 * best friend ;).
 *
 * Patches to support buffered events are welcome too.
 *
 *
 * @author Leandro Lucarella <llucax+eventxx@gmail.com>
 *
 * @version 0.4
 *
 * @par License
 * This program is under the BOLA license (see
 * http://auriga.wearlab.de/~alb/bola/ for more details or read the
 * <a href="http://www.llucax.com.ar/~luca/repos/eventxx/LICENSE">LICENSE</a>
 * file itself, it's very short and it basically says it's Public Domain).
 *
 */

/** @example c-way.cpp
 *
 * This is a simple example illustrating the usage with C-like callback
 * functions.
 */

/** @example functor-way.cpp
 *
 * This is a simple example illustrating the usage with function object
 * callbacks.
 */

/** @example wrapped-functor-way.cpp
 *
 * This is a simple example illustrating the usage with an arbitrary member
 * function as an event handler callbacks.
 */

/** @example mixed-way.cpp
 *
 * This is a simple example illustrating the usage with a mix of C-like callbacks
 * and function object callbacks.
 */

/** @example bench.cpp
 *
 * This is a benchmark example, extracted from libevent and ported to eventxx.
 */

/** @example prio-test.cpp
 *
 * This is a priority usage example.
 */

/** @example test-time.cpp
 *
 * This is a timer usage example ported from libevent.
 */

/** @example test-eof.cpp
 *
 * This is some kind of test of EOF ported from libevent.
 */

/** @example test-weof.cpp
 *
 * Another test of EOF ported from libevent.
 */

/** @example trivial.cpp
 *
 * This is the most trivial example.
 */

/**
 * Namespace for all symbols libevent C++ wrapper defines.
 */
namespace eventxx
{


// All libevent C API symbols and other internal stuff goes here.
namespace internal
{
#include <event.h>
}


/** @defgroup exceptions Exceptions
 *
 * eventxx makes a heavy use of exceptions. Each function has it's exceptions
 * specified, so it's very easy to find out what exceptions to expect.
 *
 * Exceptions are mostly thrown when there is a programming error. So if you get
 * an exception check your code.
 */
//@{


/**
 * Base class for all libevent exceptions.
 */
struct exception: public std::exception
{
};


/**
 * Invalid event exception.
 *
 * This exception is thrown when passing an invalid event to a function, the
 * reason is given in the what() description but it usually means that the you
 * are making some restricted operation with an active event.
 *
 * If you hit this exception, you probably got a programming error.
 */
struct invalid_event: public std::invalid_argument, public exception
{

        /**
         * Creates an invalid event exception with a reason.
         *
         * @param what Reason why the event is invalid).
         */
        explicit invalid_event(const std::string& what) throw():
                std::invalid_argument(what)
        {
        }

}; // struct invalid_event


/**
 * Invalid priority exception.
 *
 * This exception is thrown when passing an invalid priority to a function. This
 * usually means you don't have enough priority queues in your dispatcher, so
 * you should have allocated more in the constructor.
 *
 * If you hit this exception, you probably got a programming error.
 *
 * @see dispatcher::dispatcher(int) to allocate more priority queues.
 */
struct invalid_priority: public std::invalid_argument, public exception
{

        /**
         * Creates an invalid priority exception with a reason.
         *
         * @param what Reason why the priority is invalid).
         */
        explicit invalid_priority(const std::string& what
                        = "invalid priority value") throw():
                std::invalid_argument(what)
        {
        }

}; // struct invalid_priority

//@}


/// Miscellaneous constants
enum
{
        DEFAULT_PRIORITY = -1,      ///< Default priority (the middle value).
        ONCE = EVLOOP_ONCE,         ///< Loop just once.
        NONBLOCK = EVLOOP_NONBLOCK  ///< Don't block the event loop.
};


/**
 * Time used for timeout values.
 *
 * This timeout is compose of seconds and microseconds.
 */
struct time: ::timeval
{

        /**
         * Creates a new time with @p sec seconds and @p usec microseconds.
         *
         * @param sec Number of seconds.
         * @param usec Number of microseconds.
         */
        time(long sec = 0l, long usec = 0l) throw()
                { tv_sec = sec; tv_usec = usec; }

        /**
         * Gets the number of seconds.
         *
         * @return Number of seconds.
         */
        long sec() const throw() { return tv_sec; };

        /**
         * Gets the number of microseconds.
         *
         * @return Number of microseconds.
         */
        long usec() const throw() { return tv_usec; };

        /**
         * Sets the number of seconds.
         *
         * @param s Number of seconds.
         */
        void sec(long s) throw() { tv_sec = s; };

        /**
         * Sets the number of microseconds.
         *
         * @param u Number of microseconds.
         */
        void usec(long u) throw() { tv_usec = u; };

}; // struct time


/** @defgroup events Events
 *
 * There are many ways to specify how to handle an event. You can use use the
 * same plain functions callbacks (see eventxx::cevent, eventxx::ctimer and
 * eventxx::csignal) like in C or the other kind of more advanced, stateful
 * function objects (see eventxx::event, eventxx::timer and eventxx::signal
 * templates). The former are just typedef'ed specialization of the later.
 *
 * A member function wrapper functor (eventxx::mem_cb) is also included,
 * so you can use any member function (method) as an event handler.
 *
 * Please note that C-like function callback take a short as the type of event,
 * while functors (or member functions) use eventxx::type.
 *
 * All events derive from a plain class (not template) eventxx::basic_event, one
 * of the main utilities of it (besides containing common code ;) is to be used
 * in STL containers.
 *
 * Please see each class documentation for details and examples.
 */
//@{


/// C function used as callback in the C API.
typedef void (*ccallback_type)(int, short, void*);


/**
 * Type of events.
 *
 * There are 4 kind of events: eventxx::TIMEOUT, eventxx::READ, eventxx::WRITE
 * or eventxx::SIGNAL. eventxx::PERSIST is not an event, is an event modifier
 * flag, that tells eventxx that this event should live until dispatcher::del()
 * is called. You can use, for example:
 * @code
 * eventxx::event(fd, eventxx::READ | eventxx::PERSIST, ...);
 * @endcode
 */
enum type
{
        TIMEOUT = EV_TIMEOUT, ///< Timeout event.
        READ = EV_READ,       ///< Read event.
        WRITE = EV_WRITE,     ///< Write event.
        SIGNAL = EV_SIGNAL,   ///< Signal event.
        PERSIST = EV_PERSIST  ///< Not really an event, is an event modifier.
};

inline
type operator| (const type& t1, const type& t2)
{
        int r = static_cast< int >(t1) | static_cast< int >(t2);
        return *reinterpret_cast< type* >(&r);
}


/**
 * Basic event from which all events derive.
 *
 * All events derive from this class, so it's useful for use in containers,
 * like:
 * @code
 * std::list< eventxx::basic_event* > events;
 * @endcode
 */
struct basic_event: internal::event
{

        /**
         * Checks if there is an event pending.
         *
         * @param ev Type of event to check.
         *
         * @return true if there is a pending event, false if not.
         */
        bool pending(type ev) const throw()
        {
                // HACK libevent don't use const
                return event_pending(const_cast< basic_event* >(this), ev, 0);
        }

        /**
         * Timeout of the event.
         *
         * @return Timeout of the event.
         */
        time timeout() const throw()
        {
                time tv;
                // HACK libevent don't use const
                event_pending(const_cast< basic_event* >(this), EV_TIMEOUT, &tv);
                return tv;
        }

        /**
         * Sets the event's priority.
         *
         * @param priority New event priority.
         *
         * @pre The event must be added to some dispatcher.
         *
         * @see dispatcher::dispatcher(int)
         */
        void priority(int priority) const throw(invalid_event, invalid_priority)
        {
                if (ev_flags & EVLIST_ACTIVE)
                        throw invalid_event("can't change the priority of an "
                                        "active event");
                // HACK libevent don't use const
                if (event_priority_set(const_cast< basic_event* >(this),
                                        priority))
                        throw invalid_priority();
        }

        /**
         * Event's file descriptor.
         *
         * @return Event's file descriptor.
         */
        int fd() const throw()
        {
                return EVENT_FD(this);
        }

        /// @note This is an abstract class, you can't instantiate it.
        protected:
                basic_event() throw() {}
                basic_event(const basic_event&);
                basic_event& operator= (const basic_event&);

}; // struct basic_event


/**
 * Generic event object.
 *
 * This object stores all the information about an event, including a callback
 * functor, which is called when the event is fired. The template parameter
 * must be a functor (callable object or function) that can take 2 parameters:
 * an integer (the file descriptor of the fired event) and an event::type (the
 * type of event being fired).
 * There is a specialized version of this class which takes as the template
 * parameter a C function with the eventxx::ccallback_type signature, just like
 * C @libevent API does.
 *
 * @see eventxx::event< ccallback_type >
 */
template < typename F >
struct event: basic_event
{

        /**
         * Creates a new event.
         *
         * @param fd File descriptor to monitor for events.
         * @param ev Type of events to monitor (see eventxx::type).
         * @param handler Callback functor.
         */
        event(int fd, type ev, F& handler) throw()
        {
                event_set(this, fd, static_cast< short >(ev), &wrapper,
                                reinterpret_cast< void* >(&handler));
        }

        protected:
                event() {}
                static void wrapper(int fd, short ev, void* h)
                {
                        F& handler = *reinterpret_cast< F* >(h);
                        // Hackish, but this way the handler can get a clean
                        // event type
                        handler(fd, *reinterpret_cast< type* >(&ev));
                }

}; // struct event< F >


/**
 * This is the specialization of eventxx::event for C-style callbacks.
 *
 * @see eventxx::event
 */
template <>
struct event< ccallback_type >: basic_event
{

        /**
         * Creates a new event.
         *
         * @param fd File descriptor to monitor for events.
         * @param ev Type of events to monitor (see eventxx::type).
         * @param handler C-style callback function.
         * @param arg Arbitrary pointer to pass to the handler as argument.
         */
        event(int fd, type ev, ccallback_type handler, void* arg = 0) throw()
        {
                event_set(this, fd, static_cast< short >(ev), handler, arg);
        }

        protected:
                event() {}

}; // struct event< ccallback_type >


/**
 * Timer event object.
 *
 * This is just a special case of event that is fired only when a timeout is
 * reached. It's just a shortcut to:
 * @code
 * event(-1, 0, handler);
 * @endcode
 *
 * @note This event can't eventxx::PERSIST.
 * @see timer< ccallback_type >
 */
template < typename F >
struct timer: event< F >
{

        /**
         * Creates a new timer event.
         *
         * @param handler Callback functor.
         */
        timer(F& handler) throw()
        {
                evtimer_set(this, &event< F >::wrapper,
                        reinterpret_cast< void* >(&handler));
        }

}; // struct timer< F >


/**
 * This is the specialization of eventxx::timer for C-style callbacks.
 *
 * @note This event can't eventxx::PERSIST.
 * @see timer
 */
template <>
struct timer< ccallback_type >: event< ccallback_type >
{

        /**
         * Creates a new timer event.
         *
         * @param handler C-style callback function.
         * @param arg Arbitrary pointer to pass to the handler as argument.
         */
        timer(ccallback_type handler, void* arg = 0) throw()
        {
                evtimer_set(this, handler, arg);
        }

}; // struct timer< ccallback_type >


/**
 * Signal event object.
 *
 * This is just a special case of event that is fired when a signal is raised
 * (instead of a file descriptor being active). It's just a shortcut to:
 * @code
 * event(signum, eventxx::SIGNAL, handler);
 * @endcode
 *
 * @note This event always eventxx::PERSIST.
 * @see signal< ccallback_type >
 */
template < typename F >
struct signal: event< F >
{

        /**
         * Creates a new signal event.
         *
         * @param signum Signal number to monitor.
         * @param handler Callback functor.
         */
        signal(int signum, F& handler) throw()
        {
                signal_set(this, signum, &event< F >::wrapper,
                        reinterpret_cast< void* >(&handler));
        }

        /**
         * Event's signal number.
         *
         * @return Event's signal number.
         */
        int signum() const
        {
                return EVENT_SIGNAL(this);
        }

}; // struct signal<F>


/**
 * This is the specialization of eventxx::signal for C-style callbacks.
 *
 * @note This event always eventxx::PERSIST.
 * @see signal
 */
template <>
struct signal< ccallback_type >: event< ccallback_type >
{

        /**
         * Creates a new signal event.
         *
         * @param signum Signal number to monitor.
         * @param handler C-style callback function.
         * @param arg Arbitrary pointer to pass to the handler as argument.
         */
        signal(int signum, ccallback_type handler, void* arg = 0) throw()
        {
                signal_set(this, signum, handler, arg);
        }

        /**
         * Event's signal number.
         *
         * @return Event's signal number.
         */
        int signum() const
        {
                return EVENT_SIGNAL(this);
        }

}; // struct signal< ccallback_type >


/// Shortcut to C-style event.
typedef eventxx::event< ccallback_type > cevent;

/// Shortcut to C-style timer.
typedef eventxx::timer< ccallback_type > ctimer;

/// Shortcut to C-style signal handler.
typedef eventxx::signal< ccallback_type > csignal;

/**
 * Helper functor to use an arbitrary member function as an event handler.
 *
 * With this wrapper, you can use any object method, which accepts the right
 * parameters (int, short) and returns void, as an event handler. This way you
 * don't have to overload the operator() which can be confusing depending on the
 * context.
 *
 * You can see an usage example in the Examples Section.
 */
template < typename O, typename M >
struct mem_cb
{

        /**
         * Member function callback constructor.
         *
         * It expects to receive a class as the first parameter (O), and a
         * member function (of that class O) as the second parameter.
         *
         * When this instance is called with fd and ev as function arguments,
         * object.method(fd, ev) will be called.
         *
         * @param object Object to be used.
         * @param method Method to be called.
         */
        mem_cb(O& object, M method) throw():
                _object(object), _method(method) {}

        void operator() (int fd, type ev) { (_object.*_method)(fd, ev); }
        protected:
                O& _object;
                M _method;

}; // struct mem_cb

//@}


/**
 * Event dispatcher.
 *
 * This class is the responsible for looping and dispatching events. Every time
 * you need an event loop you should create an instance of this class.
 *
 * You can @link dispatcher::add add @endlink events to the dispatcher, and you
 * can @link dispatcher::del remove @endlink them later or you can @link
 * dispatcher::add_once add events to be processed just once @endlink. You can
 * @link dispatcher::dispatch loop once or forever @endlink (well, of course you
 * can break that forever removing all the events or by @link dispatcher::exit
 * exiting the loop @endlink).
 */
struct dispatcher
{

        /**
         * Creates a default dispatcher (with just 1 priority).
         *
         * @see dispatcher(int) if you want to create a dispatcher with more
         *      priorities.
         */
        dispatcher() throw()
        {
                _event_base = static_cast< internal::event_base* >(
                                internal::event_init());
        }

        /**
         * Creates a dispatcher with npriorities priorities.
         *
         * @param npriorities Number of priority queues to use.
         */
        dispatcher(int npriorities) throw(std::bad_alloc)
        {
                _event_base = static_cast< internal::event_base* >(
                                internal::event_init());
                if (!_event_base) throw std::bad_alloc();
                // Can't fail because there is no way that it has active events
                internal::event_base_priority_init(_event_base, npriorities);
        }

#ifdef EVENT_BASE_FREE_FIX
        /// Free dispatcher resources, see @ref Status section for details.
        ~dispatcher() throw() { event_base_free(_event_base); }
#else
#warning "The dispatcher class *will* leak memory because of a libevent bug, " \
    "see http://www.mail-archive.com/libevent-users@monkey.org/msg00110.html " \
    "for more info an a patch. If you already have this patch, please " \
    "-DEVENT_BASE_FREE_FIX to your compiler to make this message disappear " \
    "and really free the dispatcher memory using event_base_free()."
#endif

        /**
         * Adds an event to the dispatcher.
         *
         * @param e Event to add.
         * @param priority Priority of the event.
         */
        void add(basic_event& e, int priority = DEFAULT_PRIORITY)
                throw(invalid_priority)
        {
                internal::event_base_set(_event_base, &e);
                if (priority != DEFAULT_PRIORITY
                                && internal::event_priority_set(&e, priority))
                        throw invalid_priority();
                internal::event_add(&e, 0);
        }

        /**
         * Adds an event to the dispatcher with a timeout.
         *
         * The event is fired when there is activity on e or when to has elapsed,
         * whatever come first.
         *
         * @param e Event to add.
         * @param to Timeout.
         * @param priority Priority of the event.
         */
        void add(basic_event& e, const time& to,
                        int priority = DEFAULT_PRIORITY)
                throw(invalid_priority)
        {
                internal::event_base_set(_event_base, &e);
                if (priority != DEFAULT_PRIORITY
                                && internal::event_priority_set(&e, priority))
                        throw invalid_priority();
                // XXX HACK libevent don't use const
                internal::event_add(&e, const_cast< time* >(&to));
        }

        /**
         * Adds a temporary event.
         *
         * Adds a temporary event, without the need of instantiating a new event
         * object. Events added this way can't eventxx::PERSIST.
         *
         * @param fd File descriptor to monitor for events.
         * @param ev Type of events to monitor.
         * @param handler Callback function.
         */
        template < typename F >
        void add_once(int fd, type ev, F& handler)
        {
                internal::event_once(fd, static_cast< short>(ev),
                        &dispatcher::wrapper< F >,
                        reinterpret_cast< void* >(&handler), 0);
        }

        /**
         * Adds a temporary event to with a C-style callback.
         *
         * Adds a temporary event, without the need of instantiating a new event
         * object. Events added this way can't eventxx::PERSIST.
         *
         * @param fd File descriptor to monitor for events.
         * @param ev Type of events to monitor.
         * @param handler Callback function.
         * @param arg Arbitrary pointer to pass to the handler as argument.
         */
        void add_once(int fd, type ev, ccallback_type handler, void* arg)
        {
                internal::event_once(fd, static_cast< short >(ev), handler,
                        arg, 0);
        }

        /**
         * Adds a temporary event.
         *
         * Adds a temporary event, without the need of instantiating a new event
         * object. Events added this way can't eventxx::PERSIST.
         *
         * @param fd File descriptor to monitor for events.
         * @param ev Type of events to monitor.
         * @param handler Callback function.
         * @param to Timeout.
         */
        template < typename F >
        void add_once(int fd, type ev, F& handler, const time& to)
        {
                internal::event_once(fd, static_cast< short >(ev),
                        &dispatcher::wrapper< F >,
                        reinterpret_cast< void* >(&handler),
                        // XXX HACK libevent don't use const
                        const_cast< time* >(&to));
        }

        /**
         * Adds a temporary event with a C-style callback.
         *
         * Adds a temporary event, without the need of instantiating a new event
         * object. Events added this way can't eventxx::PERSIST.
         *
         * @param fd File descriptor to monitor for events.
         * @param ev Type of events to monitor.
         * @param handler Callback function.
         * @param arg Arbitrary pointer to pass to the handler as argument.
         * @param to Timeout.
         */
        void add_once(int fd, type ev, ccallback_type handler, void* arg,
                        const time& to)
        {
                internal::event_once(fd, static_cast< short >(ev), handler, arg,
                                // XXX HACK libevent don't use const
                                const_cast< time* >(&to));
        }

        /**
         * Adds a temporary timer.
         *
         * Adds a temporary timer, without the need of instantiating a new timer
         * object.
         *
         * @param handler Callback function.
         * @param to Timer's timeout.
         */
        template < typename F >
        void add_once_timer(F& handler, const time& to)
        {
                internal::event_once(-1, EV_TIMEOUT, &dispatcher::wrapper< F >,
                                reinterpret_cast< void* >(&handler),
                                // XXX HACK libevent don't use const
                                const_cast< time* >(&to));
        }

        /**
         * Adds a temporary timer with a C-style callback.
         *
         * Adds a temporary timer, without the need of instantiating a new timer
         * object.
         *
         * @param handler Callback function.
         * @param arg Arbitrary pointer to pass to the handler as argument.
         * @param to Timer's timeout.
         */
        void add_once_timer(ccallback_type handler, void* arg, const time& to)
        {
                // XXX HACK libevent don't use const
                internal::event_once(-1, EV_TIMEOUT, handler, arg,
                                const_cast< time* >(&to));
        }

        /**
         * Removes an event.
         *
         * The event e will be no longer monitored by this dispatcher.
         *
         * @param e Event to remove.
         */
        void del(basic_event& e) throw()
        {
                internal::event_del(&e);
        }

        /**
         * Main dispatcher loop.
         *
         * This function takes the control of the program, waiting for an event
         * and calling its callbacks when it's fired. It only returns under
         * this conditions:
         * - exit() was called.
         * - All events were del()eted.
         * - Another internal error.
         * - eventxx::ONCE flag was set.
         * - eventxx::NONBLOCK flag was set.
         *
         * @param flags If eventxx::ONCE is specified, then just one event is
         *              processed, if eventxx::NONBLOCK is specified, then this
         *              function returns even if there are no pending events.
         *
         * @return 0 if eventxx::NONBLOCK or eventxx::ONCE is set, 1 if there
         *         are no more events registered and EINTR if you use the
         *         @libevent's  @c event_gotsig and return -1 in your
         *         @c event_sigcb callback.
         */
        int dispatch(int flags = 0) throw()
        {
                return internal::event_base_loop(_event_base, flags);
        }

        /**
         * Exit the dispatch() loop.
         *
         * @param to If a timeout is given, the loop exits after the specified
         *           time is elapsed.
         *
         * @return Not very well specified by @libevent :-/ that's why it
         *         doesn't throw an exception either.
         */
        int exit(const time& to = time()) throw() // TODO  throw(exception)
        {
                // XXX HACK libevent don't use const
                return internal::event_base_loopexit(_event_base,
                        const_cast< time* >(&to));
        }

        protected:
                internal::event_base* _event_base;
                template < typename F >
                static void wrapper(int fd, short ev, void* h)
                {
                        F& handler = *reinterpret_cast< F* >(h);
                        handler(fd, *reinterpret_cast< type* >(&ev));
                }

}; // struct dispatcher

} // namespace eventxx

#endif // _EVENTXX_HPP_

// vim: set filetype=cpp :