This manual page is for Mac OS X version 10.6

Reading manual pages

EVENT(3)                                BSD Library Functions Manual                                EVENT(3)

NAME
     event_init, event_dispatch, event_loop, event_loopexit, event_loopbreak, event_set,
     event_base_dispatch, event_base_loop, event_base_loopexit, event_base_loopbreak, event_base_set,
     event_base_free, event_add, event_del, event_once, event_base_once, event_pending, event_initialized,
     event_priority_init, event_priority_set, evtimer_set, evtimer_add, evtimer_del, evtimer_pending,
     evtimer_initialized, signal_set, signal_add, signal_del, signal_pending, signal_initialized,
     bufferevent_new, bufferevent_free, bufferevent_write, bufferevent_write_buffer, bufferevent_read,
     bufferevent_enable, bufferevent_disable, bufferevent_settimeout, bufferevent_base_set, evbuffer_new,
     evbuffer_free, evbuffer_add, evbuffer_add_buffer, evbuffer_add_printf, evbuffer_add_vprintf,
     evbuffer_drain, evbuffer_write, evbuffer_read, evbuffer_find, evbuffer_readline, evhttp_new,
     evhttp_bind_socket, evhttp_free -- execute a function when a specific event occurs

SYNOPSIS
     #include <sys/time.h>
     #include <event.h>

     struct event_base *
     event_init(void);

     int
     event_dispatch(void);

     int
     event_loop(int flags);

     int
     event_loopexit(struct timeval *tv);

     int
     event_loopbreak(void);

     void
     event_set(struct event *ev, int fd, short event, void (*fn)(int, short, void *), void *arg);

     int
     event_base_dispatch(struct event_base *base);

     int
     event_base_loop(struct event_base *base, int flags);

     int
     event_base_loopexit(struct event_base *base, struct timeval *tv);

     int
     event_base_loopbreak(struct event_base *base);

     int
     event_base_set(struct event_base *base, struct event *);

     void
     event_base_free(struct event_base *base);

     int
     event_add(struct event *ev, struct timeval *tv);

     int
     event_del(struct event *ev);

     int
     event_once(int fd, short event, void (*fn)(int, short, void *), void *arg, struct timeval *tv);

     int
     event_base_once(struct event_base *base, int fd, short event, void (*fn)(int, short, void *),
         void *arg, struct timeval *tv);

     int
     event_pending(struct event *ev, short event, struct timeval *tv);

     int
     event_initialized(struct event *ev);

     int
     event_priority_init(int npriorities);

     int
     event_priority_set(struct event *ev, int priority);

     void
     evtimer_set(struct event *ev, void (*fn)(int, short, void *), void *arg);

     void
     evtimer_add(struct event *ev, struct timeval *);

     void
     evtimer_del(struct event *ev);

     int
     evtimer_pending(struct event *ev, struct timeval *tv);

     int
     evtimer_initialized(struct event *ev);

     void
     signal_set(struct event *ev, int signal, void (*fn)(int, short, void *), void *arg);

     void
     signal_add(struct event *ev, struct timeval *);

     void
     signal_del(struct event *ev);

     int
     signal_pending(struct event *ev, struct timeval *tv);

     int
     signal_initialized(struct event *ev);

     struct bufferevent *
     bufferevent_new(int fd, evbuffercb readcb, evbuffercb writecb, everrorcb, void *cbarg);

     void
     bufferevent_free(struct bufferevent *bufev);

     int
     bufferevent_write(struct bufferevent *bufev, void *data, size_t size);

     int
     bufferevent_write_buffer(struct bufferevent *bufev, struct evbuffer *buf);

     size_t
     bufferevent_read(struct bufferevent *bufev, void *data, size_t size);

     int
     bufferevent_enable(struct bufferevent *bufev, short event);

     int
     bufferevent_disable(struct bufferevent *bufev, short event);

     void
     bufferevent_settimeout(struct bufferevent *bufev, int timeout_read, int timeout_write);

     int
     bufferevent_base_set(struct event_base *base, struct bufferevent *bufev);

     struct evbuffer *
     evbuffer_new(void);

     void
     evbuffer_free(struct evbuffer *buf);

     int
     evbuffer_add(struct evbuffer *buf, const void *data, size_t size);

     int
     evbuffer_add_buffer(struct evbuffer *dst, struct evbuffer *src);

     int
     evbuffer_add_printf(struct evbuffer *buf, const char *fmt, ...);

     int
     evbuffer_add_vprintf(struct evbuffer *buf, const char *fmt, va_list ap);

     void
     evbuffer_drain(struct evbuffer *buf, size_t size);

     int
     evbuffer_write(struct evbuffer *buf, int fd);

     int
     evbuffer_read(struct evbuffer *buf, int fd, int size);

     u_char *
     evbuffer_find(struct evbuffer *buf, const u_char *data, size_t size);

     char *
     evbuffer_readline(struct evbuffer *buf);

     struct evhttp *
     evhttp_new(struct event_base *base);

     int
     evhttp_bind_socket(struct evhttp *http, const char *address, u_short port);

     void
     evhttp_free(struct evhttp *http);

     int (*event_sigcb)(void);

     volatile sig_atomic_t event_gotsig;

DESCRIPTION
     The event API provides a mechanism to execute a function when a specific event on a file descriptor
     occurs or after a given time has passed.

     The event API needs to be initialized with event_init() before it can be used.

     In order to process events, an application needs to call event_dispatch().  This function only returns
     on error, and should replace the event core of the application program.

     The function event_set() prepares the event structure ev to be used in future calls to event_add() and
     event_del().  The event will be prepared to call the function specified by the fn argument with an int
     argument indicating the file descriptor, a short argument indicating the type of event, and a void *
     argument given in the arg argument.  The fd indicates the file descriptor that should be monitored for
     events.  The events can be either EV_READ, EV_WRITE, or both, indicating that an application can read
     or write from the file descriptor respectively without blocking.

     The function fn will be called with the file descriptor that triggered the event and the type of event
     which will be either EV_TIMEOUT, EV_SIGNAL, EV_READ, or EV_WRITE.  Additionally, an event which has
     registered interest in more than one of the preceeding events, via bitwise-OR to event_set(), can pro-vide provide
     vide its callback function with a bitwise-OR of more than one triggered event.  The additional flag
     EV_PERSIST makes an event_add() persistent until event_del() has been called.

     Once initialized, the ev structure can be used repeatedly with event_add() and event_del() and does not
     need to be reinitialized unless the function called and/or the argument to it are to be changed.  How-ever, However,
     ever, when an ev structure has been added to libevent using event_add() the structure must persist
     until the event occurs (assuming EV_PERSIST is not set) or is removed using event_del().  You may not
     reuse the same ev structure for multiple monitored descriptors; each descriptor needs its own ev.

     The function event_add() schedules the execution of the ev event when the event specified in
     event_set() occurs or in at least the time specified in the tv.  If tv is NULL, no timeout occurs and
     the function will only be called if a matching event occurs on the file descriptor.  The event in the
     ev argument must be already initialized by event_set() and may not be used in calls to event_set()
     until it has timed out or been removed with event_del().  If the event in the ev argument already has a
     scheduled timeout, the old timeout will be replaced by the new one.

     The function event_del() will cancel the event in the argument ev.  If the event has already executed
     or has never been added the call will have no effect.

     The functions evtimer_set(), evtimer_add(), evtimer_del(), evtimer_initialized(), and evtimer_pending()
     are abbreviations for common situations where only a timeout is required.  The file descriptor passed
     will be -1, and the event type will be EV_TIMEOUT.

     The functions signal_set(), signal_add(), signal_del(), signal_initialized(), and signal_pending() are
     abbreviations.  The event type will be a persistent EV_SIGNAL.  That means signal_set() adds
     EV_PERSIST.

     In order to avoid races in signal handlers, the event API provides two variables: event_sigcb and
     event_gotsig.  A signal handler sets event_gotsig to indicate that a signal has been received.  The
     application sets event_sigcb to a callback function.  After the signal handler sets event_gotsig,
     event_dispatch will execute the callback function to process received signals.  The callback returns 1
     when no events are registered any more.  It can return -1 to indicate an error to the event library,
     causing event_dispatch() to terminate with errno set to EINTR.

     The function event_once() is similar to event_set().  However, it schedules a callback to be called
     exactly once and does not require the caller to prepare an event structure.  This function supports
     EV_TIMEOUT, EV_READ, and EV_WRITE.

     The event_pending() function can be used to check if the event specified by event is pending to run.
     If EV_TIMEOUT was specified and tv is not NULL, the expiration time of the event will be returned in
     tv.

     The event_initialized() macro can be used to check if an event has been initialized.

     The event_loop function provides an interface for single pass execution of pending events.  The flags
     EVLOOP_ONCE and EVLOOP_NONBLOCK are recognized.  The event_loopexit function exits from the event loop.
     The next event_loop() iteration after the given timer expires will complete normally (handling all
     queued events) then exit without blocking for events again. Subsequent invocations of event_loop() will
     proceed normally.  The event_loopbreak function exits from the event loop immediately.  event_loop()
     will abort after the next event is completed; event_loopbreak() is typically invoked from this event's
     callback. This behavior is analogous to the "break;" statement. Subsequent invocations of event_loop()
     will proceed normally.

     It is the responsibility of the caller to provide these functions with pre-allocated event structures.

EVENT PRIORITIES
     By default libevent schedules all active events with the same priority.  However, sometimes it is
     desirable to process some events with a higher priority than others.  For that reason, libevent sup-ports supports
     ports strict priority queues.  Active events with a lower priority are always processed before events
     with a higher priority.

     The number of different priorities can be set initially with the event_priority_init() function.  This
     function should be called before the first call to event_dispatch().  The event_priority_set() function
     can be used to assign a priority to an event.  By default, libevent assigns the middle priority to all
     events unless their priority is explicitly set.

THREAD SAFE EVENTS
     Libevent has experimental support for thread-safe events.  When initializing the library via
     event_init(), an event base is returned.  This event base can be used in conjunction with calls to
     event_base_set(), event_base_dispatch(), event_base_loop(), event_base_loopexit(),
     bufferevent_base_set() and event_base_free().  event_base_set() should be called after preparing an
     event with event_set(), as event_set() assigns the provided event to the most recently created event
     base.  bufferevent_base_set() should be called after preparing a bufferevent with bufferevent_new().
     event_base_free() should be used to free memory associated with the event base when it is no longer
     needed.

BUFFERED EVENTS
     libevent provides an abstraction on top of the regular event callbacks.  This abstraction is called a
     buffered event.  A buffered event provides input and output buffers that get filled and drained auto-matically. automatically.
     matically.  The user of a buffered event no longer deals directly with the IO, but instead is reading
     from input and writing to output buffers.

     A new bufferevent is created by bufferevent_new().  The parameter fd specifies the file descriptor from
     which data is read and written to.  This file descriptor is not allowed to be a pipe(2).  The next
     three parameters are callbacks.  The read and write callback have the following form: void (*cb)(struct
     bufferevent *bufev, void *arg).  The error callback has the following form: void (*cb)(struct
     bufferevent *bufev, short what, void *arg).  The argument is specified by the fourth parameter cbarg.
     A bufferevent struct pointer is returned on success, NULL on error.  Both the read and the write call-back callback
     back may be NULL.  The error callback has to be always provided.

     Once initialized, the bufferevent structure can be used repeatedly with bufferevent_enable() and
     bufferevent_disable().  The flags parameter can be a combination of EV_READ and EV_WRITE.  When read
     enabled the bufferevent will try to read from the file descriptor and call the read callback.  The
     write callback is executed whenever the output buffer is drained below the write low watermark, which
     is 0 by default.

     The bufferevent_write() function can be used to write data to the file descriptor.  The data is
     appended to the output buffer and written to the descriptor automatically as it becomes available for
     writing.  bufferevent_write() returns 0 on success or -1 on failure.  The bufferevent_read() function
     is used to read data from the input buffer, returning the amount of data read.

     If multiple bases are in use, bufferevent_base_set() must be called before enabling the bufferevent for
     the first time.

NON-BLOCKING HTTP SUPPORT
     libevent provides a very thin HTTP layer that can be used both to host an HTTP server and also to make
     HTTP requests.  An HTTP server can be created by calling evhttp_new().  It can be bound to any port and
     address with the evhttp_bind_socket() function.  When the HTTP server is no longer used, it can be
     freed via evhttp_free().

     To be notified of HTTP requests, a user needs to register callbacks with the HTTP server.  This can be
     done by calling evhttp_set_cb().  The second argument is the URI for which a callback is being regis-tered. registered.
     tered.  The corresponding callback will receive an struct evhttp_request object that contains all
     information about the request.

     This section does not document all the possible function calls; please check event.h for the public
     interfaces.

ADDITIONAL NOTES
     It is possible to disable support for epoll, kqueue, devpoll, poll or select by setting the environment
     variable EVENT_NOEPOLL, EVENT_NOKQUEUE, EVENT_NODEVPOLL, EVENT_NOPOLL or EVENT_NOSELECT, respectively.
     By setting the environment variable EVENT_SHOW_METHOD, libevent displays the kernel notification method
     that it uses.

RETURN VALUES
     Upon successful completion event_add() and event_del() return 0.  Otherwise, -1 is returned and the
     global variable errno is set to indicate the error.

SEE ALSO
     kqueue(2), poll(2), select(2), evdns(3), timeout(9)

HISTORY
     The event API manpage is based on the timeout(9) manpage by Artur Grabowski.  The port of libevent to
     Windows is due to Michael A. Davis.  Support for real-time signals is due to Taral.

AUTHORS
     The event library was written by Niels Provos.

BUGS
     This documentation is neither complete nor authoritative.  If you are in doubt about the usage of this
     API then check the source code to find out how it works, write up the missing piece of documentation
     and send it to me for inclusion in this man page.

BSD                                            August 8, 2000                                            BSD