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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	re-
     place 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	regis-
     tered interest in more than one of	the preceeding events, via bitwise-OR
     to	event_set(), can provide 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, 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 sched-
     uled 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 applica-
     tion 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 reg-
     istered any more.	It can return -1 to indicate an	error to the event li-
     brary, causing event_dispatch() to	terminate with errno set to EINTR.

     The function event_once() is similar to event_set().  However, it sched-
     ules 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 recog-
     nized.  The event_loopexit	function exits from the	event loop. The	next
     event_loop() iteration after the given timer expires will complete	nor-
     mally (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 supports 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 as-
     signs the middle priority to all events unless their priority is explic-
     itly set.

THREAD SAFE EVENTS
     Libevent has experimental support for thread-safe events.	When initial-
     izing 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 automatically.  The
     user of a buffered	event no longer	deals directly with the	IO, but	in-
     stead 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 pa-
     rameters are callbacks.  The read and write callback have the following
     form: void	(*cb)(struct bufferevent *bufev, void *arg).  The error	call-
     back 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 er-
     ror.  Both	the read and the write callback	may be NULL.  The error	call-
     back 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 buffer-
     event will	try to read from the file descriptor and call the read call-
     back.  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 be-
     fore 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	cre-
     ated 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 sec-
     ond argument is the URI for which a callback is being registered.	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	set-
     ting 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.  Other-
     wise, -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

NAME | SYNOPSIS | DESCRIPTION | EVENT PRIORITIES | THREAD SAFE EVENTS | BUFFERED EVENTS | NON-BLOCKING HTTP SUPPORT | ADDITIONAL NOTES | RETURN VALUES | SEE ALSO | HISTORY | AUTHORS | BUGS

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