event_init, event_dispatch, event_loop, event_loopexit,
event_set,
event_add, event_del, event_once, event_pending,
event_initialized,
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, evbuffer_new,
evbuffer_free,
evbuffer_add, evbuffer_add_buffer, evbuffer_add_printf,
evbuffer_drain,
evbuffer_write, evbuffer_read, evbuffer_find - execute a
function when a
specific event occurs
#include <sys/time.h>
#include <event.h>
void
event_init();
int
event_dispatch();
int
event_loop(int flags);
int
event_loopexit(struct timeval *tv);
void
event_set(struct event *ev, int fd, short event,
void (*fn)(int, short, void *), void *arg);
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_pending(struct event *ev, short event, struct timeval
*tv);
int
event_initialized(struct event *ev);
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);
struct evbuffer *
evbuffer_new(void);
void
evbuffer_free(struct evbuffer *buf);
int
evbuffer_add(struct evbuffer *buf, u_char *data, size_t
size);
int
evbuffer_add_buffer(struct evbuffer *dst, struct evbuffer
*src);
int
evbuffer_add_printf(struct evbuffer *buf, char *fmt, ...);
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, u_char *data, size_t
size);
int (*event_sigcb)(void);
int event_gotsig;
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.
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 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 allows the loop to be
terminated after
some amount of time has passed. The parameter indicates
the time after
which the loop should terminate.
It is the responsibility of the caller to provide these
functions with
pre-allocated event structures.
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. 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.
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 function event_once() is similiar 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 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 0, 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.
It is possible to disable support for epoll, kqueue, poll,
or select by
setting the environment variable EVENT_NOEPOLL,
EVENT_NOKQUEUE,
EVENT_NOPOLL, or EVENT_NOSELECT. By setting the environment
variable
EVENT_SHOW_METHOD, libevent displays the kernel notification
method that
it uses.
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 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
argument is
specified by the fourth parameter cbarg.
By default the buffered event is read enabled and will try
to read from
the file descriptor. 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. The
bufferevent_read() function is used to read data from the
input buffer.
Both functions return the amount of data written or read.
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.
kqueue(2), poll(2), select(2), timeout(9)
The event API manpage is based on the timeout(9) manpage by
Artur
Grabowski. Support for real-time signals is due to Taral.
The event library was written by Niels Provos.
This documentation is neither complete nor authorative. 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.
OpenBSD 3.6 August 8, 2000
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