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

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

NAME         top

     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         top

     #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);

     unsigned char *
     evbuffer_find(struct evbuffer *buf, const unsigned 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,
         unsigned short port);

     void
     evhttp_free(struct evhttp *http);

     int (*event_sigcb)(void);

     volatile sig_atomic_t event_gotsig;

DESCRIPTION         top

     The event API provides a mechanism to execute a function when a spe‐
     cific 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 pre‐
     pared 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, indicat‐
     ing 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 reg‐
     istered interest in more than one of the preceeding events, via bit‐
     wise-OR to event_set(), can provide its callback function with a bit‐
     wise-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.
     However, 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 spec‐
     ified 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 com‐
     mon 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
     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 speci‐
     fied 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 rec‐
     ognized.  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 nor‐
     mally.  The event_loopbreak function exits from the event loop immedi‐
     ately.  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         top

     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 prior‐
     ity 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         top

     Libevent has experimental support for thread-safe events.  When ini‐
     tializing 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         top

     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 follow‐
     ing 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 param‐
     eter cbarg.  A bufferevent struct pointer is returned on success, NULL
     on error.  Both the read and the write callback 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         top

     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.  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         top

     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         top

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

SEE ALSO         top

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

HISTORY         top

     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         top

     The event library was written by Niels Provos.

BUGS         top

     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.

COLOPHON         top

     This page is part of the libevent (an event notification library)
     project.  Information about the project can be found at
     http://libevent.org/.  If you have a bug report for this manual page,
     see http://sourceforge.net/p/levent/bugs/.  This page was obtained from
     the project's upstream Git repository
     https://github.com/libevent/libevent.git on 2017-03-13.  If you dis‐
     cover any rendering problems in this HTML version of the page, or you
     believe there is a better or more up-to-date source for the page, or
     you have corrections or improvements to the information in this
     COLOPHON (which is not part of the original manual page), send a mail
     to man-pages@man7.org

BSD                            August 8, 2000                            BSD