EVENT(3)                    Library Functions Manual                  EVENT(3)

     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

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

     struct event_base *


     event_loop(int flags);

     event_loopexit(struct timeval *tv);


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

     event_base_dispatch(struct event_base *base);

     event_base_loop(struct event_base *base, int flags);

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

     event_base_loopbreak(struct event_base *base);

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

     event_base_free(struct event_base *base);

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

     event_del(struct event *ev);

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

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

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

     event_initialized(struct event *ev);

     event_priority_init(int npriorities);

     event_priority_set(struct event *ev, int priority);

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

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

     evtimer_del(struct event *ev);

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

     evtimer_initialized(struct event *ev);

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

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

     signal_del(struct event *ev);

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

     signal_initialized(struct event *ev);

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

     bufferevent_free(struct bufferevent *bufev);

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

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

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

     bufferevent_enable(struct bufferevent *bufev, short event);

     bufferevent_disable(struct bufferevent *bufev, short event);

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

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

     struct evbuffer *

     evbuffer_free(struct evbuffer *buf);

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

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

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

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

     evbuffer_drain(struct evbuffer *buf, size_t size);

     evbuffer_write(struct evbuffer *buf, int fd);

     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);

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

     evhttp_free(struct evhttp *http);

     int (*event_sigcb)(void);

     volatile sig_atomic_t 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

     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 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

     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 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

     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

     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.

     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
     assigns the middle priority to all events unless their priority is
     explicitly set.

     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.

     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 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 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.

     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 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.

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

     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), evdns(3), timeout(9)

     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.

     The event library was written by Niels Provos.

     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.

                                August 8, 2000