MirBSD manpage: bufferevent_base_set(3), bufferevent_disable(3), bufferevent_enable(3), bufferevent_free(3), bufferevent_new(3), bufferevent_read(3), bufferevent_settimeout(3), bufferevent_write(3), bufferevent_write_buffer(3), evbuffer_add(3), evbuffer_add_buffer(3), evbuffer_add_printf(3), evbuffer_add_vprintf(3), evbuffer_drain(3), evbuffer_find(3), evbuffer_free(3), evbuffer_new(3), evbuffer_read(3), evbuffer_readline(3), evbuffer_write(3), event(3), event_add(3), event_base_dispatch(3), event_base_free(3), event_base_loop(3), event_base_loopbreak(3), event_base_loopexit(3), event_base_once(3), event_base_set(3), event_del(3), event_dispatch(3), event_init(3), event_initialized(3), event_loop(3), event_loopbreak(3), event_loopexit(3), event_once(3), event_pending(3), event_priority_init(3), event_priority_set(3), event_set(3), evtimer_add(3), evtimer_del(3), evtimer_initialized(3), evtimer_pending(3), evtimer_set(3), signal_add(3), signal_del(3), signal_initialized(3), signal_pending(3), signal_set(3)

EVENT(3)                   BSD Programmer's 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 - 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, const 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);


     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 re-
     gistered interest in more than one of the preceding 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. 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

     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

     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 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.


     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 initializ-
     ing 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 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
     parameters 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 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 buf-
     ferevent 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 be-
     fore enabling the bufferevent for the first time.


     It is possible to disable support for kqueue, poll or select by setting
     the environment variable EVENT_NOKQUEUE, EVENT_NOPOLL or EVENT_NOSELECT,
     respectively. By 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. Other-
     wise, -1 is returned and the global variable errno is set to indicate the


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


     The event API manpage is based on the timeout(9) manpage by Artur Gra-
     bowski. Support for real-time signals was added by 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.

MirBSD #10-current             October 19, 2012                              5

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