EVENT(3)                  OpenBSD Programmer's Manual                 EVENT(3)

NAME
     event_init, event_dispatch, event_loop, event_set, event_add, event_del,
     event_pending, event_initialized, evtimer_set, evtimer_add, evtimer_del,
     evtimer_pending, evtimer_initialized, signal_set, signal_add, signal_del,
     signal_pending, signal_initialized - execute a function when a specific
     event occurs

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

     void
     event_init();

     int
     event_dispatch();

     int
     event_loop(int flags);

     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_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);

     int (*event_sigcb)(void);

     int 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.

     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 event_loop function provides an interface for single pass execution
     of pending events.  The flags EVLOOP_ONCE and EVLOOP_NONBLOCK are recog-
     nized.

     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 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 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 kqueue(2), poll(2), or select(2) by
     setting the environment variable EVENT_NOKQUEUE, EVENT_NOPOLL, or
     EVENT_NOSELECT.  By setting 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), timeout(9)

HISTORY
     The event API manpage is based on the timeout(9) manpage by Artur
     Grabowski.

AUTHORS
     The event library was written by Niels Provos.

OpenBSD 3.5                     August 8, 2000                               3
