.\" $OpenBSD: event.3,v 1.4 2002/07/12 18:50:48 provos Exp $ .\" .\" Copyright (c) 2000 Artur Grabowski .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. The name of the author may not be used to endorse or promote products .\" derived from this software without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, .\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY .\" AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL .\" THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, .\" EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, .\" PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; .\" OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, .\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR .\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF .\" ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd August 8, 2000 .Dt EVENT 3 .Os .Sh NAME .Nm event_init , .Nm event_dispatch , .Nm event_loop , .Nm event_set , .Nm event_add , .Nm event_del , .Nm event_pending , .Nm event_initialized , .Nm evtimer_set , .Nm evtimer_add , .Nm evtimer_del .Nm evtimer_pending , .Nm evtimer_initialized , .Nm signal_set , .Nm signal_add , .Nm signal_del .Nm signal_pending , .Nm signal_initialized .Nd execute a function when a specific event occurs .Sh SYNOPSIS .Fd #include .Fd #include .Ft void .Fn "event_init" .Ft int .Fn "event_dispatch" .Ft int .Fn "event_loop" "int flags" .Ft void .Fn "event_set" "struct event *ev" "int fd" "short event" "void (*fn)(int, short, void *)" "void *arg" .Ft int .Fn "event_add" "struct event *ev" "struct timeval *tv" .Ft int .Fn "event_del" "struct event *ev" .Ft int .Fn "event_pending" "struct event *ev" "short event" "struct timeval *tv" .Ft int .Fn "event_initialized" "struct event *ev" .Ft void .Fn "evtimer_set" "struct event *ev" "void (*fn)(int, short, void *)" "void *arg" .Ft void .Fn "evtimer_add" "struct event *ev" "struct timeval *" .Ft void .Fn "evtimer_del" "struct event *ev" .Ft int .Fn "evtimer_pending" "struct event *ev" "struct timeval *tv" .Ft int .Fn "evtimer_initialized" "struct event *ev" .Ft void .Fn "signal_set" "struct event *ev" "int signal" "void (*fn)(int, short, void *)" "void *arg" .Ft void .Fn "signal_add" "struct event *ev" "struct timeval *" .Ft void .Fn "signal_del" "struct event *ev" .Ft int .Fn "signal_pending" "struct event *ev" "struct timeval *tv" .Ft int .Fn "signal_initialized" "struct event *ev" .Ft int .Fa (*event_sigcb)(void) ; .Ft int .Fa event_gotsig ; .Sh DESCRIPTION The .Nm event API provides a mechanism to execute a function when a specific event on a file descriptor occurs or after at a given time has passed. .Pp The .Nm event API needs to be initialized with .Fn event_init before it can be used. .Pp In order to process events, an application needs to call .Fn event_dispatch . This functions only returns on error, and should replace the event core of the application program. .Pp In order to avoid races in signal handlers, the .Nm event API provides two variables: .Va event_sigcb and .Va event_gotsig . A signal handler sets .Va event_gotsig to indicate that a signal has been received. The application sets .Va event_sigcb to a callback function. After the signal handler sets .Va event_gotsig , .Nm 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 .Nm event library, causing .Fn event_dispatch to terminate with .Va errno set to .Er EINTR. .Pp The .Nm event_loop function provides an interface for single pass execution of pending events. The flags .Va EVLOOP_ONCE and .Va EVLOOP_NONBLOCK are recognized. .Pp It is the responsibility of the caller to provide these functions with pre-allocated event structures. .Pp The function .Fn event_set prepares the event structure .Fa ev to be used in future calls to .Fn event_add and .Fn event_del . The event will be prepared to call the function specified by the .Fa fn argument with an .Fa int argument indicating the file descriptor, a .Fa short argument indicating the type of event, and a .Fa void * argument given in the .Fa arg argument. The .Fa fd indicates the file descriptor that should be monitored for events. The events can be either .Va EV_READ , .Va EV_WRITE , or both. Indicating that an application can read or write from the file descriptor respectively without blocking. .Pp The function .Fa fn will be called with the file descriptor that triggered the event and the type of event which will be either .Va EV_TIMEOUT , .Va EV_SIGNAL , .Va EV_READ , or .Va EV_WRITE . The additional flag .Va EV_PERSIST makes an .Fn event_add persistent until .Fn event_del has been called. .Pp Once initialized, the .Fa ev structure can be used repeatedly with .Fn event_add and .Fn event_del and does not need to be reinitialized unless the function called and/or the argument to it are to be changed. .Pp The function .Fn event_add schedules the execution of the .Fa ev event when the event specified in .Fn event_set occurs or in at least the time specified in the .Fa tv . If .Fa 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 .Fa ev argument must be already initialized by .Fn event_set and may not be used in calls to .Fn event_set until it has timed out or been removed with .Fn event_del . If the event in the .Fa ev argument has already a scheduled timeout, the old timeout will be replaced by the new one. .Pp The function .Fn event_del will cancel the event in the argument .Fa ev . If the event has already executed or has never been added the call will have no effect. .Pp The .Fn event_pending function can be used to check if the event specified by .Fa event is pending to run. If .Va EV_TIMEOUT was specified and .Fa tv is not .Va NULL , the expiration time of the event will be returned in .Fa tv . .Pp The .Fn event_initialized macro can be used to check if an event has been initialized. .Pp The functions .Fn evtimer_set , .Fn evtimer_add , .Fn evtimer_del , .Fn evtimer_initialized , and .Fn 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 .Va EV_TIMEOUT . .Pp .Pp The functions .Fn signal_set , .Fn signal_add , .Fn signal_del , .Fn signal_initialized , and .Fn signal_pending are abbreviations. The event type will be a persistent .Va EV_SIGNAL . That means .Fn signal_set adds .Va EV_PERSIST . .Pp It is possible to disable support for .Va kqueue by setting the environment variable .Va EVENT_NOKQUEUE . .Pp .Sh RETURN VALUES Upon successful completion .Fn event_add and .Fn event_del return 0. Otherwise, -1 is returned and the global variable errno is set to indicate the error. .Sh SEE ALSO .Xr timeout 9 , .Xr select 2 , .Xr kqueue 2 .Sh HISTORY The .Nm event API manpage is based on the .Xr timeout 9 manpage by Artur Grabowski. .Sh AUTHORS The .Nm event library was written by Niels Provos.