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-.\" $OpenBSD: event.3,v 1.4 2002/07/12 18:50:48 provos Exp $
-.\"
-.\" Copyright (c) 2000 Artur Grabowski <art@openbsd.org>
-.\" 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_loopexit ,
-.Nm event_loopbreak ,
-.Nm event_set ,
-.Nm event_base_dispatch ,
-.Nm event_base_loop ,
-.Nm event_base_loopexit ,
-.Nm event_base_loopbreak ,
-.Nm event_base_set ,
-.Nm event_base_free ,
-.Nm event_add ,
-.Nm event_del ,
-.Nm event_once ,
-.Nm event_base_once ,
-.Nm event_pending ,
-.Nm event_initialized ,
-.Nm event_priority_init ,
-.Nm event_priority_set ,
-.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 ,
-.Nm bufferevent_new ,
-.Nm bufferevent_free ,
-.Nm bufferevent_write ,
-.Nm bufferevent_write_buffer ,
-.Nm bufferevent_read ,
-.Nm bufferevent_enable ,
-.Nm bufferevent_disable ,
-.Nm bufferevent_settimeout ,
-.Nm bufferevent_base_set ,
-.Nm evbuffer_new ,
-.Nm evbuffer_free ,
-.Nm evbuffer_add ,
-.Nm evbuffer_add_buffer ,
-.Nm evbuffer_add_printf ,
-.Nm evbuffer_add_vprintf ,
-.Nm evbuffer_drain ,
-.Nm evbuffer_write ,
-.Nm evbuffer_read ,
-.Nm evbuffer_find ,
-.Nm evbuffer_readline ,
-.Nm evhttp_new ,
-.Nm evhttp_bind_socket ,
-.Nm evhttp_free
-.Nd execute a function when a specific event occurs
-.Sh SYNOPSIS
-.Fd #include <sys/time.h>
-.Fd #include <event.h>
-.Ft "struct event_base *"
-.Fn "event_init" "void"
-.Ft int
-.Fn "event_dispatch" "void"
-.Ft int
-.Fn "event_loop" "int flags"
-.Ft int
-.Fn "event_loopexit" "struct timeval *tv"
-.Ft int
-.Fn "event_loopbreak" "void"
-.Ft void
-.Fn "event_set" "struct event *ev" "int fd" "short event" "void (*fn)(int, short, void *)" "void *arg"
-.Ft int
-.Fn "event_base_dispatch" "struct event_base *base"
-.Ft int
-.Fn "event_base_loop" "struct event_base *base" "int flags"
-.Ft int
-.Fn "event_base_loopexit" "struct event_base *base" "struct timeval *tv"
-.Ft int
-.Fn "event_base_loopbreak" "struct event_base *base"
-.Ft int
-.Fn "event_base_set" "struct event_base *base" "struct event *"
-.Ft void
-.Fn "event_base_free" "struct event_base *base"
-.Ft int
-.Fn "event_add" "struct event *ev" "struct timeval *tv"
-.Ft int
-.Fn "event_del" "struct event *ev"
-.Ft int
-.Fn "event_once" "int fd" "short event" "void (*fn)(int, short, void *)" "void *arg" "struct timeval *tv"
-.Ft int
-.Fn "event_base_once" "struct event_base *base" "int fd" "short event" "void (*fn)(int, short, void *)" "void *arg" "struct timeval *tv"
-.Ft int
-.Fn "event_pending" "struct event *ev" "short event" "struct timeval *tv"
-.Ft int
-.Fn "event_initialized" "struct event *ev"
-.Ft int
-.Fn "event_priority_init" "int npriorities"
-.Ft int
-.Fn "event_priority_set" "struct event *ev" "int priority"
-.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 "struct bufferevent *"
-.Fn "bufferevent_new" "int fd" "evbuffercb readcb" "evbuffercb writecb" "everrorcb" "void *cbarg"
-.Ft void
-.Fn "bufferevent_free" "struct bufferevent *bufev"
-.Ft int
-.Fn "bufferevent_write" "struct bufferevent *bufev" "void *data" "size_t size"
-.Ft int
-.Fn "bufferevent_write_buffer" "struct bufferevent *bufev" "struct evbuffer *buf"
-.Ft size_t
-.Fn "bufferevent_read" "struct bufferevent *bufev" "void *data" "size_t size"
-.Ft int
-.Fn "bufferevent_enable" "struct bufferevent *bufev" "short event"
-.Ft int
-.Fn "bufferevent_disable" "struct bufferevent *bufev" "short event"
-.Ft void
-.Fn "bufferevent_settimeout" "struct bufferevent *bufev" "int timeout_read" "int timeout_write"
-.Ft int
-.Fn "bufferevent_base_set" "struct event_base *base" "struct bufferevent *bufev"
-.Ft "struct evbuffer *"
-.Fn "evbuffer_new" "void"
-.Ft void
-.Fn "evbuffer_free" "struct evbuffer *buf"
-.Ft int
-.Fn "evbuffer_add" "struct evbuffer *buf" "const void *data" "size_t size"
-.Ft int
-.Fn "evbuffer_add_buffer" "struct evbuffer *dst" "struct evbuffer *src"
-.Ft int
-.Fn "evbuffer_add_printf" "struct evbuffer *buf" "const char *fmt" "..."
-.Ft int
-.Fn "evbuffer_add_vprintf" "struct evbuffer *buf" "const char *fmt" "va_list ap"
-.Ft void
-.Fn "evbuffer_drain" "struct evbuffer *buf" "size_t size"
-.Ft int
-.Fn "evbuffer_write" "struct evbuffer *buf" "int fd"
-.Ft int
-.Fn "evbuffer_read" "struct evbuffer *buf" "int fd" "int size"
-.Ft "unsigned char *"
-.Fn "evbuffer_find" "struct evbuffer *buf" "const unsigned char *data" "size_t size"
-.Ft "char *"
-.Fn "evbuffer_readline" "struct evbuffer *buf"
-.Ft "struct evhttp *"
-.Fn "evhttp_new" "struct event_base *base"
-.Ft int
-.Fn "evhttp_bind_socket" "struct evhttp *http" "const char *address" "unsigned short port"
-.Ft "void"
-.Fn "evhttp_free" "struct evhttp *http"
-.Ft int
-.Fa (*event_sigcb)(void) ;
-.Ft volatile sig_atomic_t
-.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 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 function only returns on error, and should replace the event core
-of the application program.
-.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 .
-Additionally, an event which has registered interest in more than one of the
-preceeding events, via bitwise-OR to
-.Fn event_set ,
-can provide its callback function with a bitwise-OR of more than one triggered
-event.
-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.
-However, when an
-.Fa ev
-structure has been added to libevent using
-.Fn event_add
-the structure must persist until the event occurs (assuming
-.Fa EV_PERSIST
-is not set) or is removed
-using
-.Fn event_del .
-You may not reuse the same
-.Fa ev
-structure for multiple monitored descriptors; each descriptor
-needs its own
-.Fa ev .
-.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
-.Dv 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 already has 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 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 \-1, and the event type will be
-.Va EV_TIMEOUT .
-.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
-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 function
-.Fn event_once
-is similar to
-.Fn event_set .
-However, it schedules a callback to be called exactly once and does not
-require the caller to prepare an
-.Fa event
-structure.
-This function supports
-.Fa EV_TIMEOUT ,
-.Fa EV_READ ,
-and
-.Fa EV_WRITE .
-.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
-.Dv 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
-.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.
-The
-.Nm event_loopexit
-function exits from the event loop. The next
-.Fn 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
-.Fn event_loop
-will proceed normally.
-The
-.Nm event_loopbreak
-function exits from the event loop immediately.
-.Fn event_loop
-will abort after the next event is completed;
-.Fn event_loopbreak
-is typically invoked from this event's callback. This behavior is analogous
-to the "break;" statement. Subsequent invocations of
-.Fn event_loop
-will proceed normally.
-.Pp
-It is the responsibility of the caller to provide these functions with
-pre-allocated event structures.
-.Pp
-.Sh EVENT PRIORITIES
-By default
-.Nm 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,
-.Nm libevent
-supports strict priority queues.
-Active events with a lower priority are always processed before events
-with a higher priority.
-.Pp
-The number of different priorities can be set initially with the
-.Fn event_priority_init
-function.
-This function should be called before the first call to
-.Fn event_dispatch .
-The
-.Fn event_priority_set
-function can be used to assign a priority to an event.
-By default,
-.Nm libevent
-assigns the middle priority to all events unless their priority
-is explicitly set.
-.Sh THREAD SAFE EVENTS
-.Nm Libevent
-has experimental support for thread-safe events.
-When initializing the library via
-.Fn event_init ,
-an event base is returned.
-This event base can be used in conjunction with calls to
-.Fn event_base_set ,
-.Fn event_base_dispatch ,
-.Fn event_base_loop ,
-.Fn event_base_loopexit ,
-.Fn bufferevent_base_set
-and
-.Fn event_base_free .
-.Fn event_base_set
-should be called after preparing an event with
-.Fn event_set ,
-as
-.Fn event_set
-assigns the provided event to the most recently created event base.
-.Fn bufferevent_base_set
-should be called after preparing a bufferevent with
-.Fn bufferevent_new .
-.Fn event_base_free
-should be used to free memory associated with the event base
-when it is no longer needed.
-.Sh BUFFERED EVENTS
-.Nm libevent
-provides an abstraction on top of the regular event callbacks.
-This abstraction is called a
-.Va "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.
-.Pp
-A new bufferevent is created by
-.Fn bufferevent_new .
-The parameter
-.Fa fd
-specifies the file descriptor from which data is read and written to.
-This file descriptor is not allowed to be a
-.Xr pipe 2 .
-The next three parameters are callbacks.
-The read and write callback have the following form:
-.Ft void
-.Fn "(*cb)" "struct bufferevent *bufev" "void *arg" .
-The error callback has the following form:
-.Ft void
-.Fn "(*cb)" "struct bufferevent *bufev" "short what" "void *arg" .
-The argument is specified by the fourth parameter
-.Fa "cbarg" .
-A
-.Fa 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.
-.Pp
-Once initialized, the bufferevent structure can be used repeatedly with
-bufferevent_enable() and bufferevent_disable().
-The flags parameter can be a combination of
-.Va EV_READ
-and
-.Va 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
-.Va 0
-by default.
-.Pp
-The
-.Fn 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.
-.Fn bufferevent_write
-returns 0 on success or \-1 on failure.
-The
-.Fn bufferevent_read
-function is used to read data from the input buffer,
-returning the amount of data read.
-.Pp
-If multiple bases are in use, bufferevent_base_set() must be called before
-enabling the bufferevent for the first time.
-.Sh NON-BLOCKING HTTP SUPPORT
-.Nm 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
-.Fn evhttp_new .
-It can be bound to any port and address with the
-.Fn evhttp_bind_socket
-function.
-When the HTTP server is no longer used, it can be freed via
-.Fn evhttp_free .
-.Pp
-To be notified of HTTP requests, a user needs to register callbacks with the
-HTTP server.
-This can be done by calling
-.Fn evhttp_set_cb .
-The second argument is the URI for which a callback is being registered.
-The corresponding callback will receive an
-.Va struct evhttp_request
-object that contains all information about the request.
-.Pp
-This section does not document all the possible function calls; please
-check
-.Va event.h
-for the public interfaces.
-.Sh ADDITIONAL NOTES
-It is possible to disable support for
-.Va epoll , kqueue , devpoll , poll
-or
-.Va select
-by setting the environment variable
-.Va EVENT_NOEPOLL , EVENT_NOKQUEUE , EVENT_NODEVPOLL , EVENT_NOPOLL
-or
-.Va EVENT_NOSELECT ,
-respectively.
-By setting the environment variable
-.Va EVENT_SHOW_METHOD ,
-.Nm libevent
-displays the kernel notification method that it uses.
-.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 kqueue 2 ,
-.Xr poll 2 ,
-.Xr select 2 ,
-.Xr evdns 3 ,
-.Xr timeout 9
-.Sh HISTORY
-The
-.Nm event
-API manpage is based on the
-.Xr timeout 9
-manpage by Artur Grabowski.
-The port of
-.Nm libevent
-to Windows is due to Michael A. Davis.
-Support for real-time signals is due to Taral.
-.Sh AUTHORS
-The
-.Nm event
-library was written by Niels Provos.
-.Sh BUGS
-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.