1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
|
.\" $OpenBSD: event_base_loop.3,v 1.2 2023/04/09 14:43:51 schwarze Exp $
.\" Copyright (c) 2023 Ted Bullock <tbullock@comlore.com>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: April 9 2023 $
.Dt EVENT_BASE_LOOP 3
.Os
.Sh NAME
.Nm event_base_loop ,
.Nm event_loop ,
.Nm event_base_dispatch ,
.Nm event_dispatch
.Nd run an event loop
.Sh SYNOPSIS
.In event.h
.Ft int
.Fn event_base_loop "struct event_base *base" "int flags"
.Ft int
.Fn event_loop "int flags"
.Ft int
.Fn event_base_dispatch "struct event_base *base"
.Ft int
.Fn event_dispatch void
.Sh DESCRIPTION
An event loop waits for and dispatches events in a program.
This enables asynchronous programming, allowing a program to perform other
tasks while waiting for an event to occur.
Asynchronous programming is a useful idiom for handling multiple I/O
operations, such as network connections, user interfaces, or disk operations
without blocking the main loop of a program.
The event loop continuously processes events and executes callbacks associated
with each event as they occur.
.Pp
The
.Fn event_base_loop
family of functions run an event loop.
By default, they return when there are no more scheduled events.
.Pp
There are three types of events these functions monitor including signal,
kernel and timer.
Events involving POSIX signals are configured with
.Xr signal_set 3 .
Kernel events such as network activity and changes to file descriptors are
configured with
.Xr event_set 3 .
Timer events are configured with
.Xr evtimer_set 3 .
.Pp
The event library further categorizes event states as:
.Bl -tag -width "Initialized:"
.It Sy Initialized :
These have been configured with
.Xr event_set 3
and not yet registered with an event loop.
.It Sy Scheduled :
These are registered to a loop using
.Xr event_add 3
and are idle, waiting to trigger and be processed by the loop.
They can be be queried with
.Fn event_pending 3 .
.It Sy Activated :
These are triggered events.
The loop processes events until all
.Sy activated
events are resolved, some of these such as signals, may persist and become
.Sy scheduled
events again.
.El
.Pp
The arguments are as follows:
.Bl -tag -width 6n
.It Fa base :
A pointer to an
.Vt event_base
structure returned from
.Xr event_init 3
or
.Xr event_base_new 3 .
.It Fa flags :
A set of flags that modify the behavior of the event loop.
The following flags are available:
.Pp
.Bl -hyphen -compact -width 1n
.It
.Dv EVLOOP_ONCE :
Run the event loop for one iteration and then return.
This is useful for a main program that needs to perform actions outside
the event loop.
.It
.Dv EVLOOP_NONBLOCK :
Run the event loop in non-blocking mode.
The loop returns after processing activated signal and kernel events and does
not wait for timer events to expire.
.El
.El
.Pp
The function
.Fn event_loop
is a version of
.Fn event_base_loop
that requires the library to be initialized by
.Xr event_init 3 .
.Pp
.Fn event_base_dispatch
is equivalent to calling
.Fn event_base_loop
with
.Fa flags
set to zero.
Likewise,
.Fn event_dispatch
is the same as invoking
.Fn event_loop
with
.Fa flags
set to zero.
.Sh RETURN VALUES
The event loop functions return:
.Pp
.Bl -tag -compact -offset 3n -width 3n
.It \-1
on error,
.Va errno
is set.
.It 0
on success, asked to terminate loop.
.It 1
on success, no remaining events left or scheduled in queue.
.El
.Sh ERRORS
These functions have complex interactions with
.Va errno .
Error conditions that set
.Va errno
change corresponding to the kernel notification method the event library is
using.
These values directly correspond to
.Xr kevent 2 ,
.Xr poll 2
or
.Xr select 2
system calls and default to
.Xr kevent 2
on
.Ox .
Refer to
.Xr event_base_new 3
for details on kernel notification methods.
.Bl -tag -width Er
.It Bq Er EINTR
Although the kernel notification methods can set
.Va errno
to
.Er EINTR ,
.Fn event_base_loop
and related functions never fail with
.Va errno
set to
.Er EINTR .
.El
.Sh SEE ALSO
.Xr kevent 2 ,
.Xr poll 2 ,
.Xr select 2 ,
.Xr event_base_new 3 ,
.Xr event_set 3
.Sh HISTORY
.Fn event_dispatch
first appeared in libevent-0.1 and has been available since
.Ox 3.2 .
.Pp
.Fn event_loop
first appeared in libevent-0.4 and has been available since
.Ox 3.2 .
.Pp
.Fn event_base_dispatch
and
.Fn event_base_loop
first appeared in libevent-1.0 and has been available since
.Ox 3.8 .
.Sh AUTHORS
The event library and these functions were written by
.An -nosplit
.An Niels Provos .
.Pp
This manual page was written by
.An Ted Bullock Aq Mt tbullock@comlore.com .
|
