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1 | <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*--> |
2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" | |
3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
4 | ||
5 | <!-- | |
6 | This file is part of systemd. | |
7 | ||
8 | Copyright 2015 Lennart Poettering | |
9 | ||
10 | systemd is free software; you can redistribute it and/or modify it | |
11 | under the terms of the GNU Lesser General Public License as published by | |
12 | the Free Software Foundation; either version 2.1 of the License, or | |
13 | (at your option) any later version. | |
14 | ||
15 | systemd is distributed in the hope that it will be useful, but | |
16 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
17 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
18 | Lesser General Public License for more details. | |
19 | ||
20 | You should have received a copy of the GNU Lesser General Public License | |
21 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
22 | --> | |
23 | ||
24 | <refentry id="sd_event_source_set_priority" xmlns:xi="http://www.w3.org/2001/XInclude"> | |
25 | ||
26 | <refentryinfo> | |
27 | <title>sd_event_source_set_priority</title> | |
28 | <productname>systemd</productname> | |
29 | ||
30 | <authorgroup> | |
31 | <author> | |
32 | <contrib>Developer</contrib> | |
33 | <firstname>Lennart</firstname> | |
34 | <surname>Poettering</surname> | |
35 | <email>lennart@poettering.net</email> | |
36 | </author> | |
37 | </authorgroup> | |
38 | </refentryinfo> | |
39 | ||
40 | <refmeta> | |
41 | <refentrytitle>sd_event_source_set_priority</refentrytitle> | |
42 | <manvolnum>3</manvolnum> | |
43 | </refmeta> | |
44 | ||
45 | <refnamediv> | |
46 | <refname>sd_event_source_set_priority</refname> | |
47 | <refname>sd_event_source_get_priority</refname> | |
48 | <refname>SD_EVENT_PRIORITY_IMPORTANT</refname> | |
49 | <refname>SD_EVENT_PRIORITY_NORMAL</refname> | |
50 | <refname>SD_EVENT_PRIORITY_IDLE</refname> | |
51 | ||
52 | <refpurpose>Set or retrieve the priority of event sources</refpurpose> | |
53 | </refnamediv> | |
54 | ||
55 | <refsynopsisdiv> | |
56 | <funcsynopsis> | |
57 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> | |
58 | ||
59 | <funcsynopsisinfo><token>enum</token> { | |
60 | <constant>SD_EVENT_SOURCE_IMPORTANT</constant> = -100, | |
61 | <constant>SD_EVENT_SOURCE_NORMAL</constant> = 0, | |
62 | <constant>SD_EVENT_SOURCE_IDLE</constant> = 100, | |
63 | };</funcsynopsisinfo> | |
64 | ||
65 | <funcprototype> | |
66 | <funcdef>int <function>sd_event_source_set_priority</function></funcdef> | |
67 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
68 | <paramdef>int64_t <parameter>priority</parameter></paramdef> | |
69 | </funcprototype> | |
70 | ||
71 | <funcprototype> | |
72 | <funcdef>int <function>sd_event_source_get_priority</function></funcdef> | |
73 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
74 | <paramdef>int64_t *<parameter>priority</parameter></paramdef> | |
75 | </funcprototype> | |
76 | ||
77 | </funcsynopsis> | |
78 | </refsynopsisdiv> | |
79 | ||
80 | <refsect1> | |
81 | <title>Description</title> | |
82 | ||
83 | <para><function>sd_event_source_set_priority()</function> may be | |
84 | used to set the priority for the event source object specified as | |
85 | <parameter>source</parameter>. The priority is specified as an | |
86 | arbitrary signed 64bit integer. The priority is initialized to | |
87 | <constant>SD_EVENT_PRIORITY_NORMAL</constant> (0) when the event | |
88 | source is allocated with a call such as | |
89 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
90 | or | |
91 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
92 | and may be changed with this call. If multiple event sources have seen events at the same time, they are dispatched in the order indicated by the | |
93 | event sources' priorities. Event sources with smaller priority | |
94 | values are dispatched first. As well-known points of reference, | |
95 | the constants <constant>SD_EVENT_PRIORITY_IMPORTANT</constant> | |
96 | (-100), <constant>SD_EVENT_PRIORITY_NORMAL</constant> (0) and | |
97 | <constant>SD_EVENT_PRIORITY_IDLE</constant> (100) may be used to | |
98 | indicate event sources that shall be dispatched early, normally or | |
99 | late. It is recommended to specify priorities based on these | |
ccddd104 | 100 | definitions, and relative to them — however, the full 64bit |
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101 | signed integer range is available for ordering event |
102 | sources.</para> | |
103 | ||
104 | <para>Priorities define the order in which event sources that have | |
105 | seen events are dispatched. Care should be taken to ensure that | |
106 | high-priority event sources (those with negative priority values | |
107 | assigned) do not cause starvation of low-priority event sources | |
108 | (those with positive priority values assigned).</para> | |
109 | ||
110 | <para>The order in which event sources with the same priority are | |
111 | dispatched is undefined, but the event loop generally tries to | |
112 | dispatch them in the order it learnt about events on them. As the | |
113 | backing kernel primitives do not provide accurate information | |
7f3fdb7f | 114 | about the order in which events occurred this is not necessarily |
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115 | reliable. However, it is guaranteed that if events are seen on |
116 | multiple same-priority event sources at the same time, each one is | |
117 | not dispatched again until all others have been dispatched | |
118 | once. This behaviour guarantees that within each priority | |
119 | particular event sources do not starve or dominate the event | |
120 | loop.</para> | |
121 | ||
122 | <para><function>sd_event_source_get_priority()</function> may be | |
123 | used to query the current priority assigned to the event source | |
124 | object <parameter>source</parameter>.</para> | |
125 | </refsect1> | |
126 | ||
127 | <refsect1> | |
128 | <title>Return Value</title> | |
129 | ||
130 | <para>On success, | |
131 | <function>sd_event_source_set_priority()</function> and | |
132 | <function>sd_event_source_get_priority()</function> return a | |
133 | non-negative integer. On failure, they return a negative | |
134 | errno-style error code.</para> | |
135 | </refsect1> | |
136 | ||
137 | <refsect1> | |
138 | <title>Errors</title> | |
139 | ||
140 | <para>Returned errors may indicate the following problems:</para> | |
141 | ||
142 | <variablelist> | |
143 | <varlistentry> | |
144 | <term><constant>-EINVAL</constant></term> | |
145 | ||
146 | <listitem><para><parameter>source</parameter> is not a valid | |
147 | pointer to an <structname>sd_event_source</structname> | |
148 | object.</para></listitem> | |
149 | </varlistentry> | |
150 | ||
151 | <varlistentry> | |
152 | <term><constant>-ENOMEM</constant></term> | |
153 | ||
154 | <listitem><para>Not enough memory.</para></listitem> | |
155 | </varlistentry> | |
156 | ||
157 | <varlistentry> | |
158 | <term><constant>-ESTALE</constant></term> | |
159 | ||
160 | <listitem><para>The event loop is already terminated.</para></listitem> | |
161 | ||
162 | </varlistentry> | |
163 | ||
164 | <varlistentry> | |
165 | <term><constant>-ECHILD</constant></term> | |
166 | ||
167 | <listitem><para>The event loop has been created in a different process.</para></listitem> | |
168 | ||
169 | </varlistentry> | |
170 | ||
171 | </variablelist> | |
172 | </refsect1> | |
173 | ||
174 | <xi:include href="libsystemd-pkgconfig.xml" /> | |
175 | ||
176 | <refsect1> | |
177 | <title>See Also</title> | |
178 | ||
179 | <para> | |
180 | <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
181 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
182 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
183 | <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
184 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
185 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
186 | </para> | |
187 | </refsect1> | |
188 | ||
189 | </refentry> |