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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 | <!-- | |
572eb058 ZJS |
6 | SPDX-License-Identifier: LGPL-2.1+ |
7 | ||
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8 | This file is part of systemd. |
9 | ||
10 | Copyright 2015 Lennart Poettering | |
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11 | --> |
12 | ||
13 | <refentry id="sd_event_source_set_priority" xmlns:xi="http://www.w3.org/2001/XInclude"> | |
14 | ||
15 | <refentryinfo> | |
16 | <title>sd_event_source_set_priority</title> | |
17 | <productname>systemd</productname> | |
18 | ||
19 | <authorgroup> | |
20 | <author> | |
21 | <contrib>Developer</contrib> | |
22 | <firstname>Lennart</firstname> | |
23 | <surname>Poettering</surname> | |
24 | <email>lennart@poettering.net</email> | |
25 | </author> | |
26 | </authorgroup> | |
27 | </refentryinfo> | |
28 | ||
29 | <refmeta> | |
30 | <refentrytitle>sd_event_source_set_priority</refentrytitle> | |
31 | <manvolnum>3</manvolnum> | |
32 | </refmeta> | |
33 | ||
34 | <refnamediv> | |
35 | <refname>sd_event_source_set_priority</refname> | |
36 | <refname>sd_event_source_get_priority</refname> | |
37 | <refname>SD_EVENT_PRIORITY_IMPORTANT</refname> | |
38 | <refname>SD_EVENT_PRIORITY_NORMAL</refname> | |
39 | <refname>SD_EVENT_PRIORITY_IDLE</refname> | |
40 | ||
41 | <refpurpose>Set or retrieve the priority of event sources</refpurpose> | |
42 | </refnamediv> | |
43 | ||
44 | <refsynopsisdiv> | |
45 | <funcsynopsis> | |
46 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> | |
47 | ||
48 | <funcsynopsisinfo><token>enum</token> { | |
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49 | <constant>SD_EVENT_PRIORITY_IMPORTANT</constant> = -100, |
50 | <constant>SD_EVENT_PRIORITY_NORMAL</constant> = 0, | |
51 | <constant>SD_EVENT_PRIORITY_IDLE</constant> = 100, | |
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52 | };</funcsynopsisinfo> |
53 | ||
54 | <funcprototype> | |
55 | <funcdef>int <function>sd_event_source_set_priority</function></funcdef> | |
56 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
57 | <paramdef>int64_t <parameter>priority</parameter></paramdef> | |
58 | </funcprototype> | |
59 | ||
60 | <funcprototype> | |
61 | <funcdef>int <function>sd_event_source_get_priority</function></funcdef> | |
62 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
63 | <paramdef>int64_t *<parameter>priority</parameter></paramdef> | |
64 | </funcprototype> | |
65 | ||
66 | </funcsynopsis> | |
67 | </refsynopsisdiv> | |
68 | ||
69 | <refsect1> | |
70 | <title>Description</title> | |
71 | ||
72 | <para><function>sd_event_source_set_priority()</function> may be | |
73 | used to set the priority for the event source object specified as | |
74 | <parameter>source</parameter>. The priority is specified as an | |
75 | arbitrary signed 64bit integer. The priority is initialized to | |
76 | <constant>SD_EVENT_PRIORITY_NORMAL</constant> (0) when the event | |
77 | source is allocated with a call such as | |
78 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
79 | or | |
80 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
81 | 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 | |
82 | event sources' priorities. Event sources with smaller priority | |
83 | values are dispatched first. As well-known points of reference, | |
84 | the constants <constant>SD_EVENT_PRIORITY_IMPORTANT</constant> | |
85 | (-100), <constant>SD_EVENT_PRIORITY_NORMAL</constant> (0) and | |
86 | <constant>SD_EVENT_PRIORITY_IDLE</constant> (100) may be used to | |
87 | indicate event sources that shall be dispatched early, normally or | |
88 | late. It is recommended to specify priorities based on these | |
ccddd104 | 89 | definitions, and relative to them — however, the full 64bit |
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90 | signed integer range is available for ordering event |
91 | sources.</para> | |
92 | ||
93 | <para>Priorities define the order in which event sources that have | |
94 | seen events are dispatched. Care should be taken to ensure that | |
95 | high-priority event sources (those with negative priority values | |
96 | assigned) do not cause starvation of low-priority event sources | |
97 | (those with positive priority values assigned).</para> | |
98 | ||
99 | <para>The order in which event sources with the same priority are | |
100 | dispatched is undefined, but the event loop generally tries to | |
101 | dispatch them in the order it learnt about events on them. As the | |
102 | backing kernel primitives do not provide accurate information | |
7f3fdb7f | 103 | about the order in which events occurred this is not necessarily |
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104 | reliable. However, it is guaranteed that if events are seen on |
105 | multiple same-priority event sources at the same time, each one is | |
106 | not dispatched again until all others have been dispatched | |
2dd67817 | 107 | once. This behavior guarantees that within each priority |
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108 | particular event sources do not starve or dominate the event |
109 | loop.</para> | |
110 | ||
111 | <para><function>sd_event_source_get_priority()</function> may be | |
112 | used to query the current priority assigned to the event source | |
113 | object <parameter>source</parameter>.</para> | |
114 | </refsect1> | |
115 | ||
116 | <refsect1> | |
117 | <title>Return Value</title> | |
118 | ||
119 | <para>On success, | |
120 | <function>sd_event_source_set_priority()</function> and | |
121 | <function>sd_event_source_get_priority()</function> return a | |
122 | non-negative integer. On failure, they return a negative | |
123 | errno-style error code.</para> | |
124 | </refsect1> | |
125 | ||
126 | <refsect1> | |
127 | <title>Errors</title> | |
128 | ||
129 | <para>Returned errors may indicate the following problems:</para> | |
130 | ||
131 | <variablelist> | |
132 | <varlistentry> | |
133 | <term><constant>-EINVAL</constant></term> | |
134 | ||
135 | <listitem><para><parameter>source</parameter> is not a valid | |
136 | pointer to an <structname>sd_event_source</structname> | |
137 | object.</para></listitem> | |
138 | </varlistentry> | |
139 | ||
140 | <varlistentry> | |
141 | <term><constant>-ENOMEM</constant></term> | |
142 | ||
143 | <listitem><para>Not enough memory.</para></listitem> | |
144 | </varlistentry> | |
145 | ||
146 | <varlistentry> | |
147 | <term><constant>-ESTALE</constant></term> | |
148 | ||
149 | <listitem><para>The event loop is already terminated.</para></listitem> | |
150 | ||
151 | </varlistentry> | |
152 | ||
153 | <varlistentry> | |
154 | <term><constant>-ECHILD</constant></term> | |
155 | ||
156 | <listitem><para>The event loop has been created in a different process.</para></listitem> | |
157 | ||
158 | </varlistentry> | |
159 | ||
160 | </variablelist> | |
161 | </refsect1> | |
162 | ||
163 | <xi:include href="libsystemd-pkgconfig.xml" /> | |
164 | ||
165 | <refsect1> | |
166 | <title>See Also</title> | |
167 | ||
168 | <para> | |
169 | <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
170 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
171 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
172 | <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
173 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
174 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
175 | </para> | |
176 | </refsect1> | |
177 | ||
178 | </refentry> |