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Diffstat (limited to 'man/sd_event_source_set_priority.xml')
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diff --git a/man/sd_event_source_set_priority.xml b/man/sd_event_source_set_priority.xml new file mode 100644 index 0000000..2616c12 --- /dev/null +++ b/man/sd_event_source_set_priority.xml @@ -0,0 +1,166 @@ +<?xml version='1.0'?> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> +<!-- SPDX-License-Identifier: LGPL-2.1-or-later --> + +<refentry id="sd_event_source_set_priority" xmlns:xi="http://www.w3.org/2001/XInclude"> + + <refentryinfo> + <title>sd_event_source_set_priority</title> + <productname>systemd</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>sd_event_source_set_priority</refentrytitle> + <manvolnum>3</manvolnum> + </refmeta> + + <refnamediv> + <refname>sd_event_source_set_priority</refname> + <refname>sd_event_source_get_priority</refname> + <refname>SD_EVENT_PRIORITY_IMPORTANT</refname> + <refname>SD_EVENT_PRIORITY_NORMAL</refname> + <refname>SD_EVENT_PRIORITY_IDLE</refname> + + <refpurpose>Set or retrieve the priority of event sources</refpurpose> + </refnamediv> + + <refsynopsisdiv> + <funcsynopsis> + <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> + + <funcsynopsisinfo><token>enum</token> { + <constant>SD_EVENT_PRIORITY_IMPORTANT</constant> = -100, + <constant>SD_EVENT_PRIORITY_NORMAL</constant> = 0, + <constant>SD_EVENT_PRIORITY_IDLE</constant> = 100, +};</funcsynopsisinfo> + + <funcprototype> + <funcdef>int <function>sd_event_source_set_priority</function></funcdef> + <paramdef>sd_event_source *<parameter>source</parameter></paramdef> + <paramdef>int64_t <parameter>priority</parameter></paramdef> + </funcprototype> + + <funcprototype> + <funcdef>int <function>sd_event_source_get_priority</function></funcdef> + <paramdef>sd_event_source *<parameter>source</parameter></paramdef> + <paramdef>int64_t *<parameter>priority</parameter></paramdef> + </funcprototype> + + </funcsynopsis> + </refsynopsisdiv> + + <refsect1> + <title>Description</title> + + <para><function>sd_event_source_set_priority()</function> may be + used to set the priority for the event source object specified as + <parameter>source</parameter>. The priority is specified as an + arbitrary signed 64bit integer. The priority is initialized to + <constant>SD_EVENT_PRIORITY_NORMAL</constant> (0) when the event + source is allocated with a call such as + <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry> + or + <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + 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 + event sources' priorities. Event sources with smaller priority + values are dispatched first. As well-known points of reference, + the constants <constant>SD_EVENT_PRIORITY_IMPORTANT</constant> + (-100), <constant>SD_EVENT_PRIORITY_NORMAL</constant> (0) and + <constant>SD_EVENT_PRIORITY_IDLE</constant> (100) may be used to + indicate event sources that shall be dispatched early, normally or + late. It is recommended to specify priorities based on these + definitions, and relative to them — however, the full 64bit + signed integer range is available for ordering event + sources.</para> + + <para>Priorities define the order in which event sources that have + seen events are dispatched. Care should be taken to ensure that + high-priority event sources (those with negative priority values + assigned) do not cause starvation of low-priority event sources + (those with positive priority values assigned).</para> + + <para>The order in which event sources with the same priority are + dispatched is undefined, but the event loop generally tries to + dispatch them in the order it learnt about events on them. As the + backing kernel primitives do not provide accurate information + about the order in which events occurred this is not necessarily + reliable. However, it is guaranteed that if events are seen on + multiple same-priority event sources at the same time, each one is + not dispatched again until all others have been dispatched + once. This behavior guarantees that within each priority + particular event sources do not starve or dominate the event + loop.</para> + + <para>The priority of event sources may be changed at any time of their lifetime, with the exception of inotify + event sources (i.e. those created with + <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>) whose + priority may only be changed in the time between their initial creation and the first subsequent event loop + iteration.</para> + + <para><function>sd_event_source_get_priority()</function> may be + used to query the current priority assigned to the event source + object <parameter>source</parameter>.</para> + </refsect1> + + <refsect1> + <title>Return Value</title> + + <para>On success, <function>sd_event_source_set_priority()</function> and + <function>sd_event_source_get_priority()</function> return a non-negative integer. On failure, they + return a negative errno-style error code.</para> + + <refsect2> + <title>Errors</title> + + <para>Returned errors may indicate the following problems:</para> + + <variablelist> + <varlistentry> + <term><constant>-EINVAL</constant></term> + + <listitem><para><parameter>source</parameter> is not a valid pointer to an + <structname>sd_event_source</structname> object.</para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>-ENOMEM</constant></term> + + <listitem><para>Not enough memory.</para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>-ESTALE</constant></term> + + <listitem><para>The event loop is already terminated.</para></listitem> + + </varlistentry> + + <varlistentry> + <term><constant>-ECHILD</constant></term> + + <listitem><para>The event loop has been created in a different process.</para></listitem> + + </varlistentry> + + </variablelist> + </refsect2> + </refsect1> + + <xi:include href="libsystemd-pkgconfig.xml" /> + + <refsect1> + <title>See Also</title> + + <para> + <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry> + </para> + </refsect1> + +</refentry> |