Lennart Poettering
818bf54632
This part of the copyright blurb stems from the GPL use recommendations: https://www.gnu.org/licenses/gpl-howto.en.html The concept appears to originate in times where version control was per file, instead of per tree, and was a way to glue the files together. Ultimately, we nowadays don't live in that world anymore, and this information is entirely useless anyway, as people are very welcome to copy these files into any projects they like, and they shouldn't have to change bits that are part of our copyright header for that. hence, let's just get rid of this old cruft, and shorten our codebase a bit.
183 lines
7.1 KiB
XML
183 lines
7.1 KiB
XML
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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SPDX-License-Identifier: LGPL-2.1+
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Copyright 2015 Lennart Poettering
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-->
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<refentry id="sd_event_source_set_priority" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_event_source_set_priority</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_event_source_set_priority</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_event_source_set_priority</refname>
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<refname>sd_event_source_get_priority</refname>
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<refname>SD_EVENT_PRIORITY_IMPORTANT</refname>
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<refname>SD_EVENT_PRIORITY_NORMAL</refname>
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<refname>SD_EVENT_PRIORITY_IDLE</refname>
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<refpurpose>Set or retrieve the priority of event sources</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>
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<funcsynopsisinfo><token>enum</token> {
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<constant>SD_EVENT_PRIORITY_IMPORTANT</constant> = -100,
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<constant>SD_EVENT_PRIORITY_NORMAL</constant> = 0,
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<constant>SD_EVENT_PRIORITY_IDLE</constant> = 100,
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};</funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_event_source_set_priority</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>int64_t <parameter>priority</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_get_priority</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>int64_t *<parameter>priority</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_event_source_set_priority()</function> may be
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used to set the priority for the event source object specified as
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<parameter>source</parameter>. The priority is specified as an
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arbitrary signed 64bit integer. The priority is initialized to
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<constant>SD_EVENT_PRIORITY_NORMAL</constant> (0) when the event
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source is allocated with a call such as
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<citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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or
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<citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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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
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event sources' priorities. Event sources with smaller priority
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values are dispatched first. As well-known points of reference,
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the constants <constant>SD_EVENT_PRIORITY_IMPORTANT</constant>
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(-100), <constant>SD_EVENT_PRIORITY_NORMAL</constant> (0) and
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<constant>SD_EVENT_PRIORITY_IDLE</constant> (100) may be used to
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indicate event sources that shall be dispatched early, normally or
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late. It is recommended to specify priorities based on these
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definitions, and relative to them — however, the full 64bit
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signed integer range is available for ordering event
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sources.</para>
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<para>Priorities define the order in which event sources that have
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seen events are dispatched. Care should be taken to ensure that
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high-priority event sources (those with negative priority values
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assigned) do not cause starvation of low-priority event sources
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(those with positive priority values assigned).</para>
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<para>The order in which event sources with the same priority are
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dispatched is undefined, but the event loop generally tries to
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dispatch them in the order it learnt about events on them. As the
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backing kernel primitives do not provide accurate information
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about the order in which events occurred this is not necessarily
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reliable. However, it is guaranteed that if events are seen on
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multiple same-priority event sources at the same time, each one is
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not dispatched again until all others have been dispatched
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once. This behavior guarantees that within each priority
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particular event sources do not starve or dominate the event
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loop.</para>
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<para>The priority of event sources may be changed at any time of their lifetime, with the exception of inotify
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event sources (i.e. those created with
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<citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>) whose
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priority may only be changed in the time between their initial creation and the first subsequent event loop
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iteration.</para>
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<para><function>sd_event_source_get_priority()</function> may be
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used to query the current priority assigned to the event source
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object <parameter>source</parameter>.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success,
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<function>sd_event_source_set_priority()</function> and
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<function>sd_event_source_get_priority()</function> return a
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non-negative integer. On failure, they return a negative
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errno-style error code.</para>
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</refsect1>
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<refsect1>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para><parameter>source</parameter> is not a valid
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pointer to an <structname>sd_event_source</structname>
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object.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOMEM</constant></term>
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<listitem><para>Not enough memory.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ESTALE</constant></term>
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<listitem><para>The event loop is already terminated.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ECHILD</constant></term>
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<listitem><para>The event loop has been created in a different process.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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