Lennart Poettering
0c69794138
These lines are generally out-of-date, incomplete and unnecessary. With SPDX and git repository much more accurate and fine grained information about licensing and authorship is available, hence let's drop the per-file copyright notice. Of course, removing copyright lines of others is problematic, hence this commit only removes my own lines and leaves all others untouched. It might be nicer if sooner or later those could go away too, making git the only and accurate source of authorship information.
181 lines
7.1 KiB
XML
181 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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-->
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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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