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-<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
-<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
-"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
-
-<!--
- This file is part of systemd.
-
- Copyright 2014 Lennart Poettering
-
- systemd is free software; you can redistribute it and/or modify it
- under the terms of the GNU Lesser General Public License as published by
- the Free Software Foundation; either version 2.1 of the License, or
- (at your option) any later version.
-
- systemd is distributed in the hope that it will be useful, but
- WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public License
- along with systemd; If not, see <http://www.gnu.org/licenses/>.
--->
-
-<refentry id="sd_event_add_time" xmlns:xi="http://www.w3.org/2001/XInclude">
-
- <refentryinfo>
- <title>sd_event_add_time</title>
- <productname>systemd</productname>
-
- <authorgroup>
- <author>
- <contrib>Developer</contrib>
- <firstname>Lennart</firstname>
- <surname>Poettering</surname>
- <email>lennart@poettering.net</email>
- </author>
- </authorgroup>
- </refentryinfo>
-
- <refmeta>
- <refentrytitle>sd_event_add_time</refentrytitle>
- <manvolnum>3</manvolnum>
- </refmeta>
-
- <refnamediv>
- <refname>sd_event_add_time</refname>
- <refname>sd_event_source_get_time</refname>
- <refname>sd_event_source_set_time</refname>
- <refname>sd_event_source_get_time_accuracy</refname>
- <refname>sd_event_source_set_time_accuracy</refname>
- <refname>sd_event_source_get_time_clock</refname>
- <refname>sd_event_time_handler_t</refname>
-
- <refpurpose>Add a timer event source to an event loop</refpurpose>
- </refnamediv>
-
- <refsynopsisdiv>
- <funcsynopsis>
- <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
-
- <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
-
- <funcprototype>
- <funcdef>typedef int (*<function>sd_event_time_handler_t</function>)</funcdef>
- <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
- <paramdef>uint64_t <parameter>usec</parameter></paramdef>
- <paramdef>void *<parameter>userdata</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef>int <function>sd_event_add_time</function></funcdef>
- <paramdef>sd_event *<parameter>event</parameter></paramdef>
- <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
- <paramdef>clockid_t <parameter>clock</parameter></paramdef>
- <paramdef>uint64_t <parameter>usec</parameter></paramdef>
- <paramdef>uint64_t <parameter>accuracy</parameter></paramdef>
- <paramdef>sd_event_time_handler_t <parameter>handler</parameter></paramdef>
- <paramdef>void *<parameter>userdata</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef>int <function>sd_event_source_get_time</function></funcdef>
- <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
- <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef>int <function>sd_event_source_set_time</function></funcdef>
- <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
- <paramdef>uint64_t <parameter>usec</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef>int <function>sd_event_source_get_time_accuracy</function></funcdef>
- <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
- <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef>int <function>sd_event_source_set_time_accuracy</function></funcdef>
- <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
- <paramdef>uint64_t <parameter>usec</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef>int <function>sd_event_source_get_time_clock</function></funcdef>
- <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
- <paramdef>clockid_t *<parameter>clock</parameter></paramdef>
- </funcprototype>
-
- </funcsynopsis>
- </refsynopsisdiv>
-
- <refsect1>
- <title>Description</title>
-
- <para><function>sd_event_add_time()</function> adds a new timer event source to an event loop. The event loop
- object is specified in the <parameter>event</parameter> parameter, the event source object is returned in the
- <parameter>source</parameter> parameter. The <parameter>clock</parameter> parameter takes a clock identifier, one
- of <constant>CLOCK_REALTIME</constant>, <constant>CLOCK_MONOTONIC</constant>, <constant>CLOCK_BOOTTIME</constant>,
- <constant>CLOCK_REALTIME_ALARM</constant>, or <constant>CLOCK_BOOTTIME_ALARM</constant>. See
- <citerefentry><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details
- regarding the various types of clocks. The <parameter>usec</parameter> parameter specifies the earliest time, in
- microseconds (µs), relative to the clock's epoch, when the timer shall be triggered. If a time already in the past
- is specified (including <constant>0</constant>), this timer source "fires" immediately and is ready to be
- dispatched. If the paramater is specified as <constant>UINT64_MAX</constant> the timer event will never elapse,
- which may be used as an alternative to explicitly disabling a timer event source with
- <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The
- <parameter>accuracy</parameter> parameter specifies an additional accuracy value in µs specifying how much the
- timer event may be delayed. Use <constant>0</constant> to select the default accuracy (250ms). Use 1µs for maximum
- accuracy. Consider specifying 60000000µs (1min) or larger for long-running events that may be delayed
- substantially. Picking higher accuracy values allows the system to coalesce timer events more aggressively,
- improving power efficiency. The <parameter>handler</parameter> parameter shall reference a function to call when
- the timer elapses. The handler function will be passed the <parameter>userdata</parameter> pointer, which may be
- chosen freely by the caller. The handler is also passed the configured trigger time, even if it is actually called
- slightly later, subject to the specified accuracy value, the kernel timer slack (see
- <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), and additional
- scheduling latencies. To query the actual time the handler was called use
- <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
-
- <para>By default, the timer will elapse once
- (<constant>SD_EVENT_ONESHOT</constant>), but this may be changed
- with
- <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
- If the handler function returns a negative error code, it will be
- disabled after the invocation, even if the
- <constant>SD_EVENT_ON</constant> mode was requested before. Note
- that a timer event set to <constant>SD_EVENT_ON</constant> will
- fire continuously unless its configured time is updated using
- <function>sd_event_source_set_time()</function>.
- </para>
-
- <para>To destroy an event source object use
- <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- but note that the event source is only removed from the event loop
- when all references to the event source are dropped. To make sure
- an event source does not fire anymore, even if it is still referenced,
- disable the event source using
- <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
- with <constant>SD_EVENT_OFF</constant>.</para>
-
- <para>If the second parameter of
- <function>sd_event_add_time()</function> is
- <constant>NULL</constant> no reference to the event source object
- is returned. In this case the event source is considered
- "floating", and will be destroyed implicitly when the event loop
- itself is destroyed.</para>
-
- <para>If the <parameter>handler</parameter> to
- <function>sd_event_add_time()</function> is
- <constant>NULL</constant>, and the event source fires, this will
- be considered a request to exit the event loop. In this case, the
- <parameter>userdata</parameter> parameter, cast to an integer, is
- used for the exit code passed to
- <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
-
- <para>Use <constant>CLOCK_BOOTTIME_ALARM</constant> and
- <constant>CLOCK_REALTIME_ALARM</constant> to define event sources
- that may wake up the system from suspend.</para>
-
- <para>In order to set up relative timers (that is, relative to the
- current time), retrieve the current time via
- <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- add the desired timespan to it, and use the result as
- the <parameter>usec</parameter> parameter to
- <function>sd_event_add_time()</function>.</para>
-
- <para>In order to set up repetitive timers (that is, timers that
- are triggered in regular intervals), set up the timer normally,
- for the first invocation. Each time the event handler is invoked,
- update the timer's trigger time with
- <citerefentry><refentrytitle>sd_event_source_set_time</refentrytitle><manvolnum>3</manvolnum></citerefentry> for the next timer
- iteration, and reenable the timer using
- <function>sd_event_source_set_enabled()</function>. To calculate
- the next point in time to pass to
- <function>sd_event_source_set_time()</function>, either use as
- base the <parameter>usec</parameter> parameter passed to the timer
- callback, or the timestamp returned by
- <function>sd_event_now()</function>. In the former case timer
- events will be regular, while in the latter case the scheduling
- latency will keep accumulating on the timer.</para>
-
- <para><function>sd_event_source_get_time()</function> retrieves
- the configured time value of an event source created
- previously with <function>sd_event_add_time()</function>. It takes
- the event source object and a pointer to a variable to store the
- time in, relative to the selected clock's epoch, in µs.</para>
-
- <para><function>sd_event_source_set_time()</function> changes the
- time of an event source created previously with
- <function>sd_event_add_time()</function>. It takes the event
- source object and a time relative to the selected clock's epoch,
- in µs.</para>
-
- <para><function>sd_event_source_get_time_accuracy()</function>
- retrieves the configured accuracy value of a event source
- created previously with <function>sd_event_add_time()</function>. It
- takes the event source object and a pointer to a variable to store
- the accuracy in. The accuracy is specified in µs.</para>
-
- <para><function>sd_event_source_set_time_accuracy()</function>
- changes the configured accuracy of a timer event source created
- previously with <function>sd_event_add_time()</function>. It takes
- the event source object and accuracy, in µs.</para>
-
- <para><function>sd_event_source_get_time_clock()</function>
- retrieves the configured clock of a event source created
- previously with <function>sd_event_add_time()</function>. It takes
- the event source object and a pointer to a variable to store the
- clock identifier in.</para>
- </refsect1>
-
- <refsect1>
- <title>Return Value</title>
-
- <para>On success, these functions return 0 or a positive
- integer. On failure, they return a negative errno-style error
- code. </para>
- </refsect1>
-
- <refsect1>
- <title>Errors</title>
-
- <para>Returned values may indicate the following problems:</para>
-
- <variablelist>
- <varlistentry>
- <term><constant>-ENOMEM</constant></term>
-
- <listitem><para>Not enough memory to allocate an object.</para></listitem>
- </varlistentry>
-
- <varlistentry>
- <term><constant>-EINVAL</constant></term>
-
- <listitem><para>An invalid argument has been passed.</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>
-
- <varlistentry>
- <term><constant>-EOPNOTSUPP</constant></term>
-
- <listitem><para>The selected clock is not supported by the event loop implementation.</para></listitem>
-
- </varlistentry>
-
- <varlistentry>
- <term><constant>-EDOM</constant></term>
-
- <listitem><para>The passed event source is not a timer event source.</para></listitem>
- </varlistentry>
- </variablelist>
- </refsect1>
-
- <xi:include href="libsystemd-pkgconfig.xml" />
-
- <refsect1>
- <title>See Also</title>
-
- <para>
- <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_event_add_io</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_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
- <citerefentry project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
- <citerefentry project='man-pages'><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
- </para>
- </refsect1>
-
-</refentry>