325 lines
15 KiB
XML
325 lines
15 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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This file is part of systemd.
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Copyright 2014 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="sd_event_add_time" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_event_add_time</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_add_time</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_add_time</refname>
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<refname>sd_event_source_get_time</refname>
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<refname>sd_event_source_set_time</refname>
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<refname>sd_event_source_get_time_accuracy</refname>
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<refname>sd_event_source_set_time_accuracy</refname>
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<refname>sd_event_source_get_time_clock</refname>
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<refname>sd_event_time_handler_t</refname>
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<refpurpose>Add a timer event source to an event loop</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>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
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<funcprototype>
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<funcdef>typedef int (*<function>sd_event_time_handler_t</function>)</funcdef>
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<paramdef>sd_event_source *<parameter>s</parameter></paramdef>
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<paramdef>uint64_t <parameter>usec</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_add_time</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
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<paramdef>clockid_t <parameter>clock</parameter></paramdef>
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<paramdef>uint64_t <parameter>usec</parameter></paramdef>
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<paramdef>uint64_t <parameter>accuracy</parameter></paramdef>
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<paramdef>sd_event_time_handler_t <parameter>handler</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_get_time</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>uint64_t *<parameter>usec</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_set_time</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>uint64_t <parameter>usec</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_get_time_accuracy</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>uint64_t *<parameter>usec</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_set_time_accuracy</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>uint64_t <parameter>usec</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_get_time_clock</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>clockid_t *<parameter>clock</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_add_time()</function> adds a new timer
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event source to an event loop. The event loop object is specified
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in the <parameter>event</parameter> parameter, the event source
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object is returned in the <parameter>source</parameter>
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parameter. The <parameter>clock</parameter> parameter takes a
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clock identifier, one of <constant>CLOCK_REALTIME</constant>,
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<constant>CLOCK_MONOTONIC</constant>,
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<constant>CLOCK_BOOTTIME</constant>,
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<constant>CLOCK_REALTIME_ALARM</constant> or
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<constant>CLOCK_BOOTTIME_ALARM</constant>. See
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<citerefentry><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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for details regarding the various types of clocks. The
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<parameter>usec</parameter> parameter takes a time value in
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microseconds (µs), relative to the clock's epoch, specifying when
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the timer shall elapse the earliest. If a time that already lies
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in the past is specified (including 0), the timer source is
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dispatched immediately in the next event loop iterations. The
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<parameter>accuracy</parameter> parameter takes an additional
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accuracy value in µs specifying a time the timer event may be
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delayed. Specify 0 for selecting the default accuracy
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(250ms). Specify 1µs for most accurate timers. Consider specifying
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60000000µs or larger (1min) for long-running events that may be
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delayed substantially. Picking higher accuracy values allows the
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system to coalesce timer events more aggressively, thus improving
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power efficiency. The <parameter>handler</parameter> parameter
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shall reference a function to call when the timer elapses. The
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handler function will be passed the
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<parameter>userdata</parameter> pointer, which may be chosen
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freely by the caller. The handler is also passed the configured
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time it was triggered, however it might actually have been called
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at a slightly later time, subject to the specified accuracy value,
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the kernel timer slack (see
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<citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>)
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and additional scheduling latencies. To query the actual time the
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handler was called use
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<citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>By default, the timer will elapse once
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(<constant>SD_EVENT_ONESHOT</constant>), but this may be changed
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with
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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If the handler function returns a negative error code, it will be
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disabled after the invocation, even if the
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<constant>SD_EVENT_ON</constant> mode was requested before. Note
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that a timer event set to <constant>SD_EVENT_ON</constant> will
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fire continously unless its configured time is updated using
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<function>sd_event_source_set_time()</function>.
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</para>
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<para>To destroy an event source object use
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<citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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but note that the event source is only removed from the event loop
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when all references to the event source are dropped. To make sure
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an event source does not fire anymore, even when there's still a
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reference to it kept, consider setting the event source to
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<constant>SD_EVENT_OFF</constant> with
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>If the the second parameter of
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<function>sd_event_add_time()</function> is passed as NULL no
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reference to the event source object is returned. In this case the
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event source is considered "floating", and will be destroyed
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implicitly when the event loop itself is destroyed.</para>
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<para>If the <parameter>handler</parameter> to
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<function>sd_event_add_time()</function> is passed as NULL, and
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the event source fires, this will be considered a request to exit
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the event loop. In this case, the <parameter>userdata</parameter>
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parameter, cast to an integer is used for the exit code passed to
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<citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>Use <constant>CLOCK_BOOTTIME_ALARM</constant> and
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<constant>CLOCK_REALTIME_ALARM</constant> to define event sources
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that may wake up the system from suspend.</para>
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<para>In order to set up relative timers (that is, relative to the
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current time), retrieve the current time via
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<citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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add the desired timespan to sleep to it, and pass the result as
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the <parameter>usec</parameter> parameter to
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<function>sd_event_add_time()</function>.</para>
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<para>In order to set up repetitive timers (that is, timers that
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are triggered in regular intervals), set up the timer normally,
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for the first invocation. Each time the event handler is invoked,
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update the timer's trigger time with
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<citerefentry><refentrytitle>sd_event_source_set_time</refentrytitle><manvolnum>3</manvolnum></citerefentry> for the next timer
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iteration, and reenable the timer using
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<function>sd_event_source_set_enabled()</function>. To calculate
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the next point in time to pass to
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<function>sd_event_source_set_time()</function>, either use as
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base the <parameter>usec</parameter> parameter passed to the timer
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callback, or the timestamp returned by
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<function>sd_event_now()</function>. In the former case timer
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events will be regular, while in the latter case the scheduling
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latency will keep accumulating on the timer.</para>
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<para><function>sd_event_source_get_time()</function> retrieves
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the configured time value of a timer event source created
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previously with <function>sd_event_add_time()</function>. It takes
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the event source object and a pointer to a variable to store the
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time, relative to the selected clock's epoch, in µs in.</para>
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<para><function>sd_event_source_set_time()</function> changes the
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configured time value of a timer event source created previously
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with <function>sd_event_add_time()</function>. It takes the event
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source object and a time relative to the selected clock's
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epoch, in µs.</para>
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<para><function>sd_event_source_get_time_accuracy()</function>
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retrieves the configured accuracy value of a timer event source
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created previously with <function>sd_event_add_time()</function>. It
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takes the event source object and a pointer to a variable to store
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the accuracy in µs in.</para>
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<para><function>sd_event_source_set_time_accuracy()</function>
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changes the configured accuracy of a timer event source created
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previously with <function>sd_event_add_time()</function>. It takes
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the event source object and an accuracy, in µs.</para>
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<para><function>sd_event_source_get_time_clock()</function>
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retrieves the configured clock of a timer event source created
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previously with <function>sd_event_add_time()</function>. It takes
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the event source object and a pointer to a variable to store the
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clock identifier in.</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, these functions return 0 or a positive
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integer. On failure, they return a negative errno-style error
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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>-ENOMEM</constant></term>
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<listitem><para>Not enough memory to allocate an object.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>An invalid argument has been passed.</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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<varlistentry>
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<term><constant>-EOPNOTSUPP</constant></term>
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<listitem><para>The selected clock is not supported by the event loop implementation.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EDOM</constant></term>
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<listitem><para>The passed event source is not a timer event source.</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>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_now</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_signal</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_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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