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b1de39dec8
Logically, this is better, because we're describing a subset of possible return values. Visually this also looks quite good because groff renders refsect2 much less prominently. Also rewrap things, add <constant> in various places, fix some typos.
288 lines
14 KiB
XML
288 lines
14 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1+ -->
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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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</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 event source to an event loop. The event loop
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object is specified in the <parameter>event</parameter> parameter, the event source object is returned in the
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<parameter>source</parameter> parameter. The <parameter>clock</parameter> parameter takes a clock identifier, one
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of <constant>CLOCK_REALTIME</constant>, <constant>CLOCK_MONOTONIC</constant>, <constant>CLOCK_BOOTTIME</constant>,
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<constant>CLOCK_REALTIME_ALARM</constant>, or <constant>CLOCK_BOOTTIME_ALARM</constant>. See
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<citerefentry><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details
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regarding the various types of clocks. The <parameter>usec</parameter> parameter specifies the earliest time, in
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microseconds (µs), relative to the clock's epoch, when the timer shall be triggered. If a time already in the past
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is specified (including <constant>0</constant>), this timer source "fires" immediately and is ready to be
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dispatched. If the parameter is specified as <constant>UINT64_MAX</constant> the timer event will never elapse,
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which may be used as an alternative to explicitly disabling a timer event source with
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The
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<parameter>accuracy</parameter> parameter specifies an additional accuracy value in µs specifying how much the
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timer event may be delayed. Use <constant>0</constant> to select the default accuracy (250ms). Use 1µs for maximum
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accuracy. Consider specifying 60000000µs (1min) or larger for long-running events that may be delayed
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substantially. Picking higher accuracy values allows the system to coalesce timer events more aggressively,
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improving power efficiency. The <parameter>handler</parameter> parameter shall reference a function to call when
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the timer elapses. The handler function will be passed the <parameter>userdata</parameter> pointer, which may be
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chosen freely by the caller. The handler is also passed the configured trigger time, even if it is actually called
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slightly later, subject to the specified accuracy value, the kernel timer slack (see
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<citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), and additional
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scheduling latencies. To query the actual time the 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 continuously 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 if it is still referenced,
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disable the event source using
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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with <constant>SD_EVENT_OFF</constant>.</para>
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<para>If the second parameter of
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<function>sd_event_add_time()</function> is
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<constant>NULL</constant> no reference to the event source object
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is returned. In this case the event source is considered
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"floating", and will be destroyed implicitly when the event loop
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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
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<constant>NULL</constant>, and the event source fires, this will
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be considered a request to exit the event loop. In this case, the
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<parameter>userdata</parameter> parameter, cast to an integer, is
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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 it, and use 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 an 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 in, relative to the selected clock's epoch, in µs.</para>
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<para><function>sd_event_source_set_time()</function> changes the
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time of an event source created previously with
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<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 epoch,
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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 an 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. The accuracy is specified in µs.</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 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 an 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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<refsect2>
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<title>Errors</title>
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<para>Returned values 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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</refsect2>
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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_inotify</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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