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<refentry id="sd_event_add_time">

<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>

<refpurpose>Add a timer event source to an event loop</refpurpose>

</refnamediv>

<refsynopsisdiv>

<funcsynopsis>

<funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>

<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>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_source_get_time</function></funcdef>

<paramdef>sd_event_source *<parameter>source</parameter></paramdef>

<paramdef>usec_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>usec_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>usec_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>usec_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 object. The event loop is specified

in <parameter>event</parameter>, the event source 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> and

<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 takes a time value in

microseconds, relative to the clock's epoch specifying when the

timer shall elapse the earliest. The

<parameter>accuracy</parameter> parameter takes an additional

accuracy value in microseconds specifying a time the timer event

may be delayed. Specify 0 for selecting the default accuracy

(250ms). Specify 1 for most accurate timers. Consider specifying

60000000 or larger (1h) for long-running events that may be

delayed substantially. Picking higher accuracy values allows the

system to coalesce timer events more aggressively, thus improving

power efficiency. The <parameter>handler</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 time it was triggered, however it might

actually have been called at a slightly later time, subject to the

specified accuracy value, the kernel timer slack (see

<citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>)

and additional scheduling latencies.</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

<constant>SD_EVENT_ON</constant> mode is set.

</para>

<para><function>sd_event_source_get_time()</function> retrieves

the configured time value of a timer 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 microseconds in.</para>

<para><function>sd_event_source_set_time()</function> changes the

configured time value of a timer 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 microseconds.</para>

<para><function>sd_event_source_get_time_accuracy()</function>

retrieves the configured accuracy value of a timer 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 microseconds in.</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 an accuracy, in microseconds.</para>

<para><function>sd_event_source_get_time_clock()</function>

retrieves the configured clock of a timer 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 errors 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>

</variablelist>

</refsect1>

<refsect1>

<title>Notes</title>

<para><function>sd_event_add_time()</function> and the other functions

described here are available as a shared library, which can be

compiled and linked to with the

<constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>

file.</para>

</refsect1>

<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_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>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>