<?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">

<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>