"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
+ SPDX-License-Identifier: LGPL-2.1+
+
This file is part of systemd.
Copyright 2014 Lennart Poettering
<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 takes a time value in
- microseconds (µs), relative to the clock's epoch, specifying when
- the timer shall elapse the earliest. If a time that already lies
- in the past is specified (including 0), the timer source is
- dispatched immediately in the next event loop iterations. The
- <parameter>accuracy</parameter> parameter takes an additional
- accuracy value in µs specifying a time the timer event may be
- delayed. Specify 0 for selecting the default accuracy
- (250ms). Specify 1µs for most accurate timers. Consider specifying
- 60000000µs or larger (1min) 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> 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. To query the actual time the
- handler was called use
+ <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 parameter 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
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 continously unless its configured time is updated using
+ fire continuously unless its configured time is updated using
<function>sd_event_source_set_time()</function>.
</para>
<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 when there's still a
- reference to it kept, consider setting the event source to
- <constant>SD_EVENT_OFF</constant> with
- <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
-
- <para>If the the second parameter of
- <function>sd_event_add_time()</function> is passed as NULL 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>
+ 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 passed as NULL, 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
+ <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
<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 sleep to it, and pass the result as
+ add the desired timespan to it, and use the result as
the <parameter>usec</parameter> parameter to
<function>sd_event_add_time()</function>.</para>
latency will keep accumulating on the timer.</para>
<para><function>sd_event_source_get_time()</function> retrieves
- the configured time value of a timer event source created
+ 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, relative to the selected clock's epoch, in µs in.</para>
+ time in, relative to the selected clock's epoch, in µs.</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 µs.</para>
+ 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 timer event source
+ retrieves the configured accuracy 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 accuracy in µs in.</para>
+ 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 an accuracy, in µs.</para>
+ the event source object and accuracy, in µs.</para>
<para><function>sd_event_source_get_time_clock()</function>
- retrieves the configured clock of a timer event source created
+ retrieves the configured clock 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
clock identifier in.</para>
<refsect1>
<title>Errors</title>
- <para>Returned errors may indicate the following problems:</para>
+ <para>Returned values may indicate the following problems:</para>
<variablelist>
<varlistentry>
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