along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
-<refentry id="sd_event_add_time">
+<refentry id="sd_event_add_time" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_event_add_time</title>
<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 <systemd/sd-bus.h></funcsynopsisinfo>
+ <funcsynopsisinfo>#include <systemd/sd-event.h></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>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>u
sec_t *<parameter>usec</parameter></paramdef>
+ <paramdef>u
int64_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>u
sec_t <parameter>usec</parameter></paramdef>
+ <paramdef>u
int64_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>u
sec_t *<parameter>usec</parameter></paramdef>
+ <paramdef>u
int64_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>u
sec_t <parameter>usec</parameter></paramdef>
+ <paramdef>u
int64_t <parameter>usec</parameter></paramdef>
</funcprototype>
<funcprototype>
<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
+ 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, relative to the clock's epoch specifying when the
- timer shall elapse the earliest. The
+ 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 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
+ 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> 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
+ 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.</para>
+ 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
- <constant>SD_EVENT_ON</constant> mode is set.
+ 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
+ <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 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>
+
+ <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
+ <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 sleep to it, and pass 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 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>
+ time, relative to the selected clock's epoch, in µs 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>
+ epoch, in µs.</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>
+ the accuracy in µs 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>
+ the event source object and an accuracy, in µs.</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>
<listitem><para>The selected clock is not supported by the event loop implementation.</para></listitem>
</varlistentry>
- </variablelist>
- </refsect1>
- <refsect1>
- <title>Notes</title>
+ <varlistentry>
+ <term><constant>-EDOM</constant></term>
- <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>
+ <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>
<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>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_event_source_set_enabled</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>
projects / thirdparty / systemd.git / blobdiff