units: simplify rescue.service and emergency.service (#5623)

[thirdparty/systemd.git] / man / sd_event_run.xml

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<refentry id="sd_event_run" xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>sd_event_run</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <contrib>Developer</contrib>
        <firstname>Tom</firstname>
        <surname>Gundersen</surname>
        <email>teg@jklm.no</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_event_run</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_event_run</refname>
    <refname>sd_event_loop</refname>

    <refpurpose>Run an event loop</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>

      <funcprototype>
        <funcdef>int <function>sd_event_run</function></funcdef>
        <paramdef>sd_event *<parameter>event</parameter></paramdef>
        <paramdef>uint64_t <parameter>usec</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_event_loop</function></funcdef>
        <paramdef>sd_event *<parameter>event</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_event_run()</function> may be used to run a single
    iteration of the event loop specified in the
    <parameter>event</parameter> parameter. The function waits until an event to
    process is available, and dispatches the registered handler for
    it. The <parameter>usec</parameter> parameter specifies the
    maximum time (in microseconds) to wait for an event. Use
    <constant>(uint64_t) -1</constant> to specify an infinite
    timeout.</para>

    <para><function>sd_event_loop()</function> invokes
    <function>sd_event_run()</function> in a loop, thus implementing
    the actual event loop. The call returns as soon as exiting was
    requested using
    <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>

    <para>The event loop object <parameter>event</parameter> is
    created with
    <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
    Events sources to wait for and their handlers may be registered
    with
    <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>sd_event_add_time</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_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    and
    <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
    </para>

    <para>For low-level control of event loop execution, use
    <citerefentry><refentrytitle>sd_event_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>sd_event_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    and
    <citerefentry><refentrytitle>sd_event_dispatch</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    which are wrapped by <function>sd_event_run()</function>. Along
    with
    <citerefentry><refentrytitle>sd_event_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    these functions allow integration of an
    <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    event loop into foreign event loop implementations.</para>
  </refsect1>

  <refsect1>
    <title>Return Value</title>

    <para>On failure, these functions return a negative errno-style
    error code. <function>sd_event_run()</function> returns a
    positive, non-zero integer if an event source was dispatched, and
    zero when the specified timeout hit before an event source has
    seen any event, and hence no event source was
    dispatched. <function>sd_event_loop()</function> returns the exit
    code specified when invoking
    <function>sd_event_exit()</function>.</para>
  </refsect1>

  <refsect1>
    <title>Errors</title>

    <para>Returned errors may indicate the following problems:</para>

    <variablelist>
      <varlistentry>
        <term><constant>-EINVAL</constant></term>

        <listitem><para>The <parameter>event</parameter> parameter is
        invalid or <constant>NULL</constant>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><constant>-EBUSY</constant></term>

        <listitem><para>The event loop object is not in the right
        state (see
        <citerefentry><refentrytitle>sd_event_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry>
        for an explanation of possible states).</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>

    </variablelist>

    <para>Other errors are possible, too.</para>
  </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_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <ulink url="https://developer.gnome.org/glib/unstable/glib-The-Main-Event-Loop.html">GLib Main Event Loop</ulink>.
    </para>
  </refsect1>

</refentry>