NEWS: finalize for v256~rc3

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

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->

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

  <refentryinfo>
    <title>sd_bus_attach_event</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_bus_attach_event</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_bus_attach_event</refname>
    <refname>sd_bus_detach_event</refname>
    <refname>sd_bus_get_event</refname>

    <refpurpose>Attach a bus connection object to an event loop</refpurpose>
  </refnamediv>

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

      <funcprototype>
        <funcdef>int <function>sd_bus_attach_event</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
        <paramdef>sd_event *<parameter>e</parameter></paramdef>
        <paramdef>int <parameter>priority</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_detach_event</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>sd_event *<function>sd_bus_get_event</function></funcdef>
        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_bus_attach_event()</function> attaches the specified bus connection object to an
    <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry> event loop object at
    the specified priority (see
    <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    for details on event loop priorities). When a bus connection object is attached to an event loop incoming messages
    will be automatically read and processed, and outgoing messages written, whenever the event loop is run. When the
    event loop is about to terminate, the bus connection is automatically flushed and closed (see
    <citerefentry><refentrytitle>sd_bus_set_close_on_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
    details on this). By default bus connection objects are not attached to any event loop. When a bus connection
    object is attached to one it is not necessary to invoke
    <citerefentry><refentrytitle>sd_bus_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
    <citerefentry><refentrytitle>sd_bus_process</refentrytitle><manvolnum>3</manvolnum></citerefentry> as this
    functionality is handled automatically by the event loop.</para>

    <para><function>sd_bus_detach_event()</function> detaches a bus object from its event loop.</para>

    <para>The <function>sd_bus_get_event()</function> returns the event loop object the specified bus object is
    currently attached to, or <constant>NULL</constant> if it is currently not attached to any.</para>

    <para>Note that <function>sd_bus_attach_event()</function> is only one of three supported ways to implement I/O
    event handling for bus connections. Alternatively use
    <citerefentry><refentrytitle>sd_bus_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry> for hooking up a
    bus connection object with external or manual event loops. Or use
    <citerefentry><refentrytitle>sd_bus_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry> as a simple
    synchronous, blocking I/O waiting call.</para>
  </refsect1>

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

    <para>On success, <function>sd_bus_attach_event()</function> and <function>sd_bus_detach_event()</function> return
    0 or a positive integer. On failure, they return a negative errno-style error code.</para>

    <para><function>sd_bus_get_event()</function> returns an event loop object or <constant>NULL</constant>.</para>

    <refsect2>
      <title>Errors</title>

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

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

          <listitem><para>The bus connection has been created in a different process, library or module instance.</para></listitem>
        </varlistentry>
      </variablelist>
    </refsect2>
  </refsect1>

  <xi:include href="libsystemd-pkgconfig.xml" />

  <refsect1>
    <title>History</title>
    <para><function>sd_bus_attach_event()</function>,
    <function>sd_bus_detach_event()</function>, and
    <function>sd_bus_get_event()</function> were added in version 221.</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>

    <para><simplelist type="inline">
      <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_bus_set_close_on_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_bus_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_bus_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
    </simplelist></para>
  </refsect1>

</refentry>