systemd/man/sd_event_source_set_floating.xml

<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1+ -->

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

  <refentryinfo>
    <title>sd_event_source_set_floating</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_event_source_set_floating</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_event_source_set_floating</refname>
    <refname>sd_event_source_get_floating</refname>

    <refpurpose>Set or retrieve 'floating' state of event sources</refpurpose>
  </refnamediv>

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

      <funcprototype>
        <funcdef>int <function>sd_event_source_set_floating</function></funcdef>
        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
        <paramdef>int <parameter>floating</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_event_source_get_floating</function></funcdef>
        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
      </funcprototype>

    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_event_source_set_floating()</function> takes a boolean and sets the 'floating' state
    of the specified event source object. This is used to change the direction of reference counts for the
    object and the event loop it is associated with. In non-floating mode, the event source object holds a
    reference to the event loop object, but not vice versa. The creator of the event source object must hold
    a reference to it as long as the source should exist. In floating mode, the event loop holds a reference
    to the source object, and will decrease the reference count when being freed. This means that a reference
    to the event loop should be held to prevent both from being destroyed.</para>

    <para>Various calls that allocate event source objects (i.e.
    <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry> and
    similar) will automatically set an event source object to 'floating' mode if the caller passed
    <constant>NULL</constant> in the parameter used to return a reference to the event source object.
    Nevertheless, it may be necessary to gain temporary access to the source object, for example to adjust
    event source properties after allocation (e.g. its priority or description string). In those cases the
    object may be created in non-floating mode, and the returned reference used to adjust the properties, and
    the object marked as floating afterwards, and the reference in the caller dropped.</para>

    <para><function>sd_event_source_get_floating()</function> may be used to query the current 'floating'
    state of the event source object <parameter>source</parameter>. It returns zero if 'floating' mode is
    off, positive if it is on.</para>
  </refsect1>

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

    <para>On success, <function>sd_event_source_set_floating()</function> and
    <function>sd_event_source_get_floating()</function> return a non-negative integer. On failure, they
    return a negative errno-style error code.</para>

    <refsect2>
      <title>Errors</title>

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

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

          <listitem><para><parameter>source</parameter> is not a valid pointer to an
          <structname>sd_event_source</structname> object.</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>
    </refsect2>
  </refsect1>

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

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

    <para>
      <citerefentry><refentrytitle>sd-event</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_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>