man/sd_event_source_set_enabled.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_enabled" xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>sd_event_source_set_enabled</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_event_source_set_enabled</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_event_source_set_enabled</refname>
    <refname>sd_event_source_get_enabled</refname>
    <refname>SD_EVENT_ON</refname>
    <refname>SD_EVENT_OFF</refname>
    <refname>SD_EVENT_ONESHOT</refname>

    <refpurpose>Enable or disable event sources</refpurpose>
  </refnamediv>

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

      <funcsynopsisinfo><token>enum</token> {
        <constant>SD_EVENT_OFF</constant> = 0,
        <constant>SD_EVENT_ON</constant> = 1,
        <constant>SD_EVENT_ONESHOT</constant> = -1,
};</funcsynopsisinfo>

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

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

    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_event_source_set_enabled()</function> may be
    used to enable or disable the event source object specified as
    <parameter>source</parameter>. The <parameter>enabled</parameter>
    parameter takes one of <constant>SD_EVENT_ON</constant> (to
    enable), <constant>SD_EVENT_OFF</constant> (to disable) or
    <constant>SD_EVENT_ONESHOT</constant>. If invoked with
    <constant>SD_EVENT_ONESHOT</constant> the event source will be
    enabled but automatically reset to
    <constant>SD_EVENT_OFF</constant> after the event source was
    dispatched once.</para>

    <para>Event sources that are disabled will not result in event
    loop wakeups and will not be dispatched, until they are enabled
    again.</para>

    <para><function>sd_event_source_get_enabled()</function> may be
    used to query whether the event source object
    <parameter>source</parameter> is currently enabled or not. It
    returns the enablement state (one of <constant>SD_EVENT_ON</constant>,
    <constant>SD_EVENT_OFF</constant>, <constant>SD_EVENT_ONESHOT</constant>)
    in <parameter>enabled</parameter>, if it is not <constant>NULL</constant>.
    It also returns true if the event source is not disabled.</para>

    <para>Event source objects are enabled when they are first created
    with calls such as
    <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>. However,
    depending on the event source type they are enabled continuously
    (<constant>SD_EVENT_ON</constant>) or only for a single invocation
    of the event source handler
    (<constant>SD_EVENT_ONESHOT</constant>). For details see the
    respective manual pages.</para>

    <para>As event source objects stay active and may be dispatched as
    long as there is at least one reference to them, in many cases it
    is a good idea to combine a call to
    <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    with a prior call to
    <function>sd_event_source_set_enabled()</function> with
    <constant>SD_EVENT_OFF</constant>, to ensure the event source is
    not dispatched again until all other remaining references are dropped.</para>
  </refsect1>

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

    <para>On success, <function>sd_event_source_set_enabled()</function> returns a non-negative
    integer. <function>sd_event_source_get_enabled()</function> returns zero if the source is disabled
    (<constant>SD_EVENT_OFF</constant>) and a positive integer otherwise. 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>-ENOMEM</constant></term>

          <listitem><para>Not enough memory.</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_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>