Merge pull request #2224 from keszybz/analyze-verify-warning

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

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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

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

  <refentryinfo>
    <title>sd_event_add_signal</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <contrib>More text</contrib>
        <firstname>Zbigniew</firstname>
        <surname>Jędrzejewski-Szmek</surname>
        <email>zbyszek@in.waw.pl</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_event_add_signal</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_event_add_signal</refname>
    <refname>sd_event_source_get_signal</refname>
    <refname>sd_event_signal_handler_t</refname>

    <refpurpose>Add a UNIX process signal event source to an event
    loop</refpurpose>
  </refnamediv>

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

      <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>

      <funcprototype>
        <funcdef>typedef int (*<function>sd_event_signal_handler_t</function>)</funcdef>
        <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
        <paramdef>const struct signalfd_siginfo *<parameter>si</parameter></paramdef>
        <paramdef>void *<parameter>userdata</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_event_add_signal</function></funcdef>
        <paramdef>sd_event *<parameter>event</parameter></paramdef>
        <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
        <paramdef>int <parameter>signal</parameter></paramdef>
        <paramdef>sd_event_signal_handler_t <parameter>handler</parameter></paramdef>
        <paramdef>void *<parameter>userdata</parameter></paramdef>
      </funcprototype>

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

    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_event_add_signal()</function> adds a new UNIX
    process signal event source to an event loop. The event loop
    object is specified in the <parameter>event</parameter> parameter,
    and the event source object is returned in the
    <parameter>source</parameter> parameter. The
    <parameter>signal</parameter> parameter specifies the numeric
    signal to be handled (see <citerefentry
    project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>).
    The <parameter>handler</parameter> parameter must reference a
    function to call when the signal is received or be
    <constant>NULL</constant>.  The handler function will be passed
    the <parameter>userdata</parameter> pointer, which may be chosen
    freely by the caller. The handler also receives a pointer to a
    <structname>signalfd_siginfo</structname> structure containing
    information about the received signal. See <citerefentry
    project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>
    for further information.</para>

    <para>Only a single handler may be installed for a specific
    signal. The signal will be unblocked by this call, and must be
    blocked before this function is called in all threads (using
    <citerefentry
    project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry>). If
    the handler is not specified (<parameter>handler</parameter> is
    <constant>NULL</constant>), a default handler which causes the
    program to exit cleanly will be used.</para>

    <para>By default, the event source is enabled permanently
    (<constant>SD_EVENT_ON</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 the
    <constant>SD_EVENT_ON</constant> mode was requested before.
    </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_signal()</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><function>sd_event_source_get_signal()</function> retrieves
    the configured UNIX process signal number of a signal event source
    created previously with
    <function>sd_event_add_signal()</function>. It takes the event
    source object as the <parameter>source</parameter>
    parameter.</para>

  </refsect1>

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

    <para>On success, these functions return 0 or a positive
    integer. On failure, they return a negative errno-style error
    code. </para>
  </refsect1>

  <refsect1>
    <title>Errors</title>

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

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

        <listitem><para>Not enough memory to allocate an object.</para></listitem>
      </varlistentry>

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

        <listitem><para>An invalid argument has been passed.</para></listitem>

      </varlistentry>

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

        <listitem><para>A handler is already installed for this
        signal or the signal was not blocked previously.</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>

      <varlistentry>
        <term><constant>-EDOM</constant></term>

        <listitem><para>The passed event source is not a signal event source.</para></listitem>
      </varlistentry>

    </variablelist>
  </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</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_time</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_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>