--- /dev/null
+<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<!--
+ This file is part of systemd.
+
+ Copyright 2016 Lennart Poettering
+
+ systemd is free software; you can redistribute it and/or modify it
+ under the terms of the GNU Lesser General Public License as published by
+ the Free Software Foundation; either version 2.1 of the License, or
+ (at your option) any later version.
+
+ systemd is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License
+ along with systemd; If not, see <http://www.gnu.org/licenses/>.
+-->
+
+<refentry id="sd_bus_track_new">
+
+ <refentryinfo>
+ <title>sd_bus_track_new</title>
+ <productname>systemd</productname>
+
+ <authorgroup>
+ <author>
+ <contrib>Developer</contrib>
+ <firstname>Lennart</firstname>
+ <surname>Poettering</surname>
+ <email>lennart@poettering.net</email>
+ </author>
+ </authorgroup>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>sd_bus_track_new</refentrytitle>
+ <manvolnum>3</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>sd_bus_track_new</refname>
+ <refname>sd_bus_track_ref</refname>
+ <refname>sd_bus_track_unref</refname>
+ <refname>sd_bus_track_unrefp</refname>
+ <refname>sd_bus_track_set_recursive</refname>
+ <refname>sd_bus_track_get_recursive</refname>
+ <refname>sd_bus_track_get_bus</refname>
+ <refname>sd_bus_track_get_userdata</refname>
+ <refname>sd_bus_track_set_userdata</refname>
+
+ <refpurpose>Track bus peers</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
+
+ <funcprototype>
+ <funcdef>int <function>sd_bus_track_new</function></funcdef>
+ <paramdef>sd_bus* <parameter>bus</parameter></paramdef>
+ <paramdef>sd_bus_track** <parameter>ret</parameter></paramdef>
+ <paramdef>sd_bus_track_handler_t <parameter>handler</parameter></paramdef>
+ <paramdef>void* <parameter>userdata</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>sd_bus_track *<function>sd_bus_track_ref</function></funcdef>
+ <paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>sd_bus_track *<function>sd_bus_track_unref</function></funcdef>
+ <paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>void <function>sd_bus_track_unrefp</function></funcdef>
+ <paramdef>sd_bus_track **<parameter>t</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_bus_track_get_recursive</function></funcdef>
+ <paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_bus_track_set_recursive</function></funcdef>
+ <paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
+ <paramdef>int <parameter>b</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>sd_bus* <function>sd_bus_track_get_bus</function></funcdef>
+ <paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>void* <function>sd_bus_track_get_userdata</function></funcdef>
+ <paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>void* <function>sd_bus_track_set_userdata</function></funcdef>
+ <paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
+ <paramdef>void *userdata</paramdef>
+ </funcprototype>
+
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para><function>sd_bus_track_new()</function> creates a new bus peer tracking object. The object is allocated for
+ the specified bus, and returned in the <parameter>*ret</parameter> parameter. After use, the object should be freed
+ again by dropping the acquired reference with <function>sd_bus_track_unref()</function> (see below). A bus peer
+ tracking object may be used to keep track of peers on a specific IPC bus, for cases where peers are making use of
+ one or more local objects, in order to control the lifecycle of the local objects and ensure they stay around as
+ long as the peers needing them are around, and unreferenced (and possibly destroyed) as soon as all relevant peers
+ have vanished. Each bus peer tracking object may be used to track zero, one or more peers add a time. References to
+ specific bus peers are added via
+ <citerefentry><refentrytitle>sd_bus_track_add_name</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
+ <function>sd_bus_track_add_sender()</function>. They may be dropped again via
+ <function>sd_bus_track_remove_name()</function> and
+ <function>sd_bus_track_remove_sender()</function>. Alternatively, references on peers are removed automatically
+ when they disconnect from the bus. If non-NULL the <parameter>handler</parameter> may specify a function that is
+ invoked whenever the last reference is dropped, regardless whether the reference is dropped explicitly via
+ <function>sd_bus_track_remove_name()</function> or implicitly because the peer disconnected from the bus. The final
+ argument <parameter>userdata</parameter> may be used to attach a generic user data pointer to the object. This
+ pointer is passed to the handler callback when it is invoked.</para>
+
+ <para><function>sd_bus_track_ref()</function> creates a new reference to a bus peer tracking object. This object
+ will not be destroyed until <function>sd_bus_track_unref()</function> has been called as many times plus once
+ more. Once the reference count has dropped to zero, the specified object cannot be used anymore, further calls to
+ <function>sd_bus_track_ref()</function> or <function>sd_bus_track_unref()</function> on the same object are
+ illegal.</para>
+
+ <para><function>sd_bus_track_unref()</function> destroys a reference to a bus peer tracking object.</para>
+
+ <para><function>sd_bus_track_unrefp()</function> is similar to <function>sd_bus_track_unref()</function> but takes
+ a pointer to a pointer to an <type>sd_bus_track</type> object. This call is useful in conjunction with GCC's and
+ LLVM's <ulink url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up Variable
+ Attribute</ulink>. Note that this function is defined as inline function.</para>
+
+ <para><function>sd_bus_track_ref()</function>, <function>sd_bus_track_unref()</function> and
+ <function>sd_bus_track_unrefp()</function> execute no operation if the passed in bus peer tracking object is
+ <constant>NULL</constant>.</para>
+
+ <para>Bus peer tracking objects may exist in two modes: by default they operate in non-recursive mode, but may
+ optionally be switched into recursive mode. If operating in the default non-recursive mode a peer is either tracked
+ or not tracked. In this mode invoking <function>sd_bus_track_add_name()</function> multiple times in a row for the
+ same peer is fully equivalent to calling it just once, as the call adds the peer to the set of tracked peers if
+ necessary, and executes no operation if the peer is already being tracked. A single invocation of
+ <function>sd_bus_track_remove_name()</function> removes the reference on the peer again, regardless how many times
+ <function>sd_bus_track_add_name()</function> was called before. If operating in recursive mode, the number of times
+ <function>sd_bus_track_add_name()</function> is invoked for the same peer name is counted and
+ <function>sd_bus_track_remove_name()</function> must be called the same number of times before the peer is not
+ tracked anymore, with the exception when the tracked peer vanishes from the bus, in which case the count is
+ irrelevant and the tracking of the specific peer is immediately
+ removed. <function>sd_bus_track_get_recursive()</function> may be used to determine whether the bus peer tracking
+ object is operating in recursive mode. <function>sd_bus_track_set_recursive()</function> may be used to enable or
+ disable recursive mode. By default a bus peer tracking object operates in non-recursive mode, and
+ <function>sd_bus_track_get_recursive()</function> for a newly allocated object hence returns a value equal to
+ zero. Use <function>sd_bus_track_set_recursive()</function> to enable recursive mode, right after allocation. It
+ takes a boolean argument to enable or disable recursive mode. Note that tracking objects for which
+ <function>sd_bus_track_add_name()</function> was already invoked at least once (and which hence track already one
+ or more peers) may not be switched from recursive to non-recursive mode anymore.</para>
+
+ <para><function>sd_bus_track_get_bus()</function> returns the bus object the bus peer tracking object belongs
+ to. It returns the bus object initially passed to <function>sd_bus_track_new()</function> when the object was
+ allocated.</para>
+
+ <para><function>sd_bus_track_get_userdata()</function> returns the generic user data pointer set on the bus peer
+ tracking object at the time of creation using <function>sd_bus_track_new()</function> or at a later time, using
+ <function>sd_bus_track_set_userdata()</function>.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Return Value</title>
+
+ <para>On success, <function>sd_bus_track_new()</function> and <function>sd_bus_track_set_recursive()</function>
+ return 0 or a positive integer. On failure, they return a negative errno-style error code.</para>
+
+ <para><function>sd_bus_track_ref()</function> always returns the argument.</para>
+
+ <para><function>sd_bus_track_unref()</function> always returns <constant>NULL</constant>.</para>
+
+ <para><function>sd_bus_track_get_recursive()</function> returns 0 if non-recursive mode is selected (default), and
+ greater than 0 if recursive mode is selected. On failure a negative errno-style error code is returned.</para>
+
+ <para><function>sd_bus_track_get_bus()</function> returns the bus object associated to the bus peer tracking
+ object.</para>
+
+ <para><function>sd_bus_track_get_userdata()</function> returns the generic user data pointer associated with the
+ bus peer tracking object. <function>sd_bus_track_set_userdata()</function> returns the previous user data pointer
+ set.</para>
+
+ </refsect1>
+
+ <refsect1>
+ <title>Reference ownership</title>
+
+ <para>The <function>sd_bus_track_new()</function> function creates a new object and the caller owns the sole
+ reference. When not needed anymore, this reference should be destroyed with
+ <function>sd_bus_track_unref()</function>.
+ </para>
+ </refsect1>
+
+ <refsect1>
+ <title>Errors</title>
+
+ <para>Returned errors may indicate the following problems:</para>
+
+ <variablelist>
+
+ <varlistentry>
+ <term><constant>-EBUSY</constant></term>
+
+ <listitem><para>Bus peers have already been added to the bus peer tracking object and
+ <function>sd_bus_track_set_recursive()</function> was called to change tracking mode.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><constant>-EINVAL</constant></term>
+
+ <listitem><para>Specified parameter is invalid
+ (<constant>NULL</constant> in case of output
+ parameters).</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><constant>-ENOMEM</constant></term>
+
+ <listitem><para>Memory allocation failed.</para></listitem>
+ </varlistentry>
+
+ </variablelist>
+ </refsect1>
+
+ <refsect1>
+ <title>Notes</title>
+
+ <para><function>sd_bus_track_new()</function> and the other calls described here are available as a shared library,
+ which can be compiled and linked to with the <constant>libelogind</constant> <citerefentry
+ project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ <citerefentry><refentrytitle>sd_bus_track_add_name</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>
~ianmdlvl / elogind.git / blobdiff