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man: document the new sd_bus_slot_set_floating() call

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Also extend the memory management description of sd-bus highlighting the
effect of "floating" slot objects a bit.
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Lennart Poettering 2018-05-30 16:33:12 +02:00
parent 303acb7f2d
commit 1004b2c7bc
4 changed files with 144 additions and 17 deletions
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1
man/rules/meson.build
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@ -231,6 +231,7 @@ manpages = [
['sd_bus_set_connected_signal', '3', ['sd_bus_get_connected_signal'], ''],
['sd_bus_set_sender', '3', ['sd_bus_get_sender'], ''],
['sd_bus_set_watch_bind', '3', ['sd_bus_get_watch_bind'], ''],
['sd_bus_slot_set_floating', '3', ['sd_bus_slot_get_floating'], ''],
['sd_bus_track_add_name',
'3',
['sd_bus_track_add_sender',

7
man/sd_bus_add_match.xml
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@ -132,7 +132,9 @@
at a later time with
<citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If specified
as <constant>NULL</constant> the lifetime of the match is bound to the lifetime of the bus object itself, and the
match cannot be removed independently.</para>
match is generally not removed independently. See
<citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
details.</para>
<para>The message <parameter>m</parameter> passed to the callback is only borrowed, that is, the callback should
not call <citerefentry><refentrytitle>sd_bus_message_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
@ -175,7 +177,8 @@
<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_message_ref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_set_bus_client</refentrytitle><manvolnum>3</manvolnum></citerefentry>
<citerefentry><refentrytitle>sd_bus_set_bus_client</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>

35
man/sd_bus_default.xml
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@ -206,21 +206,26 @@
<citerefentry><refentrytitle>sd_bus_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>
to drop the reference.</para>
<para>Queued but unwritten/unread messages also keep a reference
to their bus connection object. For this reason, even if an
application dropped all references to a bus connection, it might
not get destroyed right away. Until all incoming queued
messages are read, and until all outgoing unwritten messages are
written, the bus object will stay
alive. <function>sd_bus_flush()</function> may be used to write
all outgoing queued messages so they drop their references. To
flush the unread incoming messages, use
<function>sd_bus_close()</function>, which will also close the bus
connection. When using the default bus logic, it is a good idea to
first invoke <function>sd_bus_flush()</function> followed by
<function>sd_bus_close()</function> when a thread or process
terminates, and thus its bus connection object should be
freed.</para>
<para>Queued but unwritten/unread messages keep a reference to their bus connection object. For this reason, even
if an application dropped all references to a bus connection, it might not get destroyed right away. Until all
incoming queued messages are read, and until all outgoing unwritten messages are written, the bus object will stay
alive. <function>sd_bus_flush()</function> may be used to write all outgoing queued messages so they drop their
references. To flush the unread incoming messages, use <function>sd_bus_close()</function>, which will also close
the bus connection. When using the default bus logic, it is a good idea to first invoke
<function>sd_bus_flush()</function> followed by <function>sd_bus_close()</function> when a thread or process
terminates, and thus its bus connection object should be freed.</para>
<para>Normally, slot objects (as created by
<citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry> and similar
calls) keep a reference to their bus connection object, too. Thus, as long as a bus slot object remains referenced
its bus object will remain allocated too. Optionally, bus slot objects may be placed in "floating" mode. When in
floating mode the life cycle of the bus slot object is bound to the bus object, i.e. when the bus object is freed
the bus slot object is automatically unreferenced too. The floating state of a slot object may be controlled
explicitly with
<citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
though usually floating bus slot objects are created by passing <constant>NULL</constant> as the
<parameter>slot</parameter> parameter of <function>sd_bus_add_match()</function> and related calls, thus indicating
that the caller is not directly interested in referencing and managing the bus slot object.</para>
<para>The life cycle of the default bus connection should be the
responsibility of the code that creates/owns the thread the

118
man/sd_bus_slot_set_floating.xml Normal file
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@ -0,0 +1,118 @@
<?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">
<!-- SPDX-License-Identifier: LGPL-2.1+ -->
<refentry id="sd_bus_slot_set_floating">
<refentryinfo>
<title>sd_bus_slot_set_floating</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_bus_slot_set_floating</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_bus_slot_set_floating</refname>
<refname>sd_bus_slot_get_floating</refname>
<refpurpose>Control whether a bus slot object is "floating".</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_bus_slot_set_floating</function></funcdef>
<paramdef>sd_bus_slot *<parameter>bus</parameter></paramdef>
<paramdef>int <parameter>b</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_bus_slot_get_floating</function></funcdef>
<paramdef>sd_bus_slot *<parameter>slot</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_bus_slot_set_floating()</function> controls whether the specified bus slot object
<parameter>slot</parameter> shall be "floating" or not. A floating bus slot object's lifetime is bound to the
lifetime of the bus object it is associated with, meaning that it remains allocated as long as the bus object
itself and is freed automatically when the bus object is freed. Regular (i.e. non-floating) bus slot objects keep
the bus referenced, hence the bus object remains allocated at least as long as there remains at least one
referenced bus slot object around. The floating state hence controls the direction of referencing between the bus
object and the bus slot objects: if floating the bus pins the the bus slot, and otherwise the bus slot pins the bus
objects. Use <function>sd_bus_slot_set_floating()</function> to switch between both modes: if the
<parameter>b</parameter> parameter is zero, the slot object is considered floating, otherwise it is made a regular
(non-floating) slot object.</para>
<para>Bus slot objects may be allocated with calls such as
<citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If the
<parameter>slot</parameter> of these functions is non-<constant>NULL</constant> the slot object will be of the
regular kind (i.e. non-floating), otherwise it will be created floating. With
<function>sd_bus_slot_set_floating()</function> a bus slot object allocated as regular can be converted into a
floating object and back. This is particularly useful for creating a bus slot object, then changing parameters of
it, and then turning it into a floating object, whose lifecycle is managed by the bus object.</para>
<para><function>sd_bus_slot_get_floating()</function> returns the current floating state of the specified bus slot
object. It returns negative on error, zero if the bus slot object is a regular (non-floating) object and positive
otherwise.</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>-ECHILD</constant></term>
<listitem><para>The bus connection has been created in a different process.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ESTALE</constant></term>
<listitem><para>The bus object the specified bus slot object is associated with has already been freed, and
hence no change in the floating state can be made anymore.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Notes</title>
<para><function>sd_bus_slot_set_floating()</function> and <function>sd_bus_slot_get_floating()</function> are
available as a shared library, which can be compiled and linked to with the
<constant>libsystemd</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_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>