fa17b4e8d9
This adds a function sd_bus_slot_set_destroy_callback() to set a function which can free userdata or perform other cleanups. sd_bus_slot_get_destory_callback() queries the callback, and is included for completeness. Without something like this, for floating asynchronous callbacks, which might be called or not, depending on the sequence of events, it's hard to perform resource cleanup. The alternative would be to always perform the cleanup from the caller too, but that requires more coordination and keeping of some shared state. It's nicer to keep the cleanup contained between the callback and the function that requests the callback.
106 lines
4 KiB
XML
106 lines
4 KiB
XML
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1+ -->
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<refentry id="sd_bus_slot_set_destroy_callback"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_bus_slot_set_destroy_callback</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_bus_slot_set_destroy_callback</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_bus_slot_set_destroy_callback</refname>
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<refname>sd_bus_slot_get_destroy_callback</refname>
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<refpurpose>Define the callback function for resource cleanup.</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>typedef int (*<function>sd_bus_destroy_t</function>)</funcdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_slot_set_destroy_callback</function></funcdef>
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<paramdef>sd_bus_slot *<parameter>slot</parameter></paramdef>
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<paramdef>sd_bus_destroy_t <parameter>callback</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_slot_get_destroy_callback</function></funcdef>
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<paramdef>sd_bus_slot *<parameter>slot</parameter></paramdef>
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<paramdef>sd_bus_destroy_t *<parameter>callback</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_bus_slot_set_destroy_callback()</function> sets
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<parameter>callback</parameter> as the callback function to be called right before the bus slot
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object <parameter>slot</parameter> is deallocated. The <parameter>userdata</parameter> pointer
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from the slot object will be passed as the <parameter>userdata</parameter> parameter. This
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pointer can be set specified as an argument to the constuctor functions, see
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<citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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or directly, see
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<citerefentry><refentrytitle>sd_bus_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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This callback function is called even if <parameter>userdata</parameter> is
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<constant>NULL</constant>.</para>
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<para><function>sd_bus_slot_get_destroy_callback()</function> returns the current callback
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for <parameter>slot</parameter> in the <parameter>callback</parameter> parameter.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success, <function>sd_bus_slot_set_destroy_callback()</function> returns 0 or a
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positive integer. On failure, it returns a negative errno-style error code.</para>
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<para><function>sd_bus_slot_get_destroy_callback()</function> returns 1 if the destroy callback
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function is set, 0 if not. On failure, it returns a negative errno-style error code.</para>
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</refsect1>
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<refsect1>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>The <parameter>slot</parameter> parameter is <constant>NULL</constant>.
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</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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