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<?xml version='1.0'?>
<!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+
Copyright © 2016 Julian Orth
-->
<refentry id="sd_bus_process" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_bus_process</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_bus_process</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_bus_process</refname>
<refpurpose>Drive the connection</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_bus_process</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
<paramdef>sd_bus_message **<parameter>ret</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_bus_process()</function> drives the connection between the client and the message bus. That is,
it handles connecting, authentication, and message processing. When invoked pending I/O work is executed, and
queued incoming messages are dispatched to registered callbacks. Each time it is invoked a single operation is
executed. It returns zero when no operations were pending and positive if a message was processed. When zero is
returned the caller should synchronously poll for I/O events before calling into
<function>sd_bus_process()</function> again. For that either user the simple, synchronous
<citerefentry><refentrytitle>sd_bus_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry> call, or hook up
the bus connection object to an external or manual event loop using
<citerefentry><refentrytitle>sd_bus_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para>
<para><function>sd_bus_process()</function> processes at most one incoming message per call. If the parameter
<parameter>ret</parameter> is not <constant>NULL</constant> and the call processed a message,
<parameter>*ret</parameter> is set to this message. The caller owns a reference to this message and should call
<citerefentry><refentrytitle>sd_bus_message_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry> when the
message is no longer needed. If <parameter>ret</parameter> is not NULL, progress was made, but no message was
processed, <parameter>*ret</parameter> is set to <constant>NULL</constant>.</para>
<para>If a the bus object is connected to an
<citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry> event loop (with
<citerefentry><refentrytitle>sd_bus_attach_event</refentrytitle><manvolnum>3</manvolnum></citerefentry>), it is not
necessary to call <function>sd_bus_process()</function> directly as it is invoked automatically when
necessary.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>If progress was made, a positive integer is returned. If no progress was made, 0 is returned. If an error
occurs, a negative <varname>errno</varname>-style error code is returned.</para>
</refsect1>
<refsect1>
<title>Errors</title>
<para>Returned errors may indicate the following problems:</para>
<variablelist>
<varlistentry>
<term><constant>-EINVAL</constant></term>
<listitem><para>An invalid bus object was passed.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ECHILD</constant></term>
<listitem><para>The bus connection was allocated in a parent process and is being reused in a child process
after <function>fork()</function>.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ENOTCONN</constant></term>
<listitem><para>The bus connection has been terminated already.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ECONNRESET</constant></term>
<listitem><para>The bus connection has been terminated just now.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-EBUSY</constant></term>
<listitem><para>This function is already being called, i.e. <function>sd_bus_process()</function> has been
called from a callback function that itself was called by
<function>sd_bus_process()</function>.</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-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_message_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_attach_event</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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