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<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="sd_bus_get_n_queued_read">
<refentryinfo>
<title>sd_bus_get_fd</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_bus_get_n_queued_read</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_bus_get_n_queued_read</refname>
<refname>sd_bus_get_n_queued_write</refname>
<refpurpose>Get the number of pending bus messages in the read and write queues of a bus connection object</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_bus_get_n_queued_read</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
<paramdef>uint64_t *<parameter>ret</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_bus_get_n_queued_write</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
<paramdef>uint64_t *<parameter>ret</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
<function>sd_bus_get_n_queued_read()</function> may be used to query the number of bus messages in the read queue
of a bus connection object. The read queue contains all messages read from the transport medium (e.g. network
socket) but not yet processed locally. The function expects two arguments: the bus object to query, and a pointer
to a 64bit counter variable to write the current queue size to. Use <function>sd_bus_process()</function> in
order to process queued messages, i.e. to reduce the size of the read queue (as well as, in fact, the write
queue, see below).
</para>
<para>
Similarly, <function>sd_bus_get_n_queued_write()</function> may be used to query the number of currently pending
bus messages in the write queue of a bus connection object. The write queue contains all messages enqueued into
the connection with a call such as <function>sd_bus_send()</function> but not yet written to the transport
medium. The expected arguments are similar to <function>sd_bus_get_n_queued_read()</function>. Here too, use
<function>sd_bus_process()</function> to reduce the size of the write queue. Alternatively, use
<function>sd_bus_flush()</function> to synchronously write out any pending bus messages until the write queue is
empty.
</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>
<refsect2>
<title>Errors</title>
<para>Returned errors may indicate the following problems:</para>
<variablelist>
<varlistentry>
<term><constant>-ECHILD</constant></term>
<listitem><para>The bus connection was created in a different process.</para></listitem>
</varlistentry>
</variablelist>
</refsect2>
</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_process</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_flush</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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