sd-bus: add APIs to query the current read and write queue size

1 files changed, 129 insertions, 0 deletions

diff --git a/man/sd_bus_get_n_queued_read.xml b/man/sd_bus_get_n_queued_read.xml
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+<?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+
+
+  This file is part of systemd.
+
+  Copyright 2018 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_get_n_queued_read">
+
+  <refentryinfo>
+    <title>sd_bus_get_fd</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_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 &lt;systemd/sd-bus.h&gt;</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 the number of
+      queued messages of, 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) when it is non-zero.
+    </para>
+
+    <para>
+      Similar, <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 the ones of <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>
+  </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>
+
+    </variablelist>
+  </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>