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<ol class="chapter"><li class="chapter-item expanded "><a href="index.html"><strong aria-hidden="true">1.</strong> Top</a></li><li class="chapter-item expanded "><a href="tutorial.html"><strong aria-hidden="true">2.</strong> Tutorial</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="setup.html"><strong aria-hidden="true">2.1.</strong> Setting-up</a></li><li class="chapter-item expanded "><a href="pubsub.html"><strong aria-hidden="true">2.2.</strong> Publish and Subscribe</a></li><li class="chapter-item expanded "><a href="timer.html"><strong aria-hidden="true">2.3.</strong> Timer</a></li><li class="chapter-item expanded "><a href="multi_pubsub.html"><strong aria-hidden="true">2.4.</strong> Multi-threaded Publish and Subscribe</a></li><li class="chapter-item expanded "><a href="message.html"><strong aria-hidden="true">2.5.</strong> User Defined Data Structure</a></li><li class="chapter-item expanded "><a href="service.html"><strong aria-hidden="true">2.6.</strong> Service</a></li><li class="chapter-item expanded "><a href="parameter.html"><strong aria-hidden="true">2.7.</strong> Parameter</a></li><li class="chapter-item expanded "><a href="zerocopy.html" class="active"><strong aria-hidden="true">2.8.</strong> Zero Copy Publish and Subscribe</a></li><li class="chapter-item expanded "><a href="allocator.html"><strong aria-hidden="true">2.9.</strong> Custom Memory Allocator</a></li><li class="chapter-item expanded "><a href="pusbsub_and_service.html"><strong aria-hidden="true">2.10.</strong> Request to Server in Callback</a></li></ol></li><li class="chapter-item expanded "><a href="contribution.html"><strong aria-hidden="true">3.</strong> Contribution Guide</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="setup_contribution.html"><strong aria-hidden="true">3.1.</strong> Setting-up for Contribution</a></li><li class="chapter-item expanded "><a href="build_and_test.html"><strong aria-hidden="true">3.2.</strong> Build and Test</a></li><li class="chapter-item expanded "><a href="editor_setup.html"><strong aria-hidden="true">3.3.</strong> Editor Setting-up</a></li><li class="chapter-item expanded "><a href="internal_msgs.html"><strong aria-hidden="true">3.4.</strong> Generating Messages Included by safe_drive</a></li><li class="chapter-item expanded "><a href="c_apis.html"><strong aria-hidden="true">3.5.</strong> C APIs</a></li><li class="chapter-item expanded "><a href="document.html"><strong aria-hidden="true">3.6.</strong> Documentation</a></li></ol></li></ol>
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<h1 class="menu-title">safe_drive: Formally Specified Rust Bindings for ROS2</h1>
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<h1 id="zero-copy-publish-and-subscribe"><a class="header" href="#zero-copy-publish-and-subscribe">Zero Copy Publish and Subscribe</a></h1>
<p><a href="https://github.com/tier4/safe_drive_tutorial/tree/main/zerocopy">Source code</a>.</p>
<p>In this chapter, we will introduce how to use zero copy communications by CycloneDDS.
To use CycloneDDS, please install it as <a href="http://docs.ros.org.ros.informatik.uni-freiburg.de/en/humble/Installation/DDS-Implementations/Working-with-Eclipse-CycloneDDS.html">Eclipse Cyclone DDS</a>.</p>
<h2 id="create-project"><a class="header" href="#create-project">Create Project</a></h2>
<p>First of all, create a project as follows.</p>
<pre><code>$ cargo new zerocpy
</code></pre>
<p>The files we use are as follows. <code>cyclonedds.xml</code> will be created and used later.</p>
<div class="table-wrapper"><table><thead><tr><th>Files</th><th>What?</th></tr></thead><tbody>
<tr><td>zerocopy/Cargo.toml</td><td>Cargo.toml</td></tr>
<tr><td>zerocopy/src/main.rs</td><td>main.rs</td></tr>
<tr><td>zerocopy/cyclonedds.xml</td><td>configuration of CycloneDDS</td></tr>
</tbody></table>
</div>
<p>Add <code>safe_drive</code> to dependencies section of <code>Cargo.toml</code> as follows.</p>
<p><code>Cargo.toml</code></p>
<pre><code class="language-toml">[dependencies]
safe_drive = "0.4"
</code></pre>
<h2 id="mainrs"><a class="header" href="#mainrs"><code>main.rs</code></a></h2>
<p><code>main.rs</code> can be implemented as follows,
but almost every lines are same as shown before.</p>
<p><code>main.rs</code></p>
<pre><pre class="playground"><code class="language-rust">use safe_drive::{context::Context, msg::common_interfaces::std_msgs};
use std::{error::Error, time::Duration};
const TOPIC_NAME: &str = "pubsub_loaned";
fn main() -> Result<(), Box<dyn Error + Sync + Send + 'static>> {
// create a context
let ctx = Context::new()?;
// create a subscribe node
let node_sub = ctx.create_node("loaned_sub_node", None, Default::default())?;
// create a publish node
let node_pub = ctx.create_node("loaned_pub_node", None, Default::default())?;
std::thread::sleep(Duration::from_millis(500));
// create a publisher and a subscriber
let subscriber = node_sub.create_subscriber::<std_msgs::msg::Bool>(TOPIC_NAME, None)?;
let publisher = node_pub.create_publisher::<std_msgs::msg::Bool>(TOPIC_NAME, None)?;
let mut loaned = publisher.borrow_loaned_message()?;
*loaned = std_msgs::msg::Bool::new().ok_or("failed to new Bool")?;
loaned.data = false;
publisher.send_loaned(loaned)?; // send message
std::thread::sleep(Duration::from_millis(500));
// wait messages
let mut selector = ctx.create_selector()?;
selector.add_subscriber(
subscriber,
Box::new(move |msg| {
assert!(!msg.data);
}),
);
selector.wait()?;
Ok(())
}</code></pre></pre>
<p>The important thing is using <code>borrow_loaned_message()</code> and <code>send_loaned()</code> methods as follows.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>let mut loaned = publisher.borrow_loaned_message()?;
*loaned = std_msgs::msg::Bool::new().ok_or("failed to new Bool")?;
loaned.data = false;
publisher.send_loaned(loaned)?; // send message
<span class="boring">}</span></code></pre></pre>
<p><code>borrow_loaned_message()</code> borrows a memory region from CycloneDDS and
<code>send_loaned()</code> sends a message in the borrowed region.
<code>safe_drive</code> automatically check whether zero copy is available or not,
and it uses conventional copied APIs if zero copy is not available.</p>
<h2 id="setting-up-zero-copy"><a class="header" href="#setting-up-zero-copy">Setting-up Zero Copy</a></h2>
<p>To enable zero copy, please prepare cyclonedds.xml, which is a configuration file of CycloneDDS, as follows.
You can use arbitrary name for it.</p>
<p><code>cyclonedds.xml</code></p>
<pre><code class="language-xml"><?xml version="1.0" encoding="UTF-8" ?>
<CycloneDDS xmlns="https://cdds.io/config" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://cdds.io/config https://raw.githubusercontent.com/eclipse-cyclonedds/cyclonedds/iceoryx/etc/cyclonedds.xsd">
<Domain id="any">
<SharedMemory>
<Enable>true</Enable>
<LogLevel>info</LogLevel>
</SharedMemory>
</Domain>
</CycloneDDS>
</code></pre>
<p><code><SharedMemory></code> tag indicates the configuration of zero copy.</p>
<p>To use zero copy enabled CycloneDDS, please set environment arguments as follows.</p>
<pre><code class="language-text">$ export RMW_IMPLEMENTATION=rmw_cyclonedds_cpp
$ export CYCLONEDDS_URI=file://path/to/cyclonedds.xml
</code></pre>
<p>In addition to that, CycloneDDS requires <code>iox-roudi</code> daemon to use zero copy.
It can be launched as follows.</p>
<pre><code class="language-text">$ iox-roudi
</code></pre>
<h2 id="execute"><a class="header" href="#execute">Execute</a></h2>
<p>After that, zero copy communications can be performed!</p>
<pre><code class="language-text">$ cargo run
</code></pre>
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