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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" class="active"><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"><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="timer"><a class="header" href="#timer">Timer</a></h1>
<p><a href="https://github.com/tier4/safe_drive_tutorial/tree/main/timers">Source code</a>.</p>
<p>This tutorial does not use <code>colcon</code> to build.
We use only <code>cargo</code>, which is a Rust's standard build system.</p>
<p>Don't forget loading ROS2's environment as follows.
If you already done so, you do not need this.</p>
<pre><code class="language-text">$ . /opt/ros/iron/setup.bash
</code></pre>
<h2 id="wall-timer"><a class="header" href="#wall-timer">Wall-timer</a></h2>
<p>A wall-timer is a timer which periodically invoked.
This section describes how to use a wall-timer.</p>
<p>Let's create a package by using a <code>cargo</code> as follows.</p>
<pre><code class="language-text">$ cargo new wall_timer
$ cd wall_timer
</code></pre>
<p>Then, add <code>safe_drive</code> to the dependencies of <code>Cargo.toml</code>.</p>
<pre><code class="language-toml">[dependencies]
safe_drive = "0.4"
</code></pre>
<p>The following code is an example using a wall-timer.
The important method is <code>Selector::add_wall_timer()</code> which takes
a name, a duration, and a callback function.</p>
<pre><pre class="playground"><code class="language-rust">use safe_drive::{
context::Context, error::DynError, logger::Logger, msg::common_interfaces::std_msgs, pr_info,
};
use std::{rc::Rc, time::Duration};
fn main() -> Result<(), DynError> {
// Create a context, a node, a subscriber, a publisher, and a selector.
let ctx = Context::new()?;
let node = ctx.create_node("my_node", None, Default::default())?;
let subscriber = node.create_subscriber::<std_msgs::msg::UInt64>("my_topic", None)?;
let publisher = node.create_publisher::<std_msgs::msg::UInt64>("my_topic", None)?;
let mut selector = ctx.create_selector()?;
// Create a logger.
// To share this by multiple callback functions, use Rc.
let logger = Rc::new(Logger::new("wall timer example"));
// Add a wall timer to publish periodically.
let mut cnt = Box::new(0);
let mut msg = std_msgs::msg::UInt64::new().unwrap();
let logger1 = logger.clone();
selector.add_wall_timer(
"publisher", // the name of timer
Duration::from_secs(1),
Box::new(move || {
msg.data = *cnt;
*cnt += 1;
publisher.send(&msg).unwrap();
pr_info!(logger1, "send: msg.data = {}", msg.data);
}),
);
// Add a subscriber.
selector.add_subscriber(
subscriber,
Box::new(move |msg| {
pr_info!(logger, "received: msg.data = {}", msg.data);
}),
);
// Spin.
loop {
selector.wait()?;
}
}</code></pre></pre>
<p>Timers can be set by a method of selector as follows,
and the timers will be invoked when calling the <code>Selector::wait()</code> methods.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>selector.add_wall_timer(
"publisher", // the name of timer
Duration::from_secs(1),
Box::new(move || {
msg.data = *cnt;
*cnt += 1;
publisher.send(&msg).unwrap();
pr_info!(logger1, "send: msg.data = {}", msg.data);
}),
);
<span class="boring">}</span></code></pre></pre>
<ul>
<li><code>"publisher"</code> is the name of this timer. The name is used for statistics. You can use any name.</li>
<li><code>Duration::from_secs(1)</code> is the duration for periodic invoking. This argument means the callback function is invoked every 1 second.</li>
<li><code>Box::new(move || ...)</code> is the callback function.</li>
</ul>
<p>There is a publisher invoked by a timer, and a subscriber in this code.
When executing this, transmission and reception will be confirmed as follows.</p>
<pre><code class="language-text">$ cargo run
[INFO] [1656557242.842509800] [wall timer example]: send: msg.data = 0
[INFO] [1656557242.842953300] [wall timer example]: received: msg.data = 0
[INFO] [1656557243.843103800] [wall timer example]: send: msg.data = 1
[INFO] [1656557243.843272900] [wall timer example]: received: msg.data = 1
[INFO] [1656557244.843574600] [wall timer example]: send: msg.data = 2
[INFO] [1656557244.844021200] [wall timer example]: received: msg.data = 2
[INFO] [1656557245.844349800] [wall timer example]: send: msg.data = 3
[INFO] [1656557245.844702900] [wall timer example]: received: msg.data = 3
</code></pre>
<h2 id="one-shot-timer"><a class="header" href="#one-shot-timer">One-shot Timer</a></h2>
<p>A wall-timer is invoked periodically,
but one-shot timer is invoked only once.
A one-shot can be set by the <code>Selector::add_timer()</code> method as follows.</p>
<pre><pre class="playground"><code class="language-rust">use safe_drive::{context::Context, error::DynError, logger::Logger, pr_info};
use std::{cell::RefCell, collections::VecDeque, rc::Rc, time::Duration};
pub fn main() -> Result<(), DynError> {
// Create a context, a publisher, and a logger.
let ctx = Context::new()?;
let mut selector = ctx.create_selector()?;
let logger = Rc::new(Logger::new("one-shot timer example"));
let queue = Rc::new(RefCell::new(VecDeque::new()));
// Add a one-shot timer.
let queue1 = queue.clone();
selector.add_timer(
Duration::from_secs(2),
Box::new(move || {
pr_info!(logger, "fired!");
// Insert a timer to the queue.
let mut q = queue1.borrow_mut();
let logger1 = logger.clone();
q.push_back((
Duration::from_secs(2),
(Box::new(move || pr_info!(logger1, "fired! again!"))),
));
}),
);
// Spin.
loop {
{
// Set timers.
let mut q = queue.borrow_mut();
while let Some((dur, f)) = q.pop_front() {
selector.add_timer(dur, f);
}
}
selector.wait()?;
}
}</code></pre></pre>
<p><code>Selector::add_timer()</code> does not take the name,
but other arguments are same as <code>Selector::add_wall_timer()</code>.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>selector.add_timer(
Duration::from_secs(2),
Box::new(move || ...),
);
<span class="boring">}</span></code></pre></pre>
<ul>
<li><code>Duration::from_secs(2)</code> is a duration indicating when the timer will be invoked.</li>
<li><code>Box::new(move || ...)</code> is the callback function.</li>
</ul>
<p>This code reenables a timer in the callback function.
To reenable, the callback takes a <code>queue</code> and
timers in the <code>queue</code> is reenabled in the spin as follows.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// Spin.
loop {
{
// Set timers.
let mut q = queue.borrow_mut();
while let Some((dur, f)) = q.pop_front() {
selector.add_timer(dur, f);
}
}
selector.wait()?;
}
<span class="boring">}</span></code></pre></pre>
<p>The important thing is that the borrowed resources must be released.
To release definitely, the code fraction borrowing the <code>queue</code> is surrounded by braces.</p>
<p>The following is a execution result of this code.</p>
<pre><code>$ cargo run
[INFO] [1657070943.324438900] [one-shot timer example]: fired!
[INFO] [1657070945.324675600] [one-shot timer example]: fired! again!
</code></pre>
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