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<h1 class="menu-title">safe_drive: Formally Specified Rust Bindings for ROS2</h1>
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<h1 id="parameter"><a class="header" href="#parameter">Parameter</a></h1>
<p><a href="https://github.com/tier4/safe_drive_tutorial/tree/main/params">Source code</a>.</p>
<p>This chapter introduces how to use parameters.
A node can have parameters as follows.</p>
<pre class="mermaid">graph TD;
NodeA --> ParamA1:i64;
NodeA --> ParamA2:bool;
NodeA --> ParamA3:String;
NodeB --> ParamB1:f64;
NodeB --> ParamB2:f64;
</pre>
<p>In this figure, NodeA has 3 parameters whose types are
<code>i64</code>, <code>bool</code>, and <code>String</code>, respectively,
and NodeB has 2 parameters whose types are <code>f64</code>.
Parameters can be read/write from external nodes.</p>
<p>To receive a notification of updating a parameter,
we can use a callback function or async/await.
In this chapter, we will explain how to handle it.</p>
<h2 id="packages"><a class="header" href="#packages">Packages</a></h2>
<p>We will prepare 2 packages as follows.</p>
<pre><code class="language-text">$ mkdir params
$ cd params
$ cargo new param_server
$ cargo new async_param_server
</code></pre>
<p><code>param_server</code> explains a callback based parameter handling, and <code>async_param_server</code> explains an async/await based.</p>
<p>To manage 2 packages, let's prepare <code>Cargo.toml</code> file for a workspace as follows.</p>
<p><code>params/Cargo.toml</code></p>
<pre><code class="language-toml">[workspace]
members = ["param_server", "async_param_server"]
</code></pre>
<p>The following table shows files we use in this chapter.</p>
<div class="table-wrapper"><table><thead><tr><th>File</th><th>What?</th></tr></thead><tbody>
<tr><td>params/param_server/</td><td>callback based parameter server</td></tr>
<tr><td>params/async_param_server/</td><td>async/await based parameter server</td></tr>
<tr><td>params/Cargo.toml</td><td>workspace configuration</td></tr>
</tbody></table>
</div>
<h2 id="type-of-parameter"><a class="header" href="#type-of-parameter">Type of Parameter</a></h2>
<p>Before explaining handlers,
let's see types of parameters.</p>
<p>The type of parameter value is defined by <code>safe_drive::parameter::Value</code> as follows.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>pub enum Value {
NotSet,
Bool(bool),
I64(i64),
F64(f64),
String(String),
VecBool(Vec<bool>),
VecI64(Vec<i64>),
VecU8(Vec<u8>),
VecF64(Vec<f64>),
VecString(Vec<String>),
}
<span class="boring">}</span></code></pre></pre>
<p>This means that <code>i64</code> is valid,
but <code>i8</code>, <code>i32</code>, and other user defined types are invalid.</p>
<p>A parameter is associated with a descriptor of <code>safe_drive::parameter::Descriptor</code> as follows.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>pub struct Descriptor {
pub description: String,
pub additional_constraints: String,
pub read_only: bool,
pub dynamic_typing: bool,
pub floating_point_range: Option<FloatingPointRange>,
pub integer_range: Option<IntegerRange>,
}
<span class="boring">}</span></code></pre></pre>
<p>So, a parameter and parameters can be represented by <code>safe_drive::parameter::{Parameter, Parameters}</code> as follows.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>pub struct Parameter {
pub descriptor: Descriptor,
pub value: Value,
}
pub struct Parameters { /* omitted private fields */ }
<span class="boring">}</span></code></pre></pre>
<p>and a parameter server can be represented by
<code>safe_drive::parameter::ParameterServer</code> as follows.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>pub struct ParameterServer {
pub params: Arc<RwLock<Parameters>>
// omitted private fields
}
<span class="boring">}</span></code></pre></pre>
<p>In summary, a parameter server can be represented as follows.</p>
<pre class="mermaid">graph TD;
ParameterServer --> Parameters;
Parameters --> Parameter;
Parameter --> Descriptor;
Parameter --> Value;
</pre>
<h2 id="parameter-setting-and-waiting-update-by-callback"><a class="header" href="#parameter-setting-and-waiting-update-by-callback">Parameter Setting and Waiting Update by Callback</a></h2>
<p>We will explain how to set parameters,
and how to wait updating by using a callback function.</p>
<h3 id="edit-param_servercargotoml"><a class="header" href="#edit-param_servercargotoml">Edit <code>param_server/Cargo.toml</code></a></h3>
<p>Add <code>safe_drive</code> to the dependencies section of <code>Cargo.toml</code> as follows.</p>
<pre><code class="language-toml">[dependencies]
safe_drive = "0.4"
</code></pre>
<h3 id="edit-param_serversrcmainrs"><a class="header" href="#edit-param_serversrcmainrs">Edit <code>param_server/src/main.rs</code></a></h3>
<p><code>param_server</code> can be implemented as follows.
This sets 2 parameters up and waits updating.</p>
<pre><pre class="playground"><code class="language-rust">use safe_drive::{
context::Context,
error::DynError,
logger::Logger,
parameter::{Descriptor, Parameter, Value},
pr_info,
};
fn main() -> Result<(), DynError> {
// Create a context and a node.
let ctx = Context::new()?;
let node = ctx.create_node("param_server", None, Default::default())?;
// Create a parameter server.
let param_server = node.create_parameter_server()?;
{
// Set parameters.
let mut params = param_server.params.write(); // Write lock
// Statically typed parameter.
params.set_parameter(
"my_flag".to_string(), // parameter name
Value::Bool(false), // value
false, // read only?
Some("my flag's description".to_string()), // description
)?;
// Dynamically typed parameter.
params.set_dynamically_typed_parameter(
"my_dynamic_type_flag".to_string(), // parameter name
Value::Bool(false), // value
false, // read only?
Some("my dynamic type flag's description".to_string()), // description
)?;
// Add Directly from Parameter struct
let parameter_to_set = Parameter {
descriptor: Descriptor {
description: "my parameter description".to_string(), // parameter description
additional_constraints: "my parameter addutional_constraints".to_string(), // parameter additional constraints
read_only: false, // read only ?
dynamic_typing: false, // static or Dynamic
floating_point_range: None, // floating point range
integer_range: None, // integer point range
},
value: Value::Bool(false), // value
};
params.add_parameter(
("my parameter").to_string(), // name
parameter_to_set, // parameter
)?;
}
// Create a logger and a selector.
let logger = Logger::new("param_server");
let mut selector = ctx.create_selector()?;
// Add a callback function to the parameter server.
selector.add_parameter_server(
param_server,
Box::new(move |params, updated| {
// Print updated parameters.
let mut keys = String::new();
for key in updated.iter() {
let value = &params.get_parameter(key).unwrap().value;
keys = format!("{keys}{key} = {}, ", value);
}
pr_info!(logger, "updated parameters: {keys}");
}),
);
// Spin.
loop {
selector.wait()?;
}
}</code></pre></pre>
<h3 id="param_server-in-detail"><a class="header" href="#param_server-in-detail"><code>param_server</code> in Detail</a></h3>
<p>First of all, we have to create a parameter server by <code>create_parameter_server()</code> method as follows.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// Create a parameter server.
let param_server = node.create_parameter_server()?;
<span class="boring">}</span></code></pre></pre>
<p>Then set parameters as follows.
To update parameters, we have to acquire a write lock
for mutual exclusion by <code>write()</code> method.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>{
// Set parameters.
let mut params = param_server.params.write(); // Write lock
// Statically typed parameter.
params.set_parameter(
"my_flag".to_string(), // parameter name
Value::Bool(false), // value
false, // read only?
Some("my flag's description".to_string()), // description
)?;
// Dynamically typed parameter.
params.set_dynamically_typed_parameter(
"my_dynamic_type_flag".to_string(), // parameter name
Value::Bool(false), // value
false, // read only?
Some("my dynamic type flag's description".to_string()), // description
)?;
// Add Directly from Parameter struct
let parameter_to_set = Parameter {
descriptor: Descriptor {
description: "my parameter description".to_string(), // parameter description
additional_constraints: "my parameter addutional_constraints".to_string(), // parameter additional constraints
read_only: false, // read only ?
dynamic_typing: false, // static or Dynamic
floating_point_range: None, // floating point range
integer_range: None, // integer point range
},
value: Value::Bool(false), // value
};
params.add_parameter(
("my parameter").to_string(), // name
parameter_to_set, // parameter
)?;
}
<span class="boring">}</span></code></pre></pre>
<p>To set a statically typed parameters, use <code>set_parameter()</code>.
A statically typed parameter cannot be updated
by a value whose type is different from original type.</p>
<p>To set a dynamically typed parameters, use <code>set_dynamically_typed_parameter()</code>.
A dynamically typed parameter can be updated by an arbitrary type.</p>
<p>To set directly from the Parameter struct, use <code>add_parameter()</code>.
A Parameter struct can contain additional_constraints.</p>
<p>Finally, register a callback function to wait updating
parameters as follows.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// Add a callback function to the parameter server.
selector.add_parameter_server(
param_server,
Box::new(move |params, updated| {
// Print updated parameters.
let mut keys = String::new();
for key in updated.iter() {
let value = &params.get_parameter(key).unwrap().value;
keys = format!("{keys}{key} = {}, ", value);
}
pr_info!(logger, "updated parameters: {keys}");
}),
);
// Spin.
loop {
selector.wait()?;
}
<span class="boring">}</span></code></pre></pre>
<p>1st argument of the closure, <code>params</code>, is a value of parameters,
and 2nd argument, <code>updated</code> is a value containing updated parameters.</p>
<h3 id="execute-param_server"><a class="header" href="#execute-param_server">Execute <code>param_server</code></a></h3>
<p>Then, let's execute <code>param_server</code> and get/set a parameter.
First, execute <code>param_server</code> in a terminal application window as follows.</p>
<pre><code class="language-text">$ cargo run --bin param_server
Finished dev [unoptimized + debuginfo] target(s) in 0.01s
Running `target/debug/param_server`
[INFO] [1669873997.622330908] [param_server]: updated parameters: my_flag = true,
</code></pre>
<p>Then, get and set the parameter by using <code>ros2</code> command in another terminal application window as follows.</p>
<pre><code class="language-text">$ ros2 param get param_server my_flag
Boolean value is: False
$ ros2 param set param_server my_flag True
Set parameter successful
$ ros2 param get param_server my_flag
Boolean value is: True
$ ros2 param set param_server my_flag 10
Setting parameter failed: failed type checking: dst = Bool, src = I64
</code></pre>
<p>We can get and set boolean values,
but integer value cannot be set because <code>my_flag</code> is boolean type
and statically typed.</p>
<hr />
<h2 id="asynchronous-wait"><a class="header" href="#asynchronous-wait">Asynchronous Wait</a></h2>
<p>Then, we explain async/await based parameter server.</p>
<h3 id="edit-async_param_servercargotoml"><a class="header" href="#edit-async_param_servercargotoml">Edit <code>async_param_server/Cargo.toml</code></a></h3>
<p>Add <code>safe_drive</code> and <code>tokio</code> to the dependencies section of <code>Cargo.toml</code> as follows.</p>
<pre><code class="language-toml">[dependencies]
safe_drive = "0.4"
tokio = { version = "1", features = ["full"] }
</code></pre>
<h3 id="edit-async_param_serversrcmainrs"><a class="header" href="#edit-async_param_serversrcmainrs">Edit <code>async_param_server/src/main.rs</code></a></h3>
<p><code>async_param_server</code> can be implemented as follows.
This sets 2 parameters up and waits updating.</p>
<pre><pre class="playground"><code class="language-rust">use safe_drive::{
context::Context,
error::DynError,
logger::Logger,
parameter::{Descriptor, Parameter, Value},
pr_info,
};
#[tokio::main]
async fn main() -> Result<(), DynError> {
// Create a context and a node.
let ctx = Context::new()?;
let node = ctx.create_node("async_param_server", None, Default::default())?;
// Create a parameter server.
let mut param_server = node.create_parameter_server()?;
{
// Set parameters.
let mut params = param_server.params.write(); // Write lock
// Statically typed parameter.
params.set_parameter(
"my_flag".to_string(), // parameter name
Value::Bool(false), // value
false, // read only?
Some("my flag's description".to_string()), // description
)?;
// Dynamically typed parameter.
params.set_dynamically_typed_parameter(
"my_dynamic_type_flag".to_string(), // parameter name
Value::Bool(false), // value
false, // read only?
Some("my dynamic type flag's description".to_string()), // description
)?;
// Add Directly from Parameter struct
let parameter_to_set = Parameter {
descriptor: Descriptor {
description: "my parameter description".to_string(), // parameter description
additional_constraints: "my parameter addutional_constraints".to_string(), // parameter additional constraints
read_only: false, // read only ?
dynamic_typing: false, // static or Dynamic
floating_point_range: None, // floating point range
integer_range: None, // integer point range
},
value: Value::Bool(false), // value
};
params.add_parameter(
("my parameter").to_string(), // name
parameter_to_set, // parameter
)?;
}
// Create a logger.
let logger = Logger::new("async_param_server");
loop {
// Wait update asynchronously.
let updated = param_server.wait().await?;
let params = param_server.params.read(); // Read lock
// Print updated parameters.
let mut keys = String::new();
for key in updated.iter() {
let value = &params.get_parameter(key).unwrap().value;
keys = format!("{keys}{key} = {}, ", value);
}
pr_info!(logger, "updated parameters: {keys}");
}
}</code></pre></pre>
<p>Important things are only following 2 lines.</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// Wait update asynchronously.
let updated = param_server.wait().await?;
let params = param_server.params.read(); // Read lock
<span class="boring">}</span></code></pre></pre>
<p>To wait updating, use <code>wait().await</code>
and acquire a read lock by <code>read()</code> method
to read parameters.
<code>wait().await</code> returns updated parameters.</p>
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