Add support for tokio runtime metrics

autometrics/Cargo.toml

@@ -15,6 +15,7 @@ readme = "README.md"
 default = ["opentelemetry"]
 metrics = ["dep:metrics"]
 opentelemetry = ["opentelemetry_api"]
+prometheus-tokio = [ "dep:prometheus_tokio", "tokio" ]
 prometheus = ["const_format", "dep:prometheus", "once_cell"]
 prometheus-exporter = [
   "metrics-exporter-prometheus",
@@ -45,6 +46,10 @@ prometheus = { version = "0.13", default-features = false, optional = true }
 # Used for prometheus feature
 const_format = { version = "0.2", features = ["rust_1_51"], optional = true }
 
+# Used for prometheus-tokio feature
+prometheus_tokio = { version = "0.2", optional = true }
+tokio = { version = "1.26", features = ["rt"], optional = true }
+
 [package.metadata.docs.rs]
 all-features = true
 rustdoc-args = ["--cfg", "docsrs"]

autometrics/src/prometheus_exporter.rs

@@ -32,6 +32,20 @@ impl GlobalPrometheus {
 
         Ok(output)
     }
+
+    /// Add tokio runtime metrics from the given [Runtime handle](tokio::runtime::Handle)
+    ///
+    /// On top of the feature, you also need to add the RUSTFLAGS to [enable
+    /// `tokio_unstable`](https://docs.rs/tokio/latest/tokio/#unstable-features)
+    /// in order to use this method.
+    #[cfg(feature = "prometheus-tokio")]
+    pub fn with_tokio(&self, handle: &tokio::runtime::Handle) -> &Self {
+        use prometheus_tokio::TokioCollector;
+        self.exporter
+            .registry()
+            .register(Box::new(TokioCollector::new(handle, "autometrics")));
+        &self
+    }
 }
 
 /// Initialize the global Prometheus metrics collector and exporter.
@@ -48,6 +62,21 @@ impl GlobalPrometheus {
 /// let _exporter = global_metrics_exporter();
 /// # }
 /// ```
+///
+/// # Tokio runtime metrics support
+///
+/// If you both:
+/// - enabled the `prometheus-tokio` feature of autometrics, and
+/// - added the RUSTFLAGS to [enable `tokio_unstable`](https://docs.rs/tokio/latest/tokio/#unstable-features), then
+///
+/// you can also add the Tokio related runtime metrics to the exporter:
+/// ```rust,ignore
+/// #[tokio::main]
+/// async fn main() {
+/// let _exporter = global_metrics_exporter().with_tokio(&tokio::runtime::Handle::current());
+/// // ...
+/// }
+/// ```
 pub fn global_metrics_exporter() -> GlobalPrometheus {
     GLOBAL_EXPORTER.clone()
 }