fix(node): allow dropping a nested runtime

core/node/src/lib.rs

@@ -1,3 +1,4 @@
+use std::future::Future;
 use std::marker::PhantomData;
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::time::Duration;
@@ -11,6 +12,9 @@ use tokio::time::timeout;
 
 /// A single [Node] instance that has ownership over its tokio runtime.
 pub struct ContainedNode<C: Collection> {
+    /// The name of this contained node.
+    name: String,
+
     /// The dependency injection data provider which can contain most of the items that make up
     /// a node.
     provider: fdi::MultiThreadedProvider,
@@ -26,6 +30,8 @@ pub struct ContainedNode<C: Collection> {
 
 impl<C: Collection> ContainedNode<C> {
     pub fn new(provider: fdi::MultiThreadedProvider, name: Option<String>) -> Self {
+        let name = name.unwrap_or_else(|| "LIGHTNING".into());
+
         // Create and insert the shutdown controller to the provider.
         let trace_shutdown = std::env::var("TRACE_SHUTDOWN").is_ok();
         let shutdown = ShutdownController::new(trace_shutdown);
@@ -40,10 +46,11 @@ impl<C: Collection> ContainedNode<C> {
 
         // Create the tokio runtime.
         let worker_id = AtomicUsize::new(0);
+        let node_name = name.clone();
         let runtime = tokio::runtime::Builder::new_multi_thread()
             .thread_name_fn(move || {
                 let id = worker_id.fetch_add(1, Ordering::SeqCst);
-                format!("{}#{id}", name.as_deref().unwrap_or("LIGHTNING"))
+                format!("{node_name}#{id}")
             })
             .on_thread_start(move || {
                 let permit = permit.clone();
@@ -59,6 +66,7 @@ impl<C: Collection> ContainedNode<C> {
             .expect("Failed to build tokio runtime for node container.");
 
         Self {
+            name,
             provider,
             runtime,
             shutdown,
@@ -90,50 +98,79 @@ impl<C: Collection> ContainedNode<C> {
         })
     }
 
-    pub async fn shutdown(mut self) {
+    /// Shut down the node and return a future that will be resolved when the node is fully down.
+    ///
+    /// Unlike other async method this function can trigger the shutdown without it being polled.
+    /// In other words you can still trigger the shutdown event by calling this method and never
+    /// awaiting the returned future.
+    pub fn shutdown(mut self) -> impl Future<Output = ()> {
         // Tell the controller it's time to go down.
         self.shutdown.trigger_shutdown();
 
-        // Give the runtime 30 seconds to stop.
-        self.runtime.shutdown_timeout(Duration::from_secs(30));
-
-        for i in 0.. {
-            if timeout(Duration::from_secs(3), self.shutdown.wait_for_completion())
-                .await
-                .is_ok()
-            {
-                // shutdown completed.
-                return;
-            }
+        let task_name = format!("{}::RuntimeDrop", self.name);
 
-            match i {
-                0 | 1 => {
-                    // 3s, 6s
-                    tracing::trace!("Still shutting down...");
-                    continue;
-                },
-                2 => {
-                    // 9s
-                    tracing::warn!("Still shutting down...");
+        // Give the runtime 30 seconds to stop.
+        match tokio::runtime::Handle::try_current() {
+            Ok(handle) => {
+                tokio::task::Builder::new()
+                    .name(&task_name)
+                    .spawn_blocking_on(
+                        || {
+                            self.runtime.shutdown_timeout(Duration::from_secs(30));
+                        },
+                        &handle,
+                    )
+                    .unwrap();
+            },
+            Err(_) => {
+                std::thread::Builder::new()
+                    .name(task_name)
+                    .spawn(|| {
+                        self.runtime.shutdown_timeout(Duration::from_secs(30));
+                    })
+                    .unwrap();
+            },
+        };
+
+        async move {
+            for i in 0.. {
+                if timeout(Duration::from_secs(3), self.shutdown.wait_for_completion())
+                    .await
+                    .is_ok()
+                {
+                    // shutdown completed.
+                    return;
+                }
+
+                match i {
+                    0 | 1 => {
+                        // 3s, 6s
+                        tracing::trace!("Still shutting down...");
+                        continue;
+                    },
+                    2 => {
+                        // 9s
+                        tracing::warn!("Still shutting down...");
+                        continue;
+                    },
+                    _ => {
+                        // 12s
+                        tracing::error!("Shutdown taking too long..")
+                    },
+                }
+
+                if i == 10 {
+                    // 33s
+                    break;
+                }
+
+                let Some(iter) = self.shutdown.pending_backtraces() else {
                     continue;
-                },
-                _ => {
-                    // 12s
-                    tracing::error!("Shutdown taking too long..")
-                },
-            }
-
-            if i == 10 {
-                // 33s
-                break;
-            }
-
-            let Some(iter) = self.shutdown.pending_backtraces() else {
-                continue;
-            };
+                };
 
-            for (i, trace) in iter.enumerate() {
-                eprintln!("Pending task backtrace #{i}:\n{trace:#?}");
+                for (i, trace) in iter.enumerate() {
+                    eprintln!("Pending task backtrace #{i}:\n{trace:#?}");
+                }
             }
         }
     }