Spawn a heartbeat task while players are connected to the server, aborting it once they're off.

src/net/server.rs

@@ -4,7 +4,7 @@ use futures::{channel::mpsc::*, future::try_join, lock::Mutex, prelude::*};
 use serde_json::json;
 use std::sync::Arc;
 use stream::iter;
-use future::abortable;
+use future::{AbortHandle, abortable};
 
 /// There is a point at which a client falls far enough behind
 /// that it's probably not worth trying to catch them up; for now,
@@ -38,6 +38,7 @@ pub struct PlayerState {
 
 pub struct Server {
     players: Vec<Option<PlayerState>>,
+    heartbeat_task: Option<AbortHandle>,
 }
 
 #[derive(Clone)]
@@ -50,6 +51,7 @@ impl Server {
         Handle {
             server: Arc::new(Mutex::new(Server {
                 players: Vec::new(),
+                heartbeat_task: None,
             })),
         }
     }
@@ -75,6 +77,10 @@ impl Server {
         greet(&mut sender).await?;
         self.players[player_id] = Some(PlayerState { sender });
         info!("Client#{} connected", player_id);
+
+        // ensure server task is running
+        self.spinup();
+
         Ok(player_id)
     }
 
@@ -85,6 +91,31 @@ impl Server {
         } else {
             error!("Tried to disconnect Client#{} but there was no record for them", player_id);
         }
+
+        // check if no players left
+        if self.players.iter().all(Option::is_none) {
+            self.shutdown();
+        }
+    }
+
+    /// Start the heartbeat task, if it's not running
+    fn spinup(&mut self) {
+        if let None = self.heartbeat_task {
+            info!("Starting heartbeat task");
+            let (task, handle) = abortable(async {
+                info!("Heartbeat task started");
+            });
+            self.heartbeat_task = Some(handle);
+            tokio::spawn(task);
+        }
+    }
+
+    /// Stop any active heartbeat task
+    fn shutdown(&mut self) {
+        if let Some(handle) = self.heartbeat_task.take() {
+            info!("Stopping heartbeat task");
+            handle.abort();
+        }
     }
 }