Cancel generation when its handle is dropped

src/runtime.rs

@@ -3,7 +3,7 @@ use crate::metrics::{Metrics, WorkSource};
 use crate::settings::{EngineSettings, TurnSettings};
 use std::path::PathBuf;
 use std::sync::Arc;
-use std::sync::atomic::AtomicBool;
+use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::mpsc::{self, Receiver, Sender};
 use std::thread;
 use std::time::{Duration, Instant};
@@ -19,6 +19,12 @@ pub(crate) struct ActiveGeneration {
     pub(crate) cancel: Arc<AtomicBool>,
 }
 
+impl Drop for ActiveGeneration {
+    fn drop(&mut self) {
+        self.cancel.store(true, Ordering::Relaxed);
+    }
+}
+
 pub(crate) enum CheckpointTarget {
     Local(PathBuf),
     Transient(PathBuf),
@@ -218,3 +224,21 @@ fn run(commands: Receiver<Command>, metrics: Arc<Metrics>) {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn dropping_active_generation_cancels_it() {
+        let cancel = Arc::new(AtomicBool::new(false));
+        let (_, events) = mpsc::channel();
+
+        drop(ActiveGeneration {
+            events,
+            cancel: Arc::clone(&cancel),
+        });
+
+        assert!(cancel.load(Ordering::Relaxed));
+    }
+}