Ensure crossbeam-epoch to run GC when dropping a cache

src/future/base_cache.rs

@@ -1050,6 +1050,21 @@ pub(crate) struct Inner<K, V, S> {
     clocks: Clocks,
 }
 
+impl<K, V, S> Drop for Inner<K, V, S> {
+    fn drop(&mut self) {
+        // Ensure crossbeam-epoch to collect garbages (`deferred_fn`s) in the
+        // global bag so that previously cached values will be dropped.
+        for _ in 0..128 {
+            crossbeam_epoch::pin().flush();
+        }
+
+        // NOTE: The `CacheStore` (`cht`) will be dropped after returning from this
+        // `drop` method. It uses crossbeam-epoch internally, but we do not have to
+        // call `flush` for it because its `drop` methods do not create
+        // `deferred_fn`s, and drop its values in place.
+    }
+}
+
 //
 // functions/methods used by BaseCache
 //

src/future/cache.rs

@@ -3812,7 +3812,7 @@
         // Note that MyError does not implement std::error::Error trait
         // like anyhow::Error.
         #[derive(Debug)]
         pub struct MyError(String);
 
         type MyResult<T> = Result<T, Arc<MyError>>;
 
@@ -3949,7 +3949,7 @@
         // Note that MyError does not implement std::error::Error trait
         // like anyhow::Error.
         #[derive(Debug)]
         pub struct MyError(String);
 
         type MyResult<T> = Result<T, Arc<MyError>>;
 
@@ -5454,6 +5454,18 @@
         assert_eq!(counters.value_dropped(), KEYS, "value_dropped");
     }
 
+    // https://github.com/moka-rs/moka/issues/383
+    #[tokio::test]
+    async fn ensure_gc_runs_when_dropping_cache() {
+        let cache = Cache::builder().build();
+        let val = Arc::new(0);
+        cache
+            .get_with(1, std::future::ready(Arc::clone(&val)))
+            .await;
+        drop(cache);
+        assert_eq!(Arc::strong_count(&val), 1);
+    }
+
     #[tokio::test]
     async fn test_debug_format() {
         let cache = Cache::new(10);

src/sync/cache.rs

@@ -3456,7 +3456,7 @@
         // Note that MyError does not implement std::error::Error trait like
         // anyhow::Error.
         #[derive(Debug)]
         pub struct MyError(String);
 
         type MyResult<T> = Result<T, Arc<MyError>>;
 
@@ -3597,7 +3597,7 @@
         // Note that MyError does not implement std::error::Error trait like
         // anyhow::Error.
         #[derive(Debug)]
         pub struct MyError(String);
 
         type MyResult<T> = Result<T, Arc<MyError>>;
 
@@ -4831,6 +4831,19 @@
         assert_eq!(counters.value_dropped(), KEYS, "value_dropped");
     }
 
+    // https://github.com/moka-rs/moka/issues/383
+    #[test]
+    fn ensure_gc_runs_when_dropping_cache() {
+        let cache = Cache::builder().build();
+        let val = Arc::new(0);
+        {
+            let val = Arc::clone(&val);
+            cache.get_with(1, move || val);
+        }
+        drop(cache);
+        assert_eq!(Arc::strong_count(&val), 1);
+    }
+
     #[test]
     fn test_debug_format() {
         let cache = Cache::new(10);

src/sync_base/base_cache.rs

@@ -910,6 +910,21 @@ pub(crate) struct Inner<K, V, S> {
     clocks: Clocks,
 }
 
+impl<K, V, S> Drop for Inner<K, V, S> {
+    fn drop(&mut self) {
+        // Ensure crossbeam-epoch to collect garbages (`deferred_fn`s) in the
+        // global bag so that previously cached values will be dropped.
+        for _ in 0..128 {
+            crossbeam_epoch::pin().flush();
+        }
+
+        // NOTE: The `CacheStore` (`cht`) will be dropped after returning from this
+        // `drop` method. It uses crossbeam-epoch internally, but we do not have to
+        // call `flush` for it because its `drop` methods do not create
+        // `deferred_fn`s, and drop its values in place.
+    }
+}
+
 //
 // functions/methods used by BaseCache
 //