feat(queue, stack): faster entry garbage collection

Previously, popped entries are holding strong references to the next
one, even those having been deleted, thus causing a very slow garbage
collection of entries.

Now, deleted entries attached to an entry being dropped are immediately
passed to the garbage collector.

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Version 2
 
+2.0.17
+
+* Faster `Queue` and `Stack` entry garbage collection.
+
 2.0.16
 
 * Fix an issue with `HashCache` where an evicted entry is dropped without notifying it when `HashCache` shrinks.

Cargo.toml

@@ -2,7 +2,7 @@
 name = "scc"
 description = "High performance containers and utilities for concurrent and asynchronous programming"
 documentation = "https://docs.rs/scc"
-version = "2.0.16"
+version = "2.0.17"
 authors = ["wvwwvwwv <[email protected]>"]
 edition = "2021"
 rust-version = "1.65.0"

src/linked_list.rs

@@ -408,6 +408,15 @@ impl<T> DerefMut for Entry<T> {
     }
 }
 
+impl<T> Drop for Entry<T> {
+    #[inline]
+    fn drop(&mut self) {
+        if !self.next.is_null(Relaxed) {
+            self.next_ptr(Relaxed, &Guard::new());
+        }
+    }
+}
+
 impl<T: Display> Display for Entry<T> {
     #[inline]
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {