nuno-faria commented on code in PR #17031:
URL: https://github.com/apache/datafusion/pull/17031#discussion_r2255095258
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datafusion/execution/src/cache/lru_queue.rs:
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@@ -0,0 +1,490 @@
+use std::{
+ collections::HashMap,
+ hash::Hash,
+ sync::{Arc, Mutex, Weak},
+};
+
+#[derive(Default)]
+/// Provides a Least Recently Used queue with unbounded capacity.
+///
+/// # Examples
+///
+/// ```
+/// use datafusion_execution::cache::lru_queue::LruQueue;
+///
+/// let mut lru_queue: LruQueue<i32, i32> = LruQueue::new();
+/// lru_queue.put(1, 10);
+/// lru_queue.put(2, 20);
+/// lru_queue.put(3, 30);
+/// assert_eq!(lru_queue.get(&2), Some(&20));
+/// assert_eq!(lru_queue.pop(), Some((1, 10)));
+/// assert_eq!(lru_queue.pop(), Some((3, 30)));
+/// assert_eq!(lru_queue.pop(), Some((2, 20)));
+/// assert_eq!(lru_queue.pop(), None);
+/// ```
+pub struct LruQueue<K: Eq + Hash + Clone, V> {
Review Comment:
This implementation uses no unsafe blocks. The "unsafest" part is when we
upgrade the `Weak` pointers in the doubly-linked list and then unwrap them,
however we guarantee that the strong reference is always in the `data` map.
While I believe this implementation could be more efficient, I tried to keep
it as simple as possible (e.g., `get` does a `remove` and a `put`, instead of
something more complex). A quick bench shows that it reaches >1M puts/gets/pops
per second, which should be enough.
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