2 files changed, 93 insertions, 0 deletions
diff --git a/src/util/lib.rs b/src/util/lib.rs
index 7ed00034..e83fc2e6 100644
--- a/src/util/lib.rs
+++ b/src/util/lib.rs
@@ -10,6 +10,7 @@ pub mod data;
 pub mod error;
 pub mod metrics;
 pub mod persister;
+pub mod sled_counter;
 pub mod time;
 pub mod token_bucket;
 pub mod tranquilizer;
diff --git a/src/util/sled_counter.rs b/src/util/sled_counter.rs
new file mode 100644
index 00000000..8af04f50
--- /dev/null
+++ b/src/util/sled_counter.rs
@@ -0,0 +1,92 @@
+use std::sync::{
+	atomic::{AtomicUsize, Ordering},
+	Arc,
+};
+
+use sled::{CompareAndSwapError, IVec, Iter, Result, Tree};
+
+#[derive(Clone)]
+pub struct SledCountedTree(Arc<SledCountedTreeInternal>);
+
+struct SledCountedTreeInternal {
+	tree: Tree,
+	len: AtomicUsize,
+}
+
+impl SledCountedTree {
+	pub fn new(tree: Tree) -> Self {
+		let len = tree.len();
+		Self(Arc::new(SledCountedTreeInternal {
+			tree,
+			len: AtomicUsize::new(len),
+		}))
+	}
+
+	pub fn len(&self) -> usize {
+		self.0.len.load(Ordering::Relaxed)
+	}
+
+	pub fn is_empty(&self) -> bool {
+		self.0.tree.is_empty()
+	}
+
+	pub fn get<K: AsRef<[u8]>>(&self, key: K) -> Result<Option<IVec>> {
+		self.0.tree.get(key)
+	}
+
+	pub fn iter(&self) -> Iter {
+		self.0.tree.iter()
+	}
+
+	// ---- writing functions ----
+
+	pub fn insert<K, V>(&self, key: K, value: V) -> Result<Option<IVec>>
+	where
+		K: AsRef<[u8]>,
+		V: Into<IVec>,
+	{
+		let res = self.0.tree.insert(key, value);
+		if res == Ok(None) {
+			self.0.len.fetch_add(1, Ordering::Relaxed);
+		}
+		res
+	}
+
+	pub fn pop_min(&self) -> Result<Option<(IVec, IVec)>> {
+		let res = self.0.tree.pop_min();
+		if let Ok(Some(_)) = &res {
+			self.0.len.fetch_sub(1, Ordering::Relaxed);
+		};
+		res
+	}
+
+	pub fn compare_and_swap<K, OV, NV>(
+		&self,
+		key: K,
+		old: Option<OV>,
+		new: Option<NV>,
+	) -> Result<std::result::Result<(), CompareAndSwapError>>
+	where
+		K: AsRef<[u8]>,
+		OV: AsRef<[u8]>,
+		NV: Into<IVec>,
+	{
+		let old_some = old.is_some();
+		let new_some = new.is_some();
+
+		let res = self.0.tree.compare_and_swap(key, old, new);
+
+		if res == Ok(Ok(())) {
+			match (old_some, new_some) {
+				(false, true) => {
+					self.0.len.fetch_add(1, Ordering::Relaxed);
+				}
+				(true, false) => {
+					self.0.len.fetch_sub(1, Ordering::Relaxed);
+				}
+				_ => (),
+			}
+		}
+		res
+	}
+}