Bring back the counted tree hack for Sled (with caveat)

caveat: it's not only for sled

src/block/manager.rs

@@ -20,6 +20,7 @@ use opentelemetry::{
 };
 
 use garage_db as db;
+use garage_db::counted_tree_hack::CountedTree;
 
 use garage_util::data::*;
 use garage_util::error::*;
@@ -94,9 +95,9 @@ pub struct BlockManager {
 
 	rc: BlockRc,
 
-	resync_queue: db::Tree,
+	resync_queue: CountedTree,
 	resync_notify: Notify,
-	resync_errors: db::Tree,
+	resync_errors: CountedTree,
 
 	system: Arc<System>,
 	endpoint: Arc<Endpoint<BlockRpc, Self>>,
@@ -126,10 +127,14 @@ impl BlockManager {
 		let resync_queue = db
 			.open_tree("block_local_resync_queue")
 			.expect("Unable to open block_local_resync_queue tree");
+		let resync_queue =
+			CountedTree::new(resync_queue).expect("Could not count block_local_resync_queue");
 
 		let resync_errors = db
 			.open_tree("block_local_resync_errors")
 			.expect("Unable to open block_local_resync_errors tree");
+		let resync_errors =
+			CountedTree::new(resync_errors).expect("Could not count block_local_resync_errors");
 
 		let endpoint = system
 			.netapp
@@ -299,12 +304,16 @@ impl BlockManager {
 
 	/// Get lenght of resync queue
 	pub fn resync_queue_len(&self) -> Result<usize, Error> {
-		Ok(self.resync_queue.len()?)
+		// This currently can't return an error because the CountedTree hack
+		// doesn't error on .len(), but this will change when we remove the hack
+		// (hopefully someday!)
+		Ok(self.resync_queue.len())
 	}
 
 	/// Get number of blocks that have an error
 	pub fn resync_errors_len(&self) -> Result<usize, Error> {
-		Ok(self.resync_errors.len()?)
+		// (see resync_queue_len comment)
+		Ok(self.resync_errors.len())
 	}
 
 	/// Get number of items in the refcount table

src/block/metrics.rs

@@ -1,6 +1,6 @@
 use opentelemetry::{global, metrics::*};
 
-use garage_db as db;
+use garage_db::counted_tree_hack::CountedTree;
 
 /// TableMetrics reference all counter used for metrics
 pub struct BlockManagerMetrics {
@@ -23,14 +23,12 @@ pub struct BlockManagerMetrics {
 }
 
 impl BlockManagerMetrics {
-	pub fn new(resync_queue: db::Tree, resync_errors: db::Tree) -> Self {
+	pub fn new(resync_queue: CountedTree, resync_errors: CountedTree) -> Self {
 		let meter = global::meter("garage_model/block");
 		Self {
 			_resync_queue_len: meter
 				.u64_value_observer("block.resync_queue_length", move |observer| {
-					if let Ok(v) = resync_queue.len() {
-						observer.observe(v as u64, &[]);
-					}
+					observer.observe(resync_queue.len() as u64, &[]);
 				})
 				.with_description(
 					"Number of block hashes queued for local check and possible resync",
@@ -38,9 +36,7 @@ impl BlockManagerMetrics {
 				.init(),
 			_resync_errored_blocks: meter
 				.u64_value_observer("block.resync_errored_blocks", move |observer| {
-					if let Ok(v) = resync_errors.len() {
-						observer.observe(v as u64, &[]);
-					}
+					observer.observe(resync_errors.len() as u64, &[]);
 				})
 				.with_description("Number of block hashes whose last resync resulted in an error")
 				.init(),

src/db/counted_tree_hack.rs

@@ -0,0 +1,130 @@
+//! This hack allows a db tree to keep in RAM a counter of the number of entries
+//! it contains, which is used to call .len() on it.  This is usefull only for
+//! the sled backend where .len() otherwise would have to traverse the whole
+//! tree to count items.  For sqlite and lmdb, this is mostly useless (but
+//! hopefully not harmfull!). Note that a CountedTree cannot be part of a
+//! transaction.
+
+use std::sync::{
+	atomic::{AtomicUsize, Ordering},
+	Arc,
+};
+
+use crate::{Result, Tree, TxError, Value, ValueIter};
+
+#[derive(Clone)]
+pub struct CountedTree(Arc<CountedTreeInternal>);
+
+struct CountedTreeInternal {
+	tree: Tree,
+	len: AtomicUsize,
+}
+
+impl CountedTree {
+	pub fn new(tree: Tree) -> Result<Self> {
+		let len = tree.len()?;
+		Ok(Self(Arc::new(CountedTreeInternal {
+			tree,
+			len: AtomicUsize::new(len),
+		})))
+	}
+
+	pub fn len(&self) -> usize {
+		self.0.len.load(Ordering::Relaxed)
+	}
+
+	pub fn is_empty(&self) -> bool {
+		self.len() == 0
+	}
+
+	pub fn get<K: AsRef<[u8]>>(&self, key: K) -> Result<Option<Value>> {
+		self.0.tree.get(key)
+	}
+
+	pub fn first(&self) -> Result<Option<(Value, Value)>> {
+		self.0.tree.first()
+	}
+
+	pub fn iter(&self) -> Result<ValueIter<'_>> {
+		self.0.tree.iter()
+	}
+
+	// ---- writing functions ----
+
+	pub fn insert<K, V>(&self, key: K, value: V) -> Result<bool>
+	where
+		K: AsRef<[u8]>,
+		V: AsRef<[u8]>,
+	{
+		let inserted = self.0.tree.insert(key, value)?;
+		if inserted {
+			self.0.len.fetch_add(1, Ordering::Relaxed);
+		}
+		Ok(inserted)
+	}
+
+	pub fn remove<K: AsRef<[u8]>>(&self, key: K) -> Result<bool> {
+		let removed = self.0.tree.remove(key)?;
+		if removed {
+			self.0.len.fetch_sub(1, Ordering::Relaxed);
+		}
+		Ok(removed)
+	}
+
+	/*
+	pub fn pop_min(&self) -> Result<Option<(Value, Value)>> {
+		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,
+		expected_old: Option<OV>,
+		new: Option<NV>,
+	) -> Result<bool>
+	where
+		K: AsRef<[u8]>,
+		OV: AsRef<[u8]>,
+		NV: AsRef<[u8]>,
+	{
+		let old_some = expected_old.is_some();
+		let new_some = new.is_some();
+
+		match self.0.tree.db().transaction(|mut tx| {
+			let old_val = tx.get(&self.0.tree, &key)?;
+			if old_val.as_ref().map(|x| &x[..]) == expected_old.as_ref().map(AsRef::as_ref) {
+				match &new {
+					Some(v) => {
+						tx.insert(&self.0.tree, &key, v)?;
+					}
+					None => {
+						tx.remove(&self.0.tree, &key)?;
+					}
+				}
+				tx.commit(())
+			} else {
+				tx.abort(())
+			}
+		}) {
+			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);
+					}
+					_ => (),
+				}
+				Ok(true)
+			}
+			Err(TxError::Abort(())) => Ok(false),
+			Err(TxError::Db(e)) => Err(e),
+		}
+	}
+}

src/db/lib.rs

@@ -2,6 +2,8 @@ pub mod lmdb_adapter;
 pub mod sled_adapter;
 pub mod sqlite_adapter;
 
+pub mod counted_tree_hack;
+
 #[cfg(test)]
 pub mod test;
 
@@ -164,10 +166,13 @@ impl Tree {
 			.transpose()
 	}
 
+	/// True if item didn't exist before, false if item already existed
+	/// and was replaced.
 	#[inline]
-	pub fn insert<T: AsRef<[u8]>, U: AsRef<[u8]>>(&self, key: T, value: U) -> Result<()> {
+	pub fn insert<T: AsRef<[u8]>, U: AsRef<[u8]>>(&self, key: T, value: U) -> Result<bool> {
 		self.0.insert(self.1, key.as_ref(), value.as_ref())
 	}
+	/// True if item was removed, false if item already didn't exist
 	#[inline]
 	pub fn remove<T: AsRef<[u8]>>(&self, key: T) -> Result<bool> {
 		self.0.remove(self.1, key.as_ref())
@@ -215,15 +220,18 @@ impl<'a> Transaction<'a> {
 		self.0.len(tree.1)
 	}
 
+	/// True if item didn't exist before, false if item already existed
+	/// and was replaced.
 	#[inline]
 	pub fn insert<T: AsRef<[u8]>, U: AsRef<[u8]>>(
 		&mut self,
 		tree: &Tree,
 		key: T,
 		value: U,
-	) -> Result<()> {
+	) -> Result<bool> {
 		self.0.insert(tree.1, key.as_ref(), value.as_ref())
 	}
+	/// True if item was removed, false if item already didn't exist
 	#[inline]
 	pub fn remove<T: AsRef<[u8]>>(&mut self, tree: &Tree, key: T) -> Result<bool> {
 		self.0.remove(tree.1, key.as_ref())
@@ -281,7 +289,7 @@ pub(crate) trait IDb: Send + Sync {
 	fn get(&self, tree: usize, key: &[u8]) -> Result<Option<Value>>;
 	fn len(&self, tree: usize) -> Result<usize>;
 
-	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<()>;
+	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<bool>;
 	fn remove(&self, tree: usize, key: &[u8]) -> Result<bool>;
 
 	fn iter(&self, tree: usize) -> Result<ValueIter<'_>>;
@@ -307,7 +315,7 @@ pub(crate) trait ITx {
 	fn get(&self, tree: usize, key: &[u8]) -> Result<Option<Value>>;
 	fn len(&self, tree: usize) -> Result<usize>;
 
-	fn insert(&mut self, tree: usize, key: &[u8], value: &[u8]) -> Result<()>;
+	fn insert(&mut self, tree: usize, key: &[u8], value: &[u8]) -> Result<bool>;
 	fn remove(&mut self, tree: usize, key: &[u8]) -> Result<bool>;
 
 	fn iter(&self, tree: usize) -> Result<ValueIter<'_>>;

src/db/lmdb_adapter.rs

@@ -122,12 +122,13 @@ impl IDb for LmdbDb {
 		Ok(tree.len(&tx)?.try_into().unwrap())
 	}
 
-	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<()> {
+	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<bool> {
 		let tree = self.get_tree(tree)?;
 		let mut tx = self.db.write_txn()?;
+		let old_val = tree.get(&tx, key)?.map(Vec::from);
 		tree.put(&mut tx, key, value)?;
 		tx.commit()?;
-		Ok(())
+		Ok(old_val.is_none())
 	}
 
 	fn iter(&self, tree: usize) -> Result<ValueIter<'_>> {
@@ -221,10 +222,11 @@ impl<'a, 'db> ITx for LmdbTx<'a, 'db> {
 		unimplemented!(".len() in transaction not supported with LMDB backend")
 	}
 
-	fn insert(&mut self, tree: usize, key: &[u8], value: &[u8]) -> Result<()> {
+	fn insert(&mut self, tree: usize, key: &[u8], value: &[u8]) -> Result<bool> {
 		let tree = *self.get_tree(tree)?;
+		let old_val = tree.get(&self.tx, key)?.map(Vec::from);
 		tree.put(&mut self.tx, key, value)?;
-		Ok(())
+		Ok(old_val.is_none())
 	}
 	fn remove(&mut self, tree: usize, key: &[u8]) -> Result<bool> {
 		let tree = *self.get_tree(tree)?;

src/db/sled_adapter.rs

@@ -93,10 +93,10 @@ impl IDb for SledDb {
 		Ok(tree.len())
 	}
 
-	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<()> {
+	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<bool> {
 		let tree = self.get_tree(tree)?;
-		tree.insert(key, value)?;
-		Ok(())
+		let old_val = tree.insert(key, value)?;
+		Ok(old_val.is_none())
 	}
 
 	fn iter(&self, tree: usize) -> Result<ValueIter<'_>> {
@@ -206,10 +206,10 @@ impl<'a> ITx for SledTx<'a> {
 		unimplemented!(".len() in transaction not supported with Sled backend")
 	}
 
-	fn insert(&mut self, tree: usize, key: &[u8], value: &[u8]) -> Result<()> {
+	fn insert(&mut self, tree: usize, key: &[u8], value: &[u8]) -> Result<bool> {
 		let tree = self.get_tree(tree)?;
-		self.save_error(tree.insert(key, value))?;
-		Ok(())
+		let old_val = self.save_error(tree.insert(key, value))?;
+		Ok(old_val.is_none())
 	}
 	fn remove(&mut self, tree: usize, key: &[u8]) -> Result<bool> {
 		let tree = self.get_tree(tree)?;

src/db/sqlite_adapter.rs

@@ -54,6 +54,17 @@ impl SqliteDbInner {
 			.map(String::as_str)
 			.ok_or_else(|| Error("invalid tree id".into()))
 	}
+
+	fn internal_get(&self, tree: &str, key: &[u8]) -> Result<Option<Value>> {
+		let mut stmt = self
+			.db
+			.prepare(&format!("SELECT v FROM {} WHERE k = ?1", tree))?;
+		let mut res_iter = stmt.query([key])?;
+		match res_iter.next()? {
+			None => Ok(None),
+			Some(v) => Ok(Some(v.get::<_, Vec<u8>>(0)?)),
+		}
+	}
 }
 
 impl IDb for SqliteDb {
@@ -111,15 +122,7 @@ impl IDb for SqliteDb {
 		trace!("get {}: lock acquired", tree);
 
 		let tree = this.get_tree(tree)?;
-
-		let mut stmt = this
-			.db
-			.prepare(&format!("SELECT v FROM {} WHERE k = ?1", tree))?;
-		let mut res_iter = stmt.query([key])?;
-		match res_iter.next()? {
-			None => Ok(None),
-			Some(v) => Ok(Some(v.get::<_, Vec<u8>>(0)?)),
-		}
+		this.internal_get(tree, key)
 	}
 
 	fn remove(&self, tree: usize, key: &[u8]) -> Result<bool> {
@@ -148,17 +151,18 @@ impl IDb for SqliteDb {
 		}
 	}
 
-	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<()> {
+	fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<bool> {
 		trace!("insert {}: lock db", tree);
 		let this = self.0.lock().unwrap();
 		trace!("insert {}: lock acquired", tree);
 
 		let tree = this.get_tree(tree)?;
+		let old_val = this.internal_get(tree, key)?;
 		this.db.execute(
 			&format!("INSERT OR REPLACE INTO {} (k, v) VALUES (?1, ?2)", tree),
 			params![key, value],
 		)?;
-		Ok(())
+		Ok(old_val.is_none())
 	}
 
 	fn iter(&self, tree: usize) -> Result<ValueIter<'_>> {
@@ -276,11 +280,8 @@ impl<'a> SqliteTx<'a> {
 			)
 		})
 	}
-}
 
-impl<'a> ITx for SqliteTx<'a> {
-	fn get(&self, tree: usize, key: &[u8]) -> Result<Option<Value>> {
-		let tree = self.get_tree(tree)?;
+	fn internal_get(&self, tree: &str, key: &[u8]) -> Result<Option<Value>> {
 		let mut stmt = self
 			.tx
 			.prepare(&format!("SELECT v FROM {} WHERE k = ?1", tree))?;
@@ -290,6 +291,13 @@ impl<'a> ITx for SqliteTx<'a> {
 			Some(v) => Ok(Some(v.get::<_, Vec<u8>>(0)?)),
 		}
 	}
+}
+
+impl<'a> ITx for SqliteTx<'a> {
+	fn get(&self, tree: usize, key: &[u8]) -> Result<Option<Value>> {
+		let tree = self.get_tree(tree)?;
+		self.internal_get(tree, key)
+	}
 	fn len(&self, tree: usize) -> Result<usize> {
 		let tree = self.get_tree(tree)?;
 		let mut stmt = self.tx.prepare(&format!("SELECT COUNT(*) FROM {}", tree))?;
@@ -300,13 +308,14 @@ impl<'a> ITx for SqliteTx<'a> {
 		}
 	}
 
-	fn insert(&mut self, tree: usize, key: &[u8], value: &[u8]) -> Result<()> {
+	fn insert(&mut self, tree: usize, key: &[u8], value: &[u8]) -> Result<bool> {
 		let tree = self.get_tree(tree)?;
+		let old_val = self.internal_get(tree, key)?;
 		self.tx.execute(
 			&format!("INSERT OR REPLACE INTO {} (k, v) VALUES (?1, ?2)", tree),
 			params![key, value],
 		)?;
-		Ok(())
+		Ok(old_val.is_none())
 	}
 	fn remove(&mut self, tree: usize, key: &[u8]) -> Result<bool> {
 		let tree = self.get_tree(tree)?;

src/table/data.rs

@@ -6,6 +6,7 @@ use serde_bytes::ByteBuf;
 use tokio::sync::Notify;
 
 use garage_db as db;
+use garage_db::counted_tree_hack::CountedTree;
 
 use garage_util::data::*;
 use garage_util::error::*;
@@ -30,7 +31,7 @@ pub struct TableData<F: TableSchema, R: TableReplication> {
 	pub(crate) merkle_tree: db::Tree,
 	pub(crate) merkle_todo: db::Tree,
 	pub(crate) merkle_todo_notify: Notify,
-	pub(crate) gc_todo: db::Tree,
+	pub(crate) gc_todo: CountedTree,
 
 	pub(crate) metrics: TableMetrics,
 }
@@ -55,6 +56,7 @@ where
 		let gc_todo = db
 			.open_tree(&format!("{}:gc_todo_v2", F::TABLE_NAME))
 			.expect("Unable to open DB tree");
+		let gc_todo = CountedTree::new(gc_todo).expect("Cannot count gc_todo_v2");
 
 		let metrics = TableMetrics::new(F::TABLE_NAME, merkle_todo.clone(), gc_todo.clone());
 
@@ -319,6 +321,6 @@ where
 	}
 
 	pub fn gc_todo_len(&self) -> Result<usize, Error> {
-		Ok(self.gc_todo.len()?)
+		Ok(self.gc_todo.len())
 	}
 }

src/table/gc.rs

@@ -12,7 +12,7 @@ use futures::select;
 use futures_util::future::*;
 use tokio::sync::watch;
 
-use garage_db as db;
+use garage_db::counted_tree_hack::CountedTree;
 
 use garage_util::data::*;
 use garage_util::error::*;
@@ -370,7 +370,7 @@ impl GcTodoEntry {
 	}
 
 	/// Saves the GcTodoEntry in the gc_todo tree
-	pub(crate) fn save(&self, gc_todo_tree: &db::Tree) -> Result<(), Error> {
+	pub(crate) fn save(&self, gc_todo_tree: &CountedTree) -> Result<(), Error> {
 		gc_todo_tree.insert(self.todo_table_key(), self.value_hash.as_slice())?;
 		Ok(())
 	}
@@ -380,16 +380,12 @@ impl GcTodoEntry {
 	/// This is usefull to remove a todo entry only under the condition
 	/// that it has not changed since the time it was read, i.e.
 	/// what we have to do is still the same
-	pub(crate) fn remove_if_equal(&self, gc_todo_tree: &db::Tree) -> Result<(), Error> {
-		let key = self.todo_table_key();
-		gc_todo_tree.db().transaction(|mut tx| {
-			let remove =
-				matches!(tx.get(gc_todo_tree, &key)?, Some(ov) if ov == self.value_hash.as_slice());
-			if remove {
-				tx.remove(gc_todo_tree, &key)?;
-			}
-			tx.commit(())
-		})?;
+	pub(crate) fn remove_if_equal(&self, gc_todo_tree: &CountedTree) -> Result<(), Error> {
+		gc_todo_tree.compare_and_swap::<_, _, &[u8]>(
+			&self.todo_table_key(),
+			Some(self.value_hash),
+			None,
+		)?;
 		Ok(())
 	}
 

src/table/metrics.rs

@@ -1,6 +1,7 @@
 use opentelemetry::{global, metrics::*, KeyValue};
 
 use garage_db as db;
+use garage_db::counted_tree_hack::CountedTree;
 
 /// TableMetrics reference all counter used for metrics
 pub struct TableMetrics {
@@ -19,7 +20,7 @@ pub struct TableMetrics {
 	pub(crate) sync_items_received: Counter<u64>,
 }
 impl TableMetrics {
-	pub fn new(table_name: &'static str, merkle_todo: db::Tree, gc_todo: db::Tree) -> Self {
+	pub fn new(table_name: &'static str, merkle_todo: db::Tree, gc_todo: CountedTree) -> Self {
 		let meter = global::meter(table_name);
 		TableMetrics {
 			_merkle_todo_len: meter
@@ -40,12 +41,10 @@ impl TableMetrics {
 				.u64_value_observer(
 					"table.gc_todo_queue_length",
 					move |observer| {
-						if let Ok(v) = gc_todo.len() {
-							observer.observe(
-								v as u64,
-								&[KeyValue::new("table_name", table_name)],
-							);
-						}
+						observer.observe(
+							gc_todo.len() as u64,
+							&[KeyValue::new("table_name", table_name)],
+						);
 					},
 				)
 				.with_description("Table garbage collector TODO queue length")

src/util/sled_counter.rs

@@ -1,100 +0,0 @@
-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 remove<K: AsRef<[u8]>>(&self, key: K) -> Result<Option<IVec>> {
-		let res = self.0.tree.remove(key);
-		if matches!(res, Ok(Some(_))) {
-			self.0.len.fetch_sub(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
-	}
-}