layou: implement ack locking

src/rpc/layout/history.rs

@@ -1,5 +1,7 @@
+use std::collections::HashMap;
 use std::collections::HashSet;
 use std::ops::Deref;
+use std::sync::atomic::{AtomicUsize, Ordering};
 
 use garage_util::crdt::{Crdt, Lww, LwwMap};
 use garage_util::data::*;
@@ -21,6 +23,11 @@ pub struct LayoutHelper {
 
 	trackers_hash: Hash,
 	staging_hash: Hash,
+
+	// ack lock: counts in-progress write operations for each
+	// layout version ; we don't increase the ack update tracker
+	// while this lock is nonzero
+	pub(crate) ack_lock: HashMap<u64, AtomicUsize>,
 }
 
 impl Deref for LayoutHelper {
@@ -31,7 +38,7 @@ impl Deref for LayoutHelper {
 }
 
 impl LayoutHelper {
-	pub fn new(mut layout: LayoutHistory) -> Self {
+	pub fn new(mut layout: LayoutHistory, mut ack_lock: HashMap<u64, AtomicUsize>) -> Self {
 		layout.cleanup_old_versions();
 
 		let all_nongateway_nodes = layout.get_all_nongateway_nodes();
@@ -51,6 +58,11 @@ impl LayoutHelper {
 		let trackers_hash = layout.calculate_trackers_hash();
 		let staging_hash = layout.calculate_staging_hash();
 
+		ack_lock.retain(|_, cnt| *cnt.get_mut() > 0);
+		ack_lock
+			.entry(layout.current().version)
+			.or_insert(AtomicUsize::new(0));
+
 		LayoutHelper {
 			layout: Some(layout),
 			ack_map_min,
@@ -59,6 +71,7 @@ impl LayoutHelper {
 			all_nongateway_nodes,
 			trackers_hash,
 			staging_hash,
+			ack_lock,
 		}
 	}
 
@@ -74,7 +87,10 @@ impl LayoutHelper {
 	{
 		let changed = f(&mut self.layout.as_mut().unwrap());
 		if changed {
-			*self = Self::new(self.layout.take().unwrap());
+			*self = Self::new(
+				self.layout.take().unwrap(),
+				std::mem::take(&mut self.ack_lock),
+			);
 		}
 		changed
 	}
@@ -115,7 +131,7 @@ impl LayoutHelper {
 			.collect()
 	}
 
-	pub fn write_sets_of(&self, position: &Hash) -> Vec<Vec<Uuid>> {
+	pub(crate) fn write_sets_of(&self, position: &Hash) -> Vec<Vec<Uuid>> {
 		self.layout()
 			.versions
 			.iter()
@@ -143,42 +159,72 @@ impl LayoutHelper {
 
 	// ------------------ helpers for update tracking ---------------
 
-	pub(crate) fn sync_first(&mut self, node: Uuid) {
-		let first_version = self.versions.first().as_ref().unwrap().version;
-		self.update(|layout| layout.update_trackers.sync_map.set_max(node, first_version));
+	pub(crate) fn update_trackers(&mut self, local_node_id: Uuid) {
+		// Ensure trackers for this node's values are up-to-date
+
+		// 1. Acknowledge the last layout version which is not currently
+		//    locked by an in-progress write operation
+		self.ack_max_free(local_node_id);
+
+		// 2. Assume the data on this node is sync'ed up at least to
+		//    the first layout version in the history
+		self.sync_first(local_node_id);
+
+		// 3. Acknowledge everyone has synced up to min(self.sync_map)
+		self.sync_ack(local_node_id);
+
+		info!("ack_map: {:?}", self.update_trackers.ack_map);
+		info!("sync_map: {:?}", self.update_trackers.sync_map);
+		info!("sync_ack_map: {:?}", self.update_trackers.sync_ack_map);
 	}
 
-	pub(crate) fn sync_ack(&mut self, node: Uuid) {
+	fn sync_first(&mut self, local_node_id: Uuid) {
+		let first_version = self.versions.first().as_ref().unwrap().version;
+		self.update(|layout| {
+			layout
+				.update_trackers
+				.sync_map
+				.set_max(local_node_id, first_version)
+		});
+	}
+
+	fn sync_ack(&mut self, local_node_id: Uuid) {
 		let sync_map_min = self.sync_map_min;
 		self.update(|layout| {
 			layout
 				.update_trackers
 				.sync_ack_map
-				.set_max(node, sync_map_min)
+				.set_max(local_node_id, sync_map_min)
 		});
 	}
 
-	pub(crate) fn ack_last(&mut self, node: Uuid) {
-		let last_version = self.current().version;
-		self.update(|layout| layout.update_trackers.ack_map.set_max(node, last_version));
+	pub(crate) fn ack_max_free(&mut self, local_node_id: Uuid) -> bool {
+		let max_ack = self.max_free_ack();
+		let changed = self.update(|layout| {
+			layout
+				.update_trackers
+				.ack_map
+				.set_max(local_node_id, max_ack)
+		});
+		if changed {
+			info!("ack_until updated to {}", max_ack);
+		}
+		changed
 	}
 
-	pub(crate) fn update_trackers_of(&mut self, node_id: Uuid) {
-		// Ensure trackers for this node's values are up-to-date
-
-		// 1. Acknowledge the last layout version in the history
-		self.ack_last(node_id);
-
-		// 2. Assume the data on this node is sync'ed up at least to
-		//    the first layout version in the history
-		self.sync_first(node_id);
-
-		// 3. Acknowledge everyone has synced up to min(self.sync_map)
-		self.sync_ack(node_id);
-
-		info!("ack_map: {:?}", self.update_trackers.ack_map);
-		info!("sync_map: {:?}", self.update_trackers.sync_map);
-		info!("sync_ack_map: {:?}", self.update_trackers.sync_ack_map);
+	pub(crate) fn max_free_ack(&self) -> u64 {
+		self.layout()
+			.versions
+			.iter()
+			.map(|x| x.version)
+			.take_while(|v| {
+				self.ack_lock
+					.get(v)
+					.map(|x| x.load(Ordering::Relaxed) == 0)
+					.unwrap_or(true)
+			})
+			.max()
+			.unwrap_or(self.min_stored())
 	}
 }
 

src/rpc/layout/manager.rs

@@ -1,5 +1,5 @@
 use std::collections::HashMap;
-use std::sync::{Arc, Mutex, RwLock, RwLockReadGuard};
+use std::sync::{atomic::Ordering, Arc, Mutex, RwLock, RwLockReadGuard};
 use std::time::Duration;
 
 use serde::{Deserialize, Serialize};
@@ -74,8 +74,8 @@ impl LayoutManager {
 			}
 		};
 
-		let mut cluster_layout = LayoutHelper::new(cluster_layout);
-		cluster_layout.update_trackers_of(node_id.into());
+		let mut cluster_layout = LayoutHelper::new(cluster_layout, Default::default());
+		cluster_layout.update_trackers(node_id.into());
 
 		let layout = Arc::new(RwLock::new(cluster_layout));
 		let change_notify = Arc::new(Notify::new());
@@ -139,13 +139,36 @@ impl LayoutManager {
 
 		let mut layout = self.layout.write().unwrap();
 		if layout.update(|l| l.update_trackers.sync_map.set_max(self.node_id, sync_until)) {
-			debug!("sync_until updated to {}", sync_until);
+			info!("sync_until updated to {}", sync_until);
 			self.broadcast_update(SystemRpc::AdvertiseClusterLayoutTrackers(
 				layout.update_trackers.clone(),
 			));
 		}
 	}
 
+	fn ack_new_version(self: &Arc<Self>) {
+		let mut layout = self.layout.write().unwrap();
+		if layout.ack_max_free(self.node_id) {
+			self.broadcast_update(SystemRpc::AdvertiseClusterLayoutTrackers(
+				layout.update_trackers.clone(),
+			));
+		}
+	}
+
+	// ---- ACK LOCKING ----
+
+	pub fn write_sets_of(self: &Arc<Self>, position: &Hash) -> WriteLock<Vec<Vec<Uuid>>> {
+		let layout = self.layout();
+		let version = layout.current().version;
+		let nodes = layout.write_sets_of(position);
+		layout
+			.ack_lock
+			.get(&version)
+			.unwrap()
+			.fetch_add(1, Ordering::Relaxed);
+		WriteLock::new(version, self, nodes)
+	}
+
 	// ---- INTERNALS ---
 
 	fn merge_layout(&self, adv: &LayoutHistory) -> Option<LayoutHistory> {
@@ -154,7 +177,7 @@ impl LayoutManager {
 
 		if !prev_layout_check || adv.check().is_ok() {
 			if layout.update(|l| l.merge(adv)) {
-				layout.update_trackers_of(self.node_id);
+				layout.update_trackers(self.node_id);
 				if prev_layout_check && layout.check().is_err() {
 					panic!("Merged two correct layouts and got an incorrect layout.");
 				}
@@ -168,7 +191,7 @@ impl LayoutManager {
 		let mut layout = self.layout.write().unwrap();
 		if layout.update_trackers != *adv {
 			if layout.update(|l| l.update_trackers.merge(adv)) {
-				layout.update_trackers_of(self.node_id);
+				layout.update_trackers(self.node_id);
 				return Some(layout.update_trackers.clone());
 			}
 		}
@@ -317,3 +340,42 @@ impl LayoutManager {
 		Ok(SystemRpc::Ok)
 	}
 }
+
+// ---- ack lock ----
+
+pub struct WriteLock<T> {
+	layout_version: u64,
+	layout_manager: Arc<LayoutManager>,
+	value: T,
+}
+
+impl<T> WriteLock<T> {
+	fn new(version: u64, layout_manager: &Arc<LayoutManager>, value: T) -> Self {
+		Self {
+			layout_version: version,
+			layout_manager: layout_manager.clone(),
+			value,
+		}
+	}
+}
+
+impl<T> AsRef<T> for WriteLock<T> {
+	fn as_ref(&self) -> &T {
+		&self.value
+	}
+}
+
+impl<T> Drop for WriteLock<T> {
+	fn drop(&mut self) {
+		let layout = self.layout_manager.layout(); // acquire read lock
+		if let Some(counter) = layout.ack_lock.get(&self.layout_version) {
+			let prev_lock = counter.fetch_sub(1, Ordering::Relaxed);
+			if prev_lock == 1 && layout.current().version > self.layout_version {
+				drop(layout); // release read lock, write lock will be acquired
+				self.layout_manager.ack_new_version();
+			}
+		} else {
+			error!("Could not find ack lock counter for layout version {}. This probably indicates a bug in Garage.", self.layout_version);
+		}
+	}
+}

src/rpc/layout/mod.rs

@@ -11,6 +11,7 @@ pub mod manager;
 // ---- re-exports ----
 
 pub use history::*;
+pub use manager::WriteLock;
 pub use schema::*;
 pub use version::*;