Uniform framework for bg variable management

src/block/resync.rs

@@ -3,7 +3,6 @@ use std::convert::TryInto;
 use std::sync::{Arc, Mutex};
 use std::time::Duration;
 
-use arc_swap::ArcSwap;
 use async_trait::async_trait;
 use serde::{Deserialize, Serialize};
 
@@ -22,7 +21,7 @@ use garage_util::background::*;
 use garage_util::data::*;
 use garage_util::error::*;
 use garage_util::metrics::RecordDuration;
-use garage_util::persister::Persister;
+use garage_util::persister::PersisterShared;
 use garage_util::time::*;
 use garage_util::tranquilizer::Tranquilizer;
 
@@ -49,13 +48,12 @@ const INITIAL_RESYNC_TRANQUILITY: u32 = 2;
 
 pub struct BlockResyncManager {
 	pub(crate) queue: CountedTree,
-	pub(crate) notify: Notify,
+	pub(crate) notify: Arc<Notify>,
 	pub(crate) errors: CountedTree,
 
 	busy_set: BusySet,
 
-	persister: Persister<ResyncPersistedConfig>,
-	persisted: ArcSwap<ResyncPersistedConfig>,
+	persister: PersisterShared<ResyncPersistedConfig>,
 }
 
 #[derive(Serialize, Deserialize, Clone, Copy)]
@@ -64,6 +62,14 @@ struct ResyncPersistedConfig {
 	tranquility: u32,
 }
 impl garage_util::migrate::InitialFormat for ResyncPersistedConfig {}
+impl Default for ResyncPersistedConfig {
+	fn default() -> Self {
+		ResyncPersistedConfig {
+			n_workers: 1,
+			tranquility: INITIAL_RESYNC_TRANQUILITY,
+		}
+	}
+}
 
 enum ResyncIterResult {
 	BusyDidSomething,
@@ -91,22 +97,14 @@ impl BlockResyncManager {
 			.expect("Unable to open block_local_resync_errors tree");
 		let errors = CountedTree::new(errors).expect("Could not count block_local_resync_errors");
 
-		let persister = Persister::new(&system.metadata_dir, "resync_cfg");
-		let persisted = match persister.load() {
-			Ok(v) => v,
-			Err(_) => ResyncPersistedConfig {
-				n_workers: 1,
-				tranquility: INITIAL_RESYNC_TRANQUILITY,
-			},
-		};
+		let persister = PersisterShared::new(&system.metadata_dir, "resync_cfg");
 
 		Self {
 			queue,
-			notify: Notify::new(),
+			notify: Arc::new(Notify::new()),
 			errors,
 			busy_set: Arc::new(Mutex::new(HashSet::new())),
 			persister,
-			persisted: ArcSwap::new(Arc::new(persisted)),
 		}
 	}
 
@@ -142,6 +140,38 @@ impl BlockResyncManager {
 		)))
 	}
 
+	pub fn register_bg_vars(&self, vars: &mut vars::BgVars) {
+		let notify = self.notify.clone();
+		vars.register_rw(
+			&self.persister,
+			"resync-worker-count",
+			|p| p.get_with(|x| x.n_workers),
+			move |p, n_workers| {
+				if !(1..=MAX_RESYNC_WORKERS).contains(&n_workers) {
+					return Err(Error::Message(format!(
+						"Invalid number of resync workers, must be between 1 and {}",
+						MAX_RESYNC_WORKERS
+					)));
+				}
+				p.set_with(|x| x.n_workers = n_workers)?;
+				notify.notify_waiters();
+				Ok(())
+			},
+		);
+
+		let notify = self.notify.clone();
+		vars.register_rw(
+			&self.persister,
+			"resync-tranquility",
+			|p| p.get_with(|x| x.tranquility),
+			move |p, tranquility| {
+				p.set_with(|x| x.tranquility = tranquility)?;
+				notify.notify_waiters();
+				Ok(())
+			},
+		);
+	}
+
 	// ---- Resync loop ----
 
 	// This part manages a queue of blocks that need to be
@@ -436,33 +466,6 @@ impl BlockResyncManager {
 
 		Ok(())
 	}
-
-	async fn update_persisted(
-		&self,
-		update: impl Fn(&mut ResyncPersistedConfig),
-	) -> Result<(), Error> {
-		let mut cfg: ResyncPersistedConfig = *self.persisted.load().as_ref();
-		update(&mut cfg);
-		self.persister.save_async(&cfg).await?;
-		self.persisted.store(Arc::new(cfg));
-		self.notify.notify_waiters();
-		Ok(())
-	}
-
-	pub async fn set_n_workers(&self, n_workers: usize) -> Result<(), Error> {
-		if !(1..=MAX_RESYNC_WORKERS).contains(&n_workers) {
-			return Err(Error::Message(format!(
-				"Invalid number of resync workers, must be between 1 and {}",
-				MAX_RESYNC_WORKERS
-			)));
-		}
-		self.update_persisted(|cfg| cfg.n_workers = n_workers).await
-	}
-
-	pub async fn set_tranquility(&self, tranquility: u32) -> Result<(), Error> {
-		self.update_persisted(|cfg| cfg.tranquility = tranquility)
-			.await
-	}
 }
 
 impl Drop for BusyBlock {
@@ -477,15 +480,18 @@ pub(crate) struct ResyncWorker {
 	manager: Arc<BlockManager>,
 	tranquilizer: Tranquilizer,
 	next_delay: Duration,
+	persister: PersisterShared<ResyncPersistedConfig>,
 }
 
 impl ResyncWorker {
 	pub(crate) fn new(index: usize, manager: Arc<BlockManager>) -> Self {
+		let persister = manager.resync.persister.clone();
 		Self {
 			index,
 			manager,
 			tranquilizer: Tranquilizer::new(30),
 			next_delay: Duration::from_secs(10),
+			persister,
 		}
 	}
 }
@@ -497,9 +503,9 @@ impl Worker for ResyncWorker {
 	}
 
 	fn status(&self) -> WorkerStatus {
-		let persisted = self.manager.resync.persisted.load();
+		let (n_workers, tranquility) = self.persister.get_with(|x| (x.n_workers, x.tranquility));
 
-		if self.index >= persisted.n_workers {
+		if self.index >= n_workers {
 			return WorkerStatus {
 				freeform: vec!["This worker is currently disabled".into()],
 				..Default::default()
@@ -508,22 +514,24 @@ impl Worker for ResyncWorker {
 
 		WorkerStatus {
 			queue_length: Some(self.manager.resync.queue_len().unwrap_or(0) as u64),
-			tranquility: Some(persisted.tranquility),
+			tranquility: Some(tranquility),
 			persistent_errors: Some(self.manager.resync.errors_len().unwrap_or(0) as u64),
 			..Default::default()
 		}
 	}
 
 	async fn work(&mut self, _must_exit: &mut watch::Receiver<bool>) -> Result<WorkerState, Error> {
-		if self.index >= self.manager.resync.persisted.load().n_workers {
+		let (n_workers, tranquility) = self.persister.get_with(|x| (x.n_workers, x.tranquility));
+
+		if self.index >= n_workers {
 			return Ok(WorkerState::Idle);
 		}
 
 		self.tranquilizer.reset();
 		match self.manager.resync.resync_iter(&self.manager).await {
-			Ok(ResyncIterResult::BusyDidSomething) => Ok(self
-				.tranquilizer
-				.tranquilize_worker(self.manager.resync.persisted.load().tranquility)),
+			Ok(ResyncIterResult::BusyDidSomething) => {
+				Ok(self.tranquilizer.tranquilize_worker(tranquility))
+			}
 			Ok(ResyncIterResult::BusyDidNothing) => Ok(WorkerState::Busy),
 			Ok(ResyncIterResult::IdleFor(delay)) => {
 				self.next_delay = delay;
@@ -542,7 +550,7 @@ impl Worker for ResyncWorker {
 	}
 
 	async fn wait_for_work(&mut self) -> WorkerState {
-		while self.index >= self.manager.resync.persisted.load().n_workers {
+		while self.index >= self.persister.get_with(|x| x.n_workers) {
 			self.manager.resync.notify.notified().await
 		}