Keep network status & ring in a tokio::sync::watch

advantages
- reads don't prevent preparing writes
- can be followed from other parts of the system by cloning the receiver

src/membership.rs

@@ -13,7 +13,7 @@ use futures_util::future::*;
 use sha2::{Digest, Sha256};
 use tokio::prelude::*;
 use tokio::sync::watch;
-use tokio::sync::RwLock;
+use tokio::sync::Mutex;
 
 use crate::background::BackgroundRunner;
 use crate::data::*;
@@ -32,36 +32,44 @@ pub struct System {
 
 	pub rpc_client: RpcClient,
 
-	pub members: RwLock<Members>,
+	pub status: watch::Receiver<Arc<Status>>,
+	pub ring: watch::Receiver<Arc<Ring>>,
+
+	update_lock: Mutex<(watch::Sender<Arc<Status>>, watch::Sender<Arc<Ring>>)>,
 
 	pub background: Arc<BackgroundRunner>,
 }
 
-pub struct Members {
-	pub status: HashMap<UUID, NodeStatus>,
-	pub status_hash: Hash,
-
-	pub config: NetworkConfig,
-	pub ring: Vec<RingEntry>,
-	pub n_datacenters: usize,
+#[derive(Debug, Clone)]
+pub struct Status {
+	pub nodes: HashMap<UUID, NodeStatus>,
+	pub hash: Hash,
 }
 
+#[derive(Debug, Clone)]
 pub struct NodeStatus {
 	pub addr: SocketAddr,
 	pub remaining_ping_attempts: usize,
 }
 
-#[derive(Debug)]
+#[derive(Clone)]
+pub struct Ring {
+	pub config: NetworkConfig,
+	pub ring: Vec<RingEntry>,
+	pub n_datacenters: usize,
+}
+
+#[derive(Clone, Debug)]
 pub struct RingEntry {
 	pub location: Hash,
 	pub node: UUID,
 	pub datacenter: u64,
 }
 
-impl Members {
+impl Status {
 	fn handle_ping(&mut self, ip: IpAddr, info: &PingMessage) -> bool {
 		let addr = SocketAddr::new(ip, info.rpc_port);
-		let old_status = self.status.insert(
+		let old_status = self.nodes.insert(
 			info.id.clone(),
 			NodeStatus {
 				addr: addr.clone(),
@@ -77,8 +85,8 @@ impl Members {
 		}
 	}
 
-	fn recalculate_status_hash(&mut self) {
-		let mut nodes = self.status.iter().collect::<Vec<_>>();
+	fn recalculate_hash(&mut self) {
+		let mut nodes = self.nodes.iter().collect::<Vec<_>>();
 		nodes.sort_unstable_by_key(|(id, _status)| *id);
 
 		let mut hasher = Sha256::new();
@@ -88,11 +96,13 @@ impl Members {
 			hasher.input(format!("{} {}\n", hex::encode(&id), status.addr));
 		}
 		eprintln!("END --");
-		self.status_hash
+		self.hash
 			.as_slice_mut()
 			.copy_from_slice(&hasher.result()[..]);
 	}
+}
 
+impl Ring {
 	fn rebuild_ring(&mut self) {
 		let mut new_ring = vec![];
 		let mut datacenters = vec![];
@@ -201,20 +211,28 @@ impl System {
 				}
 			}
 		};
-		let mut members = Members {
-			status: HashMap::new(),
-			status_hash: Hash::default(),
+		let mut status = Status {
+			nodes: HashMap::new(),
+			hash: Hash::default(),
+		};
+		status.recalculate_hash();
+		let (update_status, status) = watch::channel(Arc::new(status));
+
+		let mut ring = Ring {
 			config: net_config,
 			ring: Vec::new(),
 			n_datacenters: 0,
 		};
-		members.recalculate_status_hash();
-		members.rebuild_ring();
+		ring.rebuild_ring();
+		let (update_ring, ring) = watch::channel(Arc::new(ring));
+
 		System {
 			config,
 			id,
 			rpc_client: RpcClient::new(),
-			members: RwLock::new(members),
+			status,
+			ring,
+			update_lock: Mutex::new((update_status, update_ring)),
 			background,
 		}
 	}
@@ -223,37 +241,33 @@ impl System {
 		let mut path = self.config.metadata_dir.clone();
 		path.push("network_config");
 
-		let members = self.members.read().await;
-		let data =
-			rmp_to_vec_all_named(&members.config)?;
-		drop(members);
+		let ring = self.ring.borrow().clone();
+		let data = rmp_to_vec_all_named(&ring.config)?;
 
-		let mut f = tokio::fs::File::create(path.as_path())
-			.await?;
-		f.write_all(&data[..])
-			.await?;
+		let mut f = tokio::fs::File::create(path.as_path()).await?;
+		f.write_all(&data[..]).await?;
 		Ok(())
 	}
 
-	pub async fn make_ping(&self) -> Message {
-		let members = self.members.read().await;
+	pub fn make_ping(&self) -> Message {
+		let status = self.status.borrow().clone();
+		let ring = self.ring.borrow().clone();
 		Message::Ping(PingMessage {
 			id: self.id.clone(),
 			rpc_port: self.config.rpc_port,
-			status_hash: members.status_hash.clone(),
-			config_version: members.config.version,
+			status_hash: status.hash.clone(),
+			config_version: ring.config.version,
 		})
 	}
 
 	pub async fn broadcast(self: Arc<Self>, msg: Message, timeout: Duration) {
-		let members = self.members.read().await;
-		let to = members
-			.status
+		let status = self.status.borrow().clone();
+		let to = status
+			.nodes
 			.keys()
 			.filter(|x| **x != self.id)
 			.cloned()
 			.collect::<Vec<_>>();
-		drop(members);
 		rpc_call_many(self.clone(), &to[..], &msg, timeout).await;
 	}
 
@@ -273,7 +287,7 @@ impl System {
 	}
 
 	pub async fn ping_nodes(self: Arc<Self>, peers: Vec<(SocketAddr, Option<UUID>)>) {
-		let ping_msg = self.make_ping().await;
+		let ping_msg = self.make_ping();
 		let ping_resps = join_all(peers.iter().map(|(addr, id_option)| {
 			let sys = self.clone();
 			let ping_msg_ref = &ping_msg;
@@ -287,14 +301,16 @@ impl System {
 		}))
 		.await;
 
-		let mut members = self.members.write().await;
+		let update_locked = self.update_lock.lock().await;
+		let mut status: Status = self.status.borrow().as_ref().clone();
+		let ring = self.ring.borrow().clone();
 
 		let mut has_changes = false;
 		let mut to_advertise = vec![];
 
 		for (id_option, addr, ping_resp) in ping_resps {
 			if let Ok(Message::Ping(info)) = ping_resp {
-				let is_new = members.handle_ping(addr.ip(), &info);
+				let is_new = status.handle_ping(addr.ip(), &info);
 				if is_new {
 					has_changes = true;
 					to_advertise.push(AdvertisedNode {
@@ -302,17 +318,17 @@ impl System {
 						addr: addr.clone(),
 					});
 				}
-				if is_new || members.status_hash != info.status_hash {
+				if is_new || status.hash != info.status_hash {
 					self.background
 						.spawn_cancellable(self.clone().pull_status(info.id.clone()).map(Ok));
 				}
-				if is_new || members.config.version < info.config_version {
+				if is_new || ring.config.version < info.config_version {
 					self.background
 						.spawn_cancellable(self.clone().pull_config(info.id.clone()).map(Ok));
 				}
 			} else if let Some(id) = id_option {
-				let remaining_attempts = members
-					.status
+				let remaining_attempts = status
+					.nodes
 					.get(id)
 					.map(|x| x.remaining_ping_attempts)
 					.unwrap_or(0);
@@ -321,19 +337,22 @@ impl System {
 						"Removing node {} after too many failed pings",
 						hex::encode(&id)
 					);
-					members.status.remove(&id);
+					status.nodes.remove(&id);
 					has_changes = true;
 				} else {
-					if let Some(st) = members.status.get_mut(id) {
+					if let Some(st) = status.nodes.get_mut(id) {
 						st.remaining_ping_attempts = remaining_attempts - 1;
 					}
 				}
 			}
 		}
 		if has_changes {
-			members.recalculate_status_hash();
+			status.recalculate_hash();
 		}
-		drop(members);
+		if let Err(e) = update_locked.0.broadcast(Arc::new(status)) {
+			eprintln!("In ping_nodes: could not save status update ({})", e);
+		}
+		drop(update_locked);
 
 		if to_advertise.len() > 0 {
 			self.broadcast(Message::AdvertiseNodesUp(to_advertise), PING_TIMEOUT)
@@ -346,29 +365,35 @@ impl System {
 		from: &SocketAddr,
 		ping: &PingMessage,
 	) -> Result<Message, Error> {
-		let mut members = self.members.write().await;
-		let is_new = members.handle_ping(from.ip(), ping);
+		let update_locked = self.update_lock.lock().await;
+		let mut status: Status = self.status.borrow().as_ref().clone();
+
+		let is_new = status.handle_ping(from.ip(), ping);
 		if is_new {
-			members.recalculate_status_hash();
+			status.recalculate_hash();
 		}
-		let status_hash = members.status_hash.clone();
-		let config_version = members.config.version;
-		drop(members);
+		let status_hash = status.hash.clone();
+		let config_version = self.ring.borrow().config.version;
+
+		update_locked.0.broadcast(Arc::new(status))?;
+		drop(update_locked);
 
 		if is_new || status_hash != ping.status_hash {
-			self.background.spawn_cancellable(self.clone().pull_status(ping.id.clone()).map(Ok));
+			self.background
+				.spawn_cancellable(self.clone().pull_status(ping.id.clone()).map(Ok));
 		}
 		if is_new || config_version < ping.config_version {
-			self.background.spawn_cancellable(self.clone().pull_config(ping.id.clone()).map(Ok));
+			self.background
+				.spawn_cancellable(self.clone().pull_config(ping.id.clone()).map(Ok));
 		}
 
-		Ok(self.make_ping().await)
+		Ok(self.make_ping())
 	}
 
-	pub async fn handle_pull_status(&self) -> Result<Message, Error> {
-		let members = self.members.read().await;
+	pub fn handle_pull_status(&self) -> Result<Message, Error> {
+		let status = self.status.borrow().clone();
 		let mut mem = vec![];
-		for (node, status) in members.status.iter() {
+		for (node, status) in status.nodes.iter() {
 			mem.push(AdvertisedNode {
 				id: node.clone(),
 				addr: status.addr.clone(),
@@ -377,9 +402,9 @@ impl System {
 		Ok(Message::AdvertiseNodesUp(mem))
 	}
 
-	pub async fn handle_pull_config(&self) -> Result<Message, Error> {
-		let members = self.members.read().await;
-		Ok(Message::AdvertiseConfig(members.config.clone()))
+	pub fn handle_pull_config(&self) -> Result<Message, Error> {
+		let ring = self.ring.borrow().clone();
+		Ok(Message::AdvertiseConfig(ring.config.clone()))
 	}
 
 	pub async fn handle_advertise_nodes_up(
@@ -388,14 +413,15 @@ impl System {
 	) -> Result<Message, Error> {
 		let mut to_ping = vec![];
 
-		let mut members = self.members.write().await;
+		let update_lock = self.update_lock.lock().await;
+		let mut status: Status = self.status.borrow().as_ref().clone();
 		let mut has_changed = false;
 
 		for node in adv.iter() {
 			if node.id == self.id {
 				// learn our own ip address
 				let self_addr = SocketAddr::new(node.addr.ip(), self.config.rpc_port);
-				let old_self = members.status.insert(
+				let old_self = status.nodes.insert(
 					node.id.clone(),
 					NodeStatus {
 						addr: self_addr,
@@ -406,17 +432,19 @@ impl System {
 					None => true,
 					Some(x) => x.addr != self_addr,
 				};
-			} else if !members.status.contains_key(&node.id) {
+			} else if !status.nodes.contains_key(&node.id) {
 				to_ping.push((node.addr.clone(), Some(node.id.clone())));
 			}
 		}
 		if has_changed {
-			members.recalculate_status_hash();
+			status.recalculate_hash();
 		}
-		drop(members);
+		update_lock.0.broadcast(Arc::new(status))?;
+		drop(update_lock);
 
 		if to_ping.len() > 0 {
-			self.background.spawn_cancellable(self.clone().ping_nodes(to_ping).map(Ok));
+			self.background
+				.spawn_cancellable(self.clone().ping_nodes(to_ping).map(Ok));
 		}
 
 		Ok(Message::Ok)
@@ -426,10 +454,14 @@ impl System {
 		self: Arc<Self>,
 		adv: &NetworkConfig,
 	) -> Result<Message, Error> {
-		let mut members = self.members.write().await;
-		if adv.version > members.config.version {
-			members.config = adv.clone();
-			members.rebuild_ring();
+		let mut ring: Ring = self.ring.borrow().as_ref().clone();
+		let update_lock = self.update_lock.lock().await;
+
+		if adv.version > ring.config.version {
+			ring.config = adv.clone();
+			ring.rebuild_ring();
+			update_lock.1.broadcast(Arc::new(ring))?;
+			drop(update_lock);
 
 			self.background.spawn_cancellable(
 				self.clone()
@@ -446,14 +478,13 @@ impl System {
 		loop {
 			let restart_at = tokio::time::delay_for(PING_INTERVAL);
 
-			let members = self.members.read().await;
-			let ping_addrs = members
-				.status
+			let status = self.status.borrow().clone();
+			let ping_addrs = status
+				.nodes
 				.iter()
 				.filter(|(id, _)| **id != self.id)
 				.map(|(id, status)| (status.addr.clone(), Some(id.clone())))
 				.collect::<Vec<_>>();
-			drop(members);
 
 			self.clone().ping_nodes(ping_addrs).await;