Release write lock between monitor update iterations.

Previously, updating block data on a chain monitor
would acquire a write lock on all of its associated
channel monitors and not release it until the loop
completed.

Now, we instead acquire it on each iteration,
fixing #2470.

Author: arik-so

lightning/src/chain/chainmonitor.rs

@@ -42,6 +42,7 @@ use crate::ln::channelmanager::ChannelDetails;
 
 use crate::prelude::*;
 use crate::sync::{RwLock, RwLockReadGuard, Mutex, MutexGuard};
+use core::iter::FromIterator;
 use core::ops::Deref;
 use core::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
 use bitcoin::secp256k1::PublicKey;
@@ -285,7 +286,22 @@ where C::Target: chain::Filter,
 	where
 		FN: Fn(&ChannelMonitor<ChannelSigner>, &TransactionData) -> Vec<TransactionOutputs>
 	{
+		let funding_outpoints: HashSet<OutPoint> = HashSet::from_iter(self.monitors.read().unwrap().keys().cloned());
+		for funding_outpoint in funding_outpoints.iter() {
+			let monitor_lock = self.monitors.read().unwrap();
+			if let Some(monitor_state) = monitor_lock.get(funding_outpoint) {
+				self.update_monitor_with_chain_data(header, best_height, txdata, &process, funding_outpoint, &monitor_state);
+			}
+		}
+
+		// do some followup cleanup if any funding outpoints were added in between iterations
 		let monitor_states = self.monitors.write().unwrap();
+		for (funding_outpoint, monitor_state) in monitor_states.iter() {
+			if !funding_outpoints.contains(funding_outpoint) {
+				self.update_monitor_with_chain_data(header, best_height, txdata, &process, funding_outpoint, &monitor_state);
+			}
+		}
+
 		if let Some(height) = best_height {
 			// If the best block height is being updated, update highest_chain_height under the
 			// monitors write lock.
@@ -295,55 +311,55 @@ where C::Target: chain::Filter,
 				self.highest_chain_height.store(new_height, Ordering::Release);
 			}
 		}
+	}
 
-		for (funding_outpoint, monitor_state) in monitor_states.iter() {
-			let monitor = &monitor_state.monitor;
-			let mut txn_outputs;
-			{
-				txn_outputs = process(monitor, txdata);
-				let update_id = MonitorUpdateId {
-					contents: UpdateOrigin::ChainSync(self.sync_persistence_id.get_increment()),
-				};
-				let mut pending_monitor_updates = monitor_state.pending_monitor_updates.lock().unwrap();
-				if let Some(height) = best_height {
-					if !monitor_state.has_pending_chainsync_updates(&pending_monitor_updates) {
-						// If there are not ChainSync persists awaiting completion, go ahead and
-						// set last_chain_persist_height here - we wouldn't want the first
-						// InProgress to always immediately be considered "overly delayed".
-						monitor_state.last_chain_persist_height.store(height as usize, Ordering::Release);
-					}
+	fn update_monitor_with_chain_data<FN>(&self, header: &BlockHeader, best_height: Option<u32>, txdata: &TransactionData, process: FN, funding_outpoint: &OutPoint, monitor_state: &&MonitorHolder<ChannelSigner>) where FN: Fn(&ChannelMonitor<ChannelSigner>, &TransactionData) -> Vec<TransactionOutputs> {
+		let monitor = &monitor_state.monitor;
+		let mut txn_outputs;
+		{
+			txn_outputs = process(monitor, txdata);
+			let update_id = MonitorUpdateId {
+				contents: UpdateOrigin::ChainSync(self.sync_persistence_id.get_increment()),
+			};
+			let mut pending_monitor_updates = monitor_state.pending_monitor_updates.lock().unwrap();
+			if let Some(height) = best_height {
+				if !monitor_state.has_pending_chainsync_updates(&pending_monitor_updates) {
+					// If there are not ChainSync persists awaiting completion, go ahead and
+					// set last_chain_persist_height here - we wouldn't want the first
+					// InProgress to always immediately be considered "overly delayed".
+					monitor_state.last_chain_persist_height.store(height as usize, Ordering::Release);
 				}
+			}
 
-				log_trace!(self.logger, "Syncing Channel Monitor for channel {}", log_funding_info!(monitor));
-				match self.persister.update_persisted_channel(*funding_outpoint, None, monitor, update_id) {
-					ChannelMonitorUpdateStatus::Completed =>
-						log_trace!(self.logger, "Finished syncing Channel Monitor for channel {}", log_funding_info!(monitor)),
-					ChannelMonitorUpdateStatus::PermanentFailure => {
-						monitor_state.channel_perm_failed.store(true, Ordering::Release);
-						self.pending_monitor_events.lock().unwrap().push((*funding_outpoint, vec![MonitorEvent::UpdateFailed(*funding_outpoint)], monitor.get_counterparty_node_id()));
-						self.event_notifier.notify();
-					},
-					ChannelMonitorUpdateStatus::InProgress => {
-						log_debug!(self.logger, "Channel Monitor sync for channel {} in progress, holding events until completion!", log_funding_info!(monitor));
-						pending_monitor_updates.push(update_id);
-					},
+			log_trace!(self.logger, "Syncing Channel Monitor for channel {}", log_funding_info!(monitor));
+			match self.persister.update_persisted_channel(*funding_outpoint, None, monitor, update_id) {
+				ChannelMonitorUpdateStatus::Completed =>
+					log_trace!(self.logger, "Finished syncing Channel Monitor for channel {}", log_funding_info!(monitor)),
+				ChannelMonitorUpdateStatus::PermanentFailure => {
+					monitor_state.channel_perm_failed.store(true, Ordering::Release);
+					self.pending_monitor_events.lock().unwrap().push((*funding_outpoint, vec![MonitorEvent::UpdateFailed(*funding_outpoint)], monitor.get_counterparty_node_id()));
+					self.event_notifier.notify();
+				}
+				ChannelMonitorUpdateStatus::InProgress => {
+					log_debug!(self.logger, "Channel Monitor sync for channel {} in progress, holding events until completion!", log_funding_info!(monitor));
+					pending_monitor_updates.push(update_id);
 				}
 			}
+		}
 
-			// Register any new outputs with the chain source for filtering, storing any dependent
-			// transactions from within the block that previously had not been included in txdata.
-			if let Some(ref chain_source) = self.chain_source {
-				let block_hash = header.block_hash();
-				for (txid, mut outputs) in txn_outputs.drain(..) {
-					for (idx, output) in outputs.drain(..) {
-						// Register any new outputs with the chain source for filtering
-						let output = WatchedOutput {
-							block_hash: Some(block_hash),
-							outpoint: OutPoint { txid, index: idx as u16 },
-							script_pubkey: output.script_pubkey,
-						};
-						chain_source.register_output(output)
-					}
+		// Register any new outputs with the chain source for filtering, storing any dependent
+		// transactions from within the block that previously had not been included in txdata.
+		if let Some(ref chain_source) = self.chain_source {
+			let block_hash = header.block_hash();
+			for (txid, mut outputs) in txn_outputs.drain(..) {
+				for (idx, output) in outputs.drain(..) {
+					// Register any new outputs with the chain source for filtering
+					let output = WatchedOutput {
+						block_hash: Some(block_hash),
+						outpoint: OutPoint { txid, index: idx as u16 },
+						script_pubkey: output.script_pubkey,
+					};
+					chain_source.register_output(output)
 				}
 			}
 		}
@@ -976,7 +992,7 @@ mod tests {
 			assert!(err.contains("ChannelMonitor storage failure")));
 		check_added_monitors!(nodes[0], 2); // After the failure we generate a close-channel monitor update
 		check_closed_broadcast!(nodes[0], true);
-		check_closed_event!(nodes[0], 1, ClosureReason::ProcessingError { err: "ChannelMonitor storage failure".to_string() }, 
+		check_closed_event!(nodes[0], 1, ClosureReason::ProcessingError { err: "ChannelMonitor storage failure".to_string() },
 			[nodes[1].node.get_our_node_id()], 100000);
 
 		// However, as the ChainMonitor is still waiting for the original persistence to complete,