Use read lock on individual monitor.

Author: arik-so

lightning/src/chain/chainmonitor.rs

@@ -288,9 +288,8 @@ where C::Target: chain::Filter,
 	{
 		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.write().unwrap();
-			let monitor_state = monitor_lock.get(funding_outpoint);
-			if let Some(monitor_state) = monitor_state {
+			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);
 			}
 		}