Implement chain::Listen without using RefCell

The implementation of chain::Listen for ChannelMonitor required using a
RefCell since its block_connected method required a mutable borrow. This
is no longer the case since ChannelMonitor now uses interior mutability
via a Mutex. So the RefCell is no longer needed.

Author: jkczyz

lightning-block-sync/src/init.rs

@@ -38,7 +38,6 @@ use lightning::chain;
 ///
 /// use lightning_block_sync::*;
 ///
-/// use std::cell::RefCell;
 /// use std::io::Cursor;
 ///
 /// async fn init_sync<
@@ -83,7 +82,7 @@ use lightning::chain;
 ///
 /// 	// Synchronize any channel monitors and the channel manager to be on the best block.
 /// 	let mut cache = UnboundedCache::new();
-/// 	let mut monitor_listener = (RefCell::new(monitor), &*tx_broadcaster, &*fee_estimator, &*logger);
+/// 	let mut monitor_listener = (monitor, &*tx_broadcaster, &*fee_estimator, &*logger);
 /// 	let listeners = vec![
 /// 		(monitor_block_hash, &mut monitor_listener as &mut dyn chain::Listen),
 /// 		(manager_block_hash, &mut manager as &mut dyn chain::Listen),
@@ -92,7 +91,7 @@ use lightning::chain;
 /// 		block_source, Network::Bitcoin, &mut cache, listeners).await.unwrap();
 ///
 /// 	// Allow the chain monitor to watch any channels.
-/// 	let monitor = monitor_listener.0.into_inner();
+/// 	let monitor = monitor_listener.0;
 /// 	chain_monitor.watch_channel(monitor.get_funding_txo().0, monitor);
 ///
 /// 	// Create an SPV client to notify the chain monitor and channel manager of block events.

lightning/src/chain/channelmonitor.rs

@@ -50,7 +50,6 @@ use util::ser::{Readable, ReadableArgs, MaybeReadable, Writer, Writeable, U48};
 use util::byte_utils;
 use util::events::Event;
 
-use std::cell::RefCell;
 use std::collections::{HashMap, HashSet, hash_map};
 use std::{cmp, mem};
 use std::io::Error;
@@ -2474,19 +2473,19 @@ pub trait Persist<ChannelSigner: Sign>: Send + Sync {
 	fn update_persisted_channel(&self, id: OutPoint, update: &ChannelMonitorUpdate, data: &ChannelMonitor<ChannelSigner>) -> Result<(), ChannelMonitorUpdateErr>;
 }
 
-impl<Signer: Sign, T: Deref, F: Deref, L: Deref> chain::Listen for (RefCell<ChannelMonitor<Signer>>, T, F, L)
+impl<Signer: Sign, T: Deref, F: Deref, L: Deref> chain::Listen for (ChannelMonitor<Signer>, T, F, L)
 where
 	T::Target: BroadcasterInterface,
 	F::Target: FeeEstimator,
 	L::Target: Logger,
 {
 	fn block_connected(&self, block: &Block, height: u32) {
 		let txdata: Vec<_> = block.txdata.iter().enumerate().collect();
-		self.0.borrow_mut().block_connected(&block.header, &txdata, height, &*self.1, &*self.2, &*self.3);
+		self.0.block_connected(&block.header, &txdata, height, &*self.1, &*self.2, &*self.3);
 	}
 
 	fn block_disconnected(&self, header: &BlockHeader, height: u32) {
-		self.0.borrow_mut().block_disconnected(header, height, &*self.1, &*self.2, &*self.3);
+		self.0.block_disconnected(header, height, &*self.1, &*self.2, &*self.3);
 	}
 }