[rust-lightning] / lightning-background-processor / src / lib.rs

//! Utilities that take care of tasks that (1) need to happen periodically to keep Rust-Lightning
//! running properly, and (2) either can or should be run in the background. See docs for
//! [`BackgroundProcessor`] for more details on the nitty-gritty.

#![deny(broken_intra_doc_links)]
#![deny(missing_docs)]
#![deny(unsafe_code)]

#[macro_use] extern crate lightning;

use lightning::chain;
use lightning::chain::chaininterface::{BroadcasterInterface, FeeEstimator};
use lightning::chain::chainmonitor::ChainMonitor;
use lightning::chain::channelmonitor;
use lightning::chain::keysinterface::{Sign, KeysInterface};
use lightning::ln::channelmanager::ChannelManager;
use lightning::ln::msgs::{ChannelMessageHandler, RoutingMessageHandler};
use lightning::ln::peer_handler::{PeerManager, SocketDescriptor};
use lightning::util::events::{EventHandler, EventsProvider};
use lightning::util::logger::Logger;
use std::sync::Arc;
use std::sync::atomic::{AtomicBool, Ordering};
use std::thread;
use std::thread::JoinHandle;
use std::time::{Duration, Instant};
use std::ops::Deref;

/// BackgroundProcessor takes care of tasks that (1) need to happen periodically to keep
/// Rust-Lightning running properly, and (2) either can or should be run in the background. Its
/// responsibilities are:
/// * Monitoring whether the ChannelManager needs to be re-persisted to disk, and if so,
///   writing it to disk/backups by invoking the callback given to it at startup.
///   ChannelManager persistence should be done in the background.
/// * Calling `ChannelManager::timer_tick_occurred()` and
///   `PeerManager::timer_tick_occurred()` every minute (can be done in the
///   background).
///
/// Note that if ChannelManager persistence fails and the persisted manager becomes out-of-date,
/// then there is a risk of channels force-closing on startup when the manager realizes it's
/// outdated. However, as long as `ChannelMonitor` backups are sound, no funds besides those used
/// for unilateral chain closure fees are at risk.
#[must_use = "BackgroundProcessor will immediately stop on drop. It should be stored until shutdown."]
pub struct BackgroundProcessor {
        stop_thread: Arc<AtomicBool>,
        thread_handle: Option<JoinHandle<Result<(), std::io::Error>>>,
}

#[cfg(not(test))]
const FRESHNESS_TIMER: u64 = 60;
#[cfg(test)]
const FRESHNESS_TIMER: u64 = 1;

const PING_TIMER: u64 = 5;

/// Trait which handles persisting a [`ChannelManager`] to disk.
///
/// [`ChannelManager`]: lightning::ln::channelmanager::ChannelManager
pub trait ChannelManagerPersister<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref>
where
        M::Target: 'static + chain::Watch<Signer>,
        T::Target: 'static + BroadcasterInterface,
        K::Target: 'static + KeysInterface<Signer = Signer>,
        F::Target: 'static + FeeEstimator,
        L::Target: 'static + Logger,
{
        /// Persist the given [`ChannelManager`] to disk, returning an error if persistence failed
        /// (which will cause the [`BackgroundProcessor`] which called this method to exit.
        ///
        /// [`ChannelManager`]: lightning::ln::channelmanager::ChannelManager
        fn persist_manager(&self, channel_manager: &ChannelManager<Signer, M, T, K, F, L>) -> Result<(), std::io::Error>;
}

impl<Fun, Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref>
ChannelManagerPersister<Signer, M, T, K, F, L> for Fun where
        M::Target: 'static + chain::Watch<Signer>,
        T::Target: 'static + BroadcasterInterface,
        K::Target: 'static + KeysInterface<Signer = Signer>,
        F::Target: 'static + FeeEstimator,
        L::Target: 'static + Logger,
        Fun: Fn(&ChannelManager<Signer, M, T, K, F, L>) -> Result<(), std::io::Error>,
{
        fn persist_manager(&self, channel_manager: &ChannelManager<Signer, M, T, K, F, L>) -> Result<(), std::io::Error> {
                self(channel_manager)
        }
}

impl BackgroundProcessor {
        /// Start a background thread that takes care of responsibilities enumerated in the [top-level
        /// documentation].
        ///
        /// The thread runs indefinitely unless the object is dropped, [`stop`] is called, or
        /// `persist_manager` returns an error. In case of an error, the error is retrieved by calling
        /// either [`join`] or [`stop`].
        ///
        /// Typically, users should either implement [`ChannelManagerPersister`] to never return an
        /// error or call [`join`] and handle any error that may arise. For the latter case, the
        /// `BackgroundProcessor` must be restarted by calling `start` again after handling the error.
        ///
        /// `persist_manager` is responsible for writing out the [`ChannelManager`] to disk, and/or
        /// uploading to one or more backup services. See [`ChannelManager::write`] for writing out a
        /// [`ChannelManager`]. See [`FilesystemPersister::persist_manager`] for Rust-Lightning's
        /// provided implementation.
        ///
        /// [top-level documentation]: Self
        /// [`join`]: Self::join
        /// [`stop`]: Self::stop
        /// [`ChannelManager`]: lightning::ln::channelmanager::ChannelManager
        /// [`ChannelManager::write`]: lightning::ln::channelmanager::ChannelManager#impl-Writeable
        /// [`FilesystemPersister::persist_manager`]: lightning_persister::FilesystemPersister::persist_manager
        pub fn start<
                Signer: 'static + Sign,
                CF: 'static + Deref + Send + Sync,
                CW: 'static + Deref + Send + Sync,
                T: 'static + Deref + Send + Sync,
                K: 'static + Deref + Send + Sync,
                F: 'static + Deref + Send + Sync,
                L: 'static + Deref + Send + Sync,
                P: 'static + Deref + Send + Sync,
                Descriptor: 'static + SocketDescriptor + Send + Sync,
                CMH: 'static + Deref + Send + Sync,
                RMH: 'static + Deref + Send + Sync,
                EH: 'static + EventHandler + Send + Sync,
                CMP: 'static + Send + ChannelManagerPersister<Signer, CW, T, K, F, L>,
                M: 'static + Deref<Target = ChainMonitor<Signer, CF, T, F, L, P>> + Send + Sync,
                CM: 'static + Deref<Target = ChannelManager<Signer, CW, T, K, F, L>> + Send + Sync,
                PM: 'static + Deref<Target = PeerManager<Descriptor, CMH, RMH, L>> + Send + Sync,
        >
        (persister: CMP, event_handler: EH, chain_monitor: M, channel_manager: CM, peer_manager: PM, logger: L) -> Self
        where
                CF::Target: 'static + chain::Filter,
                CW::Target: 'static + chain::Watch<Signer>,
                T::Target: 'static + BroadcasterInterface,
                K::Target: 'static + KeysInterface<Signer = Signer>,
                F::Target: 'static + FeeEstimator,
                L::Target: 'static + Logger,
                P::Target: 'static + channelmonitor::Persist<Signer>,
                CMH::Target: 'static + ChannelMessageHandler,
                RMH::Target: 'static + RoutingMessageHandler,
        {
                let stop_thread = Arc::new(AtomicBool::new(false));
                let stop_thread_clone = stop_thread.clone();
                let handle = thread::spawn(move || -> Result<(), std::io::Error> {
                        let mut last_freshness_call = Instant::now();
                        let mut last_ping_call = Instant::now();
                        loop {
                                peer_manager.process_events();
                                channel_manager.process_pending_events(&event_handler);
                                chain_monitor.process_pending_events(&event_handler);
                                let updates_available =
                                        channel_manager.await_persistable_update_timeout(Duration::from_millis(100));
                                if updates_available {
                                        persister.persist_manager(&*channel_manager)?;
                                }
                                // Exit the loop if the background processor was requested to stop.
                                if stop_thread.load(Ordering::Acquire) == true {
                                        log_trace!(logger, "Terminating background processor.");
                                        return Ok(());
                                }
                                if last_freshness_call.elapsed().as_secs() > FRESHNESS_TIMER {
                                        log_trace!(logger, "Calling ChannelManager's timer_tick_occurred");
                                        channel_manager.timer_tick_occurred();
                                        last_freshness_call = Instant::now();
                                }
                                if last_ping_call.elapsed().as_secs() > PING_TIMER * 2 {
                                        // On various platforms, we may be starved of CPU cycles for several reasons.
                                        // E.g. on iOS, if we've been in the background, we will be entirely paused.
                                        // Similarly, if we're on a desktop platform and the device has been asleep, we
                                        // may not get any cycles.
                                        // In any case, if we've been entirely paused for more than double our ping
                                        // timer, we should have disconnected all sockets by now (and they're probably
                                        // dead anyway), so disconnect them by calling `timer_tick_occurred()` twice.
                                        log_trace!(logger, "Awoke after more than double our ping timer, disconnecting peers.");
                                        peer_manager.timer_tick_occurred();
                                        peer_manager.timer_tick_occurred();
                                        last_ping_call = Instant::now();
                                } else if last_ping_call.elapsed().as_secs() > PING_TIMER {
                                        log_trace!(logger, "Calling PeerManager's timer_tick_occurred");
                                        peer_manager.timer_tick_occurred();
                                        last_ping_call = Instant::now();
                                }
                        }
                });
                Self { stop_thread: stop_thread_clone, thread_handle: Some(handle) }
        }

        /// Join `BackgroundProcessor`'s thread, returning any error that occurred while persisting
        /// [`ChannelManager`].
        ///
        /// # Panics
        ///
        /// This function panics if the background thread has panicked such as while persisting or
        /// handling events.
        ///
        /// [`ChannelManager`]: lightning::ln::channelmanager::ChannelManager
        pub fn join(mut self) -> Result<(), std::io::Error> {
                assert!(self.thread_handle.is_some());
                self.join_thread()
        }

        /// Stop `BackgroundProcessor`'s thread, returning any error that occurred while persisting
        /// [`ChannelManager`].
        ///
        /// # Panics
        ///
        /// This function panics if the background thread has panicked such as while persisting or
        /// handling events.
        ///
        /// [`ChannelManager`]: lightning::ln::channelmanager::ChannelManager
        pub fn stop(mut self) -> Result<(), std::io::Error> {
                assert!(self.thread_handle.is_some());
                self.stop_and_join_thread()
        }

        fn stop_and_join_thread(&mut self) -> Result<(), std::io::Error> {
                self.stop_thread.store(true, Ordering::Release);
                self.join_thread()
        }

        fn join_thread(&mut self) -> Result<(), std::io::Error> {
                match self.thread_handle.take() {
                        Some(handle) => handle.join().unwrap(),
                        None => Ok(()),
                }
        }
}

impl Drop for BackgroundProcessor {
        fn drop(&mut self) {
                self.stop_and_join_thread().unwrap();
        }
}

#[cfg(test)]
mod tests {
        use bitcoin::blockdata::block::BlockHeader;
        use bitcoin::blockdata::constants::genesis_block;
        use bitcoin::blockdata::transaction::{Transaction, TxOut};
        use bitcoin::network::constants::Network;
        use lightning::chain::{BestBlock, Confirm, chainmonitor};
        use lightning::chain::channelmonitor::ANTI_REORG_DELAY;
        use lightning::chain::keysinterface::{InMemorySigner, KeysInterface, KeysManager};
        use lightning::chain::transaction::OutPoint;
        use lightning::get_event_msg;
        use lightning::ln::channelmanager::{BREAKDOWN_TIMEOUT, ChainParameters, ChannelManager, SimpleArcChannelManager};
        use lightning::ln::features::InitFeatures;
        use lightning::ln::msgs::{ChannelMessageHandler, Init};
        use lightning::ln::peer_handler::{PeerManager, MessageHandler, SocketDescriptor};
        use lightning::util::config::UserConfig;
        use lightning::util::events::{Event, MessageSendEventsProvider, MessageSendEvent};
        use lightning::util::ser::Writeable;
        use lightning::util::test_utils;
        use lightning_persister::FilesystemPersister;
        use std::fs;
        use std::path::PathBuf;
        use std::sync::{Arc, Mutex};
        use std::time::Duration;
        use super::{BackgroundProcessor, FRESHNESS_TIMER};

        const EVENT_DEADLINE: u64 = 5 * FRESHNESS_TIMER;

        #[derive(Clone, Eq, Hash, PartialEq)]
        struct TestDescriptor{}
        impl SocketDescriptor for TestDescriptor {
                fn send_data(&mut self, _data: &[u8], _resume_read: bool) -> usize {
                        0
                }

                fn disconnect_socket(&mut self) {}
        }

        type ChainMonitor = chainmonitor::ChainMonitor<InMemorySigner, Arc<test_utils::TestChainSource>, Arc<test_utils::TestBroadcaster>, Arc<test_utils::TestFeeEstimator>, Arc<test_utils::TestLogger>, Arc<FilesystemPersister>>;

        struct Node {
                node: Arc<SimpleArcChannelManager<ChainMonitor, test_utils::TestBroadcaster, test_utils::TestFeeEstimator, test_utils::TestLogger>>,
                peer_manager: Arc<PeerManager<TestDescriptor, Arc<test_utils::TestChannelMessageHandler>, Arc<test_utils::TestRoutingMessageHandler>, Arc<test_utils::TestLogger>>>,
                chain_monitor: Arc<ChainMonitor>,
                persister: Arc<FilesystemPersister>,
                tx_broadcaster: Arc<test_utils::TestBroadcaster>,
                logger: Arc<test_utils::TestLogger>,
                best_block: BestBlock,
        }

        impl Drop for Node {
                fn drop(&mut self) {
                        let data_dir = self.persister.get_data_dir();
                        match fs::remove_dir_all(data_dir.clone()) {
                                Err(e) => println!("Failed to remove test persister directory {}: {}", data_dir, e),
                                _ => {}
                        }
                }
        }

        fn get_full_filepath(filepath: String, filename: String) -> String {
                let mut path = PathBuf::from(filepath);
                path.push(filename);
                path.to_str().unwrap().to_string()
        }

        fn create_nodes(num_nodes: usize, persist_dir: String) -> Vec<Node> {
                let mut nodes = Vec::new();
                for i in 0..num_nodes {
                        let tx_broadcaster = Arc::new(test_utils::TestBroadcaster{txn_broadcasted: Mutex::new(Vec::new()), blocks: Arc::new(Mutex::new(Vec::new()))});
                        let fee_estimator = Arc::new(test_utils::TestFeeEstimator { sat_per_kw: Mutex::new(253) });
                        let chain_source = Arc::new(test_utils::TestChainSource::new(Network::Testnet));
                        let logger = Arc::new(test_utils::TestLogger::with_id(format!("node {}", i)));
                        let persister = Arc::new(FilesystemPersister::new(format!("{}_persister_{}", persist_dir, i)));
                        let seed = [i as u8; 32];
                        let network = Network::Testnet;
                        let now = Duration::from_secs(genesis_block(network).header.time as u64);
                        let keys_manager = Arc::new(KeysManager::new(&seed, now.as_secs(), now.subsec_nanos()));
                        let chain_monitor = Arc::new(chainmonitor::ChainMonitor::new(Some(chain_source.clone()), tx_broadcaster.clone(), logger.clone(), fee_estimator.clone(), persister.clone()));
                        let best_block = BestBlock::from_genesis(network);
                        let params = ChainParameters { network, best_block };
                        let manager = Arc::new(ChannelManager::new(fee_estimator.clone(), chain_monitor.clone(), tx_broadcaster.clone(), logger.clone(), keys_manager.clone(), UserConfig::default(), params));
                        let msg_handler = MessageHandler { chan_handler: Arc::new(test_utils::TestChannelMessageHandler::new()), route_handler: Arc::new(test_utils::TestRoutingMessageHandler::new() )};
                        let peer_manager = Arc::new(PeerManager::new(msg_handler, keys_manager.get_node_secret(), &seed, logger.clone()));
                        let node = Node { node: manager, peer_manager, chain_monitor, persister, tx_broadcaster, logger, best_block };
                        nodes.push(node);
                }

                for i in 0..num_nodes {
                        for j in (i+1)..num_nodes {
                                nodes[i].node.peer_connected(&nodes[j].node.get_our_node_id(), &Init { features: InitFeatures::known() });
                                nodes[j].node.peer_connected(&nodes[i].node.get_our_node_id(), &Init { features: InitFeatures::known() });
                        }
                }

                nodes
        }

        macro_rules! open_channel {
                ($node_a: expr, $node_b: expr, $channel_value: expr) => {{
                        begin_open_channel!($node_a, $node_b, $channel_value);
                        let events = $node_a.node.get_and_clear_pending_events();
                        assert_eq!(events.len(), 1);
                        let (temporary_channel_id, tx) = handle_funding_generation_ready!(events[0], $channel_value);
                        end_open_channel!($node_a, $node_b, temporary_channel_id, tx);
                        tx
                }}
        }

        macro_rules! begin_open_channel {
                ($node_a: expr, $node_b: expr, $channel_value: expr) => {{
                        $node_a.node.create_channel($node_b.node.get_our_node_id(), $channel_value, 100, 42, None).unwrap();
                        $node_b.node.handle_open_channel(&$node_a.node.get_our_node_id(), InitFeatures::known(), &get_event_msg!($node_a, MessageSendEvent::SendOpenChannel, $node_b.node.get_our_node_id()));
                        $node_a.node.handle_accept_channel(&$node_b.node.get_our_node_id(), InitFeatures::known(), &get_event_msg!($node_b, MessageSendEvent::SendAcceptChannel, $node_a.node.get_our_node_id()));
                }}
        }

        macro_rules! handle_funding_generation_ready {
                ($event: expr, $channel_value: expr) => {{
                        match $event {
                                Event::FundingGenerationReady { ref temporary_channel_id, ref channel_value_satoshis, ref output_script, user_channel_id } => {
                                        assert_eq!(*channel_value_satoshis, $channel_value);
                                        assert_eq!(user_channel_id, 42);

                                        let tx = Transaction { version: 1 as i32, lock_time: 0, input: Vec::new(), output: vec![TxOut {
                                                value: *channel_value_satoshis, script_pubkey: output_script.clone(),
                                        }]};
                                        (*temporary_channel_id, tx)
                                },
                                _ => panic!("Unexpected event"),
                        }
                }}
        }

        macro_rules! end_open_channel {
                ($node_a: expr, $node_b: expr, $temporary_channel_id: expr, $tx: expr) => {{
                        $node_a.node.funding_transaction_generated(&$temporary_channel_id, $tx.clone()).unwrap();
                        $node_b.node.handle_funding_created(&$node_a.node.get_our_node_id(), &get_event_msg!($node_a, MessageSendEvent::SendFundingCreated, $node_b.node.get_our_node_id()));
                        $node_a.node.handle_funding_signed(&$node_b.node.get_our_node_id(), &get_event_msg!($node_b, MessageSendEvent::SendFundingSigned, $node_a.node.get_our_node_id()));
                }}
        }

        fn confirm_transaction_depth(node: &mut Node, tx: &Transaction, depth: u32) {
                for i in 1..=depth {
                        let prev_blockhash = node.best_block.block_hash();
                        let height = node.best_block.height() + 1;
                        let header = BlockHeader { version: 0x20000000, prev_blockhash, merkle_root: Default::default(), time: height, bits: 42, nonce: 42 };
                        let txdata = vec![(0, tx)];
                        node.best_block = BestBlock::new(header.block_hash(), height);
                        match i {
                                1 => {
                                        node.node.transactions_confirmed(&header, &txdata, height);
                                        node.chain_monitor.transactions_confirmed(&header, &txdata, height);
                                },
                                x if x == depth => {
                                        node.node.best_block_updated(&header, height);
                                        node.chain_monitor.best_block_updated(&header, height);
                                },
                                _ => {},
                        }
                }
        }
        fn confirm_transaction(node: &mut Node, tx: &Transaction) {
                confirm_transaction_depth(node, tx, ANTI_REORG_DELAY);
        }

        #[test]
        fn test_background_processor() {
                // Test that when a new channel is created, the ChannelManager needs to be re-persisted with
                // updates. Also test that when new updates are available, the manager signals that it needs
                // re-persistence and is successfully re-persisted.
                let nodes = create_nodes(2, "test_background_processor".to_string());

                // Go through the channel creation process so that each node has something to persist. Since
                // open_channel consumes events, it must complete before starting BackgroundProcessor to
                // avoid a race with processing events.
                let tx = open_channel!(nodes[0], nodes[1], 100000);

                // Initiate the background processors to watch each node.
                let data_dir = nodes[0].persister.get_data_dir();
                let persister = move |node: &ChannelManager<InMemorySigner, Arc<ChainMonitor>, Arc<test_utils::TestBroadcaster>, Arc<KeysManager>, Arc<test_utils::TestFeeEstimator>, Arc<test_utils::TestLogger>>| FilesystemPersister::persist_manager(data_dir.clone(), node);
                let event_handler = |_| {};
                let bg_processor = BackgroundProcessor::start(persister, event_handler, nodes[0].chain_monitor.clone(), nodes[0].node.clone(), nodes[0].peer_manager.clone(), nodes[0].logger.clone());

                macro_rules! check_persisted_data {
                        ($node: expr, $filepath: expr, $expected_bytes: expr) => {
                                match $node.write(&mut $expected_bytes) {
                                        Ok(()) => {
                                                loop {
                                                        match std::fs::read($filepath) {
                                                                Ok(bytes) => {
                                                                        if bytes == $expected_bytes {
                                                                                break
                                                                        } else {
                                                                                continue
                                                                        }
                                                                },
                                                                Err(_) => continue
                                                        }
                                                }
                                        },
                                        Err(e) => panic!("Unexpected error: {}", e)
                                }
                        }
                }

                // Check that the initial channel manager data is persisted as expected.
                let filepath = get_full_filepath("test_background_processor_persister_0".to_string(), "manager".to_string());
                let mut expected_bytes = Vec::new();
                check_persisted_data!(nodes[0].node, filepath.clone(), expected_bytes);
                loop {
                        if !nodes[0].node.get_persistence_condvar_value() { break }
                }

                // Force-close the channel.
                nodes[0].node.force_close_channel(&OutPoint { txid: tx.txid(), index: 0 }.to_channel_id()).unwrap();

                // Check that the force-close updates are persisted.
                let mut expected_bytes = Vec::new();
                check_persisted_data!(nodes[0].node, filepath.clone(), expected_bytes);
                loop {
                        if !nodes[0].node.get_persistence_condvar_value() { break }
                }

                assert!(bg_processor.stop().is_ok());
        }

        #[test]
        fn test_timer_tick_called() {
                // Test that ChannelManager's and PeerManager's `timer_tick_occurred` is called every
                // `FRESHNESS_TIMER`.
                let nodes = create_nodes(1, "test_timer_tick_called".to_string());
                let data_dir = nodes[0].persister.get_data_dir();
                let persister = move |node: &ChannelManager<InMemorySigner, Arc<ChainMonitor>, Arc<test_utils::TestBroadcaster>, Arc<KeysManager>, Arc<test_utils::TestFeeEstimator>, Arc<test_utils::TestLogger>>| FilesystemPersister::persist_manager(data_dir.clone(), node);
                let event_handler = |_| {};
                let bg_processor = BackgroundProcessor::start(persister, event_handler, nodes[0].chain_monitor.clone(), nodes[0].node.clone(), nodes[0].peer_manager.clone(), nodes[0].logger.clone());
                loop {
                        let log_entries = nodes[0].logger.lines.lock().unwrap();
                        let desired_log = "Calling ChannelManager's timer_tick_occurred".to_string();
                        let second_desired_log = "Calling PeerManager's timer_tick_occurred".to_string();
                        if log_entries.get(&("lightning_background_processor".to_string(), desired_log)).is_some() &&
                                        log_entries.get(&("lightning_background_processor".to_string(), second_desired_log)).is_some() {
                                break
                        }
                }

                assert!(bg_processor.stop().is_ok());
        }

        #[test]
        fn test_persist_error() {
                // Test that if we encounter an error during manager persistence, the thread panics.
                let nodes = create_nodes(2, "test_persist_error".to_string());
                open_channel!(nodes[0], nodes[1], 100000);

                let persister = |_: &_| Err(std::io::Error::new(std::io::ErrorKind::Other, "test"));
                let event_handler = |_| {};
                let bg_processor = BackgroundProcessor::start(persister, event_handler, nodes[0].chain_monitor.clone(), nodes[0].node.clone(), nodes[0].peer_manager.clone(), nodes[0].logger.clone());
                match bg_processor.join() {
                        Ok(_) => panic!("Expected error persisting manager"),
                        Err(e) => {
                                assert_eq!(e.kind(), std::io::ErrorKind::Other);
                                assert_eq!(e.get_ref().unwrap().to_string(), "test");
                        },
                }
        }

        #[test]
        fn test_background_event_handling() {
                let mut nodes = create_nodes(2, "test_background_event_handling".to_string());
                let channel_value = 100000;
                let data_dir = nodes[0].persister.get_data_dir();
                let persister = move |node: &_| FilesystemPersister::persist_manager(data_dir.clone(), node);

                // Set up a background event handler for FundingGenerationReady events.
                let (sender, receiver) = std::sync::mpsc::sync_channel(1);
                let event_handler = move |event| {
                        sender.send(handle_funding_generation_ready!(event, channel_value)).unwrap();
                };
                let bg_processor = BackgroundProcessor::start(persister.clone(), event_handler, nodes[0].chain_monitor.clone(), nodes[0].node.clone(), nodes[0].peer_manager.clone(), nodes[0].logger.clone());

                // Open a channel and check that the FundingGenerationReady event was handled.
                begin_open_channel!(nodes[0], nodes[1], channel_value);
                let (temporary_channel_id, funding_tx) = receiver
                        .recv_timeout(Duration::from_secs(EVENT_DEADLINE))
                        .expect("FundingGenerationReady not handled within deadline");
                end_open_channel!(nodes[0], nodes[1], temporary_channel_id, funding_tx);

                // Confirm the funding transaction.
                confirm_transaction(&mut nodes[0], &funding_tx);
                let as_funding = get_event_msg!(nodes[0], MessageSendEvent::SendFundingLocked, nodes[1].node.get_our_node_id());
                confirm_transaction(&mut nodes[1], &funding_tx);
                let bs_funding = get_event_msg!(nodes[1], MessageSendEvent::SendFundingLocked, nodes[0].node.get_our_node_id());
                nodes[0].node.handle_funding_locked(&nodes[1].node.get_our_node_id(), &bs_funding);
                let _as_channel_update = get_event_msg!(nodes[0], MessageSendEvent::SendChannelUpdate, nodes[1].node.get_our_node_id());
                nodes[1].node.handle_funding_locked(&nodes[0].node.get_our_node_id(), &as_funding);
                let _bs_channel_update = get_event_msg!(nodes[1], MessageSendEvent::SendChannelUpdate, nodes[0].node.get_our_node_id());

                assert!(bg_processor.stop().is_ok());

                // Set up a background event handler for SpendableOutputs events.
                let (sender, receiver) = std::sync::mpsc::sync_channel(1);
                let event_handler = move |event| sender.send(event).unwrap();
                let bg_processor = BackgroundProcessor::start(persister, event_handler, nodes[0].chain_monitor.clone(), nodes[0].node.clone(), nodes[0].peer_manager.clone(), nodes[0].logger.clone());

                // Force close the channel and check that the SpendableOutputs event was handled.
                nodes[0].node.force_close_channel(&nodes[0].node.list_channels()[0].channel_id).unwrap();
                let commitment_tx = nodes[0].tx_broadcaster.txn_broadcasted.lock().unwrap().pop().unwrap();
                confirm_transaction_depth(&mut nodes[0], &commitment_tx, BREAKDOWN_TIMEOUT as u32);
                let event = receiver
                        .recv_timeout(Duration::from_secs(EVENT_DEADLINE))
                        .expect("SpendableOutputs not handled within deadline");
                match event {
                        Event::SpendableOutputs { .. } => {},
                        _ => panic!("Unexpected event: {:?}", event),
                }

                assert!(bg_processor.stop().is_ok());
        }
}