[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.

// Prefix these with `rustdoc::` when we update our MSRV to be >= 1.52 to remove warnings.
#![deny(broken_intra_doc_links)]
#![deny(private_intra_doc_links)]

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

#![cfg_attr(docsrs, feature(doc_auto_cfg))]

#[macro_use] extern crate lightning;
extern crate lightning_rapid_gossip_sync;

use lightning::chain;
use lightning::chain::chaininterface::{BroadcasterInterface, FeeEstimator};
use lightning::chain::chainmonitor::{ChainMonitor, Persist};
use lightning::chain::keysinterface::{Sign, KeysInterface};
use lightning::ln::channelmanager::ChannelManager;
use lightning::ln::msgs::{ChannelMessageHandler, OnionMessageHandler, RoutingMessageHandler};
use lightning::ln::peer_handler::{CustomMessageHandler, PeerManager, SocketDescriptor};
use lightning::routing::gossip::{NetworkGraph, P2PGossipSync};
use lightning::routing::scoring::WriteableScore;
use lightning::util::events::{Event, EventHandler, EventsProvider};
use lightning::util::logger::Logger;
use lightning::util::persist::Persister;
use lightning_rapid_gossip_sync::RapidGossipSync;
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;

#[cfg(feature = "futures")]
use futures_util::{select_biased, future::FutureExt};

/// `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:
/// * Processing [`Event`]s with a user-provided [`EventHandler`].
/// * 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`]
///   at the appropriate intervals.
/// * Calling [`NetworkGraph::remove_stale_channels_and_tracking`] (if a [`GossipSync`] with a
///   [`NetworkGraph`] is provided to [`BackgroundProcessor::start`]).
///
/// It will also call [`PeerManager::process_events`] periodically though this shouldn't be relied
/// upon as doing so may result in high latency.
///
/// # Note
///
/// 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.
///
/// [`ChannelMonitor`]: lightning::chain::channelmonitor::ChannelMonitor
/// [`Event`]: lightning::util::events::Event
#[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;

#[cfg(all(not(test), not(debug_assertions)))]
const PING_TIMER: u64 = 10;
/// Signature operations take a lot longer without compiler optimisations.
/// Increasing the ping timer allows for this but slower devices will be disconnected if the
/// timeout is reached.
#[cfg(all(not(test), debug_assertions))]
const PING_TIMER: u64 = 30;
#[cfg(test)]
const PING_TIMER: u64 = 1;

/// Prune the network graph of stale entries hourly.
const NETWORK_PRUNE_TIMER: u64 = 60 * 60;

#[cfg(not(test))]
const SCORER_PERSIST_TIMER: u64 = 30;
#[cfg(test)]
const SCORER_PERSIST_TIMER: u64 = 1;

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

/// Either [`P2PGossipSync`] or [`RapidGossipSync`].
pub enum GossipSync<
        P: Deref<Target = P2PGossipSync<G, A, L>>,
        R: Deref<Target = RapidGossipSync<G, L>>,
        G: Deref<Target = NetworkGraph<L>>,
        A: Deref,
        L: Deref,
>
where A::Target: chain::Access, L::Target: Logger {
        /// Gossip sync via the lightning peer-to-peer network as defined by BOLT 7.
        P2P(P),
        /// Rapid gossip sync from a trusted server.
        Rapid(R),
        /// No gossip sync.
        None,
}

impl<
        P: Deref<Target = P2PGossipSync<G, A, L>>,
        R: Deref<Target = RapidGossipSync<G, L>>,
        G: Deref<Target = NetworkGraph<L>>,
        A: Deref,
        L: Deref,
> GossipSync<P, R, G, A, L>
where A::Target: chain::Access, L::Target: Logger {
        fn network_graph(&self) -> Option<&G> {
                match self {
                        GossipSync::P2P(gossip_sync) => Some(gossip_sync.network_graph()),
                        GossipSync::Rapid(gossip_sync) => Some(gossip_sync.network_graph()),
                        GossipSync::None => None,
                }
        }

        fn prunable_network_graph(&self) -> Option<&G> {
                match self {
                        GossipSync::P2P(gossip_sync) => Some(gossip_sync.network_graph()),
                        GossipSync::Rapid(gossip_sync) => {
                                if gossip_sync.is_initial_sync_complete() {
                                        Some(gossip_sync.network_graph())
                                } else {
                                        None
                                }
                        },
                        GossipSync::None => None,
                }
        }
}

/// (C-not exported) as the bindings concretize everything and have constructors for us
impl<P: Deref<Target = P2PGossipSync<G, A, L>>, G: Deref<Target = NetworkGraph<L>>, A: Deref, L: Deref>
        GossipSync<P, &RapidGossipSync<G, L>, G, A, L>
where
        A::Target: chain::Access,
        L::Target: Logger,
{
        /// Initializes a new [`GossipSync::P2P`] variant.
        pub fn p2p(gossip_sync: P) -> Self {
                GossipSync::P2P(gossip_sync)
        }
}

/// (C-not exported) as the bindings concretize everything and have constructors for us
impl<'a, R: Deref<Target = RapidGossipSync<G, L>>, G: Deref<Target = NetworkGraph<L>>, L: Deref>
        GossipSync<
                &P2PGossipSync<G, &'a (dyn chain::Access + Send + Sync), L>,
                R,
                G,
                &'a (dyn chain::Access + Send + Sync),
                L,
        >
where
        L::Target: Logger,
{
        /// Initializes a new [`GossipSync::Rapid`] variant.
        pub fn rapid(gossip_sync: R) -> Self {
                GossipSync::Rapid(gossip_sync)
        }
}

/// (C-not exported) as the bindings concretize everything and have constructors for us
impl<'a, L: Deref>
        GossipSync<
                &P2PGossipSync<&'a NetworkGraph<L>, &'a (dyn chain::Access + Send + Sync), L>,
                &RapidGossipSync<&'a NetworkGraph<L>, L>,
                &'a NetworkGraph<L>,
                &'a (dyn chain::Access + Send + Sync),
                L,
        >
where
        L::Target: Logger,
{
        /// Initializes a new [`GossipSync::None`] variant.
        pub fn none() -> Self {
                GossipSync::None
        }
}

fn handle_network_graph_update<L: Deref>(
        network_graph: &NetworkGraph<L>, event: &Event
) where L::Target: Logger {
        if let Event::PaymentPathFailed { ref network_update, .. } = event {
                if let Some(network_update) = network_update {
                        network_graph.handle_network_update(&network_update);
                }
        }
}

/// Decorates an [`EventHandler`] with common functionality provided by standard [`EventHandler`]s.
struct DecoratingEventHandler<
        'a,
        E: EventHandler,
        PGS: Deref<Target = P2PGossipSync<G, A, L>>,
        RGS: Deref<Target = RapidGossipSync<G, L>>,
        G: Deref<Target = NetworkGraph<L>>,
        A: Deref,
        L: Deref,
>
where A::Target: chain::Access, L::Target: Logger {
        event_handler: E,
        gossip_sync: &'a GossipSync<PGS, RGS, G, A, L>,
}

impl<
        'a,
        E: EventHandler,
        PGS: Deref<Target = P2PGossipSync<G, A, L>>,
        RGS: Deref<Target = RapidGossipSync<G, L>>,
        G: Deref<Target = NetworkGraph<L>>,
        A: Deref,
        L: Deref,
> EventHandler for DecoratingEventHandler<'a, E, PGS, RGS, G, A, L>
where A::Target: chain::Access, L::Target: Logger {
        fn handle_event(&self, event: Event) {
                if let Some(network_graph) = self.gossip_sync.network_graph() {
                        handle_network_graph_update(network_graph, &event)
                }
                self.event_handler.handle_event(event);
        }
}

macro_rules! define_run_body {
        ($persister: ident, $chain_monitor: ident, $process_chain_monitor_events: expr,
         $channel_manager: ident, $process_channel_manager_events: expr,
         $gossip_sync: ident, $peer_manager: ident, $logger: ident, $scorer: ident,
         $loop_exit_check: expr, $await: expr)
        => { {
                log_trace!($logger, "Calling ChannelManager's timer_tick_occurred on startup");
                $channel_manager.timer_tick_occurred();

                let mut last_freshness_call = Instant::now();
                let mut last_ping_call = Instant::now();
                let mut last_prune_call = Instant::now();
                let mut last_scorer_persist_call = Instant::now();
                let mut have_pruned = false;

                loop {
                        $process_channel_manager_events;
                        $process_chain_monitor_events;

                        // Note that the PeerManager::process_events may block on ChannelManager's locks,
                        // hence it comes last here. When the ChannelManager finishes whatever it's doing,
                        // we want to ensure we get into `persist_manager` as quickly as we can, especially
                        // without running the normal event processing above and handing events to users.
                        //
                        // Specifically, on an *extremely* slow machine, we may see ChannelManager start
                        // processing a message effectively at any point during this loop. In order to
                        // minimize the time between such processing completing and persisting the updated
                        // ChannelManager, we want to minimize methods blocking on a ChannelManager
                        // generally, and as a fallback place such blocking only immediately before
                        // persistence.
                        $peer_manager.process_events();

                        // We wait up to 100ms, but track how long it takes to detect being put to sleep,
                        // see `await_start`'s use below.
                        let await_start = Instant::now();
                        let updates_available = $await;
                        let await_time = await_start.elapsed();

                        if updates_available {
                                log_trace!($logger, "Persisting ChannelManager...");
                                $persister.persist_manager(&*$channel_manager)?;
                                log_trace!($logger, "Done persisting ChannelManager.");
                        }
                        // Exit the loop if the background processor was requested to stop.
                        if $loop_exit_check {
                                log_trace!($logger, "Terminating background processor.");
                                break;
                        }
                        if last_freshness_call.elapsed().as_secs() > FRESHNESS_TIMER {
                                log_trace!($logger, "Calling ChannelManager's timer_tick_occurred");
                                $channel_manager.timer_tick_occurred();
                                last_freshness_call = Instant::now();
                        }
                        if await_time > Duration::from_secs(1) {
                                // On various platforms, we may be starved of CPU cycles for several reasons.
                                // E.g. on iOS, if we've been in the background, we will be entirely paused.
                                // Similarly, if we're on a desktop platform and the device has been asleep, we
                                // may not get any cycles.
                                // We detect this by checking if our max-100ms-sleep, above, ran longer than a
                                // full second, at which point we assume sockets may have been killed (they
                                // appear to be at least on some platforms, even if it has only been a second).
                                // Note that we have to take care to not get here just because user event
                                // processing was slow at the top of the loop. For example, the sample client
                                // may call Bitcoin Core RPCs during event handling, which very often takes
                                // more than a handful of seconds to complete, and shouldn't disconnect all our
                                // peers.
                                log_trace!($logger, "100ms sleep took more than a second, disconnecting peers.");
                                $peer_manager.disconnect_all_peers();
                                last_ping_call = Instant::now();
                        } else if last_ping_call.elapsed().as_secs() > PING_TIMER {
                                log_trace!($logger, "Calling PeerManager's timer_tick_occurred");
                                $peer_manager.timer_tick_occurred();
                                last_ping_call = Instant::now();
                        }

                        // Note that we want to run a graph prune once not long after startup before
                        // falling back to our usual hourly prunes. This avoids short-lived clients never
                        // pruning their network graph. We run once 60 seconds after startup before
                        // continuing our normal cadence.
                        if last_prune_call.elapsed().as_secs() > if have_pruned { NETWORK_PRUNE_TIMER } else { FIRST_NETWORK_PRUNE_TIMER } {
                                // The network graph must not be pruned while rapid sync completion is pending
                                log_trace!($logger, "Assessing prunability of network graph");
                                if let Some(network_graph) = $gossip_sync.prunable_network_graph() {
                                        network_graph.remove_stale_channels_and_tracking();

                                        if let Err(e) = $persister.persist_graph(network_graph) {
                                                log_error!($logger, "Error: Failed to persist network graph, check your disk and permissions {}", e)
                                        }

                                        last_prune_call = Instant::now();
                                        have_pruned = true;
                                } else {
                                        log_trace!($logger, "Not pruning network graph, either due to pending rapid gossip sync or absence of a prunable graph.");
                                }
                        }

                        if last_scorer_persist_call.elapsed().as_secs() > SCORER_PERSIST_TIMER {
                                if let Some(ref scorer) = $scorer {
                                        log_trace!($logger, "Persisting scorer");
                                        if let Err(e) = $persister.persist_scorer(&scorer) {
                                                log_error!($logger, "Error: Failed to persist scorer, check your disk and permissions {}", e)
                                        }
                                }
                                last_scorer_persist_call = Instant::now();
                        }
                }

                // After we exit, ensure we persist the ChannelManager one final time - this avoids
                // some races where users quit while channel updates were in-flight, with
                // ChannelMonitor update(s) persisted without a corresponding ChannelManager update.
                $persister.persist_manager(&*$channel_manager)?;

                // Persist Scorer on exit
                if let Some(ref scorer) = $scorer {
                        $persister.persist_scorer(&scorer)?;
                }

                // Persist NetworkGraph on exit
                if let Some(network_graph) = $gossip_sync.network_graph() {
                        $persister.persist_graph(network_graph)?;
                }

                Ok(())
        } }
}

/// Processes background events in a future.
///
/// `sleeper` should return a future which completes in the given amount of time and returns a
/// boolean indicating whether the background processing should exit. Once `sleeper` returns a
/// future which outputs true, the loop will exit and this function's future will complete.
///
/// See [`BackgroundProcessor::start`] for information on which actions this handles.
#[cfg(feature = "futures")]
pub async fn process_events_async<
        'a,
        Signer: 'static + Sign,
        CA: 'static + Deref + Send + Sync,
        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,
        G: 'static + Deref<Target = NetworkGraph<L>> + 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,
        OMH: 'static + Deref + Send + Sync,
        EventHandlerFuture: core::future::Future<Output = ()>,
        EventHandler: Fn(Event) -> EventHandlerFuture,
        PS: 'static + Deref + Send,
        M: 'static + Deref<Target = ChainMonitor<Signer, CF, T, F, L, P>> + Send + Sync,
        CM: 'static + Deref<Target = ChannelManager<CW, T, K, F, L>> + Send + Sync,
        PGS: 'static + Deref<Target = P2PGossipSync<G, CA, L>> + Send + Sync,
        RGS: 'static + Deref<Target = RapidGossipSync<G, L>> + Send,
        UMH: 'static + Deref + Send + Sync,
        PM: 'static + Deref<Target = PeerManager<Descriptor, CMH, RMH, OMH, L, UMH>> + Send + Sync,
        S: 'static + Deref<Target = SC> + Send + Sync,
        SC: WriteableScore<'a>,
        SleepFuture: core::future::Future<Output = bool>,
        Sleeper: Fn(Duration) -> SleepFuture
>(
        persister: PS, event_handler: EventHandler, chain_monitor: M, channel_manager: CM,
        gossip_sync: GossipSync<PGS, RGS, G, CA, L>, peer_manager: PM, logger: L, scorer: Option<S>,
        sleeper: Sleeper,
) -> Result<(), std::io::Error>
where
        CA::Target: 'static + chain::Access,
        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 + Persist<Signer>,
        CMH::Target: 'static + ChannelMessageHandler,
        OMH::Target: 'static + OnionMessageHandler,
        RMH::Target: 'static + RoutingMessageHandler,
        UMH::Target: 'static + CustomMessageHandler,
        PS::Target: 'static + Persister<'a, Signer, CW, T, K, F, L, SC>,
{
        let mut should_break = true;
        let async_event_handler = |event| {
                let network_graph = gossip_sync.network_graph();
                let event_handler = &event_handler;
                async move {
                        if let Some(network_graph) = network_graph {
                                handle_network_graph_update(network_graph, &event)
                        }
                        event_handler(event).await;
                }
        };
        define_run_body!(persister,
                chain_monitor, chain_monitor.process_pending_events_async(async_event_handler).await,
                channel_manager, channel_manager.process_pending_events_async(async_event_handler).await,
                gossip_sync, peer_manager, logger, scorer, should_break, {
                        select_biased! {
                                _ = channel_manager.get_persistable_update_future().fuse() => true,
                                exit = sleeper(Duration::from_millis(100)).fuse() => {
                                        should_break = exit;
                                        false
                                }
                        }
                })
}

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
        /// [`Persister::persist_manager`] returns an error. In case of an error, the error is retrieved by calling
        /// either [`join`] or [`stop`].
        ///
        /// # Data Persistence
        ///
        /// [`Persister::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 the `lightning-persister` crate for LDK's
        /// provided implementation.
        ///
        /// [`Persister::persist_graph`] is responsible for writing out the [`NetworkGraph`] to disk, if
        /// [`GossipSync`] is supplied. See [`NetworkGraph::write`] for writing out a [`NetworkGraph`].
        /// See the `lightning-persister` crate for LDK's provided implementation.
        ///
        /// Typically, users should either implement [`Persister::persist_manager`] to never return an
        /// error or call [`join`] and handle any error that may arise. For the latter case,
        /// `BackgroundProcessor` must be restarted by calling `start` again after handling the error.
        ///
        /// # Event Handling
        ///
        /// `event_handler` is responsible for handling events that users should be notified of (e.g.,
        /// payment failed). [`BackgroundProcessor`] may decorate the given [`EventHandler`] with common
        /// functionality implemented by other handlers.
        /// * [`P2PGossipSync`] if given will update the [`NetworkGraph`] based on payment failures.
        ///
        /// # Rapid Gossip Sync
        ///
        /// If rapid gossip sync is meant to run at startup, pass [`RapidGossipSync`] via `gossip_sync`
        /// to indicate that the [`BackgroundProcessor`] should not prune the [`NetworkGraph`] instance
        /// until the [`RapidGossipSync`] instance completes its first sync.
        ///
        /// [top-level documentation]: BackgroundProcessor
        /// [`join`]: Self::join
        /// [`stop`]: Self::stop
        /// [`ChannelManager`]: lightning::ln::channelmanager::ChannelManager
        /// [`ChannelManager::write`]: lightning::ln::channelmanager::ChannelManager#impl-Writeable
        /// [`Persister::persist_manager`]: lightning::util::persist::Persister::persist_manager
        /// [`Persister::persist_graph`]: lightning::util::persist::Persister::persist_graph
        /// [`NetworkGraph`]: lightning::routing::gossip::NetworkGraph
        /// [`NetworkGraph::write`]: lightning::routing::gossip::NetworkGraph#impl-Writeable
        pub fn start<
                'a,
                Signer: 'static + Sign,
                CA: 'static + Deref + Send + Sync,
                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,
                G: 'static + Deref<Target = NetworkGraph<L>> + Send + Sync,
                L: 'static + Deref + Send + Sync,
                P: 'static + Deref + Send + Sync,
                Descriptor: 'static + SocketDescriptor + Send + Sync,
                CMH: 'static + Deref + Send + Sync,
                OMH: 'static + Deref + Send + Sync,
                RMH: 'static + Deref + Send + Sync,
                EH: 'static + EventHandler + Send,
                PS: 'static + Deref + Send,
                M: 'static + Deref<Target = ChainMonitor<Signer, CF, T, F, L, P>> + Send + Sync,
                CM: 'static + Deref<Target = ChannelManager<CW, T, K, F, L>> + Send + Sync,
                PGS: 'static + Deref<Target = P2PGossipSync<G, CA, L>> + Send + Sync,
                RGS: 'static + Deref<Target = RapidGossipSync<G, L>> + Send,
                UMH: 'static + Deref + Send + Sync,
                PM: 'static + Deref<Target = PeerManager<Descriptor, CMH, RMH, OMH, L, UMH>> + Send + Sync,
                S: 'static + Deref<Target = SC> + Send + Sync,
                SC: WriteableScore<'a>,
        >(
                persister: PS, event_handler: EH, chain_monitor: M, channel_manager: CM,
                gossip_sync: GossipSync<PGS, RGS, G, CA, L>, peer_manager: PM, logger: L, scorer: Option<S>,
        ) -> Self
        where
                CA::Target: 'static + chain::Access,
                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 + Persist<Signer>,
                CMH::Target: 'static + ChannelMessageHandler,
                OMH::Target: 'static + OnionMessageHandler,
                RMH::Target: 'static + RoutingMessageHandler,
                UMH::Target: 'static + CustomMessageHandler,
                PS::Target: 'static + Persister<'a, Signer, CW, T, K, F, L, SC>,
        {
                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 event_handler = DecoratingEventHandler {
                                event_handler,
                                gossip_sync: &gossip_sync,
                        };
                        define_run_body!(persister, chain_monitor, chain_monitor.process_pending_events(&event_handler),
                                channel_manager, channel_manager.process_pending_events(&event_handler),
                                gossip_sync, peer_manager, logger, scorer, stop_thread.load(Ordering::Acquire),
                                channel_manager.await_persistable_update_timeout(Duration::from_millis(100)))
                });
                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::locktime::PackedLockTime;
        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, Recipient, KeysInterface, KeysManager};
        use lightning::chain::transaction::OutPoint;
        use lightning::get_event_msg;
        use lightning::ln::channelmanager::{self, BREAKDOWN_TIMEOUT, ChainParameters, ChannelManager, SimpleArcChannelManager};
        use lightning::ln::features::ChannelFeatures;
        use lightning::ln::msgs::{ChannelMessageHandler, Init};
        use lightning::ln::peer_handler::{PeerManager, MessageHandler, SocketDescriptor, IgnoringMessageHandler};
        use lightning::routing::gossip::{NetworkGraph, P2PGossipSync};
        use lightning::util::config::UserConfig;
        use lightning::util::events::{Event, MessageSendEventsProvider, MessageSendEvent};
        use lightning::util::ser::Writeable;
        use lightning::util::test_utils;
        use lightning::util::persist::KVStorePersister;
        use lightning_invoice::payment::{InvoicePayer, Retry};
        use lightning_invoice::utils::DefaultRouter;
        use lightning_persister::FilesystemPersister;
        use std::fs;
        use std::path::PathBuf;
        use std::sync::{Arc, Mutex};
        use std::sync::mpsc::SyncSender;
        use std::time::Duration;
        use bitcoin::hashes::Hash;
        use bitcoin::TxMerkleNode;
        use lightning::routing::scoring::{FixedPenaltyScorer};
        use lightning_rapid_gossip_sync::RapidGossipSync;
        use super::{BackgroundProcessor, GossipSync, FRESHNESS_TIMER};

        const EVENT_DEADLINE: u64 = 5 * FRESHNESS_TIMER;

        #[derive(Clone, Hash, PartialEq, Eq)]
        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>>;

        type PGS = Arc<P2PGossipSync<Arc<NetworkGraph<Arc<test_utils::TestLogger>>>, Arc<test_utils::TestChainSource>, Arc<test_utils::TestLogger>>>;
        type RGS = Arc<RapidGossipSync<Arc<NetworkGraph<Arc<test_utils::TestLogger>>>, Arc<test_utils::TestLogger>>>;

        struct Node {
                node: Arc<SimpleArcChannelManager<ChainMonitor, test_utils::TestBroadcaster, test_utils::TestFeeEstimator, test_utils::TestLogger>>,
                p2p_gossip_sync: PGS,
                rapid_gossip_sync: RGS,
                peer_manager: Arc<PeerManager<TestDescriptor, Arc<test_utils::TestChannelMessageHandler>, Arc<test_utils::TestRoutingMessageHandler>, IgnoringMessageHandler, Arc<test_utils::TestLogger>, IgnoringMessageHandler>>,
                chain_monitor: Arc<ChainMonitor>,
                persister: Arc<FilesystemPersister>,
                tx_broadcaster: Arc<test_utils::TestBroadcaster>,
                network_graph: Arc<NetworkGraph<Arc<test_utils::TestLogger>>>,
                logger: Arc<test_utils::TestLogger>,
                best_block: BestBlock,
                scorer: Arc<Mutex<FixedPenaltyScorer>>,
        }

        impl Node {
                fn p2p_gossip_sync(&self) -> GossipSync<PGS, RGS, Arc<NetworkGraph<Arc<test_utils::TestLogger>>>, Arc<test_utils::TestChainSource>, Arc<test_utils::TestLogger>> {
                        GossipSync::P2P(self.p2p_gossip_sync.clone())
                }

                fn rapid_gossip_sync(&self) -> GossipSync<PGS, RGS, Arc<NetworkGraph<Arc<test_utils::TestLogger>>>, Arc<test_utils::TestChainSource>, Arc<test_utils::TestLogger>> {
                        GossipSync::Rapid(self.rapid_gossip_sync.clone())
                }

                fn no_gossip_sync(&self) -> GossipSync<PGS, RGS, Arc<NetworkGraph<Arc<test_utils::TestLogger>>>, Arc<test_utils::TestChainSource>, Arc<test_utils::TestLogger>> {
                        GossipSync::None
                }
        }

        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),
                                _ => {}
                        }
                }
        }

        struct Persister {
                graph_error: Option<(std::io::ErrorKind, &'static str)>,
                graph_persistence_notifier: Option<SyncSender<()>>,
                manager_error: Option<(std::io::ErrorKind, &'static str)>,
                scorer_error: Option<(std::io::ErrorKind, &'static str)>,
                filesystem_persister: FilesystemPersister,
        }

        impl Persister {
                fn new(data_dir: String) -> Self {
                        let filesystem_persister = FilesystemPersister::new(data_dir.clone());
                        Self { graph_error: None, graph_persistence_notifier: None, manager_error: None, scorer_error: None, filesystem_persister }
                }

                fn with_graph_error(self, error: std::io::ErrorKind, message: &'static str) -> Self {
                        Self { graph_error: Some((error, message)), ..self }
                }

                fn with_graph_persistence_notifier(self, sender: SyncSender<()>) -> Self {
                        Self { graph_persistence_notifier: Some(sender), ..self }
                }

                fn with_manager_error(self, error: std::io::ErrorKind, message: &'static str) -> Self {
                        Self { manager_error: Some((error, message)), ..self }
                }

                fn with_scorer_error(self, error: std::io::ErrorKind, message: &'static str) -> Self {
                        Self { scorer_error: Some((error, message)), ..self }
                }
        }

        impl KVStorePersister for Persister {
                fn persist<W: Writeable>(&self, key: &str, object: &W) -> std::io::Result<()> {
                        if key == "manager" {
                                if let Some((error, message)) = self.manager_error {
                                        return Err(std::io::Error::new(error, message))
                                }
                        }

                        if key == "network_graph" {
                                if let Some(sender) = &self.graph_persistence_notifier {
                                        sender.send(()).unwrap();
                                };

                                if let Some((error, message)) = self.graph_error {
                                        return Err(std::io::Error::new(error, message))
                                }
                        }

                        if key == "scorer" {
                                if let Some((error, message)) = self.scorer_error {
                                        return Err(std::io::Error::new(error, message))
                                }
                        }

                        self.filesystem_persister.persist(key, object)
                }
        }

        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 genesis_block = genesis_block(network);
                        let now = Duration::from_secs(genesis_block.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 network_graph = Arc::new(NetworkGraph::new(genesis_block.header.block_hash(), logger.clone()));
                        let p2p_gossip_sync = Arc::new(P2PGossipSync::new(network_graph.clone(), Some(chain_source.clone()), logger.clone()));
                        let rapid_gossip_sync = Arc::new(RapidGossipSync::new(network_graph.clone()));
                        let msg_handler = MessageHandler { chan_handler: Arc::new(test_utils::TestChannelMessageHandler::new()), route_handler: Arc::new(test_utils::TestRoutingMessageHandler::new()), onion_message_handler: IgnoringMessageHandler{}};
                        let peer_manager = Arc::new(PeerManager::new(msg_handler, keys_manager.get_node_secret(Recipient::Node).unwrap(), 0, &seed, logger.clone(), IgnoringMessageHandler{}));
                        let scorer = Arc::new(Mutex::new(test_utils::TestScorer::with_penalty(0)));
                        let node = Node { node: manager, p2p_gossip_sync, rapid_gossip_sync, peer_manager, chain_monitor, persister, tx_broadcaster, network_graph, logger, best_block, scorer };
                        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: channelmanager::provided_init_features(), remote_network_address: None }).unwrap();
                                nodes[j].node.peer_connected(&nodes[i].node.get_our_node_id(), &Init { features: channelmanager::provided_init_features(), remote_network_address: None }).unwrap();
                        }
                }

                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(), channelmanager::provided_init_features(), &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(), channelmanager::provided_init_features(), &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 { temporary_channel_id, 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: PackedLockTime(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, &$node_b.node.get_our_node_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: TxMerkleNode::all_zeros(), 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 = Arc::new(Persister::new(data_dir));
                let event_handler = |_: _| {};
                let bg_processor = BackgroundProcessor::start(persister, event_handler, nodes[0].chain_monitor.clone(), nodes[0].node.clone(), nodes[0].p2p_gossip_sync(), nodes[0].peer_manager.clone(), nodes[0].logger.clone(), Some(nodes[0].scorer.clone()));

                macro_rules! check_persisted_data {
                        ($node: expr, $filepath: expr) => {
                                let mut expected_bytes = Vec::new();
                                loop {
                                        expected_bytes.clear();
                                        match $node.write(&mut expected_bytes) {
                                                Ok(()) => {
                                                        match std::fs::read($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());
                check_persisted_data!(nodes[0].node, filepath.clone());

                loop {
                        if !nodes[0].node.get_persistence_condvar_value() { break }
                }

                // Force-close the channel.
                nodes[0].node.force_close_broadcasting_latest_txn(&OutPoint { txid: tx.txid(), index: 0 }.to_channel_id(), &nodes[1].node.get_our_node_id()).unwrap();

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

                // Check network graph is persisted
                let filepath = get_full_filepath("test_background_processor_persister_0".to_string(), "network_graph".to_string());
                check_persisted_data!(nodes[0].network_graph, filepath.clone());

                // Check scorer is persisted
                let filepath = get_full_filepath("test_background_processor_persister_0".to_string(), "scorer".to_string());
                check_persisted_data!(nodes[0].scorer, filepath.clone());

                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 = Arc::new(Persister::new(data_dir));
                let event_handler = |_: _| {};
                let bg_processor = BackgroundProcessor::start(persister, event_handler, nodes[0].chain_monitor.clone(), nodes[0].node.clone(), nodes[0].no_gossip_sync(), nodes[0].peer_manager.clone(), nodes[0].logger.clone(), Some(nodes[0].scorer.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_channel_manager_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 data_dir = nodes[0].persister.get_data_dir();
                let persister = Arc::new(Persister::new(data_dir).with_manager_error(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].no_gossip_sync(), nodes[0].peer_manager.clone(), nodes[0].logger.clone(), Some(nodes[0].scorer.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_network_graph_persist_error() {
                // Test that if we encounter an error during network graph persistence, an error gets returned.
                let nodes = create_nodes(2, "test_persist_network_graph_error".to_string());
                let data_dir = nodes[0].persister.get_data_dir();
                let persister = Arc::new(Persister::new(data_dir).with_graph_error(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].p2p_gossip_sync(), nodes[0].peer_manager.clone(), nodes[0].logger.clone(), Some(nodes[0].scorer.clone()));

                match bg_processor.stop() {
                        Ok(_) => panic!("Expected error persisting network graph"),
                        Err(e) => {
                                assert_eq!(e.kind(), std::io::ErrorKind::Other);
                                assert_eq!(e.get_ref().unwrap().to_string(), "test");
                        },
                }
        }

        #[test]
        fn test_scorer_persist_error() {
                // Test that if we encounter an error during scorer persistence, an error gets returned.
                let nodes = create_nodes(2, "test_persist_scorer_error".to_string());
                let data_dir = nodes[0].persister.get_data_dir();
                let persister = Arc::new(Persister::new(data_dir).with_scorer_error(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].no_gossip_sync(), nodes[0].peer_manager.clone(),  nodes[0].logger.clone(), Some(nodes[0].scorer.clone()));

                match bg_processor.stop() {
                        Ok(_) => panic!("Expected error persisting scorer"),
                        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 = Arc::new(Persister::new(data_dir.clone()));

                // Set up a background event handler for FundingGenerationReady events.
                let (sender, receiver) = std::sync::mpsc::sync_channel(1);
                let event_handler = move |event: Event| match event {
                        Event::FundingGenerationReady { .. } => sender.send(handle_funding_generation_ready!(event, channel_value)).unwrap(),
                        Event::ChannelReady { .. } => {},
                        _ => panic!("Unexpected event: {:?}", event),
                };

                let bg_processor = BackgroundProcessor::start(persister, event_handler, nodes[0].chain_monitor.clone(), nodes[0].node.clone(), nodes[0].no_gossip_sync(), nodes[0].peer_manager.clone(), nodes[0].logger.clone(), Some(nodes[0].scorer.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::SendChannelReady, nodes[1].node.get_our_node_id());
                confirm_transaction(&mut nodes[1], &funding_tx);
                let bs_funding = get_event_msg!(nodes[1], MessageSendEvent::SendChannelReady, nodes[0].node.get_our_node_id());
                nodes[0].node.handle_channel_ready(&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_channel_ready(&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: Event| match event {
                        Event::SpendableOutputs { .. } => sender.send(event.clone()).unwrap(),
                        Event::ChannelReady { .. } => {},
                        Event::ChannelClosed { .. } => {},
                        _ => panic!("Unexpected event: {:?}", event),
                };
                let persister = Arc::new(Persister::new(data_dir));
                let bg_processor = BackgroundProcessor::start(persister, event_handler, nodes[0].chain_monitor.clone(), nodes[0].node.clone(), nodes[0].no_gossip_sync(), nodes[0].peer_manager.clone(), nodes[0].logger.clone(), Some(nodes[0].scorer.clone()));

                // Force close the channel and check that the SpendableOutputs event was handled.
                nodes[0].node.force_close_broadcasting_latest_txn(&nodes[0].node.list_channels()[0].channel_id, &nodes[1].node.get_our_node_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("Events not handled within deadline");
                match event {
                        Event::SpendableOutputs { .. } => {},
                        _ => panic!("Unexpected event: {:?}", event),
                }

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

        #[test]
        fn test_scorer_persistence() {
                let nodes = create_nodes(2, "test_scorer_persistence".to_string());
                let data_dir = nodes[0].persister.get_data_dir();
                let persister = Arc::new(Persister::new(data_dir));
                let event_handler = |_: _| {};
                let bg_processor = BackgroundProcessor::start(persister, event_handler, nodes[0].chain_monitor.clone(), nodes[0].node.clone(), nodes[0].no_gossip_sync(), nodes[0].peer_manager.clone(), nodes[0].logger.clone(), Some(nodes[0].scorer.clone()));

                loop {
                        let log_entries = nodes[0].logger.lines.lock().unwrap();
                        let expected_log = "Persisting scorer".to_string();
                        if log_entries.get(&("lightning_background_processor".to_string(), expected_log)).is_some() {
                                break
                        }
                }

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

        #[test]
        fn test_not_pruning_network_graph_until_graph_sync_completion() {
                let nodes = create_nodes(2, "test_not_pruning_network_graph_until_graph_sync_completion".to_string());
                let data_dir = nodes[0].persister.get_data_dir();
                let (sender, receiver) = std::sync::mpsc::sync_channel(1);
                let persister = Arc::new(Persister::new(data_dir.clone()).with_graph_persistence_notifier(sender));
                let network_graph = nodes[0].network_graph.clone();
                let features = ChannelFeatures::empty();
                network_graph.add_channel_from_partial_announcement(42, 53, features, nodes[0].node.get_our_node_id(), nodes[1].node.get_our_node_id())
                        .expect("Failed to update channel from partial announcement");
                let original_graph_description = network_graph.to_string();
                assert!(original_graph_description.contains("42: features: 0000, node_one:"));
                assert_eq!(network_graph.read_only().channels().len(), 1);

                let event_handler = |_: _| {};
                let background_processor = BackgroundProcessor::start(persister, event_handler, nodes[0].chain_monitor.clone(), nodes[0].node.clone(), nodes[0].rapid_gossip_sync(), nodes[0].peer_manager.clone(), nodes[0].logger.clone(), Some(nodes[0].scorer.clone()));

                loop {
                        let log_entries = nodes[0].logger.lines.lock().unwrap();
                        let expected_log_a = "Assessing prunability of network graph".to_string();
                        let expected_log_b = "Not pruning network graph, either due to pending rapid gossip sync or absence of a prunable graph.".to_string();
                        if log_entries.get(&("lightning_background_processor".to_string(), expected_log_a)).is_some() &&
                                log_entries.get(&("lightning_background_processor".to_string(), expected_log_b)).is_some() {
                                break
                        }
                }

                let initialization_input = vec![
                        76, 68, 75, 1, 111, 226, 140, 10, 182, 241, 179, 114, 193, 166, 162, 70, 174, 99, 247,
                        79, 147, 30, 131, 101, 225, 90, 8, 156, 104, 214, 25, 0, 0, 0, 0, 0, 97, 227, 98, 218,
                        0, 0, 0, 4, 2, 22, 7, 207, 206, 25, 164, 197, 231, 230, 231, 56, 102, 61, 250, 251,
                        187, 172, 38, 46, 79, 247, 108, 44, 155, 48, 219, 238, 252, 53, 192, 6, 67, 2, 36, 125,
                        157, 176, 223, 175, 234, 116, 94, 248, 201, 225, 97, 235, 50, 47, 115, 172, 63, 136,
                        88, 216, 115, 11, 111, 217, 114, 84, 116, 124, 231, 107, 2, 158, 1, 242, 121, 152, 106,
                        204, 131, 186, 35, 93, 70, 216, 10, 237, 224, 183, 89, 95, 65, 3, 83, 185, 58, 138,
                        181, 64, 187, 103, 127, 68, 50, 2, 201, 19, 17, 138, 136, 149, 185, 226, 156, 137, 175,
                        110, 32, 237, 0, 217, 90, 31, 100, 228, 149, 46, 219, 175, 168, 77, 4, 143, 38, 128,
                        76, 97, 0, 0, 0, 2, 0, 0, 255, 8, 153, 192, 0, 2, 27, 0, 0, 0, 1, 0, 0, 255, 2, 68,
                        226, 0, 6, 11, 0, 1, 2, 3, 0, 0, 0, 2, 0, 40, 0, 0, 0, 0, 0, 0, 3, 232, 0, 0, 3, 232,
                        0, 0, 0, 1, 0, 0, 0, 0, 58, 85, 116, 216, 255, 8, 153, 192, 0, 2, 27, 0, 0, 25, 0, 0,
                        0, 1, 0, 0, 0, 125, 255, 2, 68, 226, 0, 6, 11, 0, 1, 5, 0, 0, 0, 0, 29, 129, 25, 192,
                ];
                nodes[0].rapid_gossip_sync.update_network_graph(&initialization_input[..]).unwrap();

                // this should have added two channels
                assert_eq!(network_graph.read_only().channels().len(), 3);

                let _ = receiver
                        .recv_timeout(Duration::from_secs(super::FIRST_NETWORK_PRUNE_TIMER * 5))
                        .expect("Network graph not pruned within deadline");

                background_processor.stop().unwrap();

                // all channels should now be pruned
                assert_eq!(network_graph.read_only().channels().len(), 0);
        }

        #[test]
        fn test_invoice_payer() {
                let keys_manager = test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
                let random_seed_bytes = keys_manager.get_secure_random_bytes();
                let nodes = create_nodes(2, "test_invoice_payer".to_string());

                // Initiate the background processors to watch each node.
                let data_dir = nodes[0].persister.get_data_dir();
                let persister = Arc::new(Persister::new(data_dir));
                let router = DefaultRouter::new(Arc::clone(&nodes[0].network_graph), Arc::clone(&nodes[0].logger), random_seed_bytes, Arc::clone(&nodes[0].scorer));
                let invoice_payer = Arc::new(InvoicePayer::new(Arc::clone(&nodes[0].node), router, Arc::clone(&nodes[0].logger), |_: _| {}, Retry::Attempts(2)));
                let event_handler = Arc::clone(&invoice_payer);
                let bg_processor = BackgroundProcessor::start(persister, event_handler, nodes[0].chain_monitor.clone(), nodes[0].node.clone(), nodes[0].no_gossip_sync(), nodes[0].peer_manager.clone(), nodes[0].logger.clone(), Some(nodes[0].scorer.clone()));
                assert!(bg_processor.stop().is_ok());
        }
}