Merge pull request #1035 from TheBlueMatt/2021-08-faster-pings

Suggest faster ping in `PeerManager::timer_tick_occurred` docs

diff --combined lightning-background-processor/src/lib.rs
index afa3633bee69bea6b4fd2a8e2bf330a55147d143,c75c47262e51d2873a335acc37518bccd6ed2984..8af4cc6b3e51727c7c8261604342a8485bd6cc24
--- 1/lightning-background-processor/src/lib.rs
--- 2/lightning-background-processor/src/lib.rs
+++ b/lightning-background-processor/src/lib.rs
@@@ -39,7 -39,6 +39,7 @@@ use std::ops::Deref
  /// 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  /// outdated.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>>>,
@@@ -50,6 -49,8 +50,8 @@@ 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
@@@ -138,7 -139,8 +140,8 @@@ impl BackgroundProcessor 
                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 current_time = Instant::now();
+                       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);
@@@ -153,11 -155,27 +156,27 @@@
                                        log_trace!(logger, "Terminating background processor.");
                                        return Ok(());
                                }
-                               if current_time.elapsed().as_secs() > FRESHNESS_TIMER {
-                                       log_trace!(logger, "Calling ChannelManager's and PeerManager's timer_tick_occurred");
+                               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();
-                                       current_time = Instant::now();
+                                       last_ping_call = Instant::now();
                                }
                        }
                });
@@@ -441,8 -459,10 +460,10 @@@ mod tests 
                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 and PeerManager's timer_tick_occurred".to_string();
-                       if log_entries.get(&("lightning_background_processor".to_string(), desired_log)).is_some() {
+                       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
                        }
                }