Reorder the BP loop to make manager persistence more reliable

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

diff --git a/lightning-background-processor/src/lib.rs b/lightning-background-processor/src/lib.rs
index 6beee915b309772ae500bd61211a929e6382682d..255fb245e0543a16ad0a38fbd0e3e267b25954ec 100644 (file)
--- a/lightning-background-processor/src/lib.rs
+++ b/lightning-background-processor/src/lib.rs
@@ -203,10 +203,22 @@ impl BackgroundProcessor {
                        let mut have_pruned = false;
 
                        loop {
-                               peer_manager.process_events(); // Note that this may block on ChannelManager's locking
                                channel_manager.process_pending_events(&event_handler);
                                chain_monitor.process_pending_events(&event_handler);
 
+                               // 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();