Merge pull request #2280 from TheBlueMatt/2023-05-event-deadlock
[rust-lightning] / lightning / src / ln / peer_handler.rs
index a20b316eb0a93e997a162e9857ef3cd60ad02373..3cb6a55f2e80ae0a8a1f717f6e03afe66a9faa64 100644 (file)
@@ -36,7 +36,7 @@ use crate::prelude::*;
 use crate::io;
 use alloc::collections::LinkedList;
 use crate::sync::{Arc, Mutex, MutexGuard, FairRwLock};
-use core::sync::atomic::{AtomicBool, AtomicU32, Ordering};
+use core::sync::atomic::{AtomicBool, AtomicU32, AtomicI32, Ordering};
 use core::{cmp, hash, fmt, mem};
 use core::ops::Deref;
 use core::convert::Infallible;
@@ -696,15 +696,18 @@ pub struct PeerManager<Descriptor: SocketDescriptor, CM: Deref, RM: Deref, OM: D
        /// lock held. Entries may be added with only the `peers` read lock held (though the
        /// `Descriptor` value must already exist in `peers`).
        node_id_to_descriptor: Mutex<HashMap<PublicKey, Descriptor>>,
-       /// We can only have one thread processing events at once, but we don't usually need the full
-       /// `peers` write lock to do so, so instead we block on this empty mutex when entering
-       /// `process_events`.
-       event_processing_lock: Mutex<()>,
-       /// Because event processing is global and always does all available work before returning,
-       /// there is no reason for us to have many event processors waiting on the lock at once.
-       /// Instead, we limit the total blocked event processors to always exactly one by setting this
-       /// when an event process call is waiting.
-       blocked_event_processors: AtomicBool,
+       /// We can only have one thread processing events at once, but if a second call to
+       /// `process_events` happens while a first call is in progress, one of the two calls needs to
+       /// start from the top to ensure any new messages are also handled.
+       ///
+       /// Because the event handler calls into user code which may block, we don't want to block a
+       /// second thread waiting for another thread to handle events which is then blocked on user
+       /// code, so we store an atomic counter here:
+       ///  * 0 indicates no event processor is running
+       ///  * 1 indicates an event processor is running
+       ///  * > 1 indicates an event processor is running but needs to start again from the top once
+       ///        it finishes as another thread tried to start processing events but returned early.
+       event_processing_state: AtomicI32,
 
        /// Used to track the last value sent in a node_announcement "timestamp" field. We ensure this
        /// value increases strictly since we don't assume access to a time source.
@@ -874,8 +877,7 @@ impl<Descriptor: SocketDescriptor, CM: Deref, RM: Deref, OM: Deref, L: Deref, CM
                        message_handler,
                        peers: FairRwLock::new(HashMap::new()),
                        node_id_to_descriptor: Mutex::new(HashMap::new()),
-                       event_processing_lock: Mutex::new(()),
-                       blocked_event_processors: AtomicBool::new(false),
+                       event_processing_state: AtomicI32::new(0),
                        ephemeral_key_midstate,
                        peer_counter: AtomicCounter::new(),
                        gossip_processing_backlogged: AtomicBool::new(false),
@@ -1814,356 +1816,351 @@ impl<Descriptor: SocketDescriptor, CM: Deref, RM: Deref, OM: Deref, L: Deref, CM
        /// [`ChannelManager::process_pending_htlc_forwards`]: crate::ln::channelmanager::ChannelManager::process_pending_htlc_forwards
        /// [`send_data`]: SocketDescriptor::send_data
        pub fn process_events(&self) {
-               let mut _single_processor_lock = self.event_processing_lock.try_lock();
-               if _single_processor_lock.is_err() {
-                       // While we could wake the older sleeper here with a CV and make more even waiting
-                       // times, that would be a lot of overengineering for a simple "reduce total waiter
-                       // count" goal.
-                       match self.blocked_event_processors.compare_exchange(false, true, Ordering::AcqRel, Ordering::Acquire) {
-                               Err(val) => {
-                                       debug_assert!(val, "compare_exchange failed spuriously?");
-                                       return;
-                               },
-                               Ok(val) => {
-                                       debug_assert!(!val, "compare_exchange succeeded spuriously?");
-                                       // We're the only waiter, as the running process_events may have emptied the
-                                       // pending events "long" ago and there are new events for us to process, wait until
-                                       // its done and process any leftover events before returning.
-                                       _single_processor_lock = Ok(self.event_processing_lock.lock().unwrap());
-                                       self.blocked_event_processors.store(false, Ordering::Release);
-                               }
-                       }
+               if self.event_processing_state.fetch_add(1, Ordering::AcqRel) > 0 {
+                       // If we're not the first event processor to get here, just return early, the increment
+                       // we just did will be treated as "go around again" at the end.
+                       return;
                }
 
-               self.update_gossip_backlogged();
-               let flush_read_disabled = self.gossip_processing_backlog_lifted.swap(false, Ordering::Relaxed);
-
-               let mut peers_to_disconnect = HashMap::new();
-               let mut events_generated = self.message_handler.chan_handler.get_and_clear_pending_msg_events();
-               events_generated.append(&mut self.message_handler.route_handler.get_and_clear_pending_msg_events());
+               loop {
+                       self.update_gossip_backlogged();
+                       let flush_read_disabled = self.gossip_processing_backlog_lifted.swap(false, Ordering::Relaxed);
 
-               {
-                       // TODO: There are some DoS attacks here where you can flood someone's outbound send
-                       // buffer by doing things like announcing channels on another node. We should be willing to
-                       // drop optional-ish messages when send buffers get full!
+                       let mut peers_to_disconnect = HashMap::new();
+                       let mut events_generated = self.message_handler.chan_handler.get_and_clear_pending_msg_events();
+                       events_generated.append(&mut self.message_handler.route_handler.get_and_clear_pending_msg_events());
 
-                       let peers_lock = self.peers.read().unwrap();
-                       let peers = &*peers_lock;
-                       macro_rules! get_peer_for_forwarding {
-                               ($node_id: expr) => {
-                                       {
-                                               if peers_to_disconnect.get($node_id).is_some() {
-                                                       // If we've "disconnected" this peer, do not send to it.
-                                                       continue;
-                                               }
-                                               let descriptor_opt = self.node_id_to_descriptor.lock().unwrap().get($node_id).cloned();
-                                               match descriptor_opt {
-                                                       Some(descriptor) => match peers.get(&descriptor) {
-                                                               Some(peer_mutex) => {
-                                                                       let peer_lock = peer_mutex.lock().unwrap();
-                                                                       if !peer_lock.handshake_complete() {
+                       {
+                               // TODO: There are some DoS attacks here where you can flood someone's outbound send
+                               // buffer by doing things like announcing channels on another node. We should be willing to
+                               // drop optional-ish messages when send buffers get full!
+
+                               let peers_lock = self.peers.read().unwrap();
+                               let peers = &*peers_lock;
+                               macro_rules! get_peer_for_forwarding {
+                                       ($node_id: expr) => {
+                                               {
+                                                       if peers_to_disconnect.get($node_id).is_some() {
+                                                               // If we've "disconnected" this peer, do not send to it.
+                                                               continue;
+                                                       }
+                                                       let descriptor_opt = self.node_id_to_descriptor.lock().unwrap().get($node_id).cloned();
+                                                       match descriptor_opt {
+                                                               Some(descriptor) => match peers.get(&descriptor) {
+                                                                       Some(peer_mutex) => {
+                                                                               let peer_lock = peer_mutex.lock().unwrap();
+                                                                               if !peer_lock.handshake_complete() {
+                                                                                       continue;
+                                                                               }
+                                                                               peer_lock
+                                                                       },
+                                                                       None => {
+                                                                               debug_assert!(false, "Inconsistent peers set state!");
                                                                                continue;
                                                                        }
-                                                                       peer_lock
                                                                },
                                                                None => {
-                                                                       debug_assert!(false, "Inconsistent peers set state!");
                                                                        continue;
-                                                               }
-                                                       },
-                                                       None => {
-                                                               continue;
-                                                       },
+                                                               },
+                                                       }
                                                }
                                        }
                                }
-                       }
-                       for event in events_generated.drain(..) {
-                               match event {
-                                       MessageSendEvent::SendAcceptChannel { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendAcceptChannel event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.temporary_channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendAcceptChannelV2 { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendAcceptChannelV2 event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.temporary_channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendOpenChannel { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendOpenChannel event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.temporary_channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendOpenChannelV2 { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendOpenChannelV2 event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.temporary_channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendFundingCreated { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendFundingCreated event in peer_handler for node {} for channel {} (which becomes {})",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.temporary_channel_id),
-                                                               log_funding_channel_id!(msg.funding_txid, msg.funding_output_index));
-                                               // TODO: If the peer is gone we should generate a DiscardFunding event
-                                               // indicating to the wallet that they should just throw away this funding transaction
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendFundingSigned { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendFundingSigned event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendChannelReady { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendChannelReady event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendTxAddInput { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendTxAddInput event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendTxAddOutput { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendTxAddOutput event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendTxRemoveInput { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendTxRemoveInput event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendTxRemoveOutput { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendTxRemoveOutput event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendTxComplete { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendTxComplete event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendTxSignatures { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendTxSignatures event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendTxInitRbf { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendTxInitRbf event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendTxAckRbf { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendTxAckRbf event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendTxAbort { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendTxAbort event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendAnnouncementSignatures { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendAnnouncementSignatures event in peer_handler for node {} for channel {})",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::UpdateHTLCs { ref node_id, updates: msgs::CommitmentUpdate { ref update_add_htlcs, ref update_fulfill_htlcs, ref update_fail_htlcs, ref update_fail_malformed_htlcs, ref update_fee, ref commitment_signed } } => {
-                                               log_debug!(self.logger, "Handling UpdateHTLCs event in peer_handler for node {} with {} adds, {} fulfills, {} fails for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               update_add_htlcs.len(),
-                                                               update_fulfill_htlcs.len(),
-                                                               update_fail_htlcs.len(),
-                                                               log_bytes!(commitment_signed.channel_id));
-                                               let mut peer = get_peer_for_forwarding!(node_id);
-                                               for msg in update_add_htlcs {
-                                                       self.enqueue_message(&mut *peer, msg);
-                                               }
-                                               for msg in update_fulfill_htlcs {
-                                                       self.enqueue_message(&mut *peer, msg);
-                                               }
-                                               for msg in update_fail_htlcs {
-                                                       self.enqueue_message(&mut *peer, msg);
-                                               }
-                                               for msg in update_fail_malformed_htlcs {
-                                                       self.enqueue_message(&mut *peer, msg);
-                                               }
-                                               if let &Some(ref msg) = update_fee {
-                                                       self.enqueue_message(&mut *peer, msg);
-                                               }
-                                               self.enqueue_message(&mut *peer, commitment_signed);
-                                       },
-                                       MessageSendEvent::SendRevokeAndACK { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendRevokeAndACK event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendClosingSigned { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendClosingSigned event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendShutdown { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling Shutdown event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendChannelReestablish { ref node_id, ref msg } => {
-                                               log_debug!(self.logger, "Handling SendChannelReestablish event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id),
-                                                               log_bytes!(msg.channel_id));
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendChannelAnnouncement { ref node_id, ref msg, ref update_msg } => {
-                                               log_debug!(self.logger, "Handling SendChannelAnnouncement event in peer_handler for node {} for short channel id {}",
-                                                               log_pubkey!(node_id),
-                                                               msg.contents.short_channel_id);
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), update_msg);
-                                       },
-                                       MessageSendEvent::BroadcastChannelAnnouncement { msg, update_msg } => {
-                                               log_debug!(self.logger, "Handling BroadcastChannelAnnouncement event in peer_handler for short channel id {}", msg.contents.short_channel_id);
-                                               match self.message_handler.route_handler.handle_channel_announcement(&msg) {
-                                                       Ok(_) | Err(LightningError { action: msgs::ErrorAction::IgnoreDuplicateGossip, .. }) =>
-                                                               self.forward_broadcast_msg(peers, &wire::Message::ChannelAnnouncement(msg), None),
-                                                       _ => {},
-                                               }
-                                               if let Some(msg) = update_msg {
+                               for event in events_generated.drain(..) {
+                                       match event {
+                                               MessageSendEvent::SendAcceptChannel { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendAcceptChannel event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.temporary_channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendAcceptChannelV2 { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendAcceptChannelV2 event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.temporary_channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendOpenChannel { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendOpenChannel event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.temporary_channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendOpenChannelV2 { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendOpenChannelV2 event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.temporary_channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendFundingCreated { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendFundingCreated event in peer_handler for node {} for channel {} (which becomes {})",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.temporary_channel_id),
+                                                                       log_funding_channel_id!(msg.funding_txid, msg.funding_output_index));
+                                                       // TODO: If the peer is gone we should generate a DiscardFunding event
+                                                       // indicating to the wallet that they should just throw away this funding transaction
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendFundingSigned { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendFundingSigned event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendChannelReady { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendChannelReady event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendTxAddInput { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendTxAddInput event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendTxAddOutput { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendTxAddOutput event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendTxRemoveInput { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendTxRemoveInput event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendTxRemoveOutput { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendTxRemoveOutput event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendTxComplete { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendTxComplete event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendTxSignatures { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendTxSignatures event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendTxInitRbf { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendTxInitRbf event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendTxAckRbf { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendTxAckRbf event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendTxAbort { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendTxAbort event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendAnnouncementSignatures { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendAnnouncementSignatures event in peer_handler for node {} for channel {})",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::UpdateHTLCs { ref node_id, updates: msgs::CommitmentUpdate { ref update_add_htlcs, ref update_fulfill_htlcs, ref update_fail_htlcs, ref update_fail_malformed_htlcs, ref update_fee, ref commitment_signed } } => {
+                                                       log_debug!(self.logger, "Handling UpdateHTLCs event in peer_handler for node {} with {} adds, {} fulfills, {} fails for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       update_add_htlcs.len(),
+                                                                       update_fulfill_htlcs.len(),
+                                                                       update_fail_htlcs.len(),
+                                                                       log_bytes!(commitment_signed.channel_id));
+                                                       let mut peer = get_peer_for_forwarding!(node_id);
+                                                       for msg in update_add_htlcs {
+                                                               self.enqueue_message(&mut *peer, msg);
+                                                       }
+                                                       for msg in update_fulfill_htlcs {
+                                                               self.enqueue_message(&mut *peer, msg);
+                                                       }
+                                                       for msg in update_fail_htlcs {
+                                                               self.enqueue_message(&mut *peer, msg);
+                                                       }
+                                                       for msg in update_fail_malformed_htlcs {
+                                                               self.enqueue_message(&mut *peer, msg);
+                                                       }
+                                                       if let &Some(ref msg) = update_fee {
+                                                               self.enqueue_message(&mut *peer, msg);
+                                                       }
+                                                       self.enqueue_message(&mut *peer, commitment_signed);
+                                               },
+                                               MessageSendEvent::SendRevokeAndACK { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendRevokeAndACK event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendClosingSigned { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendClosingSigned event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendShutdown { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling Shutdown event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendChannelReestablish { ref node_id, ref msg } => {
+                                                       log_debug!(self.logger, "Handling SendChannelReestablish event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id),
+                                                                       log_bytes!(msg.channel_id));
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendChannelAnnouncement { ref node_id, ref msg, ref update_msg } => {
+                                                       log_debug!(self.logger, "Handling SendChannelAnnouncement event in peer_handler for node {} for short channel id {}",
+                                                                       log_pubkey!(node_id),
+                                                                       msg.contents.short_channel_id);
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), update_msg);
+                                               },
+                                               MessageSendEvent::BroadcastChannelAnnouncement { msg, update_msg } => {
+                                                       log_debug!(self.logger, "Handling BroadcastChannelAnnouncement event in peer_handler for short channel id {}", msg.contents.short_channel_id);
+                                                       match self.message_handler.route_handler.handle_channel_announcement(&msg) {
+                                                               Ok(_) | Err(LightningError { action: msgs::ErrorAction::IgnoreDuplicateGossip, .. }) =>
+                                                                       self.forward_broadcast_msg(peers, &wire::Message::ChannelAnnouncement(msg), None),
+                                                               _ => {},
+                                                       }
+                                                       if let Some(msg) = update_msg {
+                                                               match self.message_handler.route_handler.handle_channel_update(&msg) {
+                                                                       Ok(_) | Err(LightningError { action: msgs::ErrorAction::IgnoreDuplicateGossip, .. }) =>
+                                                                               self.forward_broadcast_msg(peers, &wire::Message::ChannelUpdate(msg), None),
+                                                                       _ => {},
+                                                               }
+                                                       }
+                                               },
+                                               MessageSendEvent::BroadcastChannelUpdate { msg } => {
+                                                       log_debug!(self.logger, "Handling BroadcastChannelUpdate event in peer_handler for short channel id {}", msg.contents.short_channel_id);
                                                        match self.message_handler.route_handler.handle_channel_update(&msg) {
                                                                Ok(_) | Err(LightningError { action: msgs::ErrorAction::IgnoreDuplicateGossip, .. }) =>
                                                                        self.forward_broadcast_msg(peers, &wire::Message::ChannelUpdate(msg), None),
                                                                _ => {},
                                                        }
+                                               },
+                                               MessageSendEvent::BroadcastNodeAnnouncement { msg } => {
+                                                       log_debug!(self.logger, "Handling BroadcastNodeAnnouncement event in peer_handler for node {}", msg.contents.node_id);
+                                                       match self.message_handler.route_handler.handle_node_announcement(&msg) {
+                                                               Ok(_) | Err(LightningError { action: msgs::ErrorAction::IgnoreDuplicateGossip, .. }) =>
+                                                                       self.forward_broadcast_msg(peers, &wire::Message::NodeAnnouncement(msg), None),
+                                                               _ => {},
+                                                       }
+                                               },
+                                               MessageSendEvent::SendChannelUpdate { ref node_id, ref msg } => {
+                                                       log_trace!(self.logger, "Handling SendChannelUpdate event in peer_handler for node {} for channel {}",
+                                                                       log_pubkey!(node_id), msg.contents.short_channel_id);
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::HandleError { ref node_id, ref action } => {
+                                                       match *action {
+                                                               msgs::ErrorAction::DisconnectPeer { ref msg } => {
+                                                                       // We do not have the peers write lock, so we just store that we're
+                                                                       // about to disconenct the peer and do it after we finish
+                                                                       // processing most messages.
+                                                                       peers_to_disconnect.insert(*node_id, msg.clone());
+                                                               },
+                                                               msgs::ErrorAction::IgnoreAndLog(level) => {
+                                                                       log_given_level!(self.logger, level, "Received a HandleError event to be ignored for node {}", log_pubkey!(node_id));
+                                                               },
+                                                               msgs::ErrorAction::IgnoreDuplicateGossip => {},
+                                                               msgs::ErrorAction::IgnoreError => {
+                                                                       log_debug!(self.logger, "Received a HandleError event to be ignored for node {}", log_pubkey!(node_id));
+                                                               },
+                                                               msgs::ErrorAction::SendErrorMessage { ref msg } => {
+                                                                       log_trace!(self.logger, "Handling SendErrorMessage HandleError event in peer_handler for node {} with message {}",
+                                                                                       log_pubkey!(node_id),
+                                                                                       msg.data);
+                                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                                               },
+                                                               msgs::ErrorAction::SendWarningMessage { ref msg, ref log_level } => {
+                                                                       log_given_level!(self.logger, *log_level, "Handling SendWarningMessage HandleError event in peer_handler for node {} with message {}",
+                                                                                       log_pubkey!(node_id),
+                                                                                       msg.data);
+                                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                                               },
+                                                       }
+                                               },
+                                               MessageSendEvent::SendChannelRangeQuery { ref node_id, ref msg } => {
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
+                                               },
+                                               MessageSendEvent::SendShortIdsQuery { ref node_id, ref msg } => {
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
                                                }
-                                       },
-                                       MessageSendEvent::BroadcastChannelUpdate { msg } => {
-                                               log_debug!(self.logger, "Handling BroadcastChannelUpdate event in peer_handler for short channel id {}", msg.contents.short_channel_id);
-                                               match self.message_handler.route_handler.handle_channel_update(&msg) {
-                                                       Ok(_) | Err(LightningError { action: msgs::ErrorAction::IgnoreDuplicateGossip, .. }) =>
-                                                               self.forward_broadcast_msg(peers, &wire::Message::ChannelUpdate(msg), None),
-                                                       _ => {},
+                                               MessageSendEvent::SendReplyChannelRange { ref node_id, ref msg } => {
+                                                       log_gossip!(self.logger, "Handling SendReplyChannelRange event in peer_handler for node {} with num_scids={} first_blocknum={} number_of_blocks={}, sync_complete={}",
+                                                               log_pubkey!(node_id),
+                                                               msg.short_channel_ids.len(),
+                                                               msg.first_blocknum,
+                                                               msg.number_of_blocks,
+                                                               msg.sync_complete);
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
                                                }
-                                       },
-                                       MessageSendEvent::BroadcastNodeAnnouncement { msg } => {
-                                               log_debug!(self.logger, "Handling BroadcastNodeAnnouncement event in peer_handler for node {}", msg.contents.node_id);
-                                               match self.message_handler.route_handler.handle_node_announcement(&msg) {
-                                                       Ok(_) | Err(LightningError { action: msgs::ErrorAction::IgnoreDuplicateGossip, .. }) =>
-                                                               self.forward_broadcast_msg(peers, &wire::Message::NodeAnnouncement(msg), None),
-                                                       _ => {},
+                                               MessageSendEvent::SendGossipTimestampFilter { ref node_id, ref msg } => {
+                                                       self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
                                                }
-                                       },
-                                       MessageSendEvent::SendChannelUpdate { ref node_id, ref msg } => {
-                                               log_trace!(self.logger, "Handling SendChannelUpdate event in peer_handler for node {} for channel {}",
-                                                               log_pubkey!(node_id), msg.contents.short_channel_id);
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::HandleError { ref node_id, ref action } => {
-                                               match *action {
-                                                       msgs::ErrorAction::DisconnectPeer { ref msg } => {
-                                                               // We do not have the peers write lock, so we just store that we're
-                                                               // about to disconenct the peer and do it after we finish
-                                                               // processing most messages.
-                                                               peers_to_disconnect.insert(*node_id, msg.clone());
-                                                       },
-                                                       msgs::ErrorAction::IgnoreAndLog(level) => {
-                                                               log_given_level!(self.logger, level, "Received a HandleError event to be ignored for node {}", log_pubkey!(node_id));
-                                                       },
-                                                       msgs::ErrorAction::IgnoreDuplicateGossip => {},
-                                                       msgs::ErrorAction::IgnoreError => {
-                                                               log_debug!(self.logger, "Received a HandleError event to be ignored for node {}", log_pubkey!(node_id));
-                                                       },
-                                                       msgs::ErrorAction::SendErrorMessage { ref msg } => {
-                                                               log_trace!(self.logger, "Handling SendErrorMessage HandleError event in peer_handler for node {} with message {}",
-                                                                               log_pubkey!(node_id),
-                                                                               msg.data);
-                                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                                       },
-                                                       msgs::ErrorAction::SendWarningMessage { ref msg, ref log_level } => {
-                                                               log_given_level!(self.logger, *log_level, "Handling SendWarningMessage HandleError event in peer_handler for node {} with message {}",
-                                                                               log_pubkey!(node_id),
-                                                                               msg.data);
-                                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                                       },
-                                               }
-                                       },
-                                       MessageSendEvent::SendChannelRangeQuery { ref node_id, ref msg } => {
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       },
-                                       MessageSendEvent::SendShortIdsQuery { ref node_id, ref msg } => {
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       }
-                                       MessageSendEvent::SendReplyChannelRange { ref node_id, ref msg } => {
-                                               log_gossip!(self.logger, "Handling SendReplyChannelRange event in peer_handler for node {} with num_scids={} first_blocknum={} number_of_blocks={}, sync_complete={}",
-                                                       log_pubkey!(node_id),
-                                                       msg.short_channel_ids.len(),
-                                                       msg.first_blocknum,
-                                                       msg.number_of_blocks,
-                                                       msg.sync_complete);
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
-                                       }
-                                       MessageSendEvent::SendGossipTimestampFilter { ref node_id, ref msg } => {
-                                               self.enqueue_message(&mut *get_peer_for_forwarding!(node_id), msg);
                                        }
                                }
-                       }
 
-                       for (node_id, msg) in self.message_handler.custom_message_handler.get_and_clear_pending_msg() {
-                               if peers_to_disconnect.get(&node_id).is_some() { continue; }
-                               self.enqueue_message(&mut *get_peer_for_forwarding!(&node_id), &msg);
-                       }
+                               for (node_id, msg) in self.message_handler.custom_message_handler.get_and_clear_pending_msg() {
+                                       if peers_to_disconnect.get(&node_id).is_some() { continue; }
+                                       self.enqueue_message(&mut *get_peer_for_forwarding!(&node_id), &msg);
+                               }
 
-                       for (descriptor, peer_mutex) in peers.iter() {
-                               let mut peer = peer_mutex.lock().unwrap();
-                               if flush_read_disabled { peer.received_channel_announce_since_backlogged = false; }
-                               self.do_attempt_write_data(&mut (*descriptor).clone(), &mut *peer, flush_read_disabled);
+                               for (descriptor, peer_mutex) in peers.iter() {
+                                       let mut peer = peer_mutex.lock().unwrap();
+                                       if flush_read_disabled { peer.received_channel_announce_since_backlogged = false; }
+                                       self.do_attempt_write_data(&mut (*descriptor).clone(), &mut *peer, flush_read_disabled);
+                               }
                        }
-               }
-               if !peers_to_disconnect.is_empty() {
-                       let mut peers_lock = self.peers.write().unwrap();
-                       let peers = &mut *peers_lock;
-                       for (node_id, msg) in peers_to_disconnect.drain() {
-                               // Note that since we are holding the peers *write* lock we can
-                               // remove from node_id_to_descriptor immediately (as no other
-                               // thread can be holding the peer lock if we have the global write
-                               // lock).
-
-                               let descriptor_opt = self.node_id_to_descriptor.lock().unwrap().remove(&node_id);
-                               if let Some(mut descriptor) = descriptor_opt {
-                                       if let Some(peer_mutex) = peers.remove(&descriptor) {
-                                               let mut peer = peer_mutex.lock().unwrap();
-                                               if let Some(msg) = msg {
-                                                       log_trace!(self.logger, "Handling DisconnectPeer HandleError event in peer_handler for node {} with message {}",
-                                                                       log_pubkey!(node_id),
-                                                                       msg.data);
-                                                       self.enqueue_message(&mut *peer, &msg);
-                                                       // This isn't guaranteed to work, but if there is enough free
-                                                       // room in the send buffer, put the error message there...
-                                                       self.do_attempt_write_data(&mut descriptor, &mut *peer, false);
-                                               }
-                                               self.do_disconnect(descriptor, &*peer, "DisconnectPeer HandleError");
-                                       } else { debug_assert!(false, "Missing connection for peer"); }
+                       if !peers_to_disconnect.is_empty() {
+                               let mut peers_lock = self.peers.write().unwrap();
+                               let peers = &mut *peers_lock;
+                               for (node_id, msg) in peers_to_disconnect.drain() {
+                                       // Note that since we are holding the peers *write* lock we can
+                                       // remove from node_id_to_descriptor immediately (as no other
+                                       // thread can be holding the peer lock if we have the global write
+                                       // lock).
+
+                                       let descriptor_opt = self.node_id_to_descriptor.lock().unwrap().remove(&node_id);
+                                       if let Some(mut descriptor) = descriptor_opt {
+                                               if let Some(peer_mutex) = peers.remove(&descriptor) {
+                                                       let mut peer = peer_mutex.lock().unwrap();
+                                                       if let Some(msg) = msg {
+                                                               log_trace!(self.logger, "Handling DisconnectPeer HandleError event in peer_handler for node {} with message {}",
+                                                                               log_pubkey!(node_id),
+                                                                               msg.data);
+                                                               self.enqueue_message(&mut *peer, &msg);
+                                                               // This isn't guaranteed to work, but if there is enough free
+                                                               // room in the send buffer, put the error message there...
+                                                               self.do_attempt_write_data(&mut descriptor, &mut *peer, false);
+                                                       }
+                                                       self.do_disconnect(descriptor, &*peer, "DisconnectPeer HandleError");
+                                               } else { debug_assert!(false, "Missing connection for peer"); }
+                                       }
                                }
                        }
+
+                       if self.event_processing_state.fetch_sub(1, Ordering::AcqRel) != 1 {
+                               // If another thread incremented the state while we were running we should go
+                               // around again, but only once.
+                               self.event_processing_state.store(1, Ordering::Release);
+                               continue;
+                       }
+                       break;
                }
        }
 
@@ -3004,4 +3001,53 @@ mod tests {
                // For (None)
                assert_eq!(filter_addresses(None), None);
        }
+
+       #[test]
+       #[cfg(feature = "std")]
+       fn test_process_events_multithreaded() {
+               use std::time::{Duration, Instant};
+               // Test that `process_events` getting called on multiple threads doesn't generate too many
+               // loop iterations.
+               // Each time `process_events` goes around the loop we call
+               // `get_and_clear_pending_msg_events`, which we count using the `TestMessageHandler`.
+               // Because the loop should go around once more after a call which fails to take the
+               // single-threaded lock, if we write zero to the counter before calling `process_events` we
+               // should never observe there having been more than 2 loop iterations.
+               // Further, because the last thread to exit will call `process_events` before returning, we
+               // should always have at least one count at the end.
+               let cfg = Arc::new(create_peermgr_cfgs(1));
+               // Until we have std::thread::scoped we have to unsafe { turn off the borrow checker }.
+               let peer = Arc::new(create_network(1, unsafe { &*(&*cfg as *const _) as &'static _ }).pop().unwrap());
+
+               let exit_flag = Arc::new(AtomicBool::new(false));
+               macro_rules! spawn_thread { () => { {
+                       let thread_cfg = Arc::clone(&cfg);
+                       let thread_peer = Arc::clone(&peer);
+                       let thread_exit = Arc::clone(&exit_flag);
+                       std::thread::spawn(move || {
+                               while !thread_exit.load(Ordering::Acquire) {
+                                       thread_cfg[0].chan_handler.message_fetch_counter.store(0, Ordering::Release);
+                                       thread_peer.process_events();
+                                       std::thread::sleep(Duration::from_micros(1));
+                               }
+                       })
+               } } }
+
+               let thread_a = spawn_thread!();
+               let thread_b = spawn_thread!();
+               let thread_c = spawn_thread!();
+
+               let start_time = Instant::now();
+               while start_time.elapsed() < Duration::from_millis(100) {
+                       let val = cfg[0].chan_handler.message_fetch_counter.load(Ordering::Acquire);
+                       assert!(val <= 2);
+                       std::thread::yield_now(); // Winblowz seemingly doesn't ever interrupt threads?!
+               }
+
+               exit_flag.store(true, Ordering::Release);
+               thread_a.join().unwrap();
+               thread_b.join().unwrap();
+               thread_c.join().unwrap();
+               assert!(cfg[0].chan_handler.message_fetch_counter.load(Ordering::Acquire) >= 1);
+       }
 }