lnworker: fix threading issues for .channels attribute

external code (commands/gui) did not always take lock when iterating lnworker.channels.
instead of exposing lock, let's take a copy internally (as with .peers)

electrum/lnpeer.py

@@ -107,7 +107,7 @@ class Peer(Logger):
         if not (message_name.startswith("update_") or is_commitment_signed):
             return
         assert channel_id
-        chan = self.lnworker.channels[channel_id]  # type: Channel
+        chan = self.channels[channel_id]
         chan.hm.store_local_update_raw_msg(raw_msg, is_commitment_signed=is_commitment_signed)
         if is_commitment_signed:
             # saving now, to ensure replaying updates works (in case of channel reestablishment)
@@ -139,6 +139,8 @@ class Peer(Logger):
 
     @property
     def channels(self) -> Dict[bytes, Channel]:
+        # FIXME this iterates over all channels in lnworker,
+        #       so if we just want to lookup a channel by channel_id, it's wasteful
         return self.lnworker.channels_for_peer(self.pubkey)
 
     def diagnostic_name(self):

electrum/lnworker.py

@@ -491,22 +491,26 @@ class LNWallet(LNWorker):
         self.enable_htlc_settle.set()
 
         # note: accessing channels (besides simple lookup) needs self.lock!
-        self.channels = {}
+        self._channels = {}  # type: Dict[bytes, Channel]
         channels = self.db.get_dict("channels")
         for channel_id, c in channels.items():
-            self.channels[bfh(channel_id)] = Channel(c, sweep_address=self.sweep_address, lnworker=self)
+            self._channels[bfh(channel_id)] = Channel(c, sweep_address=self.sweep_address, lnworker=self)
 
         self.pending_payments = defaultdict(asyncio.Future)  # type: Dict[bytes, asyncio.Future[BarePaymentAttemptLog]]
 
+    @property
+    def channels(self) -> Mapping[bytes, Channel]:
+        """Returns a read-only copy of channels."""
+        with self.lock:
+            return self._channels.copy()
+
     @ignore_exceptions
     @log_exceptions
     async def sync_with_local_watchtower(self):
         watchtower = self.network.local_watchtower
         if watchtower:
             while True:
-                with self.lock:
-                    channels = list(self.channels.values())
-                for chan in channels:
+                for chan in self.channels.values():
                     await self.sync_channel_with_watchtower(chan, watchtower.sweepstore)
                 await asyncio.sleep(5)
 
@@ -524,12 +528,10 @@ class LNWallet(LNWorker):
             watchtower_url = self.config.get('watchtower_url')
             if not watchtower_url:
                 continue
-            with self.lock:
-                channels = list(self.channels.values())
             try:
                 async with make_aiohttp_session(proxy=self.network.proxy) as session:
                     watchtower = myAiohttpClient(session, watchtower_url)
-                    for chan in channels:
+                    for chan in self.channels.values():
                         await self.sync_channel_with_watchtower(chan, watchtower)
             except aiohttp.client_exceptions.ClientConnectorError:
                 self.logger.info(f'could not contact remote watchtower {watchtower_url}')
@@ -574,9 +576,7 @@ class LNWallet(LNWorker):
         # return one item per payment_hash
         # note: with AMP we will have several channels per payment
         out = defaultdict(list)
-        with self.lock:
-            channels = list(self.channels.values())
-        for chan in channels:
+        for chan in self.channels.values():
             d = chan.get_settled_payments()
             for k, v in d.items():
                 out[k].append(v)
@@ -628,9 +628,7 @@ class LNWallet(LNWorker):
     def get_onchain_history(self):
         out = {}
         # add funding events
-        with self.lock:
-            channels = list(self.channels.values())
-        for chan in channels:
+        for chan in self.channels.values():
             item = chan.get_funding_height()
             if item is None:
                 continue
@@ -693,8 +691,7 @@ class LNWallet(LNWorker):
 
     def channels_for_peer(self, node_id):
         assert type(node_id) is bytes
-        with self.lock:
-            return {x: y for (x, y) in self.channels.items() if y.node_id == node_id}
+        return {x: y for (x, y) in self.channels.items() if y.node_id == node_id}
 
     def channel_state_changed(self, chan):
         self.save_channel(chan)
@@ -708,9 +705,7 @@ class LNWallet(LNWorker):
         util.trigger_callback('channel', chan)
 
     def channel_by_txo(self, txo):
-        with self.lock:
-            channels = list(self.channels.values())
-        for chan in channels:
+        for chan in self.channels.values():
             if chan.funding_outpoint.to_str() == txo:
                 return chan
 
@@ -762,7 +757,7 @@ class LNWallet(LNWorker):
 
     def add_channel(self, chan):
         with self.lock:
-            self.channels[chan.channel_id] = chan
+            self._channels[chan.channel_id] = chan
         self.lnwatcher.add_channel(chan.funding_outpoint.to_str(), chan.get_funding_address())
 
     def add_new_channel(self, chan):
@@ -805,10 +800,9 @@ class LNWallet(LNWorker):
         success = fut.result()
 
     def get_channel_by_short_id(self, short_channel_id: ShortChannelID) -> Channel:
-        with self.lock:
-            for chan in self.channels.values():
-                if chan.short_channel_id == short_channel_id:
-                    return chan
+        for chan in self.channels.values():
+            if chan.short_channel_id == short_channel_id:
+                return chan
 
     async def _pay(self, invoice, amount_sat=None, attempts=1) -> bool:
         lnaddr = self._check_invoice(invoice, amount_sat)
@@ -981,8 +975,7 @@ class LNWallet(LNWorker):
         # if there are multiple hints, we will use the first one that works,
         # from a random permutation
         random.shuffle(r_tags)
-        with self.lock:
-            channels = list(self.channels.values())
+        channels = list(self.channels.values())
         scid_to_my_channels = {chan.short_channel_id: chan for chan in channels
                                if chan.short_channel_id is not None}
         for private_route in r_tags:
@@ -1196,8 +1189,7 @@ class LNWallet(LNWorker):
     async def _calc_routing_hints_for_invoice(self, amount_sat: Optional[int]):
         """calculate routing hints (BOLT-11 'r' field)"""
         routing_hints = []
-        with self.lock:
-            channels = list(self.channels.values())
+        channels = list(self.channels.values())
         scid_to_my_channels = {chan.short_channel_id: chan for chan in channels
                                if chan.short_channel_id is not None}
         ignore_min_htlc_value = False
@@ -1251,24 +1243,27 @@ class LNWallet(LNWorker):
 
     def get_balance(self):
         with self.lock:
-            return Decimal(sum(chan.balance(LOCAL) if not chan.is_closed() else 0 for chan in self.channels.values()))/1000
+            return Decimal(sum(chan.balance(LOCAL) if not chan.is_closed() else 0
+                               for chan in self.channels.values())) / 1000
 
     def num_sats_can_send(self) -> Union[Decimal, int]:
         with self.lock:
-            return Decimal(max(chan.available_to_spend(LOCAL) if chan.is_open() else 0 for chan in self.channels.values()))/1000 if self.channels else 0
+            return Decimal(max(chan.available_to_spend(LOCAL) if chan.is_open() else 0
+                               for chan in self.channels.values()))/1000 if self.channels else 0
 
     def num_sats_can_receive(self) -> Union[Decimal, int]:
         with self.lock:
-            return Decimal(max(chan.available_to_spend(REMOTE) if chan.is_open() else 0 for chan in self.channels.values()))/1000 if self.channels else 0
+            return Decimal(max(chan.available_to_spend(REMOTE) if chan.is_open() else 0
+                               for chan in self.channels.values()))/1000 if self.channels else 0
 
     async def close_channel(self, chan_id):
-        chan = self.channels[chan_id]
+        chan = self._channels[chan_id]
         peer = self._peers[chan.node_id]
         return await peer.close_channel(chan_id)
 
     async def force_close_channel(self, chan_id):
         # returns txid or raises
-        chan = self.channels[chan_id]
+        chan = self._channels[chan_id]
         tx = chan.force_close_tx()
         await self.network.broadcast_transaction(tx)
         chan.set_state(ChannelState.FORCE_CLOSING)
@@ -1276,16 +1271,16 @@ class LNWallet(LNWorker):
 
     async def try_force_closing(self, chan_id):
         # fails silently but sets the state, so that we will retry later
-        chan = self.channels[chan_id]
+        chan = self._channels[chan_id]
         tx = chan.force_close_tx()
         chan.set_state(ChannelState.FORCE_CLOSING)
         await self.network.try_broadcasting(tx, 'force-close')
 
     def remove_channel(self, chan_id):
-        chan = self.channels[chan_id]
+        chan = self._channels[chan_id]
         assert chan.get_state() == ChannelState.REDEEMED
         with self.lock:
-            self.channels.pop(chan_id)
+            self._channels.pop(chan_id)
             self.db.get('channels').pop(chan_id.hex())
 
         util.trigger_callback('channels_updated', self.wallet)
@@ -1316,9 +1311,7 @@ class LNWallet(LNWorker):
     async def reestablish_peers_and_channels(self):
         while True:
             await asyncio.sleep(1)
-            with self.lock:
-                channels = list(self.channels.values())
-            for chan in channels:
+            for chan in self.channels.values():
                 if chan.is_closed():
                     continue
                 # reestablish
@@ -1340,7 +1333,7 @@ class LNWallet(LNWorker):
         return max(253, feerate_per_kvbyte // 4)
 
     def create_channel_backup(self, channel_id):
-        chan = self.channels[channel_id]
+        chan = self._channels[channel_id]
         peer_addresses = list(chan.get_peer_addresses())
         peer_addr = peer_addresses[0]
         return ChannelBackupStorage(

electrum/tests/test_lnpeer.py

@@ -102,7 +102,7 @@ class MockLNWallet(Logger, NetworkRetryManager[LNPeerAddr]):
         self.remote_keypair = remote_keypair
         self.node_keypair = local_keypair
         self.network = MockNetwork(tx_queue)
-        self.channels = {chan.channel_id: chan}
+        self._channels = {chan.channel_id: chan}
         self.payments = {}
         self.logs = defaultdict(list)
         self.wallet = MockWallet()
@@ -122,6 +122,10 @@ class MockLNWallet(Logger, NetworkRetryManager[LNPeerAddr]):
     def lock(self):
         return noop_lock()
 
+    @property
+    def channels(self):
+        return self._channels
+
     @property
     def peers(self):
         return self._peers
@@ -131,11 +135,11 @@ class MockLNWallet(Logger, NetworkRetryManager[LNPeerAddr]):
         return {self.remote_keypair.pubkey: self.peer}
 
     def channels_for_peer(self, pubkey):
-        return self.channels
+        return self._channels
 
     def get_channel_by_short_id(self, short_channel_id):
         with self.lock:
-            for chan in self.channels.values():
+            for chan in self._channels.values():
                 if chan.short_channel_id == short_channel_id:
                     return chan