Add mutex for backfill method

mautrix_telegram/portal/base.py

@@ -96,6 +96,7 @@ class BasePortal(MautrixBasePortal, ABC):
     encrypted: bool
     deleted: bool
     backfill_lock: SimpleLock
+    backfill_method_lock: asyncio.Lock
     backfill_leave: Optional[Set[IntentAPI]]
     log: TraceLogger
 
@@ -131,6 +132,7 @@ class BasePortal(MautrixBasePortal, ABC):
         self.log = self.base_log.getChild(self.tgid_log if self.tgid else self.mxid)
         self.backfill_lock = SimpleLock("Waiting for backfilling to finish before handling %s",
                                         log=self.log)
+        self.backfill_method_lock = asyncio.Lock()
         self.backfill_leave = None
 
         self.dedup = PortalDedup(self)

mautrix_telegram/portal/telegram.py

@@ -441,6 +441,11 @@ class PortalTelegram(BasePortal, ABC):
 
     async def backfill(self, source: 'AbstractUser', is_initial: bool = False,
                        limit: Optional[int] = None, last_id: Optional[int] = None) -> None:
+        async with self.backfill_method_lock:
+            await self._locked_backfill(source, is_initial, limit, last_id)
+
+    async def _locked_backfill(self, source: 'AbstractUser', is_initial: bool = False,
+                               limit: Optional[int] = None, last_id: Optional[int] = None) -> None:
         limit = limit or (config["bridge.backfill.initial_limit"] if is_initial
                           else config["bridge.backfill.missed_limit"])
         if limit == 0: