2 files changed, 55 insertions, 0 deletions
diff --git a/synapse/replication/tcp/commands.py b/synapse/replication/tcp/commands.py
index 32f52e54d8..10f5c98ff8 100644
--- a/synapse/replication/tcp/commands.py
+++ b/synapse/replication/tcp/commands.py
@@ -422,6 +422,36 @@ class RemoteServerUpCommand(_SimpleCommand):
     NAME = "REMOTE_SERVER_UP"
 
 
+class LockReleasedCommand(Command):
+    """Sent to inform other instances that a given lock has been dropped.
+
+    Format::
+
+        LOCK_RELEASED ["<instance_name>", "<lock_name>", "<lock_key>"]
+    """
+
+    NAME = "LOCK_RELEASED"
+
+    def __init__(
+        self,
+        instance_name: str,
+        lock_name: str,
+        lock_key: str,
+    ):
+        self.instance_name = instance_name
+        self.lock_name = lock_name
+        self.lock_key = lock_key
+
+    @classmethod
+    def from_line(cls: Type["LockReleasedCommand"], line: str) -> "LockReleasedCommand":
+        instance_name, lock_name, lock_key = json_decoder.decode(line)
+
+        return cls(instance_name, lock_name, lock_key)
+
+    def to_line(self) -> str:
+        return json_encoder.encode([self.instance_name, self.lock_name, self.lock_key])
+
+
 _COMMANDS: Tuple[Type[Command], ...] = (
     ServerCommand,
     RdataCommand,
@@ -435,6 +465,7 @@ _COMMANDS: Tuple[Type[Command], ...] = (
     UserIpCommand,
     RemoteServerUpCommand,
     ClearUserSyncsCommand,
+    LockReleasedCommand,
 )
 
 # Map of command name to command type.
@@ -448,6 +479,7 @@ VALID_SERVER_COMMANDS = (
     ErrorCommand.NAME,
     PingCommand.NAME,
     RemoteServerUpCommand.NAME,
+    LockReleasedCommand.NAME,
 )
 
 # The commands the client is allowed to send
@@ -461,6 +493,7 @@ VALID_CLIENT_COMMANDS = (
     UserIpCommand.NAME,
     ErrorCommand.NAME,
     RemoteServerUpCommand.NAME,
+    LockReleasedCommand.NAME,
 )
 
 
diff --git a/synapse/replication/tcp/handler.py b/synapse/replication/tcp/handler.py
index 5d108fe11b..a2cabba7b1 100644
--- a/synapse/replication/tcp/handler.py
+++ b/synapse/replication/tcp/handler.py
@@ -39,6 +39,7 @@ from synapse.replication.tcp.commands import (
     ClearUserSyncsCommand,
     Command,
     FederationAckCommand,
+    LockReleasedCommand,
     PositionCommand,
     RdataCommand,
     RemoteServerUpCommand,
@@ -248,6 +249,9 @@ class ReplicationCommandHandler:
         if self._is_master or self._should_insert_client_ips:
             self.subscribe_to_channel("USER_IP")
 
+        if hs.config.redis.redis_enabled:
+            self._notifier.add_lock_released_callback(self.on_lock_released)
+
     def subscribe_to_channel(self, channel_name: str) -> None:
         """
         Indicates that we wish to subscribe to a Redis channel by name.
@@ -648,6 +652,17 @@ class ReplicationCommandHandler:
 
         self._notifier.notify_remote_server_up(cmd.data)
 
+    def on_LOCK_RELEASED(
+        self, conn: IReplicationConnection, cmd: LockReleasedCommand
+    ) -> None:
+        """Called when we get a new LOCK_RELEASED command."""
+        if cmd.instance_name == self._instance_name:
+            return
+
+        self._notifier.notify_lock_released(
+            cmd.instance_name, cmd.lock_name, cmd.lock_key
+        )
+
     def new_connection(self, connection: IReplicationConnection) -> None:
         """Called when we have a new connection."""
         self._connections.append(connection)
@@ -754,6 +769,13 @@ class ReplicationCommandHandler:
         """
         self.send_command(RdataCommand(stream_name, self._instance_name, token, data))
 
+    def on_lock_released(
+        self, instance_name: str, lock_name: str, lock_key: str
+    ) -> None:
+        """Called when we released a lock and should notify other instances."""
+        if instance_name == self._instance_name:
+            self.send_command(LockReleasedCommand(instance_name, lock_name, lock_key))
+
 
 UpdateToken = TypeVar("UpdateToken")
 UpdateRow = TypeVar("UpdateRow")