Clean up ShardedWorkerHandlingConfig

synapse/config/_base.py

@@ -876,4 +876,20 @@ def get_instance(self, key: str) -> str:
         return self.instances[remainder]
 
 
+@attr.s
+class RoutableShardedWorkerHandlingConfig(ShardedWorkerHandlingConfig):
+    """A version of `ShardedWorkerHandlingConfig` that is used for config
+    options where all instances know which instances are responsible for the
+    sharded work.
+    """
+
+    def __attrs_post_init__(self):
+        # We require that `self.instances` is non-empty.
+        assert self.instances
+
+    def get_instance(self, key: str) -> str:
+        """Get the instance responsible for handling the given key."""
+        return self._get_instance(key)
+
+
 __all__ = ["Config", "RootConfig", "ShardedWorkerHandlingConfig"]

synapse/config/_base.pyi

@@ -149,4 +149,6 @@ class ShardedWorkerHandlingConfig:
     instances: List[str]
     def __init__(self, instances: List[str]) -> None: ...
     def should_handle(self, instance_name: str, key: str) -> bool: ...
+
+class RoutableShardedWorkerHandlingConfig(ShardedWorkerHandlingConfig):
     def get_instance(self, key: str) -> str: ...

synapse/config/workers.py

@@ -17,7 +17,12 @@
 
 import attr
 
-from ._base import Config, ConfigError, ShardedWorkerHandlingConfig
+from ._base import (
+    Config,
+    ConfigError,
+    RoutableShardedWorkerHandlingConfig,
+    ShardedWorkerHandlingConfig,
+)
 from .server import ListenerConfig, parse_listener_def
 
 
@@ -164,7 +169,9 @@ def read_config(self, config, **kwargs):
                 "Must only specify one instance to handle `receipts` messages."
             )
 
-        self.events_shard_config = ShardedWorkerHandlingConfig(self.writers.events)
+        self.events_shard_config = RoutableShardedWorkerHandlingConfig(
+            self.writers.events
+        )
 
         # Whether this worker should run background tasks or not.
         #