Make sure that we close db connections opened during init

We should explicitly close any db connections we open, because failing to do so
can block other transactions as per
https://github.com/matrix-org/synapse/issues/3682.

Let's also try to factor out some of the boilerplate by having server classes
define their datastore class rather than duplicating the whole of `setup`.

synapse/app/appservice.py

@@ -51,10 +51,7 @@ class AppserviceSlaveStore(
 
 
 class AppserviceServer(HomeServer):
-    def setup(self):
-        logger.info("Setting up.")
-        self.datastore = AppserviceSlaveStore(self.get_db_conn(), self)
-        logger.info("Finished setting up.")
+    DATASTORE_CLASS = AppserviceSlaveStore
 
     def _listen_http(self, listener_config):
         port = listener_config["port"]

synapse/app/client_reader.py

@@ -74,10 +74,7 @@ class ClientReaderSlavedStore(
 
 
 class ClientReaderServer(HomeServer):
-    def setup(self):
-        logger.info("Setting up.")
-        self.datastore = ClientReaderSlavedStore(self.get_db_conn(), self)
-        logger.info("Finished setting up.")
+    DATASTORE_CLASS = ClientReaderSlavedStore
 
     def _listen_http(self, listener_config):
         port = listener_config["port"]

synapse/app/event_creator.py

@@ -90,10 +90,7 @@ class EventCreatorSlavedStore(
 
 
 class EventCreatorServer(HomeServer):
-    def setup(self):
-        logger.info("Setting up.")
-        self.datastore = EventCreatorSlavedStore(self.get_db_conn(), self)
-        logger.info("Finished setting up.")
+    DATASTORE_CLASS = EventCreatorSlavedStore
 
     def _listen_http(self, listener_config):
         port = listener_config["port"]

synapse/app/federation_reader.py

@@ -72,10 +72,7 @@ class FederationReaderSlavedStore(
 
 
 class FederationReaderServer(HomeServer):
-    def setup(self):
-        logger.info("Setting up.")
-        self.datastore = FederationReaderSlavedStore(self.get_db_conn(), self)
-        logger.info("Finished setting up.")
+    DATASTORE_CLASS = FederationReaderSlavedStore
 
     def _listen_http(self, listener_config):
         port = listener_config["port"]

synapse/app/federation_sender.py

@@ -78,10 +78,7 @@ class FederationSenderSlaveStore(
 
 
 class FederationSenderServer(HomeServer):
-    def setup(self):
-        logger.info("Setting up.")
-        self.datastore = FederationSenderSlaveStore(self.get_db_conn(), self)
-        logger.info("Finished setting up.")
+    DATASTORE_CLASS = FederationSenderSlaveStore
 
     def _listen_http(self, listener_config):
         port = listener_config["port"]

synapse/app/frontend_proxy.py

@@ -148,10 +148,7 @@ class FrontendProxySlavedStore(
 
 
 class FrontendProxyServer(HomeServer):
-    def setup(self):
-        logger.info("Setting up.")
-        self.datastore = FrontendProxySlavedStore(self.get_db_conn(), self)
-        logger.info("Finished setting up.")
+    DATASTORE_CLASS = FrontendProxySlavedStore
 
     def _listen_http(self, listener_config):
         port = listener_config["port"]

synapse/app/homeserver.py

@@ -62,7 +62,7 @@ from synapse.rest.key.v1.server_key_resource import LocalKey
 from synapse.rest.key.v2 import KeyApiV2Resource
 from synapse.rest.media.v0.content_repository import ContentRepoResource
 from synapse.server import HomeServer
-from synapse.storage import are_all_users_on_domain
+from synapse.storage import DataStore, are_all_users_on_domain
 from synapse.storage.engines import IncorrectDatabaseSetup, create_engine
 from synapse.storage.prepare_database import UpgradeDatabaseException, prepare_database
 from synapse.util.caches import CACHE_SIZE_FACTOR
@@ -111,6 +111,8 @@ def build_resource_for_web_client(hs):
 
 
 class SynapseHomeServer(HomeServer):
+    DATASTORE_CLASS = DataStore
+
     def _listener_http(self, config, listener_config):
         port = listener_config["port"]
         bind_addresses = listener_config["bind_addresses"]
@@ -356,13 +358,13 @@ def setup(config_options):
     logger.info("Preparing database: %s...", config.database_config['name'])
 
     try:
-        db_conn = hs.get_db_conn(run_new_connection=False)
-        prepare_database(db_conn, database_engine, config=config)
-        database_engine.on_new_connection(db_conn)
+        with hs.get_db_conn(run_new_connection=False) as db_conn:
+            prepare_database(db_conn, database_engine, config=config)
+            database_engine.on_new_connection(db_conn)
 
-        hs.run_startup_checks(db_conn, database_engine)
+            hs.run_startup_checks(db_conn, database_engine)
 
-        db_conn.commit()
+            db_conn.commit()
     except UpgradeDatabaseException:
         sys.stderr.write(
             "\nFailed to upgrade database.\n"

synapse/app/media_repository.py

@@ -60,10 +60,7 @@ class MediaRepositorySlavedStore(
 
 
 class MediaRepositoryServer(HomeServer):
-    def setup(self):
-        logger.info("Setting up.")
-        self.datastore = MediaRepositorySlavedStore(self.get_db_conn(), self)
-        logger.info("Finished setting up.")
+    DATASTORE_CLASS = MediaRepositorySlavedStore
 
     def _listen_http(self, listener_config):
         port = listener_config["port"]

synapse/app/pusher.py

@@ -78,10 +78,7 @@ class PusherSlaveStore(
 
 
 class PusherServer(HomeServer):
-    def setup(self):
-        logger.info("Setting up.")
-        self.datastore = PusherSlaveStore(self.get_db_conn(), self)
-        logger.info("Finished setting up.")
+    DATASTORE_CLASS = PusherSlaveStore
 
     def remove_pusher(self, app_id, push_key, user_id):
         self.get_tcp_replication().send_remove_pusher(app_id, push_key, user_id)

synapse/app/synchrotron.py

@@ -249,10 +249,7 @@ class SynchrotronApplicationService(object):
 
 
 class SynchrotronServer(HomeServer):
-    def setup(self):
-        logger.info("Setting up.")
-        self.datastore = SynchrotronSlavedStore(self.get_db_conn(), self)
-        logger.info("Finished setting up.")
+    DATASTORE_CLASS = SynchrotronSlavedStore
 
     def _listen_http(self, listener_config):
         port = listener_config["port"]

synapse/app/user_dir.py

@@ -94,10 +94,7 @@ class UserDirectorySlaveStore(
 
 
 class UserDirectoryServer(HomeServer):
-    def setup(self):
-        logger.info("Setting up.")
-        self.datastore = UserDirectorySlaveStore(self.get_db_conn(), self)
-        logger.info("Finished setting up.")
+    DATASTORE_CLASS = UserDirectorySlaveStore
 
     def _listen_http(self, listener_config):
         port = listener_config["port"]

synapse/server.py

@@ -81,7 +81,6 @@ from synapse.server_notices.server_notices_manager import ServerNoticesManager
 from synapse.server_notices.server_notices_sender import ServerNoticesSender
 from synapse.server_notices.worker_server_notices_sender import WorkerServerNoticesSender
 from synapse.state import StateHandler, StateResolutionHandler
-from synapse.storage import DataStore
 from synapse.streams.events import EventSources
 from synapse.util import Clock
 from synapse.util.distributor import Distributor
@@ -172,6 +171,11 @@ class HomeServer(object):
         'room_context_handler',
     ]
 
+    # This is overridden in derived application classes
+    # (such as synapse.app.homeserver.SynapseHomeServer) and gives the class to be
+    # instantiated during setup() for future return by get_datastore()
+    DATASTORE_CLASS = None
+
     def __init__(self, hostname, reactor=None, **kwargs):
         """
         Args:
@@ -188,13 +192,20 @@ class HomeServer(object):
         self.distributor = Distributor()
         self.ratelimiter = Ratelimiter()
 
+        self.datastore = None
+
         # Other kwargs are explicit dependencies
         for depname in kwargs:
             setattr(self, depname, kwargs[depname])
 
     def setup(self):
         logger.info("Setting up.")
-        self.datastore = DataStore(self.get_db_conn(), self)
+        if self.DATASTORE_CLASS is None:
+            raise RuntimeError("%s does not define a DATASTORE_CLASS" % (
+                self.__class__.__name__,
+            ))
+        with self.get_db_conn() as conn:
+            self.datastore = self.DATASTORE_CLASS(conn, self)
         logger.info("Finished setting up.")
 
     def get_reactor(self):