type annotations for non-blocking DB connection

nominatim/db/async_connection.py

@@ -4,8 +4,9 @@
 #
 # Copyright (C) 2022 by the Nominatim developer community.
 # For a full list of authors see the git log.
-""" Database helper functions for the indexer.
+""" Non-blocking database connections.
 """
+from typing import Callable, Any, Optional, List, Iterator
 import logging
 import select
 import time
@@ -21,6 +22,8 @@ try:
 except ImportError:
     __has_psycopg2_errors__ = False
 
+from nominatim.typing import T_cursor
+
 LOG = logging.getLogger()
 
 class DeadlockHandler:
@@ -29,14 +32,14 @@ class DeadlockHandler:
         normally.
     """
 
-    def __init__(self, handler, ignore_sql_errors=False):
+    def __init__(self, handler: Callable[[], None], ignore_sql_errors: bool = False) -> None:
         self.handler = handler
         self.ignore_sql_errors = ignore_sql_errors
 
-    def __enter__(self):
+    def __enter__(self) -> 'DeadlockHandler':
         return self
 
-    def __exit__(self, exc_type, exc_value, traceback):
+    def __exit__(self, exc_type: Any, exc_value: Any, traceback: Any) -> bool:
         if __has_psycopg2_errors__:
             if exc_type == psycopg2.errors.DeadlockDetected: # pylint: disable=E1101
                 self.handler()
@@ -57,26 +60,31 @@ class DBConnection:
     """ A single non-blocking database connection.
     """
 
-    def __init__(self, dsn, cursor_factory=None, ignore_sql_errors=False):
-        self.current_query = None
-        self.current_params = None
+    def __init__(self, dsn: str,
+                 cursor_factory: Optional[Callable[..., T_cursor]] = None,
+                 ignore_sql_errors: bool = False) -> None:
         self.dsn = dsn
+
+        self.current_query: Optional[str] = None
+        self.current_params: Optional[List[Any]] = None
         self.ignore_sql_errors = ignore_sql_errors
 
-        self.conn = None
-        self.cursor = None
+        self.conn: Optional['psycopg2.connection'] = None
+        self.cursor: Optional['psycopg2.cursor'] = None
         self.connect(cursor_factory=cursor_factory)
 
-    def close(self):
+    def close(self) -> None:
         """ Close all open connections. Does not wait for pending requests.
         """
         if self.conn is not None:
-            self.cursor.close()
+            if self.cursor is not None:
+                self.cursor.close() # type: ignore[no-untyped-call]
+                self.cursor = None
             self.conn.close()
 
         self.conn = None
 
-    def connect(self, cursor_factory=None):
+    def connect(self, cursor_factory: Optional[Callable[..., T_cursor]] = None) -> None:
         """ (Re)connect to the database. Creates an asynchronous connection
             with JIT and parallel processing disabled. If a connection was
             already open, it is closed and a new connection established.
@@ -89,7 +97,10 @@ class DBConnection:
         self.conn = psycopg2.connect(**{'dsn': self.dsn, 'async': True})
         self.wait()
 
-        self.cursor = self.conn.cursor(cursor_factory=cursor_factory)
+        if cursor_factory is not None:
+            self.cursor = self.conn.cursor(cursor_factory=cursor_factory)
+        else:
+            self.cursor = self.conn.cursor()
         # Disable JIT and parallel workers as they are known to cause problems.
         # Update pg_settings instead of using SET because it does not yield
         # errors on older versions of Postgres where the settings are not
@@ -100,11 +111,15 @@ class DBConnection:
                    WHERE name = 'max_parallel_workers_per_gather';""")
         self.wait()
 
-    def _deadlock_handler(self):
+    def _deadlock_handler(self) -> None:
         LOG.info("Deadlock detected (params = %s), retry.", str(self.current_params))
+        assert self.cursor is not None
+        assert self.current_query is not None
+        assert self.current_params is not None
+
         self.cursor.execute(self.current_query, self.current_params)
 
-    def wait(self):
+    def wait(self) -> None:
         """ Block until any pending operation is done.
         """
         while True:
@@ -113,25 +128,29 @@ class DBConnection:
                 self.current_query = None
                 return
 
-    def perform(self, sql, args=None):
+    def perform(self, sql: str, args: Optional[List[Any]] = None) -> None:
         """ Send SQL query to the server. Returns immediately without
             blocking.
         """
+        assert self.cursor is not None
         self.current_query = sql
         self.current_params = args
         self.cursor.execute(sql, args)
 
-    def fileno(self):
+    def fileno(self) -> int:
         """ File descriptor to wait for. (Makes this class select()able.)
         """
+        assert self.conn is not None
         return self.conn.fileno()
 
-    def is_done(self):
+    def is_done(self) -> bool:
         """ Check if the connection is available for a new query.
 
             Also checks if the previous query has run into a deadlock.
             If so, then the previous query is repeated.
         """
+        assert self.conn is not None
+
         if self.current_query is None:
             return True
 
@@ -150,14 +169,14 @@ class WorkerPool:
     """
     REOPEN_CONNECTIONS_AFTER = 100000
 
-    def __init__(self, dsn, pool_size, ignore_sql_errors=False):
+    def __init__(self, dsn: str, pool_size: int, ignore_sql_errors: bool = False) -> None:
         self.threads = [DBConnection(dsn, ignore_sql_errors=ignore_sql_errors)
                         for _ in range(pool_size)]
         self.free_workers = self._yield_free_worker()
-        self.wait_time = 0
+        self.wait_time = 0.0
 
 
-    def finish_all(self):
+    def finish_all(self) -> None:
         """ Wait for all connection to finish.
         """
         for thread in self.threads:
@@ -166,22 +185,22 @@ class WorkerPool:
 
         self.free_workers = self._yield_free_worker()
 
-    def close(self):
+    def close(self) -> None:
         """ Close all connections and clear the pool.
         """
         for thread in self.threads:
             thread.close()
         self.threads = []
-        self.free_workers = None
+        self.free_workers = iter([])
 
 
-    def next_free_worker(self):
+    def next_free_worker(self) -> DBConnection:
         """ Get the next free connection.
         """
         return next(self.free_workers)
 
 
-    def _yield_free_worker(self):
+    def _yield_free_worker(self) -> Iterator[DBConnection]:
         ready = self.threads
         command_stat = 0
         while True:
@@ -200,17 +219,17 @@ class WorkerPool:
                 self.wait_time += time.time() - tstart
 
 
-    def _reconnect_threads(self):
+    def _reconnect_threads(self) -> None:
         for thread in self.threads:
             while not thread.is_done():
                 thread.wait()
             thread.connect()
 
 
-    def __enter__(self):
+    def __enter__(self) -> 'WorkerPool':
         return self
 
 
-    def __exit__(self, exc_type, exc_value, traceback):
+    def __exit__(self, exc_type: Any, exc_value: Any, traceback: Any) -> None:
         self.finish_all()
         self.close()