Rename direction to step, apply checks consistently

synapse/storage/__init__.py

@@ -97,7 +97,7 @@ class DataStore(RoomMemberStore, RoomStore,
             db_conn, "events", "stream_ordering"
         )
         self._backfill_id_gen = StreamIdGenerator(
-            db_conn, "events", "stream_ordering", direction=-1
+            db_conn, "events", "stream_ordering", step=-1
         )
         self._receipts_id_gen = StreamIdGenerator(
             db_conn, "receipts_linearized", "stream_id"

synapse/storage/util/id_generators.py

@@ -29,16 +29,16 @@ class IdGenerator(object):
             return self._next_id
 
 
-def _load_current_id(db_conn, table, column, direction=1):
+def _load_current_id(db_conn, table, column, step=1):
     cur = db_conn.cursor()
-    if direction == 1:
+    if step == 1:
         cur.execute("SELECT MAX(%s) FROM %s" % (column, table,))
     else:
         cur.execute("SELECT MIN(%s) FROM %s" % (column, table,))
     val, = cur.fetchone()
     cur.close()
-    current_id = int(val) if val else direction
-    return (max if direction == 1 else min)(current_id, direction)
+    current_id = int(val) if val else step
+    return (max if step > 0 else min)(current_id, step)
 
 
 class StreamIdGenerator(object):
@@ -58,21 +58,21 @@ class StreamIdGenerator(object):
     :param list extra_tables: List of pairs of database tables and columns to
         use to source the initial value of the generator from. The value with
         the largest magnitude is used.
-    :param int direction: which direction the stream ids grow in. +1 to grow
+    :param int step: which direction the stream ids grow in. +1 to grow
         upwards, -1 to grow downwards.
 
     Usage:
         with stream_id_gen.get_next() as stream_id:
             # ... persist event ...
     """
-    def __init__(self, db_conn, table, column, extra_tables=[], direction=1):
+    def __init__(self, db_conn, table, column, extra_tables=[], step=1):
         self._lock = threading.Lock()
-        self._direction = direction
-        self._current = _load_current_id(db_conn, table, column, direction)
+        self._step = step
+        self._current = _load_current_id(db_conn, table, column, step)
         for table, column in extra_tables:
-            self._current = (max if direction > 0 else min)(
+            self._current = (max if step > 0 else min)(
                 self._current,
-                _load_current_id(db_conn, table, column, direction)
+                _load_current_id(db_conn, table, column, step)
             )
         self._unfinished_ids = deque()
 
@@ -83,7 +83,7 @@ class StreamIdGenerator(object):
                 # ... persist event ...
         """
         with self._lock:
-            self._current += self._direction
+            self._current += self._step
             next_id = self._current
 
             self._unfinished_ids.append(next_id)
@@ -106,9 +106,9 @@ class StreamIdGenerator(object):
         """
         with self._lock:
             next_ids = range(
-                self._current + self._direction,
-                self._current + self._direction * (n + 1),
-                self._direction
+                self._current + self._step,
+                self._current + self._step * (n + 1),
+                self._step
             )
             self._current += n
 
@@ -132,7 +132,7 @@ class StreamIdGenerator(object):
         """
         with self._lock:
             if self._unfinished_ids:
-                return self._unfinished_ids[0] - self._direction
+                return self._unfinished_ids[0] - self._step
 
             return self._current