caching: add globals for global caching structure

globals.py

+import sqlalchemy
+import threading
+
+dirty_table = {}
+dirty_table_lock = threading.RLock()
+
+
+def is_dirty(table):
+    global dirty_table
+    global dirty_table_lock
+
+    with dirty_table_lock:
+        try:
+            return dirty_table[table]
+        except KeyError:
+            dirty_table[table] = False
+            return False
+
+
+def set_dirty(table, value=True):
+    global dirty_table
+    global dirty_table_lock
+
+    if type(table) is sqlalchemy.ext.declarative.api.DeclarativeMeta:
+        table = table.__tablename__
+
+    with dirty_table_lock:
+        dirty_table[table] = value