fix: parsing date fails due to thread race

Two python threads can call get_date_helper() simultaneously, causing a
partially-contstructed DateHelper object to be returned to the caller.

Author: Rob Dinoff

influxdb_client/client/util/date_utils.py

@@ -1,11 +1,13 @@
 """Utils to get right Date parsing function."""
 import datetime
+import threading
 from datetime import timezone as tz
 
 from dateutil import parser
 
 date_helper = None
 
+lock_ = threading.Lock()
 
 class DateHelper:
     """
@@ -78,12 +80,13 @@ def get_date_helper() -> DateHelper:
     If there is a 'ciso8601' than use 'ciso8601.parse_datetime' else use 'dateutil.parse'.
     """
     global date_helper
-    if date_helper is None:
-        date_helper = DateHelper()
-        try:
-            import ciso8601
-            date_helper.parse_date = ciso8601.parse_datetime
-        except ModuleNotFoundError:
-            date_helper.parse_date = parser.parse
+    with lock_:
+        if date_helper is None:
+            date_helper = DateHelper()
+            try:
+                import ciso8601
+                date_helper.parse_date = ciso8601.parse_datetime
+            except ModuleNotFoundError:
+                date_helper.parse_date = parser.parse
 
     return date_helper