fix: parsing date fails due to thread race (#477)

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

Co-authored-by: Rob Dinoff <rob.dinoff@nokia-bell-labs.com>

Author: rdinoff

CHANGELOG.md

@@ -11,6 +11,9 @@
 ### Others
 1. [#472](https://github.com/influxdata/influxdb-client-python/pull/472): Drop supports for Python 3.6
 
+### Bug Fixes
+1. [#477](https://github.com/influxdata/influxdb-client-python/pull/477): parsing date fails due to thread race
+
 ## 1.31.0 [2022-07-29]
 
 ### Features

influxdb_client/client/util/date_utils.py

@@ -1,11 +1,14 @@
 """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:
     """
@@ -79,11 +82,15 @@ def get_date_helper() -> DateHelper:
     """
     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_:
+            # avoid duplicate initialization
+            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
+                date_helper = _date_helper
 
     return date_helper