introduce mutex to avoid multiple token refresh when using threads.

mdrsclient/api/utils.py

@@ -4,12 +4,16 @@ from mdrsclient.exceptions import UnauthorizedException
 
 
 def token_check(connection: MDRSConnection) -> None:
-    if connection.token is not None:
-        if connection.token.is_refresh_required:
-            user_api = UserApi(connection)
-            try:
-                connection.token = user_api.refresh(connection.token)
-            except UnauthorizedException:
+    try:
+        connection.lock.acquire()
+        if connection.token is not None:
+            if connection.token.is_refresh_required:
+                user_api = UserApi(connection)
+                try:
+                    connection.token = user_api.refresh(connection.token)
+                except UnauthorizedException:
+                    connection.logout()
+            elif connection.token.is_expired:
                 connection.logout()
-        elif connection.token.is_expired:
-            connection.logout()
+    finally:
+        connection.lock.release()