add warning if trying to change max_workers and failing

cognite/client/utils/_concurrency.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import functools
+import warnings
 from collections import UserList
 from concurrent.futures import CancelledError, Future, ThreadPoolExecutor, as_completed
 from typing import (
@@ -196,6 +197,9 @@ def get_thread_pool_executor(cls, max_workers: int) -> ThreadPoolExecutor:
         if max_workers < 1:
             raise RuntimeError(f"Number of workers should be >= 1, was {max_workers}")
         try:
+            # TODO: Stop-gap, max_workers should move to global_config and become static.
+            if _THREAD_POOL_EXECUTOR_SINGLETON._max_workers != max_workers:
+                warnings.warn("Can't change 'max_workers' after first API-call has been made.")
             executor = _THREAD_POOL_EXECUTOR_SINGLETON
         except NameError:
             # TPE has not been initialized