Don't configure the number of workers for default threadpool executor.

See CPython issue #26796.  Initial patch by Hans Lawrenz.

Author: 1st1

asyncio/base_events.py

@@ -41,9 +41,6 @@
 __all__ = ['BaseEventLoop']
 
 
-# Argument for default thread pool executor creation.
-_MAX_WORKERS = 5
-
 # Minimum number of _scheduled timer handles before cleanup of
 # cancelled handles is performed.
 _MIN_SCHEDULED_TIMER_HANDLES = 100
@@ -619,7 +616,7 @@ def run_in_executor(self, executor, func, *args):
         if executor is None:
             executor = self._default_executor
             if executor is None:
-                executor = concurrent.futures.ThreadPoolExecutor(_MAX_WORKERS)
+                executor = concurrent.futures.ThreadPoolExecutor()
                 self._default_executor = executor
         return futures.wrap_future(executor.submit(func, *args), loop=self)