pythongh-94440: Fix issue of ProcessPoolExecutor shutdown hanging

- documentation enhancement

Author: yonatanp

Lib/concurrent/futures/process.py

@@ -364,9 +364,9 @@ def run(self):
             if self.is_shutting_down():
                 self.flag_executor_shutting_down()
 
-                # If only canceled futures remain in pending_work_items, we
-                # should purge them now to avoid waiting forever in our
-                # subsequent call to wait_result_broken_or_wakeup.
+                # When only canceled futures remain in pending_work_items, our
+                # next call to wait_result_broken_or_wakeup would hang forever.
+                # This makes sure we have some running futures or none at all.
                 self.add_call_item_to_queue()
 
                 # Since no new work items can be added, it is safe to shutdown

Misc/ACKS

@@ -1367,6 +1367,7 @@ Thomas Perl
 Mathieu Perreault
 Mark Perrego
 Trevor Perrin
+Yonatan Perry
 Gabriel de Perthuis
 Tim Peters
 Benjamin Peterson