bpo-43498: Fix dictionary iteration error in _ExecutorManagerThread (GH-24868)

miss-islington · kulikjak · web-flow · commit 4b11d7118561 · 2021-11-29T04:24:08.000-08:00
(cherry picked from commit 7431448) Co-authored-by: Jakub Kulík <Kulikjak@gmail.com>
diff --git a/Lib/concurrent/futures/process.py b/Lib/concurrent/futures/process.py
@@ -373,7 +373,7 @@ def wait_result_broken_or_wakeup(self):
         assert not self.thread_wakeup._closed
         wakeup_reader = self.thread_wakeup._reader
         readers = [result_reader, wakeup_reader]
-        worker_sentinels = [p.sentinel for p in self.processes.values()]
+        worker_sentinels = [p.sentinel for p in list(self.processes.values())]
         ready = mp.connection.wait(readers + worker_sentinels)
 
         cause = None
diff --git a/Misc/NEWS.d/next/Library/2021-04-20-14-14-16.bpo-43498.L_Hq-8.rst b/Misc/NEWS.d/next/Library/2021-04-20-14-14-16.bpo-43498.L_Hq-8.rst
@@ -0,0 +1,2 @@
+Avoid a possible *"RuntimeError: dictionary changed size during iteration"*
+when adjusting the process count of :class:`ProcessPoolExecutor`.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	`+Avoid a possible "RuntimeError: dictionary changed size during iteration"`
	`2`	+when adjusting the process count of :class:`ProcessPoolExecutor`.