From: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com>
Date: Mon, 29 Nov 2021 12:28:46 +0000 (-0800)
Subject: bpo-43498: Fix dictionary iteration error in _ExecutorManagerThread (GH-24868)
X-Git-Tag: v3.9.10~95
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=3b9d886567c4fc6279c2198b6711f0590dbf3336;p=thirdparty%2FPython%2Fcpython.git

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

(cherry picked from commit 7431448b817d3bf87f71661cf8f3d537807ab2e2)

Co-authored-by: Jakub Kulík <Kulikjak@gmail.com>
---

diff --git a/Lib/concurrent/futures/process.py b/Lib/concurrent/futures/process.py
index 90bc98bf2ecd..a29e5247ab85 100644
--- a/Lib/concurrent/futures/process.py
+++ b/Lib/concurrent/futures/process.py
@@ -373,7 +373,7 @@ class _ExecutorManagerThread(threading.Thread):
         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
new file mode 100644
index 000000000000..4713d1427ccd
--- /dev/null
+++ 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`.