[Python-checkins] bpo-43498: Fix dictionary iteration error in _ExecutorManagerThread (GH-24868)

[miss-islington]

https://github.com/python/cpython/commit/4b11d7118561a12322d3cfa76c5941690b241149
commit: 4b11d7118561a12322d3cfa76c5941690b241149
branch: 3.10
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: miss-islington <31488909+miss-islington at users.noreply.github.com>
date: 2021-11-29T04:24:08-08:00
summary:

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

(cherry picked from commit 7431448b817d3bf87f71661cf8f3d537807ab2e2)

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

files:
A Misc/NEWS.d/next/Library/2021-04-20-14-14-16.bpo-43498.L_Hq-8.rst
M Lib/concurrent/futures/process.py

diff --git a/Lib/concurrent/futures/process.py b/Lib/concurrent/futures/process.py
index 764719859f7ce..6ee2ce626e456 100644
--- 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
new file mode 100644
index 0000000000000..4713d1427ccd3
--- /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`.