https://github.com/python/cpython/commit/8ed5a2b56cc6a8635e586c641b0b837669f6677b
commit: 8ed5a2b56cc6a8635e586c641b0b837669f6677b
branch: main
author: Albert Zeyer <[email protected]>
committer: gpshead <[email protected]>
date: 2025-09-07T07:18:28Z
summary:
gh-118981: multiprocessing.popen_spawn_posix, fix potential hang (gh-118982)
fix potential hang.
It can happen that the child crashes right in the beginning for whatever
reason. In this case, the parent will hang when writing into the pipe, because
the child fd is not closed yet.
The normal pattern is to close the child fds right after the child proc is
forked/executed/spawned, so when the child dies, then also the pipes will be
closed, and there will be no hang (the parent gets SIGPIPE instead).
files:
A Misc/NEWS.d/next/Library/2024-05-13-09-50-31.gh-issue-118981.zgOQPv.rst
M Lib/multiprocessing/popen_spawn_posix.py
diff --git a/Lib/multiprocessing/popen_spawn_posix.py
b/Lib/multiprocessing/popen_spawn_posix.py
index 24b8634523e5f2..cccd659ae77637 100644
--- a/Lib/multiprocessing/popen_spawn_posix.py
+++ b/Lib/multiprocessing/popen_spawn_posix.py
@@ -57,6 +57,10 @@ def _launch(self, process_obj):
self._fds.extend([child_r, child_w])
self.pid = util.spawnv_passfds(spawn.get_executable(),
cmd, self._fds)
+ os.close(child_r)
+ child_r = None
+ os.close(child_w)
+ child_w = None
self.sentinel = parent_r
with open(parent_w, 'wb', closefd=False) as f:
f.write(fp.getbuffer())
diff --git
a/Misc/NEWS.d/next/Library/2024-05-13-09-50-31.gh-issue-118981.zgOQPv.rst
b/Misc/NEWS.d/next/Library/2024-05-13-09-50-31.gh-issue-118981.zgOQPv.rst
new file mode 100644
index 00000000000000..72b9f6c9e4eb99
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-05-13-09-50-31.gh-issue-118981.zgOQPv.rst
@@ -0,0 +1,2 @@
+Fix potential hang in ``multiprocessing.popen_spawn_posix`` that can happen
+when the child proc dies early by closing the child fds right away.
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