From 061965c584810b97458f229a6ac5b3b79286e743 Mon Sep 17 00:00:00 2001 From: "Miss Islington (bot)" <31488909+miss-islington@users.noreply.github.com> Date: Sat, 22 Nov 2025 21:23:22 +0100 Subject: [PATCH] [3.14] gh-98552: flush std streams in the multiprocessing forkserver before fork (GH-141849) (#141851) gh-98552: flush std streams in the multiprocessing forkserver before fork (GH-141849) * flush std streams in the multiprocessing forkserver before fork * NEWS (cherry picked from commit 58badb1711e12b6e8b5240ab96cdd01b95012de7) Co-authored-by: Gregory P. Smith <68491+gpshead@users.noreply.github.com> --- Lib/multiprocessing/forkserver.py | 1 + .../Library/2025-11-22-18-00-38.gh-issue-98552.d5KNy-.rst | 4 ++++ 2 files changed, 5 insertions(+) create mode 100644 Misc/NEWS.d/next/Library/2025-11-22-18-00-38.gh-issue-98552.d5KNy-.rst diff --git a/Lib/multiprocessing/forkserver.py b/Lib/multiprocessing/forkserver.py index cc8947c5e04f..8a4e8d835b0c 100644 --- a/Lib/multiprocessing/forkserver.py +++ b/Lib/multiprocessing/forkserver.py @@ -326,6 +326,7 @@ def main(listener_fd, alive_r, preload, main_path=None, sys_path=None, len(fds))) child_r, child_w, *fds = fds s.close() + util._flush_std_streams() pid = os.fork() if pid == 0: # Child diff --git a/Misc/NEWS.d/next/Library/2025-11-22-18-00-38.gh-issue-98552.d5KNy-.rst b/Misc/NEWS.d/next/Library/2025-11-22-18-00-38.gh-issue-98552.d5KNy-.rst new file mode 100644 index 000000000000..37a71ac1fff3 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2025-11-22-18-00-38.gh-issue-98552.d5KNy-.rst @@ -0,0 +1,4 @@ +The :mod:`multiprocessing` forkserver process now flushes stdout and stderr +before it forks to avoid the confusion children inheriting any buffered but +not yet written output data. Normally there is none, but when using +:func:`multiprocessing.set_forkserver_preload` there *could* be. -- 2.47.3