From be7314ffac270bf2a52eeb4d685da631b405c973 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Sun, 29 Dec 2024 20:02:59 +0100
Subject: [PATCH] [3.12] gh-127586: multiprocessing.Pool does not properly
 restore blocked signals (try 2) (GH-128011) (#128299)

gh-127586: multiprocessing.Pool does not properly restore blocked signals (try 2) (GH-128011)

Correct pthread_sigmask in resource_tracker to restore old signals

Using SIG_UNBLOCK to remove blocked "ignored signals" may accidentally
cause side effects if the calling parent already had said signals
blocked to begin with and did not intend to unblock them when
creating a pool. Use SIG_SETMASK instead with the previous mask of
blocked signals to restore the original blocked set.
(cherry picked from commit aeb9b65aa26444529e4adc7d6e5b0d3dd9889ec2)

Co-authored-by: Stephen Hansen <stephen.paul.hansen@gmail.com>
Co-authored-by: Peter Bierma <zintensitydev@gmail.com>
Co-authored-by: Gregory P. Smith <greg@krypto.org>
---
 Lib/multiprocessing/resource_tracker.py       |  7 ++++---
 Lib/test/_test_multiprocessing.py             | 21 +++++++++++++++++++
 ...-12-03-20-28-08.gh-issue-127586.zgotYF.rst |  3 +++
 3 files changed, 28 insertions(+), 3 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2024-12-03-20-28-08.gh-issue-127586.zgotYF.rst

diff --git a/Lib/multiprocessing/resource_tracker.py b/Lib/multiprocessing/resource_tracker.py
index 79e96ecf3245f4..23fea295c357a5 100644
--- a/Lib/multiprocessing/resource_tracker.py
+++ b/Lib/multiprocessing/resource_tracker.py
@@ -142,13 +142,14 @@ def ensure_running(self):
                 # that can make the child die before it registers signal handlers
                 # for SIGINT and SIGTERM. The mask is unregistered after spawning
                 # the child.
+                prev_sigmask = None
                 try:
                     if _HAVE_SIGMASK:
-                        signal.pthread_sigmask(signal.SIG_BLOCK, _IGNORED_SIGNALS)
+                        prev_sigmask = signal.pthread_sigmask(signal.SIG_BLOCK, _IGNORED_SIGNALS)
                     pid = util.spawnv_passfds(exe, args, fds_to_pass)
                 finally:
-                    if _HAVE_SIGMASK:
-                        signal.pthread_sigmask(signal.SIG_UNBLOCK, _IGNORED_SIGNALS)
+                    if prev_sigmask is not None:
+                        signal.pthread_sigmask(signal.SIG_SETMASK, prev_sigmask)
             except:
                 os.close(w)
                 raise
diff --git a/Lib/test/_test_multiprocessing.py b/Lib/test/_test_multiprocessing.py
index 3b4415b50ae2c2..85b7290b5a516c 100644
--- a/Lib/test/_test_multiprocessing.py
+++ b/Lib/test/_test_multiprocessing.py
@@ -5826,6 +5826,27 @@ def test_too_long_name_resource(self):
             resource_tracker.register(too_long_name_resource, rtype)
 
 
+    @unittest.skipUnless(hasattr(signal, "pthread_sigmask"), "pthread_sigmask is not available")
+    def test_resource_tracker_blocked_signals(self):
+        #
+        # gh-127586: Check that resource_tracker does not override blocked signals of caller.
+        #
+        from multiprocessing.resource_tracker import ResourceTracker
+        orig_sigmask = signal.pthread_sigmask(signal.SIG_BLOCK, set())
+        signals = {signal.SIGTERM, signal.SIGINT, signal.SIGUSR1}
+
+        try:
+            for sig in signals:
+                signal.pthread_sigmask(signal.SIG_SETMASK, {sig})
+                self.assertEqual(signal.pthread_sigmask(signal.SIG_BLOCK, set()), {sig})
+                tracker = ResourceTracker()
+                tracker.ensure_running()
+                self.assertEqual(signal.pthread_sigmask(signal.SIG_BLOCK, set()), {sig})
+                tracker._stop()
+        finally:
+            # restore sigmask to what it was before executing test
+            signal.pthread_sigmask(signal.SIG_SETMASK, orig_sigmask)
+
 class TestSimpleQueue(unittest.TestCase):
 
     @classmethod
diff --git a/Misc/NEWS.d/next/Library/2024-12-03-20-28-08.gh-issue-127586.zgotYF.rst b/Misc/NEWS.d/next/Library/2024-12-03-20-28-08.gh-issue-127586.zgotYF.rst
new file mode 100644
index 00000000000000..80217bd4a10503
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-12-03-20-28-08.gh-issue-127586.zgotYF.rst
@@ -0,0 +1,3 @@
+:class:`multiprocessing.pool.Pool` now properly restores blocked signal handlers
+of the parent thread when creating processes via either *spawn* or
+*forkserver*.