From abf8be9c75d954836f2d4f36eca2b4bf76803281 Mon Sep 17 00:00:00 2001
From: Stephen Hansen <stephen.paul.hansen@gmail.com>
Date: Sun, 15 Dec 2024 14:53:22 -0500
Subject: [PATCH] gh-127586: properly restore blocked signals in
 resource_tracker.py (GH-127587)

* 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.

* Adding resource_tracker blocked signals test
(cherry picked from commit 46006a1b355f75d06c10e7b8086912c483b34487)

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                 | 15 +++++++++++++++
 ...2024-12-03-20-28-08.gh-issue-127586.zgotYF.rst |  3 +++
 3 files changed, 22 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 20ddd9c50e3d88..90e036ae905afa 100644
--- a/Lib/multiprocessing/resource_tracker.py
+++ b/Lib/multiprocessing/resource_tracker.py
@@ -155,13 +155,14 @@ 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 ce93d94699ce78..243a6887f2e0a1 100644
--- a/Lib/test/_test_multiprocessing.py
+++ b/Lib/test/_test_multiprocessing.py
@@ -5949,6 +5949,21 @@ def test_resource_tracker_exit_code(self):
                 self._test_resource_tracker_leak_resources(
                     cleanup=cleanup,
                 )
+    @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
+        signals = {signal.SIGTERM, signal.SIGINT, signal.SIGUSR1}
+
+        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()
 
 class TestSimpleQueue(unittest.TestCase):
 
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*.