gh-127586: properly restore blocked signals in resource_tracker.py

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

Misc/NEWS.d/next/Library/2024-12-03-20-28-08.gh-issue-127586.zgotYF.rst

@@ -0,0 +1,6 @@
+:class:`multiprocessing.pool.Pool` now properly restores blocked signal handlers
+of the parent thread when creating processes via either *spawn* or
+*forkserver*. Previously it would unblock **SIGTERM** and **SIGINT** in the
+parent thread on construction, even if either signal handler was
+intentionally blocked prior to the call to construct. Additionally, child
+processes can now inherit said blocked signals.