gh-139391: properly handle signal.signal() in UnixConsole when called from a non-main thread

Lib/_pyrepl/unix_console.py

@@ -28,6 +28,7 @@
 import signal
 import struct
 import termios
+import threading
 import time
 import types
 import platform
@@ -390,7 +391,15 @@ def restore(self):
             os.write(self.output_fd, b"\033[?7h")
 
         if hasattr(self, "old_sigwinch"):
-            signal.signal(signal.SIGWINCH, self.old_sigwinch)
+            if os.name != 'nt':
+                try:
+                    signal.signal(signal.SIGWINCH, self.old_sigwinch)
+                except ValueError as e:
+                    # We can silence the ValueError if signal.signal() raised it
+                    # from a non-main thread on a non-Windows platform. Otherwise,
+                    # we need to re-raise it as its cause could be different.
+                    if threading.current_thread() is threading.main_thread():
+                            raise e
             del self.old_sigwinch
 
     def push_char(self, char: int | bytes) -> None:

Lib/test/test_pyrepl/test_unix_console.py

@@ -317,6 +317,24 @@ def test_restore_with_invalid_environ_on_macos(self, _os_write):
             console.prepare()  # needed to call restore()
             console.restore()  # this should succeed
 
+    def test_restore_in_thread(self, _os_write):
+        # for gh-139391
+        import threading
+        console = unix_console([])
+        console.old_sigwinch = signal.SIG_DFL
+        exception_caught = []
+        def thread_target():
+            try:
+                console.restore()
+            except Exception as e:
+                exception_caught.append(e)
+        thread = threading.Thread(target=thread_target)
+        thread.start()
+        thread.join()
+        # gh-139391: should not raise any exception when called from non-main thread
+        self.assertEqual(len(exception_caught), 0,
+                        "restore() should not raise any exception in non-main thread")
+
 
 @unittest.skipIf(sys.platform == "win32", "No Unix console on Windows")
 class TestUnixConsoleEIOHandling(TestCase):

Misc/NEWS.d/next/Library/2025-09-28-16-34-11.gh-issue-139391.nRFnmx.rst

@@ -0,0 +1,2 @@
+Fix crash in PyREPL asyncio mode when using Ctrl+Z (suspend) followed by
+``fg`` (resume).