gh-160683: Stop half-closing the remote debugging interrupt socket

Author: summeriver13

Lib/pdb.py

@@ -3006,7 +3006,10 @@ def listener(sock):
                 # Check if the interpreter is finalizing every quarter of a second.
                 # Clean up and exit if so.
                 sock.settimeout(0.25)
-                sock.shutdown(socket.SHUT_WR)
+                # Never half-close this socket: the client only writes to it,
+                # and a half-closed connection waits in FIN_WAIT_2, which
+                # Windows resets after 120 seconds, taking the interrupt
+                # channel of a long-idle session with it. See gh-160683.
                 while not shut_down.is_set():
                     try:
                         data = sock.recv(1024)

Lib/test/test_remote_pdb.py

@@ -835,6 +835,41 @@ def test_reading_empty_json_during_completion(self):
         )
 
 
+@requires_subprocess()
+class SignalListenerTestCase(unittest.TestCase):
+    def test_interrupt_socket_is_not_half_closed(self):
+        # gh-160683: half-closing leaves the connection in FIN_WAIT_2, which
+        # Windows tears down after 120 seconds, so a session that has been
+        # idle that long loses its interrupt channel.
+        # The listener thread is kept alive by an atexit callback and cannot be
+        # joined, so start it in a subprocess to leave this interpreter's
+        # thread bookkeeping untouched.
+        with closing(socket.socket()) as listener:
+            listener.bind(("127.0.0.1", 0))
+            listener.listen(1)
+            listener.settimeout(SHORT_TIMEOUT)
+            code = textwrap.dedent(f"""
+                import sys
+                from pdb import _PdbServer
+
+                _PdbServer._start_signal_listener({listener.getsockname()})
+                sys.stdin.read()
+            """)
+            with subprocess.Popen(
+                [sys.executable, "-c", code], stdin=subprocess.PIPE
+            ) as process:
+                with closing(listener.accept()[0]) as conn:
+                    conn.settimeout(1.0)
+                    try:
+                        data = conn.recv(1024)
+                    except TimeoutError:
+                        pass
+                    else:
+                        self.fail(
+                            f"interrupt socket returned {data!r} instead of staying open"
+                        )
+
+
 class RemotePdbTestCase(unittest.TestCase):
     """Tests for the _PdbServer class."""
 

Misc/NEWS.d/next/Library/2026-10-26-03-58-12.gh-issue-160683.Kz3q1P.rst

@@ -0,0 +1,5 @@
+Keep the interrupt channel of a remote debugging session open.
+
+Half-closing it left the connection in FIN_WAIT_2, which Windows resets
+after 120 seconds, so an idle session silently lost the ability to
+interrupt the debuggee.