gh-130168: pyrepl can messup and poll is not thread safe

Lib/_pyrepl/unix_console.py

@@ -28,6 +28,7 @@
 import signal
 import struct
 import termios
+import threading
 import time
 import types
 import platform
@@ -157,6 +158,8 @@ def __init__(
 
         self.pollob = poll()
         self.pollob.register(self.input_fd, select.POLLIN)
+        self._poll_lock = threading.RLock()
+        self._polling_thread: threading.Thread | None = None
         self.terminfo = terminfo.TermInfo(term or None)
         self.term = term
 
@@ -325,8 +328,11 @@ def prepare(self):
         """
         Prepare the console for input/output operations.
         """
-        self.__svtermstate = tcgetattr(self.input_fd)
-        raw = self.__svtermstate.copy()
+        # gh-130168: prevents signal handlers from overwriting the original state
+        if not hasattr(self, '_UnixConsole__svtermstate'):
+            self.__svtermstate = tcgetattr(self.input_fd)
+
+        raw = tcgetattr(self.input_fd).copy()
         raw.iflag &= ~(termios.INPCK | termios.ISTRIP | termios.IXON)
         raw.oflag &= ~(termios.OPOST)
         raw.cflag &= ~(termios.CSIZE | termios.PARENB)
@@ -368,7 +374,11 @@ def restore(self):
         self.__disable_bracketed_paste()
         self.__maybe_write_code(self._rmkx)
         self.flushoutput()
-        tcsetattr(self.input_fd, termios.TCSADRAIN, self.__svtermstate)
+
+        if hasattr(self, '_UnixConsole__svtermstate'):
+            tcsetattr(self.input_fd, termios.TCSADRAIN, self.__svtermstate)
+            # Clear the saved state so prepare() can save a fresh one next time
+            del self.__svtermstate
 
         if platform.system() == "Darwin" and os.getenv("TERM_PROGRAM") == "Apple_Terminal":
             os.write(self.output_fd, b"\033[?7h")
@@ -417,10 +427,25 @@ def wait(self, timeout: float | None = None) -> bool:
         """
         Wait for events on the console.
         """
-        return (
-            not self.event_queue.empty()
-            or bool(self.pollob.poll(timeout))
-        )
+        if not self.event_queue.empty():
+            return True
+
+        current_thread = threading.current_thread()
+
+        if self._polling_thread is current_thread:
+            # This is a re-entrant call from the same thread
+            # like old repl runtime error
+            raise RuntimeError("can't re-enter readline")
+
+        if not self._poll_lock.acquire(blocking=False):
+            return False
+
+        try:
+            self._polling_thread = current_thread
+            return bool(self.pollob.poll(timeout))
+        finally:
+            self._polling_thread = None
+            self._poll_lock.release()
 
     def set_cursor_vis(self, visible):
         """
@@ -786,7 +811,10 @@ def __tputs(self, fmt, prog=delayprog):
         # using .get() means that things will blow up
         # only if the bps is actually needed (which I'm
         # betting is pretty unlkely)
-        bps = ratedict.get(self.__svtermstate.ospeed)
+        if hasattr(self, '_UnixConsole__svtermstate'):
+            bps = ratedict.get(self.__svtermstate.ospeed)
+        else:
+            bps = None
         while True:
             m = prog.search(fmt)
             if not m:

Lib/test/test_pyrepl/test_unix_console.py

@@ -1,6 +1,7 @@
 import itertools
 import os
 import sys
+import threading
 import unittest
 from functools import partial
 from test.support import os_helper, force_not_colorized_test_class
@@ -303,3 +304,17 @@ def test_getheightwidth_with_invalid_environ(self, _os_write):
             self.assertIsInstance(console.getheightwidth(), tuple)
             os.environ = []
             self.assertIsInstance(console.getheightwidth(), tuple)
+
+    def test_wait_reentry_protection(self, _os_write):
+        # gh-130168: Test signal handler re-entry protection
+        console = UnixConsole(term="xterm")
+        console.prepare()
+
+        console._polling_thread = threading.current_thread()
+
+        with self.assertRaises(RuntimeError) as cm:
+            console.wait(timeout=0)
+        self.assertEqual(str(cm.exception), "can't re-enter readline")
+
+        console._polling_thread = None
+        console.restore()

Misc/NEWS.d/next/Library/2025-09-07-19-47-35.gh-issue-130168.qvtlOZ.rst

@@ -0,0 +1 @@
+Fix: pyrepl messed up terminal if a signal handler expects stdin.