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
@@ -161,6 +162,9 @@ 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.__svtermstate = None
         self.terminfo = terminfo.TermInfo(term or None)
         self.term = term
         self.is_apple_terminal = (
@@ -341,10 +345,12 @@ def prepare(self):
         """
         Prepare the console for input/output operations.
         """
+        # gh-130168: prevents signal handlers from overwriting the original state
+        if self.__svtermstate is None:
+            self.__svtermstate = tcgetattr(self.input_fd)
         self.__buffer = []
 
-        self.__svtermstate = tcgetattr(self.input_fd)
-        raw = self.__svtermstate.copy()
+        raw = tcgetattr(self.input_fd).copy()
         raw.iflag &= ~(termios.INPCK | termios.ISTRIP | termios.IXON)
         raw.oflag &= ~(termios.OPOST)
         raw.cflag &= ~(termios.CSIZE | termios.PARENB)
@@ -384,7 +390,15 @@ def restore(self):
         self.__disable_bracketed_paste()
         self.__maybe_write_code(self._rmkx)
         self.flushoutput()
-        self.__input_fd_set(self.__svtermstate)
+        try:
+            if self.__svtermstate is not None:
+                tcsetattr(self.input_fd, termios.TCSADRAIN, self.__svtermstate)
+                self.__input_fd_set(self.__svtermstate)
+                # Reset the state for the next prepare() call.
+                self.__svtermstate = None
+        except termios.error as e:
+            if e.args[0] != errno.EIO:
+                raise
 
         if self.is_apple_terminal:
             os.write(self.output_fd, b"\033[?7h")
@@ -435,10 +449,20 @@ 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:
+            # Forbid re-entrant calls and use the old REPL error message.
+            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):
         """
@@ -804,7 +828,10 @@ 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 self.__svtermstate is not None:
+            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

@@ -4,6 +4,7 @@
 import signal
 import subprocess
 import sys
+import threading
 import unittest
 from functools import partial
 from test.support import os_helper, force_not_colorized_test_class
@@ -308,6 +309,18 @@ def test_getheightwidth_with_invalid_environ(self, _os_write):
             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.assertRaisesRegex(RuntimeError, "can't re-enter readline"):
+            console.wait(timeout=0)
+
+        console._polling_thread = None
+        console.restore()
+
     @unittest.skipUnless(sys.platform == "darwin", "requires macOS")
     def test_restore_with_invalid_environ_on_macos(self, _os_write):
         # gh-128636 for macOS

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

@@ -0,0 +1,2 @@
+Make sure that the new REPL does not get scrambled when a signal handler
+uses interactive input.