bugfix: crash on rapidly received SIGWINCH (#165)

**Problem**: pytermgui calls print() and eventually sys.stdout.flush()
from within a signal handler, which is a blocking operating, and can
cause crashes::

    RuntimeError: reentrant call inside <_io.BufferedWriter name='<stdout>'>

<details>
Traceback (most recent call last):
  File "/home/jq/Code/pytermgui/examples/simple_app.py", line 213, in <module>
    main(sys.argv[1:])
    ~~~~^^^^^^^^^^^^^^
  File "/home/jq/Code/pytermgui/examples/simple_app.py", line 141, in main
    with ptg.WindowManager() as manager:
         ~~~~~~~~~~~~~~~~~^^
  File "/home/jq/Code/pytermgui/pytermgui/window_manager/manager.py", line 117, in __exit__
    self.run()
    ~~~~~~~~^^
  File "/home/jq/Code/pytermgui/pytermgui/window_manager/manager.py", line 198, in run
    self._run_input_loop()
    ~~~~~~~~~~~~~~~~~~~~^^
  File "/home/jq/Code/pytermgui/pytermgui/window_manager/manager.py", line 135, in _run_input_loop
    key = getch(interrupts=False)
  File "/home/jq/Code/pytermgui/pytermgui/input.py", line 438, in getch
    key = _getch()
  File "/home/jq/Code/pytermgui/pytermgui/input.py", line 152, in __call__
    buff = "".join(self.get_chars())
  File "/home/jq/Code/pytermgui/pytermgui/input.py", line 140, in get_chars
    yield self._read(1)
          ~~~~~~~~~~^^^
  File "/home/jq/Code/pytermgui/pytermgui/input.py", line 119, in _read
    char = os.read(sys.stdin.fileno(), 1)
  File "/home/jq/Code/pytermgui/pytermgui/term.py", line 358, in _update_size
    self._call_listener(self.RESIZE, self.size)
    ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jq/Code/pytermgui/pytermgui/term.py", line 339, in _call_listener
    callback(data)
    ~~~~~~~~^^^^^^
  File "/home/jq/Code/pytermgui/pytermgui/window_manager/manager.py", line 174, in on_resize
    self.compositor.redraw()
    ~~~~~~~~~~~~~~~~~~~~~~^^
  File "/home/jq/Code/pytermgui/pytermgui/window_manager/compositor.py", line 270, in redraw
    self.draw(force=True)
    ~~~~~~~~~^^^^^^^^^^^^
  File "/home/jq/Code/pytermgui/pytermgui/window_manager/compositor.py", line 259, in draw
    with self.terminal.frame() as frame:
         ~~~~~~~~~~~~~~~~~~~^^
  File "/home/jq/.pyenv/versions/3.15.0a5/lib/python3.15/contextlib.py", line 148, in __exit__
    next(self.gen)
    ~~~~^^^^^^^^^^
  File "/home/jq/Code/pytermgui/pytermgui/term.py", line 465, in frame
    self.flush()
    ~~~~~~~~~~^^
  File "/home/jq/Code/pytermgui/pytermgui/term.py", line 601, in flush
    self._stream.flush()
    ~~~~~~~~~~~~~~~~~~^^
  File "/home/jq/Code/pytermgui/pytermgui/term.py", line 353, in _update_size
    if hasattr(self, "resolution"):
       ~~~~~~~^^^^^^^^^^^^^^^^^^^^
  File "/home/jq/.pyenv/versions/3.15.0a5/lib/python3.15/functools.py", line 1146, in __get__
    val = self.func(instance)
  File "/home/jq/Code/pytermgui/pytermgui/term.py", line 308, in resolution
    sys.stdout.flush()
    ~~~~~~~~~~~~~~~~^^
RuntimeError: reentrant call inside <_io.BufferedWriter name='<stdout>'>
</details>

I have written about "signal safety" with SIGNWICH here, and apply a
similar solution for pytermgui,

https://blessed.readthedocs.io/en/latest/measuring.html#using-sigwinch

- Remove screen wipe (``\x1b[H\x1b[2J``) from resize handler
  - this was the cause of the crash
- use threading.Event() as a semaphore, thread-safe, naturally
- Reduce windows polling period from 0.001 to 0.01s
- main loop periodically checks process_pending_resize()

Co-authored-by: Balázs Cene <bczsalba@gmail.com>

Author: jquast

pytermgui/term.py

@@ -8,6 +8,7 @@
 import os
 import signal
 import sys
+import threading
 import time
 from contextlib import contextmanager
 from datetime import datetime
@@ -263,6 +264,9 @@ def __init__(
 
         self._listeners: dict[int, list[Callable[..., Any]]] = {}
 
+        # Async-signal-safe resize mechanism
+        self._resize_pending = threading.Event()
+
         if hasattr(signal, "SIGWINCH"):
             signal.signal(signal.SIGWINCH, self._update_size)
         else:
@@ -278,16 +282,16 @@ def __init__(
             ["" for _ in range(self.width)] for y in range(self.height)
         ]
 
-    def _window_terminal_resize(self):
+    def _window_terminal_resize(self) -> None:
         from time import sleep  # pylint: disable=import-outside-toplevel
 
         _previous = get_terminal_size()
         while True:
             _next = get_terminal_size()
             if _previous != _next:
-                self._update_size()
+                self._resize_pending.set()
                 _previous = _next
-            sleep(0.001)
+            sleep(0.01)
 
     def __fancy_repr__(self) -> Generator[FancyYield, None, None]:
         """Returns a cool looking repr."""
@@ -348,17 +352,34 @@ def _get_size(self) -> tuple[int, int]:
         return (size[0], size[1])
 
     def _update_size(self, *_: Any) -> None:
-        """Resize terminal when SIGWINCH occurs, and call listeners."""
+        """Signal handler for SIGWINCH - ONLY sets flag (async-signal-safe)."""
 
-        if hasattr(self, "resolution"):
-            del self.resolution
+        self._resize_pending.set()
 
-        self.size = self._get_size()
+    def process_pending_resize(self) -> bool:
+        """Process pending resize event if one is queued.
+
+        Call this periodically from the main event loop.
+
+        :returns: True if a resize was processed.
+        """
+        if not self._resize_pending.is_set():
+            return False
+
+        self._resize_pending.clear()
 
+        # Check __dict__ directly to avoid triggering the cached_property getter,
+        # which uses signals and can only run in the main thread
+        if "resolution" in self.__dict__:
+            del self.__dict__["resolution"]
+
+        self.size = self._get_size()
         self._call_listener(self.RESIZE, self.size)
 
         # Wipe the screen in case anything got messed up
         self.write("\x1b[H\x1b[2J")
+        
+        return True
 
     @property
     def width(self) -> int:
@@ -459,7 +480,6 @@ def frame(self) -> Generator[StringIO, None, None]:
             yield buffer
 
         finally:
-            # Write buffer directly to stream - bypasses write()'s \x1b[2J detection
             self._stream.write(buffer.getvalue())
             self._stream.write("\x1b[?2026l")
             self._stream.flush()

pytermgui/window_manager/compositor.py

@@ -65,6 +65,8 @@ def _draw_loop(self) -> None:
                 time.sleep(self._frametime - elapsed)
                 continue
 
+            self.terminal.process_pending_resize()
+
             animator.step(elapsed)
 
             last_frame = time.perf_counter()