Poll terminal size every 0.5 seconds.

Handles terminal resize events when the application runs in another thread, or
on Windows where SIGWINCH can't be handled. Some benchmarking shows that this
polling comes with very little cost, but does solve the issue.

Author: jonathanslenders

prompt_toolkit/application/application.py

@@ -41,6 +41,7 @@
 from prompt_toolkit.buffer import Buffer
 from prompt_toolkit.cache import SimpleCache
 from prompt_toolkit.clipboard import Clipboard, InMemoryClipboard
+from prompt_toolkit.data_structures import Size
 from prompt_toolkit.enums import EditingMode
 from prompt_toolkit.eventloop import (
     get_traceback_from_context,
@@ -147,6 +148,10 @@ class Application(Generic[_AppResult]):
         seconds. When `None` (the default), only invalidate when `invalidate`
         has been called.
 
+    :param terminal_size_polling_interval: Poll the terminal size every so many
+        seconds. Useful if the applications runs in a thread other then then
+        main thread where SIGWINCH can't be handled, or on Windows.
+
     Filters:
 
     :param mouse_support: (:class:`~prompt_toolkit.filters.Filter` or
@@ -211,14 +216,15 @@ def __init__(
         min_redraw_interval: Union[float, int, None] = None,
         max_render_postpone_time: Union[float, int, None] = 0.01,
         refresh_interval: Optional[float] = None,
+        terminal_size_polling_interval: Optional[float] = 0.5,
         on_reset: Optional[ApplicationEventHandler] = None,
         on_invalidate: Optional[ApplicationEventHandler] = None,
         before_render: Optional[ApplicationEventHandler] = None,
         after_render: Optional[ApplicationEventHandler] = None,
         # I/O.
         input: Optional[Input] = None,
         output: Optional[Output] = None,
-    ):
+    ) -> None:
 
         # If `enable_page_navigation_bindings` is not specified, enable it in
         # case of full screen applications only. This can be overridden by the user.
@@ -259,6 +265,7 @@ def __init__(
         self.min_redraw_interval = min_redraw_interval
         self.max_render_postpone_time = max_render_postpone_time
         self.refresh_interval = refresh_interval
+        self.terminal_size_polling_interval = terminal_size_polling_interval
 
         # Events.
         self.on_invalidate = Event(self, on_invalidate)
@@ -696,6 +703,8 @@ def flush_input() -> None:
             with self.input.raw_mode(), self.input.attach(
                 read_from_input
             ), attach_winch_signal_handler(self._on_resize):
+                self.create_background_task(self._poll_output_size())
+
                 # Draw UI.
                 self._request_absolute_cursor_position()
                 self._redraw()
@@ -873,6 +882,28 @@ async def cancel_and_wait_for_background_tasks(self) -> None:
             except CancelledError:
                 pass
 
+    async def _poll_output_size(self) -> None:
+        """
+        Coroutine for polling the terminal dimensions.
+
+        Useful for situations where `attach_winch_signal_handler` is not sufficient:
+        - If we are not running in the main thread.
+        - On Windows.
+        """
+        size: Optional[Size] = None
+        interval = self.terminal_size_polling_interval
+
+        if interval is None:
+            return
+
+        while True:
+            await asyncio.sleep(interval)
+            new_size = self.output.get_size()
+
+            if size is not None and new_size != size:
+                self._on_resize()
+            size = new_size
+
     def cpr_not_supported_callback(self) -> None:
         """
         Called when we don't receive the cursor position response in time.