Adds Widget.lock attribute.

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## Unreleased
+
+### Added
+
+- Added an `asyncio` lock attribute `Widget.lock` to be used to synchronize widget state https://github.com/Textualize/textual/issues/4134
+
 ## [0.51.0] - 2024-02-15
 
 ### Added

src/textual/widget.py

@@ -4,7 +4,7 @@
 
 from __future__ import annotations
 
-from asyncio import create_task, wait
+from asyncio import Lock, create_task, wait
 from collections import Counter
 from fractions import Fraction
 from itertools import islice
@@ -372,6 +372,14 @@ def __init__(
         if self.BORDER_SUBTITLE:
             self.border_subtitle = self.BORDER_SUBTITLE
 
+        self.lock = Lock()
+        """`asyncio` lock to be used to synchronize the state of the widget.
+
+        Two different tasks might call methods on a widget at the same time, which
+        might result in a race condition.
+        This can be fixed by adding `async with widget.lock:` around the method calls.
+        """
+
     virtual_size: Reactive[Size] = Reactive(Size(0, 0), layout=True)
     """The virtual (scrollable) [size][textual.geometry.Size] of the widget."""
 

src/textual/widgets/_tree.py

@@ -2,7 +2,6 @@
 
 from __future__ import annotations
 
-from asyncio import Lock
 from dataclasses import dataclass
 from typing import TYPE_CHECKING, ClassVar, Generic, Iterable, NewType, TypeVar, cast
 
@@ -618,8 +617,6 @@ def __init__(
         self._line_cache: LRUCache[LineCacheKey, Strip] = LRUCache(1024)
         self._tree_lines_cached: list[_TreeLine[TreeDataType]] | None = None
         self._cursor_node: TreeNode[TreeDataType] | None = None
-        self.lock = Lock()
-        """Used to synchronise stateful directory tree operations."""
 
         super().__init__(name=name, id=id, classes=classes, disabled=disabled)