Merge pull request #4998 from pallets/deprecate-locked_cached_property

deprecate `locked_cached_property`

CHANGES.rst

@@ -26,6 +26,10 @@ Unreleased
 -   Importing ``escape`` and ``Markup`` from ``flask`` is deprecated. Import them
     directly from ``markupsafe`` instead. :pr:`4996`
 -   The ``app.got_first_request`` property is deprecated. :pr:`4997`
+-   The ``locked_cached_property`` decorator is deprecated. Use a lock inside the
+    decorated function if locking is needed. :issue:`4993`
+-   Remove uses of locks that could cause requests to block each other very briefly.
+    :issue:`4993`
 -   Use modern packaging metadata with ``pyproject.toml`` instead of ``setup.cfg``.
     :pr:`4947`
 -   Ensure subdomains are applied with nested blueprints. :issue:`4834`

src/flask/app.py

@@ -26,6 +26,7 @@ from werkzeug.routing import RoutingException
 from werkzeug.routing import Rule
 from werkzeug.serving import is_running_from_reloader
 from werkzeug.urls import url_quote
+from werkzeug.utils import cached_property
 from werkzeug.utils import redirect as _wz_redirect
 from werkzeug.wrappers import Response as BaseResponse
 
@@ -46,7 +47,6 @@ from .helpers import _split_blueprint_path
 from .helpers import get_debug_flag
 from .helpers import get_flashed_messages
 from .helpers import get_load_dotenv
-from .helpers import locked_cached_property
 from .json.provider import DefaultJSONProvider
 from .json.provider import JSONProvider
 from .logging import create_logger
@@ -531,7 +531,7 @@ class Flask(Scaffold):
                 " running it."
             )
 
-    @locked_cached_property
+    @cached_property
     def name(self) -> str:  # type: ignore
         """The name of the application.  This is usually the import name
         with the difference that it's guessed from the run file if the
@@ -548,7 +548,7 @@ class Flask(Scaffold):
             return os.path.splitext(os.path.basename(fn))[0]
         return self.import_name
 
-    @locked_cached_property
+    @cached_property
     def logger(self) -> logging.Logger:
         """A standard Python :class:`~logging.Logger` for the app, with
         the same name as :attr:`name`.
@@ -575,7 +575,7 @@ class Flask(Scaffold):
         """
         return create_logger(self)
 
-    @locked_cached_property
+    @cached_property
     def jinja_env(self) -> Environment:
         """The Jinja environment used to load templates.
 

src/flask/helpers.py

@@ -613,6 +613,10 @@ class locked_cached_property(werkzeug.utils.cached_property):
     :class:`werkzeug.utils.cached_property` except access uses a lock
     for thread safety.
 
+    .. deprecated:: 2.3
+        Will be removed in Flask 2.4. Use a lock inside the decorated function if
+        locking is needed.
+
     .. versionchanged:: 2.0
         Inherits from Werkzeug's ``cached_property`` (and ``property``).
     """
@@ -623,6 +627,14 @@ class locked_cached_property(werkzeug.utils.cached_property):
         name: t.Optional[str] = None,
         doc: t.Optional[str] = None,
     ) -> None:
+        import warnings
+
+        warnings.warn(
+            "'locked_cached_property' is deprecated and will be removed in Flask 2.4."
+            " Use a lock inside the decorated function if locking is needed.",
+            DeprecationWarning,
+            stacklevel=2,
+        )
         super().__init__(fget, name=name, doc=doc)
         self.lock = RLock()
 

src/flask/scaffold.py

@@ -11,12 +11,12 @@ from functools import update_wrapper
 from jinja2 import FileSystemLoader
 from werkzeug.exceptions import default_exceptions
 from werkzeug.exceptions import HTTPException
+from werkzeug.utils import cached_property
 
 from . import typing as ft
 from .cli import AppGroup
 from .globals import current_app
 from .helpers import get_root_path
-from .helpers import locked_cached_property
 from .helpers import send_from_directory
 from .templating import _default_template_ctx_processor
 
@@ -317,7 +317,7 @@ class Scaffold:
             t.cast(str, self.static_folder), filename, max_age=max_age
         )
 
-    @locked_cached_property
+    @cached_property
     def jinja_loader(self) -> t.Optional[FileSystemLoader]:
         """The Jinja loader for this object's templates. By default this
         is a class :class:`jinja2.loaders.FileSystemLoader` to