v6.4.0b1

What's new in Tornado 6.4.0

In Progress
-----------

General Changes
~~~~~~~~~~~~~~~

- Python 3.12 is now supported. Older versions of Tornado will work on Python 3.12 but may log
  deprecation warnings.

Deprecation Notices
~~~~~~~~~~~~~~~~~~~

- `.IOLoop.add_callback_from_signal` is suspected to have been broken since Tornado 5.0 and will be
  removed in version 7.0.  Use `asyncio.loop.add_signal_handler` instead.
- The ``client_secret`` argument to `.OAuth2Mixin.authorize_redirect` is deprecated and will be
  removed in Tornado 7.0. This argument has never been used and other similar methods in this module
  don't have it.
- `.TwitterMixin` is deprecated and will be removed in the future.

``tornado.auth``
~~~~~~~~~~~~~~~~

- The ``client_secret`` argument to `.OAuth2Mixin.authorize_redirect` is deprecated and will be
  removed in Tornado 7.0. This argument has never been used and other similar methods in this module
  don't have it.
- `.TwitterMixin` is deprecated and will be removed in the future.

``tornado.autoreload``
~~~~~~~~~~~~~~~~~~~~~~

- Autoreload can now be used when the program is run as a directory rather than a file or module.
- New CLI flag ``--until-success`` re-runs the program on any failure but stops after the first
  successful run.

``tornado.concurrent``
~~~~~~~~~~~~~~~~~~~~~~

- Fixed reference cycles that could lead to increased memory usage.

``tornado.escape``
~~~~~~~~~~~~~~~~~~

- Several methods in this module now simply pass through to their equivalents in the standard
  library.

``tornado.gen``
~~~~~~~~~~~~~~~

- This module now holds a strong reference to all running `asyncio.Task` objects it creates. This
  prevents premature garbage collection which could cause warnings like "Task was destroyed but it
  is pending!".

``tornado.ioloop``
~~~~~~~~~~~~~~~~~~

- `.IOLoop.add_callback_from_signal` is suspected to have been broken since Tornado 5.0 and will be
  removed in version 7.0.  Use `asyncio.loop.add_signal_handler` instead.
- The type annotation for `.IOLoop.run_in_executor` has been updated to match the updated signature
  of `asyncio.loop.run_in_executor`.
- Fixed reference cycles that could lead to increased memory usage.

``tornado.locale``
~~~~~~~~~~~~~~~~~~

- `.format_timestamp` now supports "aware" datetime objects.

``tornado.platform.asyncio``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

- The shutdown protocol for `.AddThreadSelectorEventLoop` now requires the use of `asyncio.run` or
  `asyncio.loop.shutdown_asyncgens` to avoid leaking the thread.
- Introduced `.SelectorThread` class containing the core functionality of
  `.AddThreadSelectorEventLoop`.
- The ``close()`` method of `.AddThreadSelectorEventLoop` is now idempotent.

``tornado.web``
~~~~~~~~~~~~~~~

- `.StaticFileHandler.get_modified_time` now supports "aware" datetime objects and the default
  implementation now returns aware objects.

``tornado.websocket``
~~~~~~~~~~~~~~~~~~~~~

- Unclosed client connections now reliably log a warning. Previously the warning was dependent on
  garbage collection and whether the ``ping_interval`` option was used.
- The ``subprotocols`` argument to `.WebSocketClientConnection` now defaults to None instead of an
  empty list (which was mutable and reused)