`tornado.util.TimeoutError`.
- `.IOLoop.instance` is now a deprecated alias for `.IOLoop.current`.
- `.IOLoop.install` and `.IOLoop.clear_instance` are deprecated.
-- ``IOLoop.initialized`` has been removed.
+- The ``IOLoop.initialized`` method has been removed.
- On Python 3, the `asyncio`-backed `.IOLoop` is always used and
alternative `.IOLoop` implementations cannot be configured.
`.IOLoop.current` and related methods pass through to
``PYTHONASYNCIODEBUG=1`` environment variable instead.
- `.IOLoop.clear_current` now works if it is called before any
current loop is established.
-- The ``IOLoop.initialized`` method has been removed.
`tornado.iostream`
~~~~~~~~~~~~~~~~~~