mirror of
https://github.com/python/cpython.git
synced 2025-11-03 03:22:27 +00:00
201 lines
6.4 KiB
ReStructuredText
201 lines
6.4 KiB
ReStructuredText
.. currentmodule:: asyncio
|
|
|
|
Event loops
|
|
===========
|
|
|
|
Event loop functions
|
|
--------------------
|
|
|
|
The following functions are convenient shortcuts to accessing the methods of the
|
|
global policy. Note that this provides access to the default policy, unless an
|
|
alternative policy was set by calling :func:`set_event_loop_policy` earlier in
|
|
the execution of the process.
|
|
|
|
.. function:: get_event_loop()
|
|
|
|
Equivalent to calling ``get_event_loop_policy().get_event_loop()``.
|
|
|
|
.. function:: set_event_loop(loop)
|
|
|
|
Equivalent to calling ``get_event_loop_policy().set_event_loop(loop)``.
|
|
|
|
.. function:: new_event_loop()
|
|
|
|
Equivalent to calling ``get_event_loop_policy().new_event_loop()``.
|
|
|
|
|
|
.. _asyncio-event-loops:
|
|
|
|
Available event loops
|
|
---------------------
|
|
|
|
asyncio currently provides two implementations of event loops:
|
|
:class:`SelectorEventLoop` and :class:`ProactorEventLoop`.
|
|
|
|
.. class:: SelectorEventLoop
|
|
|
|
Event loop based on the :mod:`selectors` module. Subclass of
|
|
:class:`BaseEventLoop`.
|
|
|
|
Use the most efficient selector available on the platform.
|
|
|
|
On Windows, only sockets are supported (ex: pipes are not supported):
|
|
see the `MSDN documentation of select
|
|
<http://msdn.microsoft.com/en-us/library/windows/desktop/ms740141%28v=vs.85%29.aspx>`_.
|
|
|
|
.. class:: ProactorEventLoop
|
|
|
|
Proactor event loop for Windows using "I/O Completion Ports" aka IOCP.
|
|
Subclass of :class:`BaseEventLoop`.
|
|
|
|
Availability: Windows.
|
|
|
|
.. seealso::
|
|
|
|
`MSDN documentation on I/O Completion Ports
|
|
<http://msdn.microsoft.com/en-us/library/windows/desktop/aa365198%28v=vs.85%29.aspx>`_.
|
|
|
|
Example to use a :class:`ProactorEventLoop` on Windows::
|
|
|
|
import asyncio, os
|
|
|
|
if os.name == 'nt':
|
|
loop = asyncio.ProactorEventLoop()
|
|
asyncio.set_event_loop(loop)
|
|
|
|
.. _asyncio-platform-support:
|
|
|
|
Platform support
|
|
----------------
|
|
|
|
The :mod:`asyncio` module has been designed to be portable, but each platform
|
|
still has subtle differences and may not support all :mod:`asyncio` features.
|
|
|
|
Windows
|
|
^^^^^^^
|
|
|
|
Common limits of Windows event loops:
|
|
|
|
- :meth:`~BaseEventLoop.create_unix_connection` and
|
|
:meth:`~BaseEventLoop.create_unix_server` are not supported: the socket
|
|
family :data:`socket.AF_UNIX` is specific to UNIX
|
|
- :meth:`~BaseEventLoop.add_signal_handler` and
|
|
:meth:`~BaseEventLoop.remove_signal_handler` are not supported
|
|
- :meth:`EventLoopPolicy.set_child_watcher` is not supported.
|
|
:class:`ProactorEventLoop` supports subprocesses. It has only one
|
|
implementation to watch child processes, there is no need to configure it.
|
|
|
|
:class:`SelectorEventLoop` specific limits:
|
|
|
|
- :class:`~selectors.SelectSelector` is used which only supports sockets
|
|
and is limited to 512 sockets.
|
|
- :meth:`~BaseEventLoop.add_reader` and :meth:`~BaseEventLoop.add_writer` only
|
|
accept file descriptors of sockets
|
|
- Pipes are not supported
|
|
(ex: :meth:`~BaseEventLoop.connect_read_pipe`,
|
|
:meth:`~BaseEventLoop.connect_write_pipe`)
|
|
- :ref:`Subprocesses <asyncio-subprocess>` are not supported
|
|
(ex: :meth:`~BaseEventLoop.subprocess_exec`,
|
|
:meth:`~BaseEventLoop.subprocess_shell`)
|
|
|
|
:class:`ProactorEventLoop` specific limits:
|
|
|
|
- :meth:`~BaseEventLoop.create_datagram_endpoint` (UDP) is not supported
|
|
- :meth:`~BaseEventLoop.add_reader` and :meth:`~BaseEventLoop.add_writer` are
|
|
not supported
|
|
|
|
The resolution of the monotonic clock on Windows is usually around 15.6 msec.
|
|
The best resolution is 0.5 msec. The resolution depends on the hardware
|
|
(availability of `HPET
|
|
<http://fr.wikipedia.org/wiki/High_Precision_Event_Timer>`_) and on the Windows
|
|
configuration. See :ref:`asyncio delayed calls <asyncio-delayed-calls>`.
|
|
|
|
.. versionchanged:: 3.5
|
|
|
|
:class:`ProactorEventLoop` now supports SSL.
|
|
|
|
|
|
Mac OS X
|
|
^^^^^^^^
|
|
|
|
Character devices like PTY are only well supported since Mavericks (Mac OS
|
|
10.9). They are not supported at all on Mac OS 10.5 and older.
|
|
|
|
On Mac OS 10.6, 10.7 and 10.8, the default event loop is
|
|
:class:`SelectorEventLoop` which uses :class:`selectors.KqueueSelector`.
|
|
:class:`selectors.KqueueSelector` does not support character devices on these
|
|
versions. The :class:`SelectorEventLoop` can be used with
|
|
:class:`~selectors.SelectSelector` or :class:`~selectors.PollSelector` to
|
|
support character devices on these versions of Mac OS X. Example::
|
|
|
|
import asyncio
|
|
import selectors
|
|
|
|
selector = selectors.SelectSelector()
|
|
loop = asyncio.SelectorEventLoop(selector)
|
|
asyncio.set_event_loop(loop)
|
|
|
|
|
|
Event loop policies and the default policy
|
|
------------------------------------------
|
|
|
|
Event loop management is abstracted with a *policy* pattern, to provide maximal
|
|
flexibility for custom platforms and frameworks. Throughout the execution of a
|
|
process, a single global policy object manages the event loops available to the
|
|
process based on the calling context. A policy is an object implementing the
|
|
:class:`AbstractEventLoopPolicy` interface.
|
|
|
|
For most users of :mod:`asyncio`, policies never have to be dealt with
|
|
explicitly, since the default global policy is sufficient.
|
|
|
|
The default policy defines context as the current thread, and manages an event
|
|
loop per thread that interacts with :mod:`asyncio`. The module-level functions
|
|
:func:`get_event_loop` and :func:`set_event_loop` provide convenient access to
|
|
event loops managed by the default policy.
|
|
|
|
|
|
Event loop policy interface
|
|
---------------------------
|
|
|
|
An event loop policy must implement the following interface:
|
|
|
|
.. class:: AbstractEventLoopPolicy
|
|
|
|
Event loop policy.
|
|
|
|
.. method:: get_event_loop()
|
|
|
|
Get the event loop for the current context.
|
|
|
|
Returns an event loop object implementing the :class:`BaseEventLoop`
|
|
interface.
|
|
|
|
Raises an exception in case no event loop has been set for the current
|
|
context and the current policy does not specify to create one. It must
|
|
never return ``None``.
|
|
|
|
.. method:: set_event_loop(loop)
|
|
|
|
Set the event loop for the current context to *loop*.
|
|
|
|
.. method:: new_event_loop()
|
|
|
|
Create and return a new event loop object according to this policy's
|
|
rules.
|
|
|
|
If there's need to set this loop as the event loop for the current
|
|
context, :meth:`set_event_loop` must be called explicitly.
|
|
|
|
|
|
Access to the global loop policy
|
|
--------------------------------
|
|
|
|
.. function:: get_event_loop_policy()
|
|
|
|
Get the current event loop policy.
|
|
|
|
.. function:: set_event_loop_policy(policy)
|
|
|
|
Set the current event loop policy. If *policy* is ``None``, the default
|
|
policy is restored.
|
|
|