358 lines
11 KiB
ReStructuredText
358 lines
11 KiB
ReStructuredText
.. module:: asyncio
|
|
|
|
.. _event-loop:
|
|
|
|
Event loops
|
|
===========
|
|
|
|
The event loop is the central execution device provided by :mod:`asyncio`.
|
|
It provides multiple facilities, amongst which:
|
|
|
|
* Registering, executing and cancelling delayed calls (timeouts)
|
|
|
|
* Creating client and server :ref:`transports <transport>` for various
|
|
kinds of communication
|
|
|
|
* Launching subprocesses and the associated :ref:`transports <transport>`
|
|
for communication with an external program
|
|
|
|
* Delegating costly function calls to a pool of threads
|
|
|
|
Event loop functions
|
|
--------------------
|
|
|
|
The easiest way to get an event loop is to call the :func:`get_event_loop`
|
|
function.
|
|
|
|
.. function:: get_event_loop()
|
|
|
|
Get the event loop for current context. Returns an event loop object
|
|
implementing :class:`BaseEventLoop` interface, or 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 should never return ``None``.
|
|
|
|
.. function:: set_event_loop(loop)
|
|
|
|
XXX
|
|
|
|
.. function:: new_event_loop()
|
|
|
|
XXX
|
|
|
|
|
|
Event loop policy
|
|
-----------------
|
|
|
|
.. function:: get_event_loop_policy()
|
|
|
|
XXX
|
|
|
|
.. function:: set_event_loop_policy(policy)
|
|
|
|
XXX
|
|
|
|
|
|
Run an event loop
|
|
-----------------
|
|
|
|
.. method:: BaseEventLoop.run_forever()
|
|
|
|
Run until :meth:`stop` is called.
|
|
|
|
.. method:: BaseEventLoop.run_until_complete(future)
|
|
|
|
Run until the :class:`Future` is done.
|
|
|
|
If the argument is a coroutine, it is wrapped in a :class:`Task`.
|
|
|
|
Return the Future's result, or raise its exception.
|
|
|
|
.. method:: BaseEventLoop.is_running()
|
|
|
|
Returns running status of event loop.
|
|
|
|
.. method:: BaseEventLoop.stop()
|
|
|
|
Stop running the event loop.
|
|
|
|
Every callback scheduled before :meth:`stop` is called will run.
|
|
Callback scheduled after :meth:`stop` is called won't. However, those
|
|
callbacks will run if :meth:`run_forever` is called again later.
|
|
|
|
.. method:: BaseEventLoop.close()
|
|
|
|
Close the event loop. The loop should not be running.
|
|
|
|
This clears the queues and shuts down the executor, but does not wait for
|
|
the executor to finish.
|
|
|
|
This is idempotent and irreversible. No other methods should be called after
|
|
this one.
|
|
|
|
|
|
Calls
|
|
-----
|
|
|
|
.. method:: BaseEventLoop.call_soon(callback, \*args)
|
|
|
|
Arrange for a callback to be called as soon as possible.
|
|
|
|
This operates as a FIFO queue, callbacks are called in the order in
|
|
which they are registered. Each callback will be called exactly once.
|
|
|
|
Any positional arguments after the callback will be passed to the
|
|
callback when it is called.
|
|
|
|
.. method:: BaseEventLoop.call_soon_threadsafe(callback, \*args)
|
|
|
|
Like :meth:`call_soon`, but thread safe.
|
|
|
|
|
|
Delayed calls
|
|
-------------
|
|
|
|
The event loop has its own internal clock for computing timeouts.
|
|
Which clock is used depends on the (platform-specific) event loop
|
|
implementation; ideally it is a monotonic clock. This will generally be
|
|
a different clock than :func:`time.time`.
|
|
|
|
.. method:: BaseEventLoop.call_later(delay, callback, *args)
|
|
|
|
Arrange for the *callback* to be called after the given *delay*
|
|
seconds (either an int or float).
|
|
|
|
A "handle" is returned: an opaque object with a :meth:`cancel` method
|
|
that can be used to cancel the call.
|
|
|
|
*callback* will be called exactly once per call to :meth:`call_later`.
|
|
If two callbacks are scheduled for exactly the same time, it is
|
|
undefined which will be called first.
|
|
|
|
The optional positional *args* will be passed to the callback when it
|
|
is called. If you want the callback to be called with some named
|
|
arguments, use a closure or :func:`functools.partial`.
|
|
|
|
.. method:: BaseEventLoop.call_at(when, callback, *args)
|
|
|
|
Arrange for the *callback* to be called at the given absolute timestamp
|
|
*when* (an int or float), using the same time reference as :meth:`time`.
|
|
|
|
This method's behavior is the same as :meth:`call_later`.
|
|
|
|
.. method:: BaseEventLoop.time()
|
|
|
|
Return the current time, as a :class:`float` value, according to the
|
|
event loop's internal clock.
|
|
|
|
.. seealso::
|
|
|
|
The :func:`asyncio.sleep` function.
|
|
|
|
|
|
Creating connections
|
|
--------------------
|
|
|
|
.. method:: BaseEventLoop.create_connection(protocol_factory, host=None, port=None, \*, ssl=None, family=0, proto=0, flags=0, sock=None, local_addr=None, server_hostname=None)
|
|
|
|
Create a streaming transport connection to a given Internet *host* and
|
|
*port*. *protocol_factory* must be a callable returning a
|
|
:ref:`protocol <protocol>` instance.
|
|
|
|
This method returns a :ref:`coroutine <coroutine>` which will try to
|
|
establish the connection in the background. When successful, the
|
|
coroutine returns a ``(transport, protocol)`` pair.
|
|
|
|
The chronological synopsis of the underlying operation is as follows:
|
|
|
|
#. The connection is established, and a :ref:`transport <transport>`
|
|
is created to represent it.
|
|
|
|
#. *protocol_factory* is called without arguments and must return a
|
|
:ref:`protocol <protocol>` instance.
|
|
|
|
#. The protocol instance is tied to the transport, and its
|
|
:meth:`connection_made` method is called.
|
|
|
|
#. The coroutine returns successfully with the ``(transport, protocol)``
|
|
pair.
|
|
|
|
The created transport is an implementation-dependent bidirectional stream.
|
|
|
|
.. note::
|
|
*protocol_factory* can be any kind of callable, not necessarily
|
|
a class. For example, if you want to use a pre-created
|
|
protocol instance, you can pass ``lambda: my_protocol``.
|
|
|
|
Options allowing to change how the connection is created:
|
|
|
|
* *ssl*: if given and not false, a SSL/TLS transport is created
|
|
(by default a plain TCP transport is created). If *ssl* is
|
|
a :class:`ssl.SSLContext` object, this context is used to create
|
|
the transport; if *ssl* is :const:`True`, a context with some
|
|
unspecified default settings is used.
|
|
|
|
* *server_hostname*, is only for use together with *ssl*,
|
|
and sets or overrides the hostname that the target server's certificate
|
|
will be matched against. By default the value of the *host* argument
|
|
is used. If *host* is empty, there is no default and you must pass a
|
|
value for *server_hostname*. If *server_hostname* is an empty
|
|
string, hostname matching is disabled (which is a serious security
|
|
risk, allowing for man-in-the-middle-attacks).
|
|
|
|
* *family*, *proto*, *flags* are the optional address family, protocol
|
|
and flags to be passed through to getaddrinfo() for *host* resolution.
|
|
If given, these should all be integers from the corresponding
|
|
:mod:`socket` module constants.
|
|
|
|
* *sock*, if given, should be an existing, already connected
|
|
:class:`socket.socket` object to be used by the transport.
|
|
If *sock* is given, none of *host*, *port*, *family*, *proto*, *flags*
|
|
and *local_addr* should be specified.
|
|
|
|
* *local_addr*, if given, is a ``(local_host, local_port)`` tuple used
|
|
to bind the socket to locally. The *local_host* and *local_port*
|
|
are looked up using getaddrinfo(), similarly to *host* and *port*.
|
|
|
|
|
|
Creating listening connections
|
|
------------------------------
|
|
|
|
.. method:: BaseEventLoop.create_server(protocol_factory, host=None, port=None, \*, family=socket.AF_UNSPEC, flags=socket.AI_PASSIVE, sock=None, backlog=100, ssl=None, reuse_address=None)
|
|
|
|
A :ref:`coroutine <coroutine>` which creates a TCP server bound to host and
|
|
port.
|
|
|
|
The return value is a :class:`AbstractServer` object which can be used to stop
|
|
the service.
|
|
|
|
If *host* is an empty string or None all interfaces are assumed
|
|
and a list of multiple sockets will be returned (most likely
|
|
one for IPv4 and another one for IPv6).
|
|
|
|
*family* can be set to either :data:`~socket.AF_INET` or
|
|
:data:`~socket.AF_INET6` to force the socket to use IPv4 or IPv6. If not set
|
|
it will be determined from host (defaults to :data:`~socket.AF_UNSPEC`).
|
|
|
|
*flags* is a bitmask for :meth:`getaddrinfo`.
|
|
|
|
*sock* can optionally be specified in order to use a preexisting
|
|
socket object.
|
|
|
|
*backlog* is the maximum number of queued connections passed to
|
|
:meth:`~socket.socket.listen` (defaults to 100).
|
|
|
|
ssl can be set to an :class:`~ssl.SSLContext` to enable SSL over the
|
|
accepted connections.
|
|
|
|
*reuse_address* tells the kernel to reuse a local socket in
|
|
TIME_WAIT state, without waiting for its natural timeout to
|
|
expire. If not specified will automatically be set to True on
|
|
UNIX.
|
|
|
|
This method returns a :ref:`coroutine <coroutine>`.
|
|
|
|
.. method:: BaseEventLoop.create_datagram_endpoint(protocol_factory, local_addr=None, remote_addr=None, \*, family=0, proto=0, flags=0)
|
|
|
|
Create datagram connection.
|
|
|
|
This method returns a :ref:`coroutine <coroutine>`.
|
|
|
|
|
|
|
|
Resolve name
|
|
------------
|
|
|
|
.. method:: BaseEventLoop.getaddrinfo(host, port, \*, family=0, type=0, proto=0, flags=0)
|
|
|
|
XXX
|
|
|
|
.. method:: BaseEventLoop.getnameinfo(sockaddr, flags=0)
|
|
|
|
XXX
|
|
|
|
|
|
Running subprocesses
|
|
--------------------
|
|
|
|
Run subprocesses asynchronously using the :mod:`subprocess` module.
|
|
|
|
.. method:: BaseEventLoop.subprocess_exec(protocol_factory, \*args, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, universal_newlines=False, shell=False, bufsize=0, \*\*kwargs)
|
|
|
|
XXX
|
|
|
|
This method returns a :ref:`coroutine <coroutine>`.
|
|
|
|
See the constructor of the :class:`subprocess.Popen` class for parameters.
|
|
|
|
.. method:: BaseEventLoop.subprocess_shell(protocol_factory, cmd, \*, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, universal_newlines=False, shell=True, bufsize=0, \*\*kwargs)
|
|
|
|
XXX
|
|
|
|
This method returns a :ref:`coroutine <coroutine>`.
|
|
|
|
See the constructor of the :class:`subprocess.Popen` class for parameters.
|
|
|
|
.. method:: BaseEventLoop.connect_read_pipe(protocol_factory, pipe)
|
|
|
|
Register read pipe in eventloop.
|
|
|
|
*protocol_factory* should instantiate object with :class:`Protocol`
|
|
interface. pipe is file-like object already switched to nonblocking.
|
|
Return pair (transport, protocol), where transport support
|
|
:class:`ReadTransport` interface.
|
|
|
|
This method returns a :ref:`coroutine <coroutine>`.
|
|
|
|
.. method:: BaseEventLoop.connect_write_pipe(protocol_factory, pipe)
|
|
|
|
Register write pipe in eventloop.
|
|
|
|
*protocol_factory* should instantiate object with :class:`BaseProtocol`
|
|
interface. Pipe is file-like object already switched to nonblocking.
|
|
Return pair (transport, protocol), where transport support
|
|
:class:`WriteTransport` interface.
|
|
|
|
This method returns a :ref:`coroutine <coroutine>`.
|
|
|
|
|
|
Executor
|
|
--------
|
|
|
|
Call a function in an :class:`~concurrent.futures.Executor` (pool of threads or
|
|
pool of processes). By default, an event loop uses a thread pool executor
|
|
(:class:`~concurrent.futures.ThreadPoolExecutor`).
|
|
|
|
.. method:: BaseEventLoop.run_in_executor(executor, callback, \*args)
|
|
|
|
Arrange for a callback to be called in the specified executor.
|
|
|
|
*executor* is a :class:`~concurrent.futures.Executor` instance,
|
|
the default executor is used if *executor* is ``None``.
|
|
|
|
.. method:: BaseEventLoop.set_default_executor(executor)
|
|
|
|
Set the default executor used by :meth:`run_in_executor`.
|
|
|
|
|
|
.. _asyncio-hello-world-callback:
|
|
|
|
Example: Hello World (callback)
|
|
-------------------------------
|
|
|
|
Print ``Hello World`` every two seconds, using a callback::
|
|
|
|
import asyncio
|
|
|
|
def print_and_repeat(loop):
|
|
print('Hello World')
|
|
loop.call_later(2, print_and_repeat, loop)
|
|
|
|
loop = asyncio.get_event_loop()
|
|
loop.call_soon(print_and_repeat, loop)
|
|
loop.run_forever()
|
|
|
|
.. seealso::
|
|
|
|
:ref:`Hello World example using a coroutine <asyncio-hello-world-coroutine>`.
|
|
|