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Tip revision: 1bf9cc509326bc42cd8cb1650eb9bf64550d817e authored by Ned Deily on 27 June 2018, 01:03:55 UTC
3.7.0 final
3.7.0 final
Tip revision: 1bf9cc5
asyncio-eventloop.rst
.. currentmodule:: asyncio
.. _asyncio-event-loop:
Base Event Loop
===============
**Source code:** :source:`Lib/asyncio/events.py`
The event loop is the central execution device provided by :mod:`asyncio`.
It provides multiple facilities, including:
* Registering, executing and cancelling delayed calls (timeouts).
* Creating client and server :ref:`transports <asyncio-transport>` for various
kinds of communication.
* Launching subprocesses and the associated :ref:`transports
<asyncio-transport>` for communication with an external program.
* Delegating costly function calls to a pool of threads.
.. class:: BaseEventLoop
This class is an implementation detail. It is a subclass of
:class:`AbstractEventLoop` and may be a base class of concrete
event loop implementations found in :mod:`asyncio`. It should not
be used directly; use :class:`AbstractEventLoop` instead.
``BaseEventLoop`` should not be subclassed by third-party code; the
internal interface is not stable.
.. class:: AbstractEventLoop
Abstract base class of event loops.
This class is :ref:`not thread safe <asyncio-multithreading>`.
Run an event loop
-----------------
.. method:: AbstractEventLoop.run_forever()
Run until :meth:`stop` is called. If :meth:`stop` is called before
:meth:`run_forever()` is called, this polls the I/O selector once
with a timeout of zero, runs all callbacks scheduled in response to
I/O events (and those that were already scheduled), and then exits.
If :meth:`stop` is called while :meth:`run_forever` is running,
this will run the current batch of callbacks and then exit. Note
that callbacks scheduled by callbacks will not run in that case;
they will run the next time :meth:`run_forever` is called.
.. versionchanged:: 3.5.1
.. method:: AbstractEventLoop.run_until_complete(future)
Run until the :class:`Future` is done.
If the argument is a :ref:`coroutine object <coroutine>`, it is wrapped by
:func:`ensure_future`.
Return the Future's result, or raise its exception.
.. method:: AbstractEventLoop.is_running()
Returns running status of event loop.
.. method:: AbstractEventLoop.stop()
Stop running the event loop.
This causes :meth:`run_forever` to exit at the next suitable
opportunity (see there for more details).
.. versionchanged:: 3.5.1
.. method:: AbstractEventLoop.is_closed()
Returns ``True`` if the event loop was closed.
.. versionadded:: 3.4.2
.. method:: AbstractEventLoop.close()
Close the event loop. The loop must not be running. Pending
callbacks will be lost.
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.
.. coroutinemethod:: AbstractEventLoop.shutdown_asyncgens()
Schedule all currently open :term:`asynchronous generator` objects to
close with an :meth:`~agen.aclose()` call. After calling this method,
the event loop will issue a warning whenever a new asynchronous generator
is iterated. Should be used to finalize all scheduled asynchronous
generators reliably. Example::
try:
loop.run_forever()
finally:
loop.run_until_complete(loop.shutdown_asyncgens())
loop.close()
.. versionadded:: 3.6
.. _asyncio-pass-keywords:
Calls
-----
Most :mod:`asyncio` functions don't accept keywords. If you want to pass
keywords to your callback, use :func:`functools.partial`. For example,
``loop.call_soon(functools.partial(print, "Hello", flush=True))`` will call
``print("Hello", flush=True)``.
.. note::
:func:`functools.partial` is better than ``lambda`` functions, because
:mod:`asyncio` can inspect :func:`functools.partial` object to display
parameters in debug mode, whereas ``lambda`` functions have a poor
representation.
.. method:: AbstractEventLoop.call_soon(callback, *args, context=None)
Arrange for a callback to be called as soon as possible. The callback is
called after :meth:`call_soon` returns, when control returns to the event
loop.
This operates as a :abbr:`FIFO (first-in, first-out)` 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.
An optional keyword-only *context* argument allows specifying a custom
:class:`contextvars.Context` for the *callback* to run in. The current
context is used when no *context* is provided.
An instance of :class:`asyncio.Handle` is returned, which can be
used to cancel the callback.
:ref:`Use functools.partial to pass keywords to the callback
<asyncio-pass-keywords>`.
.. versionchanged:: 3.7
The *context* keyword-only parameter was added. See :pep:`567`
for more details.
.. method:: AbstractEventLoop.call_soon_threadsafe(callback, *args, context=None)
Like :meth:`call_soon`, but thread safe.
See the :ref:`concurrency and multithreading <asyncio-multithreading>`
section of the documentation.
.. versionchanged:: 3.7
The *context* keyword-only parameter was added. See :pep:`567`
for more details.
.. _asyncio-delayed-calls:
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`.
.. note::
Timeouts (relative *delay* or absolute *when*) should not exceed one day.
.. method:: AbstractEventLoop.call_later(delay, callback, *args, context=None)
Arrange for the *callback* to be called after the given *delay*
seconds (either an int or float).
An instance of :class:`asyncio.TimerHandle` is returned, which can be
used to cancel the callback.
*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`.
An optional keyword-only *context* argument allows specifying a custom
:class:`contextvars.Context` for the *callback* to run in. The current
context is used when no *context* is provided.
:ref:`Use functools.partial to pass keywords to the callback
<asyncio-pass-keywords>`.
.. versionchanged:: 3.7
The *context* keyword-only parameter was added. See :pep:`567`
for more details.
.. method:: AbstractEventLoop.call_at(when, callback, *args, context=None)
Arrange for the *callback* to be called at the given absolute timestamp
*when* (an int or float), using the same time reference as
:meth:`AbstractEventLoop.time`.
This method's behavior is the same as :meth:`call_later`.
An instance of :class:`asyncio.TimerHandle` is returned, which can be
used to cancel the callback.
:ref:`Use functools.partial to pass keywords to the callback
<asyncio-pass-keywords>`.
.. versionchanged:: 3.7
The *context* keyword-only parameter was added. See :pep:`567`
for more details.
.. method:: AbstractEventLoop.time()
Return the current time, as a :class:`float` value, according to the
event loop's internal clock.
.. seealso::
The :func:`asyncio.sleep` function.
Futures
-------
.. method:: AbstractEventLoop.create_future()
Create an :class:`asyncio.Future` object attached to the loop.
This is a preferred way to create futures in asyncio, as event
loop implementations can provide alternative implementations
of the Future class (with better performance or instrumentation).
.. versionadded:: 3.5.2
Tasks
-----
.. method:: AbstractEventLoop.create_task(coro)
Schedule the execution of a :ref:`coroutine object <coroutine>`: wrap it in
a future. Return a :class:`Task` object.
Third-party event loops can use their own subclass of :class:`Task` for
interoperability. In this case, the result type is a subclass of
:class:`Task`.
.. versionadded:: 3.4.2
.. method:: AbstractEventLoop.set_task_factory(factory)
Set a task factory that will be used by
:meth:`AbstractEventLoop.create_task`.
If *factory* is ``None`` the default task factory will be set.
If *factory* is a *callable*, it should have a signature matching
``(loop, coro)``, where *loop* will be a reference to the active
event loop, *coro* will be a coroutine object. The callable
must return an :class:`asyncio.Future` compatible object.
.. versionadded:: 3.4.4
.. method:: AbstractEventLoop.get_task_factory()
Return a task factory, or ``None`` if the default one is in use.
.. versionadded:: 3.4.4
Creating connections
--------------------
.. coroutinemethod:: AbstractEventLoop.create_connection(protocol_factory, host=None, port=None, \*, ssl=None, family=0, proto=0, flags=0, sock=None, local_addr=None, server_hostname=None, ssl_handshake_timeout=None)
Create a streaming transport connection to a given Internet *host* and
*port*: socket family :py:data:`~socket.AF_INET` or
:py:data:`~socket.AF_INET6` depending on *host* (or *family* if specified),
socket type :py:data:`~socket.SOCK_STREAM`. *protocol_factory* must be a
callable returning a :ref:`protocol <asyncio-protocol>` instance.
This method will try to establish the connection in the background.
When successful, it returns a ``(transport, protocol)`` pair.
The chronological synopsis of the underlying operation is as follows:
#. The connection is established, and a :ref:`transport <asyncio-transport>`
is created to represent it.
#. *protocol_factory* is called without arguments and must return a
:ref:`protocol <asyncio-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 that 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.
.. seealso:: :ref:`SSL/TLS security considerations <ssl-security>`
* *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*.
* *ssl_handshake_timeout* is (for an SSL connection) the time in seconds
to wait for the SSL handshake to complete before aborting the connection.
``60.0`` seconds if ``None`` (default).
.. versionadded:: 3.7
The *ssl_handshake_timeout* parameter.
.. versionchanged:: 3.5
On Windows with :class:`ProactorEventLoop`, SSL/TLS is now supported.
.. seealso::
The :func:`open_connection` function can be used to get a pair of
(:class:`StreamReader`, :class:`StreamWriter`) instead of a protocol.
.. coroutinemethod:: AbstractEventLoop.create_datagram_endpoint(protocol_factory, local_addr=None, remote_addr=None, \*, family=0, proto=0, flags=0, reuse_address=None, reuse_port=None, allow_broadcast=None, sock=None)
Create datagram connection: socket family :py:data:`~socket.AF_INET`,
:py:data:`~socket.AF_INET6` or :py:data:`~socket.AF_UNIX` depending on
*host* (or *family* if specified), socket type
:py:data:`~socket.SOCK_DGRAM`. *protocol_factory* must be a
callable returning a :ref:`protocol <asyncio-protocol>` instance.
This method will try to establish the connection in the background.
When successful, it returns a ``(transport, protocol)`` pair.
Options changing how the connection is created:
* *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 :meth:`getaddrinfo`.
* *remote_addr*, if given, is a ``(remote_host, remote_port)`` tuple used
to connect the socket to a remote address. The *remote_host* and
*remote_port* are looked up using :meth:`getaddrinfo`.
* *family*, *proto*, *flags* are the optional address family, protocol
and flags to be passed through to :meth:`getaddrinfo` for *host*
resolution. If given, these should all be integers from the
corresponding :mod:`socket` module constants.
* *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.
* *reuse_port* tells the kernel to allow this endpoint to be bound to the
same port as other existing endpoints are bound to, so long as they all
set this flag when being created. This option is not supported on Windows
and some UNIX's. If the :py:data:`~socket.SO_REUSEPORT` constant is not
defined then this capability is unsupported.
* *allow_broadcast* tells the kernel to allow this endpoint to send
messages to the broadcast address.
* *sock* can optionally be specified in order to use a preexisting,
already connected, :class:`socket.socket` object to be used by the
transport. If specified, *local_addr* and *remote_addr* should be omitted
(must be :const:`None`).
On Windows with :class:`ProactorEventLoop`, this method is not supported.
See :ref:`UDP echo client protocol <asyncio-udp-echo-client-protocol>` and
:ref:`UDP echo server protocol <asyncio-udp-echo-server-protocol>` examples.
.. versionchanged:: 3.4.4
The *family*, *proto*, *flags*, *reuse_address*, *reuse_port,
*allow_broadcast*, and *sock* parameters were added.
.. coroutinemethod:: AbstractEventLoop.create_unix_connection(protocol_factory, path=None, \*, ssl=None, sock=None, server_hostname=None, ssl_handshake_timeout=None)
Create UNIX connection: socket family :py:data:`~socket.AF_UNIX`, socket
type :py:data:`~socket.SOCK_STREAM`. The :py:data:`~socket.AF_UNIX` socket
family is used to communicate between processes on the same machine
efficiently.
This method will try to establish the connection in the background.
When successful, it returns a ``(transport, protocol)`` pair.
*path* is the name of a UNIX domain socket, and is required unless a *sock*
parameter is specified. Abstract UNIX sockets, :class:`str`,
:class:`bytes`, and :class:`~pathlib.Path` paths are supported.
See the :meth:`AbstractEventLoop.create_connection` method for parameters.
Availability: UNIX.
.. versionadded:: 3.7
The *ssl_handshake_timeout* parameter.
.. versionchanged:: 3.7
The *path* parameter can now be a :term:`path-like object`.
Creating listening connections
------------------------------
.. coroutinemethod:: AbstractEventLoop.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, reuse_port=None, ssl_handshake_timeout=None, start_serving=True)
Create a TCP server (socket type :data:`~socket.SOCK_STREAM`) bound to
*host* and *port*.
Return a :class:`Server` object, its :attr:`~Server.sockets` attribute
contains created sockets. Use the :meth:`Server.close` method to stop the
server: close listening sockets.
Parameters:
* The *host* parameter can be a string, in that case the TCP server is
bound to *host* and *port*. The *host* parameter can also be a sequence
of strings and in that case the TCP server is bound to all hosts of the
sequence. 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. If specified, *host* and *port* should be omitted (must be
:const:`None`).
* *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.
* *reuse_port* tells the kernel to allow this endpoint to be bound to the
same port as other existing endpoints are bound to, so long as they all
set this flag when being created. This option is not supported on
Windows.
* *ssl_handshake_timeout* is (for an SSL server) the time in seconds to wait
for the SSL handshake to complete before aborting the connection.
``60.0`` seconds if ``None`` (default).
* *start_serving* set to ``True`` (the default) causes the created server
to start accepting connections immediately. When set to ``False``,
the user should await on :meth:`Server.start_serving` or
:meth:`Server.serve_forever` to make the server to start accepting
connections.
.. versionadded:: 3.7
*ssl_handshake_timeout* and *start_serving* parameters.
.. versionchanged:: 3.5
On Windows with :class:`ProactorEventLoop`, SSL/TLS is now supported.
.. seealso::
The function :func:`start_server` creates a (:class:`StreamReader`,
:class:`StreamWriter`) pair and calls back a function with this pair.
.. versionchanged:: 3.5.1
The *host* parameter can now be a sequence of strings.
.. coroutinemethod:: AbstractEventLoop.create_unix_server(protocol_factory, path=None, \*, sock=None, backlog=100, ssl=None, ssl_handshake_timeout=None, start_serving=True)
Similar to :meth:`AbstractEventLoop.create_server`, but specific to the
socket family :py:data:`~socket.AF_UNIX`.
*path* is the name of a UNIX domain socket, and is required unless a *sock*
parameter is specified. Abstract UNIX sockets, :class:`str`,
:class:`bytes`, and :class:`~pathlib.Path` paths are supported.
Availability: UNIX.
.. versionadded:: 3.7
The *ssl_handshake_timeout* and *start_serving* parameters.
.. versionchanged:: 3.7
The *path* parameter can now be a :class:`~pathlib.Path` object.
.. coroutinemethod:: BaseEventLoop.connect_accepted_socket(protocol_factory, sock, \*, ssl=None, ssl_handshake_timeout=None)
Handle an accepted connection.
This is used by servers that accept connections outside of
asyncio but that use asyncio to handle them.
Parameters:
* *sock* is a preexisting socket object returned from an ``accept``
call.
* *ssl* can be set to an :class:`~ssl.SSLContext` to enable SSL over the
accepted connections.
* *ssl_handshake_timeout* is (for an SSL connection) the time in seconds to
wait for the SSL handshake to complete before aborting the connection.
``60.0`` seconds if ``None`` (default).
When completed it returns a ``(transport, protocol)`` pair.
.. versionadded:: 3.7
The *ssl_handshake_timeout* parameter.
.. versionadded:: 3.5.3
File Transferring
-----------------
.. coroutinemethod:: AbstractEventLoop.sendfile(transport, file, \
offset=0, count=None, \
*, fallback=True)
Send a *file* to *transport*, return the total number of bytes
which were sent.
The method uses high-performance :meth:`os.sendfile` if available.
*file* must be a regular file object opened in binary mode.
*offset* tells from where to start reading the file. If specified,
*count* is the total number of bytes to transmit as opposed to
sending the file until EOF is reached. File position is updated on
return or also in case of error in which case :meth:`file.tell()
<io.IOBase.tell>` can be used to figure out the number of bytes
which were sent.
*fallback* set to ``True`` makes asyncio to manually read and send
the file when the platform does not support the sendfile syscall
(e.g. Windows or SSL socket on Unix).
Raise :exc:`SendfileNotAvailableError` if the system does not support
*sendfile* syscall and *fallback* is ``False``.
.. versionadded:: 3.7
TLS Upgrade
-----------
.. coroutinemethod:: AbstractEventLoop.start_tls(transport, protocol, sslcontext, \*, server_side=False, server_hostname=None, ssl_handshake_timeout=None)
Upgrades an existing connection to TLS.
Returns a new transport instance, that the *protocol* must start using
immediately after the *await*. The *transport* instance passed to
the *start_tls* method should never be used again.
Parameters:
* *transport* and *protocol* instances that methods like
:meth:`~AbstractEventLoop.create_server` and
:meth:`~AbstractEventLoop.create_connection` return.
* *sslcontext*: a configured instance of :class:`~ssl.SSLContext`.
* *server_side* pass ``True`` when a server-side connection is being
upgraded (like the one created by :meth:`~AbstractEventLoop.create_server`).
* *server_hostname*: sets or overrides the host name that the target
server's certificate will be matched against.
* *ssl_handshake_timeout* is (for an SSL connection) the time in seconds to
wait for the SSL handshake to complete before aborting the connection.
``60.0`` seconds if ``None`` (default).
.. versionadded:: 3.7
Watch file descriptors
----------------------
On Windows with :class:`SelectorEventLoop`, only socket handles are supported
(ex: pipe file descriptors are not supported).
On Windows with :class:`ProactorEventLoop`, these methods are not supported.
.. method:: AbstractEventLoop.add_reader(fd, callback, \*args)
Start watching the file descriptor for read availability and then call the
*callback* with specified arguments.
:ref:`Use functools.partial to pass keywords to the callback
<asyncio-pass-keywords>`.
.. method:: AbstractEventLoop.remove_reader(fd)
Stop watching the file descriptor for read availability.
.. method:: AbstractEventLoop.add_writer(fd, callback, \*args)
Start watching the file descriptor for write availability and then call the
*callback* with specified arguments.
:ref:`Use functools.partial to pass keywords to the callback
<asyncio-pass-keywords>`.
.. method:: AbstractEventLoop.remove_writer(fd)
Stop watching the file descriptor for write availability.
The :ref:`watch a file descriptor for read events <asyncio-watch-read-event>`
example uses the low-level :meth:`AbstractEventLoop.add_reader` method to register
the file descriptor of a socket.
Low-level socket operations
---------------------------
.. coroutinemethod:: AbstractEventLoop.sock_recv(sock, nbytes)
Receive data from the socket. Modeled after blocking
:meth:`socket.socket.recv` method.
The return value is a bytes object
representing the data received. The maximum amount of data to be received
at once is specified by *nbytes*.
With :class:`SelectorEventLoop` event loop, the socket *sock* must be
non-blocking.
.. versionchanged:: 3.7
Even though the method was always documented as a coroutine
method, before Python 3.7 it returned a :class:`Future`.
Since Python 3.7, this is an ``async def`` method.
.. coroutinemethod:: AbstractEventLoop.sock_recv_into(sock, buf)
Receive data from the socket. Modeled after blocking
:meth:`socket.socket.recv_into` method.
The received data is written into *buf* (a writable buffer).
The return value is the number of bytes written.
With :class:`SelectorEventLoop` event loop, the socket *sock* must be
non-blocking.
.. versionadded:: 3.7
.. coroutinemethod:: AbstractEventLoop.sock_sendall(sock, data)
Send data to the socket. Modeled after blocking
:meth:`socket.socket.sendall` method.
The socket must be connected to a remote socket.
This method continues to send data from *data* until either all data has
been sent or an error occurs. ``None`` is returned on success. On error,
an exception is raised, and there is no way to determine how much data, if
any, was successfully processed by the receiving end of the connection.
With :class:`SelectorEventLoop` event loop, the socket *sock* must be
non-blocking.
.. versionchanged:: 3.7
Even though the method was always documented as a coroutine
method, before Python 3.7 it returned an :class:`Future`.
Since Python 3.7, this is an ``async def`` method.
.. coroutinemethod:: AbstractEventLoop.sock_connect(sock, address)
Connect to a remote socket at *address*. Modeled after
blocking :meth:`socket.socket.connect` method.
With :class:`SelectorEventLoop` event loop, the socket *sock* must be
non-blocking.
.. versionchanged:: 3.5.2
``address`` no longer needs to be resolved. ``sock_connect``
will try to check if the *address* is already resolved by calling
:func:`socket.inet_pton`. If not,
:meth:`AbstractEventLoop.getaddrinfo` will be used to resolve the
*address*.
.. seealso::
:meth:`AbstractEventLoop.create_connection`
and :func:`asyncio.open_connection() <open_connection>`.
.. coroutinemethod:: AbstractEventLoop.sock_accept(sock)
Accept a connection. Modeled after blocking
:meth:`socket.socket.accept`.
The socket must be bound to an address and listening
for connections. The return value is a pair ``(conn, address)`` where *conn*
is a *new* socket object usable to send and receive data on the connection,
and *address* is the address bound to the socket on the other end of the
connection.
The socket *sock* must be non-blocking.
.. versionchanged:: 3.7
Even though the method was always documented as a coroutine
method, before Python 3.7 it returned a :class:`Future`.
Since Python 3.7, this is an ``async def`` method.
.. seealso::
:meth:`AbstractEventLoop.create_server` and :func:`start_server`.
.. coroutinemethod:: AbstractEventLoop.sock_sendfile(sock, file, \
offset=0, count=None, \
*, fallback=True)
Send a file using high-performance :mod:`os.sendfile` if possible
and return the total number of bytes which were sent.
Asynchronous version of :meth:`socket.socket.sendfile`.
*sock* must be non-blocking :class:`~socket.socket` of
:const:`socket.SOCK_STREAM` type.
*file* must be a regular file object opened in binary mode.
*offset* tells from where to start reading the file. If specified,
*count* is the total number of bytes to transmit as opposed to
sending the file until EOF is reached. File position is updated on
return or also in case of error in which case :meth:`file.tell()
<io.IOBase.tell>` can be used to figure out the number of bytes
which were sent.
*fallback* set to ``True`` makes asyncio to manually read and send
the file when the platform does not support the sendfile syscall
(e.g. Windows or SSL socket on Unix).
Raise :exc:`SendfileNotAvailableError` if the system does not support
*sendfile* syscall and *fallback* is ``False``.
.. versionadded:: 3.7
Resolve host name
-----------------
.. coroutinemethod:: AbstractEventLoop.getaddrinfo(host, port, \*, family=0, type=0, proto=0, flags=0)
This method is a :ref:`coroutine <coroutine>`, similar to
:meth:`socket.getaddrinfo` function but non-blocking.
.. coroutinemethod:: AbstractEventLoop.getnameinfo(sockaddr, flags=0)
This method is a :ref:`coroutine <coroutine>`, similar to
:meth:`socket.getnameinfo` function but non-blocking.
.. versionchanged:: 3.7
Both *getaddrinfo* and *getnameinfo* methods were always documented
to return a coroutine, but prior to Python 3.7 they were, in fact,
returning :class:`asyncio.Future` objects. Starting with Python 3.7
both methods are coroutines.
Connect pipes
-------------
On Windows with :class:`SelectorEventLoop`, these methods are not supported.
Use :class:`ProactorEventLoop` to support pipes on Windows.
.. coroutinemethod:: AbstractEventLoop.connect_read_pipe(protocol_factory, pipe)
Register read pipe in eventloop.
*protocol_factory* should instantiate object with :class:`Protocol`
interface. *pipe* is a :term:`file-like object <file object>`.
Return pair ``(transport, protocol)``, where *transport* supports the
:class:`ReadTransport` interface.
With :class:`SelectorEventLoop` event loop, the *pipe* is set to
non-blocking mode.
.. coroutinemethod:: AbstractEventLoop.connect_write_pipe(protocol_factory, pipe)
Register write pipe in eventloop.
*protocol_factory* should instantiate object with :class:`BaseProtocol`
interface. *pipe* is :term:`file-like object <file object>`.
Return pair ``(transport, protocol)``, where *transport* supports
:class:`WriteTransport` interface.
With :class:`SelectorEventLoop` event loop, the *pipe* is set to
non-blocking mode.
.. seealso::
The :meth:`AbstractEventLoop.subprocess_exec` and
:meth:`AbstractEventLoop.subprocess_shell` methods.
UNIX signals
------------
Availability: UNIX only.
.. method:: AbstractEventLoop.add_signal_handler(signum, callback, \*args)
Add a handler for a signal.
Raise :exc:`ValueError` if the signal number is invalid or uncatchable.
Raise :exc:`RuntimeError` if there is a problem setting up the handler.
:ref:`Use functools.partial to pass keywords to the callback
<asyncio-pass-keywords>`.
.. method:: AbstractEventLoop.remove_signal_handler(sig)
Remove a handler for a signal.
Return ``True`` if a signal handler was removed, ``False`` if not.
.. seealso::
The :mod:`signal` module.
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:: AbstractEventLoop.run_in_executor(executor, func, \*args)
Arrange for a *func* to be called in the specified executor.
The *executor* argument should be an :class:`~concurrent.futures.Executor`
instance. The default executor is used if *executor* is ``None``.
:ref:`Use functools.partial to pass keywords to the *func*
<asyncio-pass-keywords>`.
This method returns a :class:`asyncio.Future` object.
.. versionchanged:: 3.5.3
:meth:`BaseEventLoop.run_in_executor` no longer configures the
``max_workers`` of the thread pool executor it creates, instead
leaving it up to the thread pool executor
(:class:`~concurrent.futures.ThreadPoolExecutor`) to set the
default.
.. method:: AbstractEventLoop.set_default_executor(executor)
Set the default executor used by :meth:`run_in_executor`.
Error Handling API
------------------
Allows customizing how exceptions are handled in the event loop.
.. method:: AbstractEventLoop.set_exception_handler(handler)
Set *handler* as the new event loop exception handler.
If *handler* is ``None``, the default exception handler will
be set.
If *handler* is a callable object, it should have a
matching signature to ``(loop, context)``, where ``loop``
will be a reference to the active event loop, ``context``
will be a ``dict`` object (see :meth:`call_exception_handler`
documentation for details about context).
.. method:: AbstractEventLoop.get_exception_handler()
Return the exception handler, or ``None`` if the default one
is in use.
.. versionadded:: 3.5.2
.. method:: AbstractEventLoop.default_exception_handler(context)
Default exception handler.
This is called when an exception occurs and no exception
handler is set, and can be called by a custom exception
handler that wants to defer to the default behavior.
*context* parameter has the same meaning as in
:meth:`call_exception_handler`.
.. method:: AbstractEventLoop.call_exception_handler(context)
Call the current event loop exception handler.
*context* is a ``dict`` object containing the following keys
(new keys may be introduced later):
* 'message': Error message;
* 'exception' (optional): Exception object;
* 'future' (optional): :class:`asyncio.Future` instance;
* 'handle' (optional): :class:`asyncio.Handle` instance;
* 'protocol' (optional): :ref:`Protocol <asyncio-protocol>` instance;
* 'transport' (optional): :ref:`Transport <asyncio-transport>` instance;
* 'socket' (optional): :class:`socket.socket` instance.
.. note::
Note: this method should not be overloaded in subclassed
event loops. For any custom exception handling, use
:meth:`set_exception_handler()` method.
Debug mode
----------
.. method:: AbstractEventLoop.get_debug()
Get the debug mode (:class:`bool`) of the event loop.
The default value is ``True`` if the environment variable
:envvar:`PYTHONASYNCIODEBUG` is set to a non-empty string, ``False``
otherwise.
.. versionadded:: 3.4.2
.. method:: AbstractEventLoop.set_debug(enabled: bool)
Set the debug mode of the event loop.
.. versionadded:: 3.4.2
.. seealso::
The :ref:`debug mode of asyncio <asyncio-debug-mode>`.
Server
------
.. class:: Server
Server listening on sockets.
Object created by :meth:`AbstractEventLoop.create_server`,
:meth:`AbstractEventLoop.create_unix_server`, :func:`start_server`,
and :func:`start_unix_server` functions. Don't instantiate the class
directly.
*Server* objects are asynchronous context managers. When used in an
``async with`` statement, it's guaranteed that the Server object is
closed and not accepting new connections when the ``async with``
statement is completed::
srv = await loop.create_server(...)
async with srv:
# some code
# At this point, srv is closed and no longer accepts new connections.
.. versionchanged:: 3.7
Server object is an asynchronous context manager since Python 3.7.
.. method:: close()
Stop serving: close listening sockets and set the :attr:`sockets`
attribute to ``None``.
The sockets that represent existing incoming client connections are left
open.
The server is closed asynchronously, use the :meth:`wait_closed`
coroutine to wait until the server is closed.
.. method:: get_loop()
Gives the event loop associated with the server object.
.. versionadded:: 3.7
.. coroutinemethod:: start_serving()
Start accepting connections.
This method is idempotent, so it can be called when
the server is already being serving.
The new *start_serving* keyword-only parameter to
:meth:`AbstractEventLoop.create_server` and
:meth:`asyncio.start_server` allows to create a Server object
that is not accepting connections right away. In which case
this method, or :meth:`Server.serve_forever` can be used
to make the Server object to start accepting connections.
.. versionadded:: 3.7
.. coroutinemethod:: serve_forever()
Start accepting connections until the coroutine is cancelled.
Cancellation of ``serve_forever`` task causes the server
to be closed.
This method can be called if the server is already accepting
connections. Only one ``serve_forever`` task can exist per
one *Server* object.
Example::
async def client_connected(reader, writer):
# Communicate with the client with
# reader/writer streams. For example:
await reader.readline()
async def main(host, port):
srv = await asyncio.start_server(
client_connected, host, port)
await srv.serve_forever()
asyncio.run(main('127.0.0.1', 0))
.. versionadded:: 3.7
.. method:: is_serving()
Return ``True`` if the server is accepting new connections.
.. versionadded:: 3.7
.. coroutinemethod:: wait_closed()
Wait until the :meth:`close` method completes.
.. attribute:: sockets
List of :class:`socket.socket` objects the server is listening to, or
``None`` if the server is closed.
.. versionchanged:: 3.7
Prior to Python 3.7 ``Server.sockets`` used to return the
internal list of server's sockets directly. In 3.7 a copy
of that list is returned.
Handle
------
.. class:: Handle
A callback wrapper object returned by :func:`AbstractEventLoop.call_soon`,
:func:`AbstractEventLoop.call_soon_threadsafe`.
.. method:: cancel()
Cancel the call. If the callback is already canceled or executed,
this method has no effect.
.. method:: cancelled()
Return ``True`` if the call was cancelled.
.. versionadded:: 3.7
.. class:: TimerHandle
A callback wrapper object returned by :func:`AbstractEventLoop.call_later`,
and :func:`AbstractEventLoop.call_at`.
The class is inherited from :class:`Handle`.
.. method:: when()
Return a scheduled callback time as :class:`float` seconds.
The time is an absolute timestamp, using the same time
reference as :meth:`AbstractEventLoop.time`.
.. versionadded:: 3.7
SendfileNotAvailableError
-------------------------
.. exception:: SendfileNotAvailableError
Sendfile syscall is not available, subclass of :exc:`RuntimeError`.
Raised if the OS does not support sendfile syscall for
given socket or file type.
Event loop examples
-------------------
.. _asyncio-hello-world-callback:
Hello World with call_soon()
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Example using the :meth:`AbstractEventLoop.call_soon` method to schedule a
callback. The callback displays ``"Hello World"`` and then stops the event
loop::
import asyncio
def hello_world(loop):
print('Hello World')
loop.stop()
loop = asyncio.get_event_loop()
# Schedule a call to hello_world()
loop.call_soon(hello_world, loop)
# Blocking call interrupted by loop.stop()
loop.run_forever()
loop.close()
.. seealso::
The :ref:`Hello World coroutine <asyncio-hello-world-coroutine>` example
uses a :ref:`coroutine <coroutine>`.
.. _asyncio-date-callback:
Display the current date with call_later()
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Example of callback displaying the current date every second. The callback uses
the :meth:`AbstractEventLoop.call_later` method to reschedule itself during 5
seconds, and then stops the event loop::
import asyncio
import datetime
def display_date(end_time, loop):
print(datetime.datetime.now())
if (loop.time() + 1.0) < end_time:
loop.call_later(1, display_date, end_time, loop)
else:
loop.stop()
loop = asyncio.get_event_loop()
# Schedule the first call to display_date()
end_time = loop.time() + 5.0
loop.call_soon(display_date, end_time, loop)
# Blocking call interrupted by loop.stop()
loop.run_forever()
loop.close()
.. seealso::
The :ref:`coroutine displaying the current date
<asyncio-date-coroutine>` example uses a :ref:`coroutine
<coroutine>`.
.. _asyncio-watch-read-event:
Watch a file descriptor for read events
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Wait until a file descriptor received some data using the
:meth:`AbstractEventLoop.add_reader` method and then close the event loop::
import asyncio
from socket import socketpair
# Create a pair of connected file descriptors
rsock, wsock = socketpair()
loop = asyncio.get_event_loop()
def reader():
data = rsock.recv(100)
print("Received:", data.decode())
# We are done: unregister the file descriptor
loop.remove_reader(rsock)
# Stop the event loop
loop.stop()
# Register the file descriptor for read event
loop.add_reader(rsock, reader)
# Simulate the reception of data from the network
loop.call_soon(wsock.send, 'abc'.encode())
# Run the event loop
loop.run_forever()
# We are done, close sockets and the event loop
rsock.close()
wsock.close()
loop.close()
.. seealso::
The :ref:`register an open socket to wait for data using a protocol
<asyncio-register-socket>` example uses a low-level protocol created by the
:meth:`AbstractEventLoop.create_connection` method.
The :ref:`register an open socket to wait for data using streams
<asyncio-register-socket-streams>` example uses high-level streams
created by the :func:`open_connection` function in a coroutine.
Set signal handlers for SIGINT and SIGTERM
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Register handlers for signals :py:data:`SIGINT` and :py:data:`SIGTERM` using
the :meth:`AbstractEventLoop.add_signal_handler` method::
import asyncio
import functools
import os
import signal
def ask_exit(signame):
print("got signal %s: exit" % signame)
loop.stop()
loop = asyncio.get_event_loop()
for signame in ('SIGINT', 'SIGTERM'):
loop.add_signal_handler(getattr(signal, signame),
functools.partial(ask_exit, signame))
print("Event loop running forever, press Ctrl+C to interrupt.")
print("pid %s: send SIGINT or SIGTERM to exit." % os.getpid())
try:
loop.run_forever()
finally:
loop.close()
This example only works on UNIX.
