cpython: 2c9d5f32f6c5 (original) (raw)

--- a/Doc/library/asyncio-eventloop.rst +++ b/Doc/library/asyncio-eventloop.rst @@ -2,8 +2,8 @@ .. _asyncio-event-loop: -Event loops -=========== +Base Event Loop +=============== The event loop is the central execution device provided by :mod:asyncio. It provides multiple facilities, amongst which: @@ -18,78 +18,9 @@ It provides multiple facilities, amongst

Delegating costly function calls to a pool of threads. -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 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() +.. class:: BaseEventLoop

Equivalent to calling get_event_loop_policy().new_event_loop(). -

-Event loop policy interface ---------------------------- - -An event loop policy must implement the following interface: - -.. class:: AbstractEventLoopPolicy -

.. method:: get_event_loop() -
Get the event loop for the current context. Returns an event loop object
implementing the :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. -
.. 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.

Base class of event loops.

Run an event loop ----------------- @@ -375,7 +306,6 @@ Creating listening connections Availability: UNIX. - Watch file descriptors ---------------------- @@ -624,7 +554,6 @@ Debug mode The :ref:debug mode of asyncio <asyncio-debug-mode>. - Server ------ @@ -652,7 +581,8 @@ Handle .. method:: cancel()

Cancel the call.

```
 Cancel the call.[](#l1.116)
```

+ .. _asyncio-hello-world-callback:

copy from Doc/library/asyncio-eventloop.rst copy to Doc/library/asyncio-eventloops.rst --- a/Doc/library/asyncio-eventloop.rst +++ b/Doc/library/asyncio-eventloops.rst @@ -1,40 +1,8 @@ .. currentmodule:: asyncio -.. _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 <asyncio-transport> for various

kinds of communication. - -* Launching subprocesses and the associated :ref:`transports
for communication with an external program.[](#l2.22) -[](#l2.23) -* Delegating costly function calls to a pool of threads.[](#l2.24) -[](#l2.25) -Event loop policies and the default policy[](#l2.26) -------------------------------------------[](#l2.27) -[](#l2.28) -Event loop management is abstracted with a *policy* pattern, to provide maximal[](#l2.29) -flexibility for custom platforms and frameworks. Throughout the execution of a[](#l2.30) -process, a single global policy object manages the event loops available to the[](#l2.31) -process based on the calling context. A policy is an object implementing the[](#l2.32) -:class:AbstractEventLoopPolicy interface.[](#l2.33) -[](#l2.34) -For most users of :mod:asyncio, policies never have to be dealt with[](#l2.35) -explicitly, since the default global policy is sufficient.[](#l2.36) -[](#l2.37) -The default policy defines context as the current thread, and manages an event[](#l2.38) -loop per thread that interacts with :mod:asyncio. The module-level functions[](#l2.39) -:func:get_event_loop and :func:set_event_loop provide convenient access to[](#l2.40) -event loops managed by the default policy.[](#l2.41) -[](#l2.42) Event loop functions[](#l2.43) --------------------[](#l2.44) [](#l2.45) @@ -55,6 +23,121 @@ the execution of the process.[](#l2.46) [](#l2.47) Equivalent to calling ``get_event_loop_policy().new_event_loop()``.[](#l2.48) [](#l2.49) +[](#l2.50) +Available event loops[](#l2.51) +---------------------[](#l2.52) +[](#l2.53) +asyncio currently provides two implementations of event loops:[](#l2.54) +: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. +

+.. 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[](#l2.73)

 <http://msdn.microsoft.com/en-us/library/windows/desktop/aa365198%28v=vs.85%29.aspx>`_.[](#l2.74)

+ +Example to use a :class:ProactorEventLoop on Windows:: +

import asyncio, os

if os.name == 'nt':

   loop = asyncio.ProactorEventLoop()[](#l2.81)

   asyncio.set_event_loop(loop)[](#l2.82)

+ + +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_server and

:meth:~BaseEventLoop.create_unix_server are not supported: specific to UNIX +- :meth:~BaseEventLoop.add_signal_handler and
:meth:~BaseEventLoop.remove_signal_handler are not supported +- Pipes are not supported: :meth:~BaseEventLoop.connect_read_pipe and
:meth:~BaseEventLoop.connect_write_pipe +- :meth:EventLoopPolicy.set_child_watcher is not supported + +:class:SelectorEventLoop specific limits: + +- :class:~selectors.SelectSelector is used but it only supports sockets,
see the `MSDN documentation of select
http://msdn.microsoft.com/en-us/library/windows/desktop/ms740141%28v=vs.85%29.aspx_.[](#l2.108) +- it is not possible to execute subprocesses[](#l2.109) +- :meth:~~BaseEventLoop.add_reader and :meth:~~BaseEventLoop.add_writer` only
accept file descriptors of sockets + +:class:ProactorEventLoop specific limits: + +- SSL is not supported: :meth:~BaseEventLoop.create_connection and
:meth:~BaseEventLoop.create_server cannot be used with SSL for example +- :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 exact resolution depends on the hardware +(availability of HPET) and the Windows configuration. See :ref:asyncio delayed[](#l2.123) +calls <asyncio-delayed-calls>. + + +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 --------------------------- @@ -91,618 +174,3 @@ Access to the global loop policy Set the current event loop policy. If policy is None, the default policy is restored. -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 :ref:coroutine object <coroutine>, it is wrapped by
:func:async. -
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.is_closed() -

Returns True if the event loop was closed. -
.. versionadded:: 3.4.2 -

-.. 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. -
The event loop must not be running. -
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. -
An instance of :class:asyncio.Handle is returned. -

-.. method:: BaseEventLoop.call_soon_threadsafe(callback, *args) -

Like :meth:call_soon, but thread safe. -

- -.. _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:: BaseEventLoop.call_later(delay, callback, *args) -

Arrange for the callback to be called after the given delay
seconds (either an int or float). -
An instance of :class:asyncio.Handle is returned. -
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. -

- -Coroutines ----------- - -.. method:: BaseEventLoop.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. -
.. seealso:: -
```
 The :meth:`async` function.[](#l2.300)
```

.. versionadded:: 3.4.2 -

- -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: 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 is 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 <asyncio-transport>
```
 is created to represent it.[](#l2.323)
```

#. protocol_factory is called without arguments and must return a

 :ref:`protocol <asyncio-protocol>` instance.[](#l2.326)

#. The protocol instance is tied to the transport, and its

 :meth:`connection_made` method is called.[](#l2.329)

#. The coroutine returns successfully with the (transport, protocol)
```
 pair.[](#l2.332)
```

The created transport is an implementation-dependent bidirectional stream. -
.. note::

 *protocol_factory* can be any kind of callable, not necessarily[](#l2.337)

 a class.  For example, if you want to use a pre-created[](#l2.338)

 protocol instance, you can pass ``lambda: my_protocol``.[](#l2.339)

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[](#l2.344)

a :class:`ssl.SSLContext` object, this context is used to create[](#l2.345)

the transport; if *ssl* is :const:`True`, a context with some[](#l2.346)

unspecified default settings is used.[](#l2.347)

.. seealso:: :ref:`SSL/TLS security considerations <ssl-security>`[](#l2.349)

- server_hostname, is only for use together with ssl,

and sets or overrides the hostname that the target server's certificate[](#l2.352)

will be matched against.  By default the value of the *host* argument[](#l2.353)

is used.  If *host* is empty, there is no default and you must pass a[](#l2.354)

value for *server_hostname*.  If *server_hostname* is an empty[](#l2.355)

string, hostname matching is disabled (which is a serious security[](#l2.356)

risk, allowing for man-in-the-middle-attacks).[](#l2.357)

- family, proto, flags are the optional address family, protocol

and flags to be passed through to getaddrinfo() for *host* resolution.[](#l2.360)

If given, these should all be integers from the corresponding[](#l2.361)

:mod:`socket` module constants.[](#l2.362)

- sock, if given, should be an existing, already connected

:class:`socket.socket` object to be used by the transport.[](#l2.365)

If *sock* is given, none of *host*, *port*, *family*, *proto*, *flags*[](#l2.366)

and *local_addr* should be specified.[](#l2.367)

- local_addr, if given, is a (local_host, local_port) tuple used

to bind the socket to locally.  The *local_host* and *local_port*[](#l2.370)

are looked up using getaddrinfo(), similarly to *host* and *port*.[](#l2.371)

.. seealso:: -

 The :func:`open_connection` function can be used to get a pair of[](#l2.375)

 (:class:`StreamReader`, :class:`StreamWriter`) instead of a protocol.[](#l2.376)

- - -.. method:: BaseEventLoop.create_datagram_endpoint(protocol_factory, local_addr=None, remote_addr=None, *, family=0, proto=0, flags=0) -

Create datagram connection: 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_DGRAM. -
This method is a :ref:coroutine <coroutine> which will try to
establish the connection in the background. When successful, the
coroutine returns a (transport, protocol) pair. -
See the :meth:BaseEventLoop.create_connection method for parameters. -

- -.. method:: BaseEventLoop.create_unix_connection(protocol_factory, path, *, ssl=None, sock=None, server_hostname=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 is a :ref:coroutine <coroutine> which will try to
establish the connection in the background. When successful, the
coroutine returns a (transport, protocol) pair. -
See the :meth:BaseEventLoop.create_connection method for parameters. -
Availability: UNIX. -

- -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) -

Create a TCP server bound to host and port. Return an
:class:AbstractServer object which can be used to stop the service. -
This method is a :ref:coroutine <coroutine>. -
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. -
.. seealso:: -

 The function :func:`start_server` creates a (:class:`StreamReader`,[](#l2.444)

 :class:`StreamWriter`) pair and calls back a function with this pair.[](#l2.445)

- - -.. method:: BaseEventLoop.create_unix_server(protocol_factory, path=None, *, sock=None, backlog=100, ssl=None) -

Similar to :meth:BaseEventLoop.create_server, but specific to the
socket family :py:data:~socket.AF_UNIX. -
Availability: UNIX. -

- - -Watch file descriptors ----------------------- - -.. method:: BaseEventLoop.add_reader(fd, callback, *args) -

Start watching the file descriptor for read availability and then call the
callback with specified arguments. -

-.. method:: BaseEventLoop.remove_reader(fd) -

Stop watching the file descriptor for read availability. -

-.. method:: BaseEventLoop.add_writer(fd, callback, *args) -

Start watching the file descriptor for write availability and then call the
callback with specified arguments. -

-.. method:: BaseEventLoop.remove_writer(fd) -

Stop watching the file descriptor for write availability. -

- -Low-level socket operations ---------------------------- - -.. method:: BaseEventLoop.sock_recv(sock, nbytes) -

Receive data from the socket. 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. -
This method is a :ref:coroutine <coroutine>. -
.. seealso:: -

 The :meth:`socket.socket.recv` method.[](#l2.492)

- -.. method:: BaseEventLoop.sock_sendall(sock, data) -

Send data to the socket. 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. -
This method is a :ref:coroutine <coroutine>. -
.. seealso:: -

 The :meth:`socket.socket.sendall` method.[](#l2.506)

- -.. method:: BaseEventLoop.sock_connect(sock, address) -

Connect to a remote socket at address. -
The address must be already resolved to avoid the trap of hanging the
entire event loop when the address requires doing a DNS lookup. For
example, it must be an IP address, not an hostname, for
:py:data:~socket.AF_INET and :py:data:~socket.AF_INET6 address families.
Use :meth:getaddrinfo to resolve the hostname asynchronously. -
This method is a :ref:coroutine <coroutine>. -
.. seealso:: -

 The :meth:`BaseEventLoop.create_connection` method, the[](#l2.522)

 :func:`open_connection` function and the :meth:`socket.socket.connect`[](#l2.523)

```
 method.[](#l2.524)
```

- - -.. method:: BaseEventLoop.sock_accept(sock) -

Accept a connection. 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. -
This method is a :ref:coroutine <coroutine>. -
.. seealso:: -

 The :meth:`BaseEventLoop.create_server` method, the :func:`start_server`[](#l2.539)

 function and the :meth:`socket.socket.accept` method.[](#l2.540)

- - -Resolve host name ------------------ - -.. method:: BaseEventLoop.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. -

-.. method:: BaseEventLoop.getnameinfo(sockaddr, flags=0) -

This method is a :ref:coroutine <coroutine>, similar to
:meth:socket.getnameinfo function but non-blocking. -

- -Connect pipes -------------- - -.. method:: BaseEventLoop.connect_read_pipe(protocol_factory, pipe) -

Register read pipe in eventloop. Set the pipe to non-blocking mode. -
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. -
This method is 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 is a :ref:coroutine <coroutine>. -

-.. seealso:: -

The :meth:BaseEventLoop.subprocess_exec and
:meth:BaseEventLoop.subprocess_shell methods. -

- -UNIX signals ------------- - -Availability: UNIX only. - -.. method:: BaseEventLoop.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. -

-.. method:: BaseEventLoop.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:: BaseEventLoop.run_in_executor(executor, callback, *args) -

Arrange for a callback 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. -
This method is a :ref:coroutine <coroutine>. -

-.. method:: BaseEventLoop.set_default_executor(executor) -

Set the default executor used by :meth:run_in_executor. -

- -Error Handling API ------------------- - -Allows to customize how exceptions are handled in the event loop. - -.. method:: BaseEventLoop.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:: BaseEventLoop.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:: BaseEventLoop.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[](#l2.678)

  event loops.  For any custom exception handling, use[](#l2.679)

  :meth:`set_exception_handler()` method.[](#l2.680)

- -Debug mode ----------- - -.. method:: BaseEventLoop.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:: BaseEventLoop.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:: AbstractServer -

Abstract server returned by :func:BaseEventLoop.create_server. -
.. method:: close() -

 Stop serving.  This leaves existing connections open.[](#l2.715)

.. method:: wait_closed() -

 A :ref:`coroutine <coroutine>` to wait until service is closed.[](#l2.719)

- - -Handle ------- - -.. class:: Handle -

A callback wrapper object returned by :func:BaseEventLoop.call_soon,
:func:BaseEventLoop.call_soon_threadsafe, :func:BaseEventLoop.call_later,
and :func:BaseEventLoop.call_at. -
.. method:: cancel() -
Cancel the call. -

- -.. _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')[](#l2.746)
```

   loop.call_later(2, print_and_repeat, loop)[](#l2.747)

loop = asyncio.get_event_loop()
loop.call_soon(print_and_repeat, loop)
try:
```
   loop.run_forever()[](#l2.752)
```
finally:
```
   loop.close()[](#l2.754)
```

- -.. seealso:: -

:ref:Hello World example using a coroutine <asyncio-hello-world-coroutine>. -

- -Example: Set signal handlers for SIGINT and SIGTERM ---------------------------------------------------- - -Register handlers for signals :py:data:SIGINT and :py:data:SIGTERM:: -

import asyncio
import functools
import os
import signal

def ask_exit(signame):

   print("got signal %s: exit" % signame)[](#l2.772)

```
   loop.stop()[](#l2.773)
```

loop = asyncio.get_event_loop()
for signame in ('SIGINT', 'SIGTERM'):

   loop.add_signal_handler(getattr(signal, signame),[](#l2.777)

                           functools.partial(ask_exit, signame))[](#l2.778)

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()[](#l2.783)
```
finally:
```
   loop.close()[](#l2.785)
```

--- a/Doc/library/asyncio-subprocess.rst +++ b/Doc/library/asyncio-subprocess.rst @@ -3,18 +3,18 @@ Subprocess ========== -Operating system support ------------------------- +Windows event loop +------------------ -On Windows, the default event loop uses :class:selectors.SelectSelector -which only supports sockets. The :class:ProactorEventLoop should be used to -support subprocesses. However, the latter does not support SSL. +On Windows, the default event loop is :class:SelectorEventLoop which does not +support subprocesses. :class:ProactorEventLoop should be used instead. +Example to use it on Windows:: -On Mac OS X older than 10.9 (Mavericks), :class:selectors.KqueueSelector -does not support character devices like PTY, whereas it is used by the -default event loop. The :class:SelectorEventLoop can be used with -:class:SelectSelector or :class:PollSelector to handle character -devices on Mac OS X 10.6 (Snow Leopard) and later.

import asyncio, os

if os.name == 'nt':

   loop = asyncio.ProactorEventLoop()[](#l3.27)

   asyncio.set_event_loop(loop)[](#l3.28)

Create a subprocess: high-level API using Process

--- a/Doc/library/asyncio.rst +++ b/Doc/library/asyncio.rst @@ -45,6 +45,7 @@ Table of content: :maxdepth: 3 asyncio-eventloop.rst

asyncio-eventloops.rst asyncio-task.rst asyncio-protocol.rst asyncio-stream.rst