bpo-33649: Refresh Tasks and Futures pages (#9314)

* bpo-33649: Refresh Tasks and Futures pages

* Fixes

* Fix markup
This commit is contained in:
Yury Selivanov 2018-09-14 13:32:07 -07:00 committed by Carol Willing
parent ad8a000420
commit 3faaa8857a
5 changed files with 885 additions and 721 deletions

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@ -1429,7 +1429,7 @@ event loop::
.. seealso::
A similar :ref:`Hello World <asyncio-hello-world-coroutine>`
A similar :ref:`Hello World <coroutine>`
example created with a coroutine and the :func:`run` function.

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@ -0,0 +1,240 @@
.. currentmodule:: asyncio
=======
Futures
=======
*Future* objects are used to bridge low-level callback-based code
with high-level async/await code.
Future Functions
================
.. function:: isfuture(obj)
Return ``True`` if *obj* is either of:
* an instance of :class:`asyncio.Future`,
* an instance of :class:`asyncio.Task`,
* a Future-like object with a ``_asyncio_future_blocking``
attribute.
.. versionadded:: 3.5
.. function:: ensure_future(obj, \*, loop=None)
Return:
* *obj* argument as is, if *obj* is a :class:`Future`,
a :class:`Task`, or a Future-like object (:func:`isfuture`
is used for the test.)
* a :class:`Task` object wrapping *obj*, if *obj* is a
coroutine (:func:`iscoroutine` is used for the test.)
* a :class:`Task` object that would await on *obj*, if *obj* is an
awaitable (:func:`inspect.isawaitable` is used for the test.)
If *obj* is neither of the above a :exc:`TypeError` is raised.
.. important::
See also the :func:`create_task` function which is the
preferred way for creating new Tasks.
.. versionchanged:: 3.5.1
The function accepts any :term:`awaitable` object.
.. function:: wrap_future(future, \*, loop=None)
Wrap a :class:`concurrent.futures.Future` object in a
:class:`asyncio.Future` object.
Future Object
=============
.. class:: Future(\*, loop=None)
A Future represents an eventual result of an asynchronous
operation. Not thread-safe.
Future is an :term:`awaitable` object. Coroutines can await on
Future objects until they either have a result or an exception
set, or until they are cancelled.
Typically Futures are used to enable low-level
callback-based code (e.g. in protocols implemented using asyncio
:ref:`transports <asyncio-transports-protocols>`)
to interoperate with high-level async/await code.
The rule of thumb is to never expose Future objects in user-facing
APIs, and the recommended way to create a Future object is to call
:meth:`loop.create_future`. This way alternative event loop
implementations can inject their own optimized implementations
of a Future object.
.. versionchanged:: 3.7
Added support for the :mod:`contextvars` module.
.. method:: result()
Return the result of the Future.
If the Future is *done* and has a result set by the
:meth:`set_result` method, the result value is returned.
If the Future is *done* and has an exception set by the
:meth:`set_exception` method, this method raises the exception.
If the Future has been *cancelled*, this method raises
a :exc:`CancelledError` exception.
If the Future's result isn't yet available, this method raises
a :exc:`InvalidStateError` exception.
.. method:: set_result(result)
Mark the Future as *done* and set its result.
Raises a :exc:`InvalidStateError` error if the Future is
already *done*.
.. method:: set_exception(exception)
Mark the Future as *done* and set an exception.
Raises a :exc:`InvalidStateError` error if the Future is
already *done*.
.. method:: done()
Return ``True`` if the Future is *done*.
A Future is *done* if it was *cancelled* or if it has a result
or an exception set with :meth:`set_result` or
:meth:`set_exception` calls.
.. method:: add_done_callback(callback, *, context=None)
Add a callback to be run when the Future is *done*.
The *callback* is called with the Future object as its only
argument.
If the Future is already *done* when this method is called,
the callback is scheduled with :meth:`loop.call_soon`.
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.
:func:`functools.partial` can be used to pass parameters
to the callback, e.g.::
# Call 'print("Future:", fut)' when "fut" is done.
fut.add_done_callback(
functools.partial(print, "Future:"))
.. versionchanged:: 3.7
The *context* keyword-only parameter was added.
See :pep:`567` for more details.
.. method:: remove_done_callback(callback)
Remove *callback* from the callbacks list.
Returns the number of callbacks removed, which is typically 1,
unless a callback was added more than once.
.. method:: cancel()
Cancel the Future and schedule callbacks.
If the Future is already *done* or *cancelled*, return ``False``.
Otherwise, change the Future's state to *cancelled*,
schedule the callbacks, and return ``True``.
.. method:: exception()
Return the exception that was set on this Future.
The exception (or ``None`` if no exception was set) is
returned only if the Future is *done*.
If the Future has been *cancelled*, this method raises a
:exc:`CancelledError` exception.
If the Future isn't *done* yet, this method raises an
:exc:`InvalidStateError` exception.
.. method:: get_loop()
Return the event loop the Future object is bound to.
.. versionadded:: 3.7
.. method:: cancelled()
Return ``True`` if the Future was *cancelled*.
This example creates a Future object, creates and schedules an
asynchronous Task to set result for the Future, and waits until
the Future has a result::
async def set_after(fut, delay, value):
# Sleep for *delay* seconds.
await asyncio.sleep(delay)
# Set *value* as a result of *fut* Future.
fut.set_result(value)
async def main():
# Get the current event loop.
loop = asyncio.get_running_loop()
# Create a new Future object.
fut = loop.create_future()
# Run "set_after()" coroutine in a parallel Task.
# We are using the low-level "loop.create_task()" API here because
# we already have a reference to the event loop at hand.
# Otherwise we could have just used "asyncio.create_task()".
loop.create_task(
set_after(fut, 1, '... world'))
print('hello ...')
# Wait until *fut* has a result (1 second) and print it.
print(await fut)
asyncio.run(main())
.. important::
The Future object was designed to mimic
:class:`concurrent.futures.Future`. Key differences include:
- unlike asyncio Futures, :class:`concurrent.futures.Future`
instances cannot be awaited.
- :meth:`asyncio.Future.result` and :meth:`asyncio.Future.exception`
do not accept the *timeout* argument.
- :meth:`asyncio.Future.result` and :meth:`asyncio.Future.exception`
raise an :exc:`InvalidStateError` exception when the Future is not
*done*.
- Callbacks registered with :meth:`asyncio.Future.add_done_callback`
are not called immediately. They are scheduled with
:meth:`loop.call_soon` instead.
- asyncio Future is not compatible with the
:func:`concurrent.futures.wait` and
:func:`concurrent.futures.as_completed` functions.

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@ -1,6 +1,9 @@
.. currentmodule:: asyncio
.. _asyncio-transports-protocols:
========================
Transports and Protocols
========================
@ -393,11 +396,13 @@ Subprocess Transports
.. method:: SubprocessTransport.kill()
Kill the subprocess, as in :meth:`subprocess.Popen.kill`.
Kill the subprocess.
On POSIX systems, the function sends SIGKILL to the subprocess.
On Windows, this method is an alias for :meth:`terminate`.
See also :meth:`subprocess.Popen.kill`.
.. method:: SubprocessTransport.send_signal(signal)
Send the *signal* number to the subprocess, as in
@ -405,17 +410,20 @@ Subprocess Transports
.. method:: SubprocessTransport.terminate()
Ask the subprocess to stop, as in :meth:`subprocess.Popen.terminate`.
Stop the subprocess.
On POSIX systems, this method sends SIGTERM to the subprocess.
On Windows, the Windows API function TerminateProcess() is called to
stop the subprocess.
See also :meth:`subprocess.Popen.terminate`.
.. method:: SubprocessTransport.close()
Kill the subprocess by calling the :meth:`kill` method
if the subprocess hasn't returned yet, and close transports of all
pipes (*stdin*, *stdout* and *stderr*).
Kill the subprocess by calling the :meth:`kill` method.
If the subprocess hasn't returned yet, and close transports of
*stdin*, *stdout*, and *stderr* pipes.
.. _asyncio-protocol:

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@ -1,15 +1,13 @@
:mod:`asyncio` --- Asynchronous I/O, event loop, coroutines and tasks
=====================================================================
:mod:`asyncio` --- Asynchronous I/O
===================================
.. module:: asyncio
:synopsis: Asynchronous I/O, event loop, coroutines and tasks.
.. versionadded:: 3.4
**Source code:** :source:`Lib/asyncio/`
:synopsis: Asynchronous I/O.
--------------
.. TODO: rewrite the introduction section
This module provides infrastructure for writing single-threaded concurrent
code using coroutines, multiplexing I/O access over sockets and other
resources, running network clients and servers, and other related primitives.
@ -44,25 +42,40 @@ programming: see the :ref:`Develop with asyncio <asyncio-dev>` page which lists
common traps and explains how to avoid them. :ref:`Enable the debug mode
<asyncio-debug-mode>` during development to detect common issues.
Table of contents:
High-level APIs:
.. toctree::
:maxdepth: 3
:maxdepth: 1
asyncio-task.rst
asyncio-stream.rst
asyncio-sync.rst
asyncio-subprocess.rst
asyncio-queue.rst
asyncio-exceptions.rst
Low-level APIs:
.. toctree::
:maxdepth: 1
asyncio-eventloop.rst
asyncio-future.rst
asyncio-protocol.rst
asyncio-policy.rst
asyncio-platforms.rst
asyncio-task.rst
asyncio-protocol.rst
asyncio-stream.rst
asyncio-subprocess.rst
asyncio-sync.rst
asyncio-queue.rst
Guides and Tutorials:
.. toctree::
:maxdepth: 1
asyncio-dev.rst
asyncio-exceptions.rst
.. seealso::
The :mod:`asyncio` module was designed in :PEP:`3156`. For a
motivational primer on transports and protocols, see :PEP:`3153`.
The :mod:`asyncio` module was proposed in :PEP:`3156`.
Since the acceptance of the PEP many new APIs were added and many
original APIs were altered. The PEP should be treated as a
historical document.