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PEP 3148: Resolve uses of the default role (#3386)

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@ -57,21 +57,21 @@ in that module, which work across thread and process boundaries.
Interface Interface
--------- ---------
The proposed package provides two core classes: `Executor` and The proposed package provides two core classes: ``Executor`` and
`Future`. An `Executor` receives asynchronous work requests (in terms ``Future``. An ``Executor`` receives asynchronous work requests (in terms
of a callable and its arguments) and returns a `Future` to represent of a callable and its arguments) and returns a ``Future`` to represent
the execution of that work request. the execution of that work request.
Executor Executor
'''''''' ''''''''
`Executor` is an abstract class that provides methods to execute calls ``Executor`` is an abstract class that provides methods to execute calls
asynchronously. asynchronously.
``submit(fn, *args, **kwargs)`` ``submit(fn, *args, **kwargs)``
Schedules the callable to be executed as ``fn(*args, **kwargs)`` Schedules the callable to be executed as ``fn(*args, **kwargs)``
and returns a `Future` instance representing the execution of the and returns a ``Future`` instance representing the execution of the
callable. callable.
This is an abstract method and must be implemented by Executor This is an abstract method and must be implemented by Executor
@ -81,10 +81,10 @@ asynchronously.
Equivalent to ``map(func, *iterables)`` but func is executed Equivalent to ``map(func, *iterables)`` but func is executed
asynchronously and several calls to func may be made concurrently. asynchronously and several calls to func may be made concurrently.
The returned iterator raises a `TimeoutError` if `__next__()` is The returned iterator raises a ``TimeoutError`` if ``__next__()`` is
called and the result isn't available after *timeout* seconds from called and the result isn't available after *timeout* seconds from
the original call to `map()`. If *timeout* is not specified or the original call to ``map()``. If *timeout* is not specified or
`None` then there is no limit to the wait time. If a call raises ``None`` then there is no limit to the wait time. If a call raises
an exception then that exception will be raised when its value is an exception then that exception will be raised when its value is
retrieved from the iterator. retrieved from the iterator.
@ -92,12 +92,12 @@ asynchronously.
Signal the executor that it should free any resources that it is Signal the executor that it should free any resources that it is
using when the currently pending futures are done executing. using when the currently pending futures are done executing.
Calls to `Executor.submit` and `Executor.map` and made after Calls to ``Executor.submit`` and ``Executor.map`` and made after
shutdown will raise `RuntimeError`. shutdown will raise ``RuntimeError``.
If wait is `True` then this method will not return until all the If wait is ``True`` then this method will not return until all the
pending futures are done executing and the resources associated pending futures are done executing and the resources associated
with the executor have been freed. If wait is `False` then this with the executor have been freed. If wait is ``False`` then this
method will return immediately and the resources associated with method will return immediately and the resources associated with
the executor will be freed when all pending futures are done the executor will be freed when all pending futures are done
executing. Regardless of the value of wait, the entire Python executing. Regardless of the value of wait, the entire Python
@ -107,21 +107,21 @@ asynchronously.
| ``__enter__()`` | ``__enter__()``
| ``__exit__(exc_type, exc_val, exc_tb)`` | ``__exit__(exc_type, exc_val, exc_tb)``
When using an executor as a context manager, `__exit__` will call When using an executor as a context manager, ``__exit__`` will call
``Executor.shutdown(wait=True)``. ``Executor.shutdown(wait=True)``.
ProcessPoolExecutor ProcessPoolExecutor
''''''''''''''''''' '''''''''''''''''''
The `ProcessPoolExecutor` class is an `Executor` subclass that uses a The ``ProcessPoolExecutor`` class is an ``Executor`` subclass that uses a
pool of processes to execute calls asynchronously. The callable pool of processes to execute calls asynchronously. The callable
objects and arguments passed to `ProcessPoolExecutor.submit` must be objects and arguments passed to ``ProcessPoolExecutor.submit`` must be
pickleable according to the same limitations as the multiprocessing pickleable according to the same limitations as the multiprocessing
module. module.
Calling `Executor` or `Future` methods from within a callable Calling ``Executor`` or ``Future`` methods from within a callable
submitted to a `ProcessPoolExecutor` will result in deadlock. submitted to a ``ProcessPoolExecutor`` will result in deadlock.
``__init__(max_workers)`` ``__init__(max_workers)``
@ -132,11 +132,11 @@ submitted to a `ProcessPoolExecutor` will result in deadlock.
ThreadPoolExecutor ThreadPoolExecutor
'''''''''''''''''' ''''''''''''''''''
The `ThreadPoolExecutor` class is an `Executor` subclass that uses a The ``ThreadPoolExecutor`` class is an ``Executor`` subclass that uses a
pool of threads to execute calls asynchronously. pool of threads to execute calls asynchronously.
Deadlock can occur when the callable associated with a `Future` waits Deadlock can occur when the callable associated with a ``Future`` waits
on the results of another `Future`. For example:: on the results of another ``Future``. For example::
import time import time
def wait_on_b(): def wait_on_b():
@ -173,28 +173,28 @@ And::
Future Objects Future Objects
'''''''''''''' ''''''''''''''
The `Future` class encapsulates the asynchronous execution of a The ``Future`` class encapsulates the asynchronous execution of a
callable. `Future` instances are returned by `Executor.submit`. callable. ``Future`` instances are returned by ``Executor.submit``.
``cancel()`` ``cancel()``
Attempt to cancel the call. If the call is currently being Attempt to cancel the call. If the call is currently being
executed then it cannot be cancelled and the method will return executed then it cannot be cancelled and the method will return
`False`, otherwise the call will be cancelled and the method will ``False``, otherwise the call will be cancelled and the method will
return `True`. return ``True``.
``cancelled()`` ``cancelled()``
Return `True` if the call was successfully cancelled. Return ``True`` if the call was successfully cancelled.
``running()`` ``running()``
Return `True` if the call is currently being executed and cannot Return ``True`` if the call is currently being executed and cannot
be cancelled. be cancelled.
``done()`` ``done()``
Return `True` if the call was successfully cancelled or finished Return ``True`` if the call was successfully cancelled or finished
running. running.
``result(timeout=None)`` ``result(timeout=None)``
@ -202,10 +202,10 @@ callable. `Future` instances are returned by `Executor.submit`.
Return the value returned by the call. If the call hasn't yet Return the value returned by the call. If the call hasn't yet
completed then this method will wait up to *timeout* seconds. If completed then this method will wait up to *timeout* seconds. If
the call hasn't completed in *timeout* seconds then a the call hasn't completed in *timeout* seconds then a
`TimeoutError` will be raised. If *timeout* is not specified or ``TimeoutError`` will be raised. If *timeout* is not specified or
`None` then there is no limit to the wait time. ``None`` then there is no limit to the wait time.
If the future is cancelled before completing then `CancelledError` If the future is cancelled before completing then ``CancelledError``
will be raised. will be raised.
If the call raised then this method will raise the same exception. If the call raised then this method will raise the same exception.
@ -215,13 +215,13 @@ callable. `Future` instances are returned by `Executor.submit`.
Return the exception raised by the call. If the call hasn't yet Return the exception raised by the call. If the call hasn't yet
completed then this method will wait up to *timeout* seconds. If completed then this method will wait up to *timeout* seconds. If
the call hasn't completed in *timeout* seconds then a the call hasn't completed in *timeout* seconds then a
`TimeoutError` will be raised. If *timeout* is not specified or ``TimeoutError`` will be raised. If *timeout* is not specified or
``None`` then there is no limit to the wait time. ``None`` then there is no limit to the wait time.
If the future is cancelled before completing then `CancelledError` If the future is cancelled before completing then ``CancelledError``
will be raised. will be raised.
If the call completed without raising then `None` is returned. If the call completed without raising then ``None`` is returned.
``add_done_callback(fn)`` ``add_done_callback(fn)``
@ -231,9 +231,9 @@ callable. `Future` instances are returned by `Executor.submit`.
Added callables are called in the order that they were added and Added callables are called in the order that they were added and
are always called in a thread belonging to the process that added are always called in a thread belonging to the process that added
them. If the callable raises an `Exception` then it will be them. If the callable raises an ``Exception`` then it will be
logged and ignored. If the callable raises another logged and ignored. If the callable raises another
`BaseException` then behavior is not defined. ``BaseException`` then behavior is not defined.
If the future has already completed or been cancelled then *fn* If the future has already completed or been cancelled then *fn*
will be called immediately. will be called immediately.
@ -241,43 +241,43 @@ callable. `Future` instances are returned by `Executor.submit`.
Internal Future Methods Internal Future Methods
^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^
The following `Future` methods are meant for use in unit tests and The following ``Future`` methods are meant for use in unit tests and
`Executor` implementations. ``Executor`` implementations.
``set_running_or_notify_cancel()`` ``set_running_or_notify_cancel()``
Should be called by `Executor` implementations before executing Should be called by ``Executor`` implementations before executing
the work associated with the `Future`. the work associated with the ``Future``.
If the method returns `False` then the `Future` was cancelled, If the method returns ``False`` then the ``Future`` was cancelled,
i.e. `Future.cancel` was called and returned `True`. Any threads i.e. ``Future.cancel`` was called and returned ``True``. Any threads
waiting on the `Future` completing (i.e. through `as_completed()` waiting on the ``Future`` completing (i.e. through ``as_completed()``
or `wait()`) will be woken up. or ``wait()``) will be woken up.
If the method returns `True` then the `Future` was not cancelled If the method returns ``True`` then the ``Future`` was not cancelled
and has been put in the running state, i.e. calls to and has been put in the running state, i.e. calls to
`Future.running()` will return `True`. ``Future.running()`` will return ``True``.
This method can only be called once and cannot be called after This method can only be called once and cannot be called after
`Future.set_result()` or `Future.set_exception()` have been ``Future.set_result()`` or ``Future.set_exception()`` have been
called. called.
``set_result(result)`` ``set_result(result)``
Sets the result of the work associated with the `Future`. Sets the result of the work associated with the ``Future``.
``set_exception(exception)`` ``set_exception(exception)``
Sets the result of the work associated with the `Future` to the Sets the result of the work associated with the ``Future`` to the
given `Exception`. given ``Exception``.
Module Functions Module Functions
'''''''''''''''' ''''''''''''''''
``wait(fs, timeout=None, return_when=ALL_COMPLETED)`` ``wait(fs, timeout=None, return_when=ALL_COMPLETED)``
Wait for the `Future` instances (possibly created by different Wait for the ``Future`` instances (possibly created by different
`Executor` instances) given by *fs* to complete. Returns a named ``Executor`` instances) given by *fs* to complete. Returns a named
2-tuple of sets. The first set, named "done", contains the 2-tuple of sets. The first set, named "done", contains the
futures that completed (finished or were cancelled) before the futures that completed (finished or were cancelled) before the
wait completed. The second set, named "not_done", contains wait completed. The second set, named "not_done", contains
@ -293,27 +293,27 @@ Module Functions
============================= ================================================== ============================= ==================================================
Constant Description Constant Description
============================= ================================================== ============================= ==================================================
`FIRST_COMPLETED` The method will return when any future finishes or ``FIRST_COMPLETED`` The method will return when any future finishes or
is cancelled. is cancelled.
`FIRST_EXCEPTION` The method will return when any future finishes by ``FIRST_EXCEPTION`` The method will return when any future finishes by
raising an exception. If not future raises an raising an exception. If not future raises an
exception then it is equivalent to ALL_COMPLETED. exception then it is equivalent to ALL_COMPLETED.
`ALL_COMPLETED` The method will return when all calls finish. ``ALL_COMPLETED`` The method will return when all calls finish.
============================= ================================================== ============================= ==================================================
``as_completed(fs, timeout=None)`` ``as_completed(fs, timeout=None)``
Returns an iterator over the `Future` instances given by *fs* that Returns an iterator over the ``Future`` instances given by *fs* that
yields futures as they complete (finished or were cancelled). Any yields futures as they complete (finished or were cancelled). Any
futures that completed before `as_completed()` was called will be futures that completed before ``as_completed()`` was called will be
yielded first. The returned iterator raises a `TimeoutError` if yielded first. The returned iterator raises a ``TimeoutError`` if
`__next__()` is called and the result isn't available after ``__next__()`` is called and the result isn't available after
*timeout* seconds from the original call to `as_completed()`. If *timeout* seconds from the original call to ``as_completed()``. If
*timeout* is not specified or `None` then there is no limit to the *timeout* is not specified or ``None`` then there is no limit to the
wait time. wait time.
The `Future` instances can have been created by different The ``Future`` instances can have been created by different
`Executor` instances. ``Executor`` instances.
Check Prime Example Check Prime Example
------------------- -------------------
@ -408,7 +408,7 @@ list [3]_.
The proposed design is explicit, i.e. it requires that clients be The proposed design is explicit, i.e. it requires that clients be
aware that they are consuming Futures. It would be possible to design aware that they are consuming Futures. It would be possible to design
a module that would return proxy objects (in the style of `weakref`) a module that would return proxy objects (in the style of ``weakref``)
that could be used transparently. It is possible to build a proxy that could be used transparently. It is possible to build a proxy
implementation on top of the proposed explicit mechanism. implementation on top of the proposed explicit mechanism.
@ -425,13 +425,13 @@ the API has been discussed in some detail on stdlib-sig [6]_.
The proposed design was discussed on the Python-Dev mailing list [7]_. The proposed design was discussed on the Python-Dev mailing list [7]_.
Following those discussions, the following changes were made: Following those discussions, the following changes were made:
* The `Executor` class was made into an abstract base class * The ``Executor`` class was made into an abstract base class
* The `Future.remove_done_callback` method was removed due to a lack * The ``Future.remove_done_callback`` method was removed due to a lack
of convincing use cases of convincing use cases
* The `Future.add_done_callback` method was modified to allow the * The ``Future.add_done_callback`` method was modified to allow the
same callable to be added many times same callable to be added many times
* The `Future` class's mutation methods were better documented to * The ``Future`` class's mutation methods were better documented to
indicate that they are private to the `Executor` that created them indicate that they are private to the ``Executor`` that created them
======================== ========================
Reference Implementation Reference Implementation
@ -445,7 +445,7 @@ References
========== ==========
.. [1] .. [1]
`java.util.concurrent` package documentation ``java.util.concurrent`` package documentation
http://java.sun.com/j2se/1.5.0/docs/api/java/util/concurrent/package-summary.html http://java.sun.com/j2se/1.5.0/docs/api/java/util/concurrent/package-summary.html
.. [2] .. [2]
@ -453,15 +453,15 @@ References
http://code.activestate.com/recipes/84317/ http://code.activestate.com/recipes/84317/
.. [3] .. [3]
`Python-3000` thread, "mechanism for handling asynchronous concurrency" ``Python-3000`` thread, "mechanism for handling asynchronous concurrency"
https://mail.python.org/pipermail/python-3000/2006-April/000960.html https://mail.python.org/pipermail/python-3000/2006-April/000960.html
.. [4] .. [4]
`Python 3000` thread, "Futures in Python 3000 (was Re: mechanism for handling asynchronous concurrency)" ``Python 3000`` thread, "Futures in Python 3000 (was Re: mechanism for handling asynchronous concurrency)"
https://mail.python.org/pipermail/python-3000/2006-April/000970.html https://mail.python.org/pipermail/python-3000/2006-April/000970.html
.. [5] .. [5]
A discussion of `stream`, a similar concept proposed by Anh Hai Trinh A discussion of ``stream``, a similar concept proposed by Anh Hai Trinh
http://www.mail-archive.com/stdlib-sig@python.org/msg00480.html http://www.mail-archive.com/stdlib-sig@python.org/msg00480.html
.. [6] .. [6]
@ -473,7 +473,7 @@ References
https://mail.python.org/pipermail/python-dev/2010-March/098169.html https://mail.python.org/pipermail/python-dev/2010-March/098169.html
.. [8] .. [8]
Reference `futures` implementation Reference ``futures`` implementation
http://code.google.com/p/pythonfutures/source/browse/#svn/branches/feedback http://code.google.com/p/pythonfutures/source/browse/#svn/branches/feedback
========= =========