edit concurrent.future docs
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Benjamin Peterson
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@ -7,28 +7,24 @@
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The :mod:`concurrent.futures` module provides a high-level interface for
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asynchronously executing callables.
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The asynchronous execution can be be performed by threads using
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:class:`ThreadPoolExecutor` or seperate processes using
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The asynchronous execution can be be performed with threads, using
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:class:`ThreadPoolExecutor`, or seperate processes, using
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:class:`ProcessPoolExecutor`. Both implement the same interface, which is
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defined by the abstract :class:`Executor` class.
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Executor Objects
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^^^^^^^^^^^^^^^^
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:class:`Executor` is an abstract class that provides methods to execute calls
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asynchronously. It should not be used directly, but through its two
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subclasses: :class:`ThreadPoolExecutor` and :class:`ProcessPoolExecutor`.
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.. class:: Executor()
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.. class:: Executor
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An abstract class that provides methods to execute calls asynchronously. It
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should not be used directly, but through its two subclasses:
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:class:`ThreadPoolExecutor` and :class:`ProcessPoolExecutor`.
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should not be used directly, but through its concrete subclasses.
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.. method:: submit(fn, *args, **kwargs)
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Schedules the callable to be executed as *fn*(*\*args*, *\*\*kwargs*) and
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returns a :class:`Future` representing the execution of the callable.
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Schedules the callable, *fn*, to be executed as ``fn(*args **kwargs)``
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and returns a :class:`Future` object representing the execution of the
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callable.
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::
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@ -38,14 +34,14 @@ subclasses: :class:`ThreadPoolExecutor` and :class:`ProcessPoolExecutor`.
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.. method:: map(func, *iterables, timeout=None)
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Equivalent to `map(*func*, *\*iterables*)` but func is executed
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Equivalent to ``map(func, *iterables)`` except *func* is executed
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asynchronously and several calls to *func* may be made concurrently. The
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returned iterator raises a :exc:`TimeoutError` if :meth:`__next__()` is
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called and the result isn't available after *timeout* seconds from the
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original call to :meth:`Executor.map()`. *timeout* can be an int or
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float. If *timeout* is not specified or ``None`` then there is no limit
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to the wait time. If a call raises an exception then that exception will
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be raised when its value is retrieved from the iterator.
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original call to :meth:`Executor.map`. *timeout* can be an int or a
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float. If *timeout* is not specified or ``None``, there is no limit to
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the wait time. If a call raises an exception, then that exception will be
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raised when its value is retrieved from the iterator.
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.. method:: shutdown(wait=True)
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@ -54,11 +50,11 @@ subclasses: :class:`ThreadPoolExecutor` and :class:`ProcessPoolExecutor`.
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:meth:`Executor.submit` and :meth:`Executor.map` made after shutdown will
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raise :exc:`RuntimeError`.
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If *wait* is `True` then this method will not return until all the
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If *wait* is ``True`` then this method will not return until all the
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pending futures are done executing and the resources associated with the
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executor have been freed. If *wait* is `False` then this method will
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return immediately and the resources associated with the executor will
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be freed when all pending futures are done executing. Regardless of the
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executor have been freed. If *wait* is ``False`` then this method will
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return immediately and the resources associated with the executor will be
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freed when all pending futures are done executing. Regardless of the
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value of *wait*, the entire Python program will not exit until all
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pending futures are done executing.
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@ -78,10 +74,10 @@ subclasses: :class:`ThreadPoolExecutor` and :class:`ProcessPoolExecutor`.
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ThreadPoolExecutor
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^^^^^^^^^^^^^^^^^^
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The :class:`ThreadPoolExecutor` class is an :class:`Executor` subclass that uses
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a pool of threads to execute calls asynchronously.
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:class:`ThreadPoolExecutor` is a :class:`Executor` subclass that uses a pool of
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threads to execute calls asynchronously.
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Deadlock can occur when the callable associated with a :class:`Future` waits on
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Deadlocks can occur when the callable associated with a :class:`Future` waits on
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the results of another :class:`Future`. For example:
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::
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@ -121,9 +117,6 @@ And:
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An :class:`Executor` subclass that uses a pool of at most *max_workers*
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threads to execute calls asynchronously.
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Deadlock can occur when the callable associated with a :class:`Future` waits
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on the results of another :class:`Future`.
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.. _threadpoolexecutor-example:
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ThreadPoolExecutor Example
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@ -169,10 +162,9 @@ to a :class:`ProcessPoolExecutor` will result in deadlock.
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.. class:: ProcessPoolExecutor(max_workers=None)
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An :class:`Executor` subclass that executes calls asynchronously using a
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pool of at most *max_workers* processes. If *max_workers* is ``None`` or
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not given then as many worker processes will be created as the machine has
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processors.
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An :class:`Executor` subclass that executes calls asynchronously using a pool
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of at most *max_workers* processes. If *max_workers* is ``None`` or not
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given, it will default to the number of processors on the machine.
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.. _processpoolexecutor-example:
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@ -215,7 +207,7 @@ Future Objects
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The :class:`Future` class encapulates the asynchronous execution of a callable.
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:class:`Future` instances are created by :meth:`Executor.submit`.
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.. class:: Future()
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.. class:: Future
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Encapulates the asynchronous execution of a callable. :class:`Future`
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instances are created by :meth:`Executor.submit` and should not be created
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@ -223,48 +215,49 @@ The :class:`Future` class encapulates the asynchronous execution of a callable.
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.. method:: cancel()
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Attempt to cancel the call. If the call is currently being executed then
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it cannot be cancelled and the method will return `False`, otherwise the
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call will be cancelled and the method will return `True`.
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Attempt to cancel the call. If the call is currently being executed and
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cannot be cancelled and the method will return ``False``, otherwise the
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call will be cancelled and the method will return ``True``.
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.. method:: cancelled()
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Return `True` if the call was successfully cancelled.
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Return ``True`` if the call was successfully cancelled.
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.. method:: running()
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Return `True` if the call is currently being executed and cannot be
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Return ``True`` if the call is currently being executed and cannot be
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cancelled.
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.. method:: done()
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Return `True` if the call was successfully cancelled or finished running.
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Return ``True`` if the call was successfully cancelled or finished
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running.
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.. method:: result(timeout=None)
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Return the value returned by the call. If the call hasn't yet completed
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then this method will wait up to *timeout* seconds. If the call hasn't
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completed in *timeout* seconds then a :exc:`TimeoutError` will be
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raised. *timeout* can be an int or float.If *timeout* is not specified
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or ``None`` then there is no limit to the wait time.
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completed in *timeout* seconds, then a :exc:`TimeoutError` will be
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raised. *timeout* can be an int or float. If *timeout* is not specified
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or ``None``, there is no limit to the wait time.
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If the future is cancelled before completing then :exc:`CancelledError`
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will be raised.
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If the call raised then this method will raise the same exception.
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If the call raised, this method will raise the same exception.
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.. method:: exception(timeout=None)
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Return the exception raised by the call. If the call hasn't yet completed
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then this method will wait up to *timeout* seconds. If the call hasn't
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completed in *timeout* seconds then a :exc:`TimeoutError` will be raised.
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*timeout* can be an int or float. If *timeout* is not specified or
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``None`` then there is no limit to the wait time.
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completed in *timeout* seconds, then a :exc:`TimeoutError` will be
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raised. *timeout* can be an int or float. If *timeout* is not specified
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or ``None``, there is no limit to the wait time.
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If the future is cancelled before completing then :exc:`CancelledError`
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will be raised.
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If the call completed without raising then ``None`` is returned.
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If the call completed without raising, ``None`` is returned.
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.. method:: add_done_callback(fn)
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@ -274,11 +267,11 @@ The :class:`Future` class encapulates the asynchronous execution of a callable.
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Added callables are called in the order that they were added and are
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always called in a thread belonging to the process that added them. If
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the callable raises an :exc:`Exception` then it will be logged and
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ignored. If the callable raises another :exc:`BaseException` then the
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behavior is not defined.
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the callable raises a :exc:`Exception` subclass, it will be logged and
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ignored. If the callable raises a :exc:`BaseException` subclass, the
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behavior is undefined.
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If the future has already completed or been cancelled then *fn* will be
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If the future has already completed or been cancelled, *fn* will be
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called immediately.
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The following :class:`Future` methods are meant for use in unit tests and
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@ -326,14 +319,14 @@ Module Functions
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.. function:: wait(fs, timeout=None, return_when=ALL_COMPLETED)
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Wait for the :class:`Future` instances (possibly created by different
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:class:`Executor` instances) given by *fs* to complete. Returns a named
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2-tuple of sets. The first set, named "done", contains the futures that
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:class:`Executor` instances) given by *fs* to complete. Returns a named
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2-tuple of sets. The first set, named ``done``, contains the futures that
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completed (finished or were cancelled) before the wait completed. The second
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set, named "not_done", contains uncompleted futures.
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set, named ``not_done``, contains uncompleted futures.
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*timeout* can be used to control the maximum number of seconds to wait before
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returning. *timeout* can be an int or float. If *timeout* is not specified or
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``None`` then there is no limit to the wait time.
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``None``, there is no limit to the wait time.
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*return_when* indicates when this function should return. It must be one of
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the following constants:
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@ -348,7 +341,7 @@ Module Functions
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| | future finishes by raising an |
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| | exception. If no future raises an |
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| | exception then it is equivalent to |
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| | `ALL_COMPLETED`. |
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| | :const:`ALL_COMPLETED`. |
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+-----------------------------+----------------------------------------+
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| :const:`ALL_COMPLETED` | The function will return when all |
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| | futures finish or are cancelled. |
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@ -356,11 +349,11 @@ Module Functions
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.. function:: as_completed(fs, timeout=None)
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Returns an iterator over the :class:`Future` instances (possibly created
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by different :class:`Executor` instances) given by *fs* that yields futures
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as they complete (finished or were cancelled). Any futures that completed
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before :func:`as_completed()` was called will be yielded first. The returned
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iterator raises a :exc:`TimeoutError` if :meth:`__next__()` is called and
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the result isn't available after *timeout* seconds from the original call
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to :func:`as_completed()`. *timeout* can be an int or float. If *timeout*
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is not specified or ``None`` then there is no limit to the wait time.
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Returns an iterator over the :class:`Future` instances (possibly created by
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different :class:`Executor` instances) given by *fs* that yields futures as
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they complete (finished or were cancelled). Any futures that completed before
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:func:`as_completed` is called will be yielded first. The returned iterator
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raises a :exc:`TimeoutError` if :meth:`__next__` is called and the result
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isn't available after *timeout* seconds from the original call to
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:func:`as_completed`. *timeout* can be an int or float. If *timeout* is not
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specified or ``None``, there is no limit to the wait time.
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