mirror of
https://github.com/classilla/tenfourfox.git
synced 2024-11-04 10:05:51 +00:00
348 lines
13 KiB
ReStructuredText
348 lines
13 KiB
ReStructuredText
:mod:`concurrent.futures` --- Asynchronous computation
|
|
======================================================
|
|
|
|
.. module:: concurrent.futures
|
|
:synopsis: Execute computations asynchronously using threads or processes.
|
|
|
|
The :mod:`concurrent.futures` module provides a high-level interface for
|
|
asynchronously executing callables.
|
|
|
|
The asynchronous execution can be be performed by threads using
|
|
:class:`ThreadPoolExecutor` or seperate processes using
|
|
:class:`ProcessPoolExecutor`. Both implement the same interface, which is
|
|
defined by the abstract :class:`Executor` class.
|
|
|
|
Executor Objects
|
|
----------------
|
|
|
|
:class:`Executor` is an abstract class that provides methods to execute calls
|
|
asynchronously. It should not be used directly, but through its two
|
|
subclasses: :class:`ThreadPoolExecutor` and :class:`ProcessPoolExecutor`.
|
|
|
|
.. method:: Executor.submit(fn, *args, **kwargs)
|
|
|
|
Schedules the callable to be executed as *fn*(*\*args*, *\*\*kwargs*) and
|
|
returns a :class:`Future` representing the execution of the callable.
|
|
|
|
::
|
|
|
|
with ThreadPoolExecutor(max_workers=1) as executor:
|
|
future = executor.submit(pow, 323, 1235)
|
|
print(future.result())
|
|
|
|
.. method:: Executor.map(func, *iterables, timeout=None)
|
|
|
|
Equivalent to map(*func*, *\*iterables*) but func is executed asynchronously
|
|
and several calls to *func* may be made concurrently. The returned iterator
|
|
raises a :exc:`TimeoutError` if :meth:`__next__()` is called and the result
|
|
isn't available after *timeout* seconds from the original call to
|
|
:meth:`map()`. *timeout* can be an int or float. If *timeout* is not
|
|
specified or ``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
|
|
retrieved from the iterator.
|
|
|
|
.. method:: Executor.shutdown(wait=True)
|
|
|
|
Signal the executor that it should free any resources that it is using when
|
|
the currently pending futures are done executing. Calls to
|
|
:meth:`Executor.submit` and :meth:`Executor.map` made after shutdown will
|
|
raise :exc:`RuntimeError`.
|
|
|
|
If *wait* is `True` then this method will not return until all the pending
|
|
futures are done executing and the resources associated with the executor
|
|
have been freed. If *wait* is `False` then this method will return
|
|
immediately and the resources associated with the executor will be freed
|
|
when all pending futures are done executing. Regardless of the value of
|
|
*wait*, the entire Python program will not exit until all pending futures
|
|
are done executing.
|
|
|
|
You can avoid having to call this method explicitly if you use the `with`
|
|
statement, which will shutdown the `Executor` (waiting as if
|
|
`Executor.shutdown` were called with *wait* set to `True`):
|
|
|
|
::
|
|
|
|
import shutil
|
|
with ThreadPoolExecutor(max_workers=4) as e:
|
|
e.submit(shutil.copy, 'src1.txt', 'dest1.txt')
|
|
e.submit(shutil.copy, 'src2.txt', 'dest2.txt')
|
|
e.submit(shutil.copy, 'src3.txt', 'dest3.txt')
|
|
e.submit(shutil.copy, 'src3.txt', 'dest4.txt')
|
|
|
|
|
|
ThreadPoolExecutor Objects
|
|
--------------------------
|
|
|
|
The :class:`ThreadPoolExecutor` class is an :class:`Executor` subclass that uses
|
|
a pool of threads to execute calls asynchronously.
|
|
|
|
Deadlock can occur when the callable associated with a :class:`Future` waits on
|
|
the results of another :class:`Future`. For example:
|
|
|
|
::
|
|
|
|
import time
|
|
def wait_on_b():
|
|
time.sleep(5)
|
|
print(b.result()) # b will never complete because it is waiting on a.
|
|
return 5
|
|
|
|
def wait_on_a():
|
|
time.sleep(5)
|
|
print(a.result()) # a will never complete because it is waiting on b.
|
|
return 6
|
|
|
|
|
|
executor = ThreadPoolExecutor(max_workers=2)
|
|
a = executor.submit(wait_on_b)
|
|
b = executor.submit(wait_on_a)
|
|
|
|
And:
|
|
|
|
::
|
|
|
|
def wait_on_future():
|
|
f = executor.submit(pow, 5, 2)
|
|
# This will never complete because there is only one worker thread and
|
|
# it is executing this function.
|
|
print(f.result())
|
|
|
|
executor = ThreadPoolExecutor(max_workers=1)
|
|
executor.submit(wait_on_future)
|
|
|
|
.. class:: ThreadPoolExecutor(max_workers)
|
|
|
|
Executes calls asynchronously using at pool of at most *max_workers* threads.
|
|
|
|
.. _threadpoolexecutor-example:
|
|
|
|
ThreadPoolExecutor Example
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
::
|
|
|
|
from concurrent import futures
|
|
import urllib.request
|
|
|
|
URLS = ['http://www.foxnews.com/',
|
|
'http://www.cnn.com/',
|
|
'http://europe.wsj.com/',
|
|
'http://www.bbc.co.uk/',
|
|
'http://some-made-up-domain.com/']
|
|
|
|
def load_url(url, timeout):
|
|
return urllib.request.urlopen(url, timeout=timeout).read()
|
|
|
|
with futures.ThreadPoolExecutor(max_workers=5) as executor:
|
|
future_to_url = dict((executor.submit(load_url, url, 60), url)
|
|
for url in URLS)
|
|
|
|
for future in futures.as_completed(future_to_url):
|
|
url = future_to_url[future]
|
|
if future.exception() is not None:
|
|
print('%r generated an exception: %s' % (url,
|
|
future.exception()))
|
|
else:
|
|
print('%r page is %d bytes' % (url, len(future.result())))
|
|
|
|
ProcessPoolExecutor Objects
|
|
---------------------------
|
|
|
|
The :class:`ProcessPoolExecutor` class is an :class:`Executor` subclass that
|
|
uses a pool of processes to execute calls asynchronously.
|
|
:class:`ProcessPoolExecutor` uses the :mod:`multiprocessing` module, which
|
|
allows it to side-step the :term:`Global Interpreter Lock` but also means that
|
|
only picklable objects can be executed and returned.
|
|
|
|
Calling :class:`Executor` or :class:`Future` methods from a callable submitted
|
|
to a :class:`ProcessPoolExecutor` will result in deadlock.
|
|
|
|
.. class:: ProcessPoolExecutor(max_workers=None)
|
|
|
|
Executes calls asynchronously using a pool of at most *max_workers*
|
|
processes. If *max_workers* is ``None`` or not given then as many worker
|
|
processes will be created as the machine has processors.
|
|
|
|
.. _processpoolexecutor-example:
|
|
|
|
ProcessPoolExecutor Example
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
::
|
|
|
|
import math
|
|
|
|
PRIMES = [
|
|
112272535095293,
|
|
112582705942171,
|
|
112272535095293,
|
|
115280095190773,
|
|
115797848077099,
|
|
1099726899285419]
|
|
|
|
def is_prime(n):
|
|
if n % 2 == 0:
|
|
return False
|
|
|
|
sqrt_n = int(math.floor(math.sqrt(n)))
|
|
for i in range(3, sqrt_n + 1, 2):
|
|
if n % i == 0:
|
|
return False
|
|
return True
|
|
|
|
def main():
|
|
with futures.ProcessPoolExecutor() as executor:
|
|
for number, prime in zip(PRIMES, executor.map(is_prime, PRIMES)):
|
|
print('%d is prime: %s' % (number, prime))
|
|
|
|
if __name__ == '__main__':
|
|
main()
|
|
|
|
Future Objects
|
|
--------------
|
|
|
|
The :class:`Future` class encapulates the asynchronous execution of a callable.
|
|
:class:`Future` instances are created by :meth:`Executor.submit`.
|
|
|
|
.. method:: Future.cancel()
|
|
|
|
Attempt to cancel the call. If the call is currently being executed then
|
|
it cannot be cancelled and the method will return `False`, otherwise the call
|
|
will be cancelled and the method will return `True`.
|
|
|
|
.. method:: Future.cancelled()
|
|
|
|
Return `True` if the call was successfully cancelled.
|
|
|
|
.. method:: Future.running()
|
|
|
|
Return `True` if the call is currently being executed and cannot be
|
|
cancelled.
|
|
|
|
.. method:: Future.done()
|
|
|
|
Return `True` if the call was successfully cancelled or finished running.
|
|
|
|
.. method:: Future.result(timeout=None)
|
|
|
|
Return the value returned by the call. If the call hasn't yet completed then
|
|
this method will wait up to *timeout* seconds. If the call hasn't completed
|
|
in *timeout* seconds then a :exc:`TimeoutError` will be raised. *timeout* can
|
|
be an int or float.If *timeout* is not specified or ``None`` then there is no
|
|
limit to the wait time.
|
|
|
|
If the future is cancelled before completing then :exc:`CancelledError` will
|
|
be raised.
|
|
|
|
If the call raised then this method will raise the same exception.
|
|
|
|
.. method:: Future.exception(timeout=None)
|
|
|
|
Return the exception raised by the call. If the call hasn't yet completed
|
|
then this method will wait up to *timeout* seconds. If the call hasn't
|
|
completed in *timeout* seconds then a :exc:`TimeoutError` will be raised.
|
|
*timeout* can be an int or float. If *timeout* is not specified or ``None``
|
|
then there is no limit to the wait time.
|
|
|
|
If the future is cancelled before completing then :exc:`CancelledError` will
|
|
be raised.
|
|
|
|
If the call completed without raising then ``None`` is returned.
|
|
|
|
.. method:: Future.add_done_callback(fn)
|
|
|
|
Attaches the callable *fn* to the future. *fn* will be called, with the
|
|
future as its only argument, when the future is cancelled or finishes
|
|
running.
|
|
|
|
Added callables are called in the order that they were added and are always
|
|
called in a thread belonging to the process that added them. If the callable
|
|
raises an :exc:`Exception` then it will be logged and ignored. If the
|
|
callable raises another :exc:`BaseException` then the behavior is not
|
|
defined.
|
|
|
|
If the future has already completed or been cancelled then *fn* will be
|
|
called immediately.
|
|
|
|
Internal Future Methods
|
|
^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
The following :class:`Future` methods are meant for use in unit tests and
|
|
:class:`Executor` implementations.
|
|
|
|
.. method:: Future.set_running_or_notify_cancel()
|
|
|
|
This method should only be called by :class:`Executor` implementations before
|
|
executing the work associated with the :class:`Future` and by unit tests.
|
|
|
|
If the method returns `False` then the :class:`Future` was cancelled i.e.
|
|
:meth:`Future.cancel` was called and returned `True`. Any threads waiting
|
|
on the :class:`Future` completing (i.e. through :func:`as_completed` or
|
|
:func:`wait`) will be woken up.
|
|
|
|
If the method returns `True` then the :class:`Future` was not cancelled
|
|
and has been put in the running state i.e. calls to
|
|
:meth:`Future.running` will return `True`.
|
|
|
|
This method can only be called once and cannot be called after
|
|
:meth:`Future.set_result` or :meth:`Future.set_exception` have been
|
|
called.
|
|
|
|
.. method:: Future.set_result(result)
|
|
|
|
Sets the result of the work associated with the :class:`Future` to *result*.
|
|
|
|
This method should only be used by Executor implementations and unit tests.
|
|
|
|
.. method:: Future.set_exception(exception)
|
|
|
|
Sets the result of the work associated with the :class:`Future` to the
|
|
:class:`Exception` *exception*.
|
|
|
|
This method should only be used by Executor implementations and unit tests.
|
|
|
|
Module Functions
|
|
----------------
|
|
|
|
.. function:: wait(fs, timeout=None, return_when=ALL_COMPLETED)
|
|
|
|
Wait for the :class:`Future` instances (possibly created by different
|
|
:class:`Executor` instances) given by *fs* to complete. Returns a named
|
|
2-tuple of sets. The first set, named "done", contains the futures that
|
|
completed (finished or were cancelled) before the wait completed. The second
|
|
set, named "not_done", contains uncompleted futures.
|
|
|
|
*timeout* can be used to control the maximum number of seconds to wait before
|
|
returning. *timeout* can be an int or float. If *timeout* is not specified or
|
|
``None`` then there is no limit to the wait time.
|
|
|
|
*return_when* indicates when this function should return. It must be one of
|
|
the following constants:
|
|
|
|
+-----------------------------+----------------------------------------+
|
|
| Constant | Description |
|
|
+=============================+========================================+
|
|
| :const:`FIRST_COMPLETED` | The function will return when any |
|
|
| | future finishes or is cancelled. |
|
|
+-----------------------------+----------------------------------------+
|
|
| :const:`FIRST_EXCEPTION` | The function will return when any |
|
|
| | future finishes by raising an |
|
|
| | exception. If no future raises an |
|
|
| | exception then it is equivalent to |
|
|
| | `ALL_COMPLETED`. |
|
|
+-----------------------------+----------------------------------------+
|
|
| :const:`ALL_COMPLETED` | The function will return when all |
|
|
| | futures finish or are cancelled. |
|
|
+-----------------------------+----------------------------------------+
|
|
|
|
.. function:: as_completed(fs, timeout=None)
|
|
|
|
Returns an iterator over the :class:`Future` instances (possibly created by
|
|
different :class:`Executor` instances) given by *fs* that yields futures as
|
|
they complete (finished or were cancelled). Any futures given by *fs* that
|
|
are duplicated will be returned once. Any futures that completed
|
|
before :func:`as_completed` is called will be yielded first. The returned
|
|
iterator raises a :exc:`TimeoutError` if :meth:`~iterator.__next__` is
|
|
called and the result isn't available after *timeout* seconds from the
|
|
original call to :func:`as_completed`. *timeout* can be an int or float.
|
|
If *timeout* is not specified or ``None``, there is no limit to the wait
|
|
time.
|