在 Python 中，我看到了许多调用多处理但目标只是打印一些东西的例子。我有一个场景，其中目标返回 2 个变量，我需要稍后使用。例如：
def foo(some args):
a = someObject
b = someObject
return a,b
p1=multiprocess(target=foo,args(some args))
p2=multiprocess(target=foo,args(some args))
p3=multiprocess(target=foo,args(some args))
现在呢？我可以执行 .start 和 .join，但如何检索单个结果？我需要为我执行的所有作业捕获返回 a,b，然后处理它。
【问题讨论】：
您希望使用多个进程执行一些令人尴尬的并行工作，那么为什么不使用Pool？ Pool 将负责启动流程、检索结果并将结果返回给您。
我使用pathos，它有一个multiprocessing 的fork，因为它的序列化比标准库提供的版本好得多。
(.py) 文件
from pathos.multiprocessing import ProcessingPool as Pool
def foo(obj1, obj2):
a = obj1.x**2
b = obj2.x**2
return a,b
class Bar(object):
def __init__(self, x):
self.x = x
Pool().map(foo, [Bar(1),Bar(2),Bar(3)], [Bar(4),Bar(5),Bar(6)])
结果
[(1, 16), (4, 25), (9, 36)]
您会看到foo 接受两个参数，并返回两个对象的元组。 Pool的map方法将foo提交给底层进程，返回结果为res。
您可以在这里获取pathos：https://github.com/uqfoundation
【讨论】：
是的，当然 - 您可以使用多种方法。最简单的方法之一是共享Queue。在此处查看示例：http://eli.thegreenplace.net/2012/01/16/python-parallelizing-cpu-bound-tasks-with-multiprocessing/
【讨论】：
我直接从文档中复制了这个例子，因为我不能给你一个直接的链接。请注意，它会从 done_queue 中打印出结果，但您可以用它做任何您喜欢的事情。
#
# Simple example which uses a pool of workers to carry out some tasks.
#
# Notice that the results will probably not come out of the output
# queue in the same in the same order as the corresponding tasks were
# put on the input queue. If it is important to get the results back
# in the original order then consider using `Pool.map()` or
# `Pool.imap()` (which will save on the amount of code needed anyway).
#
# Copyright (c) 2006-2008, R Oudkerk
# All rights reserved.
#
import time
import random
from multiprocessing import Process, Queue, current_process, freeze_support
#
# Function run by worker processes
#
def worker(input, output):
for func, args in iter(input.get, 'STOP'):
result = calculate(func, args)
output.put(result)
#
# Function used to calculate result
#
def calculate(func, args):
result = func(*args)
return '%s says that %s%s = %s' % \
(current_process().name, func.__name__, args, result)
#
# Functions referenced by tasks
#
def mul(a, b):
time.sleep(0.5*random.random())
return a * b
def plus(a, b):
time.sleep(0.5*random.random())
return a + b
#
#
#
def test():
NUMBER_OF_PROCESSES = 4
TASKS1 = [(mul, (i, 7)) for i in range(20)]
TASKS2 = [(plus, (i, 8)) for i in range(10)]
# Create queues
task_queue = Queue()
done_queue = Queue()
# Submit tasks
for task in TASKS1:
task_queue.put(task)
# Start worker processes
for i in range(NUMBER_OF_PROCESSES):
Process(target=worker, args=(task_queue, done_queue)).start()
# Get and print results
print 'Unordered results:'
for i in range(len(TASKS1)):
print '\t', done_queue.get()
# Add more tasks using `put()`
for task in TASKS2:
task_queue.put(task)
# Get and print some more results
for i in range(len(TASKS2)):
print '\t', done_queue.get()
# Tell child processes to stop
for i in range(NUMBER_OF_PROCESSES):
task_queue.put('STOP')
if __name__ == '__main__':
freeze_support()
test()
【讨论】：
为什么没有人使用 callback 的 multiprocessing.Pool？
例子：
from multiprocessing import Pool
from contextlib import contextmanager
from pprint import pprint
from requests import get as get_page
@contextmanager
def _terminating(thing):
try:
yield thing
finally:
thing.terminate()
def _callback(*args, **kwargs):
print("CALBACK")
pprint(args)
pprint(kwargs)
print("Processing...")
with _terminating(Pool(processes=WORKERS)) as pool:
results = pool.map_async(get_page, URLS, callback=_callback)
start_time = time.time()
results.wait()
end_time = time.time()
print("Time for Processing: %ssecs" % (end_time - start_time))
在这里，我同时打印 args 和 kwargs。但是您可以将 callback 替换为：
def _callback2(responses):
for r in responses:
print(r.status_code) # or do whatever with response...
【讨论】：
它不能在 Windows 上工作，但这是我的多处理函数装饰器，它返回一个队列，您可以从该队列轮询并收集返回的数据
import os
from Queue import Queue
from multiprocessing import Process
def returning_wrapper(func, *args, **kwargs):
queue = kwargs.get("multiprocess_returnable")
del kwargs["multiprocess_returnable"]
queue.put(func(*args, **kwargs))
class Multiprocess(object):
"""Cute decorator to run a function in multiple processes."""
def __init__(self, func):
self.func = func
self.processes = []
def __call__(self, *args, **kwargs):
num_processes = kwargs.get("multiprocess_num_processes", 2) # default to two processes.
return_obj = kwargs.get("multiprocess_returnable", Queue()) # default to stdlib Queue
kwargs["multiprocess_returnable"] = return_obj
for i in xrange(num_processes):
pro = Process(target=returning_wrapper, args=tuple([self.func] + list(args)), kwargs=kwargs)
self.processes.append(pro)
pro.start()
return return_obj
@Multiprocess
def info():
print 'module name:', __name__
print 'parent process:', os.getppid()
print 'process id:', os.getpid()
return 4 * 22
data = info()
print data.get(False)
【讨论】：
【讨论】：