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[英]multiprocessing Manager doesn't work with spawn or forkserver start method in Jupyter Notebook
[英]Python multiprocessing with start method 'spawn' doesn't work
我編寫了一個 Python 類來並行繪制 pylots。 它在默認啟動方法是 fork 的 Linux 上運行良好,但是當我在 Windows 上嘗試時遇到了問題(可以使用 spawn start 方法在 Linux 上重現 - 請參閱下面的代碼)。 我總是最終收到此錯誤:
Traceback (most recent call last):
File "test.py", line 50, in <module>
test()
File "test.py", line 7, in test
asyncPlotter.saveLinePlotVec3("test")
File "test.py", line 41, in saveLinePlotVec3
args=(test, ))
File "test.py", line 34, in process
p.start()
File "C:\Users\adrian\AppData\Local\Programs\Python\Python37\lib\multiprocessing\process.py", line 112, in start
self._popen = self._Popen(self)
File "C:\Users\adrian\AppData\Local\Programs\Python\Python37\lib\multiprocessing\context.py", line 223, in _Popen
return _default_context.get_context().Process._Popen(process_obj)
File "C:\Users\adrian\AppData\Local\Programs\Python\Python37\lib\multiprocessing\context.py", line 322, in _Popen
return Popen(process_obj)
File "C:\Users\adrian\AppData\Local\Programs\Python\Python37\lib\multiprocessing\popen_spawn_win32.py", line 89, in __init__
reduction.dump(process_obj, to_child)
File "C:\Users\adrian\AppData\Local\Programs\Python\Python37\lib\multiprocessing\reduction.py", line 60, in dump
ForkingPickler(file, protocol).dump(obj)
TypeError: can't pickle weakref objects
C:\Python\MonteCarloTools>Traceback (most recent call last):
File "<string>", line 1, in <module>
File "C:\Users\adrian\AppData\Local\Programs\Python\Python37\lib\multiprocessing\spawn.py", line 99, in spawn_main
new_handle = reduction.steal_handle(parent_pid, pipe_handle)
File "C:\Users\adrian\AppData\Local\Programs\Python\Python37\lib\multiprocessing\reduction.py", line 82, in steal_handle
_winapi.PROCESS_DUP_HANDLE, False, source_pid)
OSError: [WinError 87] The parameter is incorrect
我希望有一種方法可以使此代碼適用於 Windows。 這是 Linux 和 Windows 上可用的不同啟動方法的鏈接: https : //docs.python.org/3/library/multiprocessing.html#contexts-and-start-methods
import multiprocessing as mp
def test():
manager = mp.Manager()
asyncPlotter = AsyncPlotter(manager.Value('i', 0))
asyncPlotter.saveLinePlotVec3("test")
asyncPlotter.saveLinePlotVec3("test")
asyncPlotter.join()
class AsyncPlotter():
def __init__(self, nc, processes=mp.cpu_count()):
self.nc = nc
self.pids = []
self.processes = processes
def linePlotVec3(self, nc, processes, test):
self.waitOnPool(nc, processes)
print(test)
nc.value -= 1
def waitOnPool(self, nc, processes):
while nc.value >= processes:
time.sleep(0.1)
nc.value += 1
def process(self, target, args):
ctx = mp.get_context('spawn')
p = ctx.Process(target=target, args=args)
p.start()
self.pids.append(p)
def saveLinePlotVec3(self, test):
self.process(target=self.linePlotVec3,
args=(self.nc, self.processes, test))
def join(self):
for p in self.pids:
p.join()
if __name__=='__main__':
test()
使用spawn
start 方法時, Process
對象本身被腌制以供子進程使用。 在您的代碼中, target=target
參數是AsyncPlotter
的綁定方法。 看起來整個asyncPlotter
實例也必須被腌制才能工作,其中包括self.manager
,它顯然不想被腌制。
簡而言之,將Manager
放在AsyncPlotter
之外。 這適用於我的 macOS 系統:
def test():
manager = mp.Manager()
asyncPlotter = AsyncPlotter(manager.Value('i', 0))
...
此外,如您的評論中所述, asyncPlotter
在重用時不起作用。 我不知道細節,但看起來它與Value
對象如何跨進程共享有關。 test
功能需要像:
def test():
manager = mp.Manager()
nc = manager.Value('i', 0)
asyncPlotter1 = AsyncPlotter(nc)
asyncPlotter1.saveLinePlotVec3("test 1")
asyncPlotter2 = AsyncPlotter(nc)
asyncPlotter2.saveLinePlotVec3("test 2")
asyncPlotter1.join()
asyncPlotter2.join()
總而言之,您可能希望重構代碼並使用進程池。 它已經通過cpu_count
和並行執行處理了AsyncPlotter
正在做的事情:
from multiprocessing import Pool, set_start_method
from random import random
import time
def linePlotVec3(test):
time.sleep(random())
print("test", test)
if __name__ == "__main__":
set_start_method("spawn")
with Pool() as pool:
pool.map(linePlotVec3, range(20))
或者您可以使用ProcessPoolExecutor
來做幾乎相同的事情。 此示例一次啟動一項任務,而不是映射到列表:
from concurrent.futures import ProcessPoolExecutor
import multiprocessing as mp
import time
from random import random
def work(i):
r = random()
print("work", i, r)
time.sleep(r)
def main():
ctx = mp.get_context("spawn")
with ProcessPoolExecutor(mp_context=ctx) as pool:
for i in range(20):
pool.submit(work, i)
if __name__ == "__main__":
main()
為了可移植性,作為參數傳遞給將在進程中運行的函數的所有對象都必須是可picklable的。
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