pyserial与多处理给我一个ctype错误

Question

嗨，我正在尝试编写一个模块，该模块可以让我通过读取和发送数据pyserial。我必须能够并行读取主脚本中的数据。随着计算器用户的帮助下，我有一个基本的和工作框架方案，但是当我尝试添加一个类我创建了一个使用pyserial（句柄找到端口，速度等），发现在这里我得到以下错误：

File "<ipython-input-1-830fa23bc600>", line 1, in <module>
    runfile('C:.../pythonInterface1/Main.py', wdir='C:/Users/Daniel.000/Desktop/Daniel/Python/pythonInterface1')

  File "C:...\Anaconda3\lib\site-packages\spyder_kernels\customize\spydercustomize.py", line 827, in runfile
    execfile(filename, namespace)

  File "C:...\Anaconda3\lib\site-packages\spyder_kernels\customize\spydercustomize.py", line 110, in execfile
    exec(compile(f.read(), filename, 'exec'), namespace)

  File "C:/Users/Daniel.000/Desktop/Daniel/Python/pythonInterface1/Main.py", line 39, in <module>
    p.start()

  File "C:...\Anaconda3\lib\multiprocessing\process.py", line 112, in start
    self._popen = self._Popen(self)

  File "C:...\Anaconda3\lib\multiprocessing\context.py", line 223, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)

  File "C:...\Anaconda3\lib\multiprocessing\context.py", line 322, in _Popen
    return Popen(process_obj)

  File "C:...\Anaconda3\lib\multiprocessing\popen_spawn_win32.py", line 89, in __init__
    reduction.dump(process_obj, to_child)

  File "C:...\Anaconda3\lib\multiprocessing\reduction.py", line 60, in dump
    ForkingPickler(file, protocol).dump(obj)

ValueError: ctypes objects containing pointers cannot be pickled

这是我用来调用该类的代码 SerialConnection.py

import multiprocessing 
from time import sleep
from operator import methodcaller

from SerialConnection import SerialConnection as SC

class Spawn:
    def __init__(self, _number, _max):
        self._number = _number
        self._max = _max
        # Don't call update here

    def request(self, x):
        print("{} was requested.".format(x))

    def update(self):
        while True:
            print("Spawned {} of {}".format(self._number, self._max))
            sleep(2)

if __name__ == '__main__':
    '''
    spawn = Spawn(1, 1)  # Create the object as normal
    p = multiprocessing.Process(target=methodcaller("update"), args=(spawn,)) # Run the loop in the process
    p.start()
    while True:
        sleep(1.5)
        spawn.request(2)  # Now you can reference the "spawn"
    '''
    device = SC()
    print(device.Port)
    print(device.Baud)
    print(device.ID)
    print(device.Error)
    print(device.EMsg)
    p = multiprocessing.Process(target=methodcaller("ReadData"), args=(device,)) # Run the loop in the process
    p.start()
    while True:
        sleep(1.5)
        device.SendData('0003')

我这堂课给我带来了问题，我做错了什么？是否有某种形式的限制才能pyserial一起使用和多处理？我知道可以做到，但是我不知道该怎么做...

这是我从python得到的回溯

Traceback (most recent call last):   File "C:...\Python\pythonInterface1\Main.py", line 45, in <module>
    p.start()

  File "C:...\AppData\Local\Programs\Python\Python36-32\lib\multiprocessing\process.py", line 105, in start
    self._popen = self._Popen(self)

  File "C:...\AppData\Local\Programs\Python\Python36-32\lib\multiprocessing\context.py", line 223, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)

  File "C:...\AppData\Local\Programs\Python\Python36-32\lib\multiprocessing\context.py", line 322, in _Popen
    return Popen(process_obj)

  File "C:...\AppData\Local\Programs\Python\Python36-32\lib\multiprocessing\popen_spawn_win32.py", line 65, in __init__
    reduction.dump(process_obj, to_child)

  File "C:...\AppData\Local\Programs\Python\Python36-32\lib\multiprocessing\reduction.py", line 60, in dump
    ForkingPickler(file, protocol).dump(obj) ValueError: ctypes objects containing pointers cannot be pickled

Answer 1

您正在尝试将SerialConnection实例作为参数传递给另一个进程。因为Python首先要序列化（pickle）对象，而SerialConnection对象是不可能的。

正如Rob Streeting 的回答中所述，一个可能的解决方案是允许SerialConnection使用调用时发生的 fork 将对象复制到其他进程的内存multiprocessing.Process.start，但这在 Windows 上不起作用，因为它不使用 fork。

在代码中实现并行性的一种更简单、跨平台且更有效的方法是使用线程而不是进程。对代码的更改很小：

import threading
p = threading.Thread(target=methodcaller("ReadData"), args=(device,))