如何在 Python 中使用 Managers() 在多个进程之间共享字符串?

2022-01-12 00:00:00 python multiprocessing shared-memory shared-state

问题描述

我需要从主进程中读取由 multiprocessing.Process 实例编写的字符串.我已经使用管理器和队列将参数传递给进程，所以使用管理器似乎很明显，但是Managers不支持字符串:

I need to read strings written by multiprocessing.Process instances from the main process. I already use Managers and queues to pass arguments to processes, so using the Managers seems obvious, but Managers do not support strings:

Manager() 返回的管理器将支持类型列表、字典、命名空间、锁、RLock、信号量、有界信号量、条件、事件、队列、值和数组.

A manager returned by Manager() will support types list, dict, Namespace, Lock, RLock, Semaphore, BoundedSemaphore, Condition, Event, Queue, Value and Array.

如何使用多处理模块中的管理器共享由字符串表示的状态?

How do I share state represented by a string using Managers from the multiprocessing module?

解决方案

multiprocessing的Managers可以持有Values 又可以包含 c_char_p 来自 ctypes 模块:

multiprocessing's Managers can hold Values which in turn can hold instances of the type c_char_p from the ctypes module:

>>> import multiprocessing
>>> import ctypes
>>> v = multiprocessing.Value('c', "Hello, World!")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/multiprocessing/__init__.py", line 253, in Value
    return Value(typecode_or_type, *args, **kwds)
  File "/usr/lib/python2.7/multiprocessing/sharedctypes.py", line 99, in Value
    obj = RawValue(typecode_or_type, *args)
  File "/usr/lib/python2.7/multiprocessing/sharedctypes.py", line 73, in RawValue
    obj.__init__(*args)
TypeError: one character string expected
>>> cstring = multiprocessing.Value(ctypes.c_char_p, "Hello, World!")
>>> cstring
<Synchronized wrapper for c_char_p(166841564)>
>>> cstring.value
'Hello, World!'

对于 Python 3， 使用 c_wchar_p 代替 c_char_p

For Python 3, use c_wchar_p instead of c_char_p

另请参阅:发布我很难找到的原始解决方案.

因此，可以使用 Manager 在 Python 中的多个进程下共享字符串，如下所示:

So a Manager can be used to share a string beneath multiple processes in Python like this:

>>> from multiprocessing import Process, Manager, Value
>>> from ctypes import c_char_p
>>> 
>>> def greet(string):
>>>     string.value = string.value + ", World!"
>>> 
>>> if __name__ == '__main__':
>>>     manager = Manager()
>>>     string = manager.Value(c_char_p, "Hello")
>>>     process = Process(target=greet, args=(string,))
>>>     process.start()
>>>     process.join()    
>>>     print string.value
'Hello, World!'

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