Python:如何传递 Autoproxy 对象

Question

我需要将一个对象的代理传递给另一个对象，但每当我这样做时，所有其他对象获取的都是代理的指示对象，而不是代理本身。这与我想做的事情类似:

import multiprocessing.managers as m

class Foo(object):

    def __init__(self):
        self.manager = MyManager()
        self.manager.register('Bar', Bar)
        self.manager.start()
        self.bar = self.manager.Bar()
        self.bar.set_proxy(self.bar)


class Bar(object):

    def __init__(self):
        self.proxy = None

    def set_proxy(self, proxy):
        self.proxy = proxy

class MyManager(m.BaseManager):
    pass

test = Foo()

每当我执行此操作时，self.proxy 中的值都是我创建的 Foo 实例，而不是管理器返回的代理。

Answer 1

这是因为设计缺陷，或者可能是 a bug ，以 Proxy 实例被 unpickled 的方式。现在，如果 unpickle 代码看到您正在 Manager 内运行，它会在您 unpickle 时为您提供指示对象，而不是 Proxy:

def RebuildProxy(func, token, serializer, kwds):
    '''
    Function used for unpickling proxy objects.

    If possible the shared object is returned, or otherwise a proxy for it.
    '''
    server = getattr(process.current_process(), '_manager_server', None)

    if server and server.address == token.address:
        return server.id_to_obj[token.id][0] # This returns the referent
    else:
        incref = (
            kwds.pop('incref', True) and
            not getattr(process.current_process(), '_inheriting', False)
            )
        return func(token, serializer, incref=incref, **kwds) # This returns the Proxy

有时这可能是可取的，但有时却不是，就像您的情况一样。您可以通过替换在程序中执行 unpickle 操作的 ReduceProxy 函数来解决此问题:

import multiprocessing.managers as m
from multiprocessing import process

def RebuildProxyNoReferent(func, token, serializer, kwds):
    '''
    Function used for unpickling proxy objects.

    The Proxy object is always returned.
    '''
    incref = (
    kwds.pop('incref', True) and
    not getattr(process.current_process(), '_inheriting', False)
    )
    return func(token, serializer, incref=incref, **kwds)

m.RebuildProxy = RebuildProxyNoReferent  # Monkey-patch it

class Foo(object):

    def __init__(self):
        self.manager = MyManager()
        self.manager.register('Bar', Bar)
        self.manager.start()
        self.bar = self.manager.Bar()
        print(type(self.bar))
        self.bar.set_proxy(self.bar)


class Bar(object):

    def __init__(self):
        self.proxy = None

    def set_proxy(self, proxy):
        print("got {}".format(type(proxy)))
        self.proxy = proxy

class MyManager(m.BaseManager):
    pass

test = Foo()

如果你不想打猴子补丁，你也可以继承BaseProxy，尽管这需要更多的工作:

import multiprocessing.managers as m
from multiprocessing.managers import BaseProxy
from multiprocessing import process

def RebuildProxyNoReferent(func, token, serializer, kwds):
    '''
    Function used for unpickling proxy objects.

    If possible the shared object is returned, or otherwise a proxy for it.
    '''
    incref = (
    kwds.pop('incref', True) and
    not getattr(process.current_process(), '_inheriting', False)
    )
    return func(token, serializer, incref=incref, **kwds)

class MyProxy(BaseProxy):
    _exposed_ = ("set_proxy",)
    def set_proxy(self, arg):
        self._callmethod('set_proxy', (arg,))

    def __reduce__(self):
        ret = super(MyProxy, self).__reduce__()
        # RebuildProxy is the first item in the ret tuple.
        # So lets replace it, just for our proxy.
        ret = (RebuildProxyNoReferent,) + ret[1:]
        return ret

class Foo(object):

    def __init__(self):
        self.manager = MyManager()
        self.manager.register('Bar', Bar, MyProxy)
        self.manager.start()
        self.bar = self.manager.Bar()
        print(type(self.bar))
        self.bar.set_proxy(self.bar)