我有一个应用程序,它使用grequests和multiprocessing.managers来组合IPC通信和HTTP上的异步RESTful通信.

似乎grequests在使用gevent.monkey的patch_all()方法时,会破坏multiprocessing.manager.SyncManager类及其派生类使用的multiprocessing.connection模块.

这显然不是一个孤立的问题,但会影响任何实现multiprocessing.connetion的用例,例如multiprocessing.pool.

深入研究gevent / monkey.py中的代码,我发现使用gevent.socket交换stdlib套接字模块是导致破坏的原因.
这可以在patch_socket()函数下的gevent / monkey.py中的第115行找到：

def patch_socket(dns=True, aggressive=True):
    """Replace the standard socket object with gevent's cooperative sockets.
    ...
    _socket.socket = socket.socket # This line breaks multiprocessing.connection!
    ...

我的问题是为什么这个swappage会破坏multiprocessing.connection,以及使用gevent.socket而不是stdlib的套接字模块会带来什么好处呢？也就是说,如果没有修补套接字模块,会产生什么性能损失？

追溯

Traceback (most recent call last):
  File "clientWithGeventMonkeyPatch.py", line 49, in <module>
    client = GetClient(host, port, authkey)
  File "clientWithGeventMonkeyPatch.py", line 39, in GetClient
    client.connect()
  File "/usr/lib/python2.7/multiprocessing/managers.py", line 500, in connect
    conn = Client(self._address, authkey=self._authkey)
  File "/usr/lib/python2.7/multiprocessing/connection.py", line 175, in Client
    answer_challenge(c, authkey)
  File "/usr/lib/python2.7/multiprocessing/connection.py", line 414, in answer_challenge
    response = connection.recv_bytes(256)        # reject large message
IOError: [Errno 11] Resource temporarily unavailable

用于重现错误的代码

(在ubuntu服务器11.10,python2.7.3上,安装了gevent,greenlet和grequests)

manager.py

## manager.py
import multiprocessing
import multiprocessing.managers
import datetime


class LocalManager(multiprocessing.managers.SyncManager):
    def __init__(self, *args, **kwargs):
        multiprocessing.managers.SyncManager.__init__(self, *args, **kwargs)
        self.__type__ = 'LocalManager'

def GetManager(host, port, authkey):
    def getdatetime():
        return '{}'.format(datetime.datetime.now())

    LocalManager.register('getdatetime', callable = getdatetime)
    manager = LocalManager(address = (host, port), authkey = authkey)
    manager.start()

    return manager

if __name__ == '__main__':
    # define our manager connection parameters
    port = 55555
    host = 'localhost'
    authkey = 'auth1234'

    # start a manager
    man = GetManager(host, port, authkey)

    # wait for user input to shut down
    raw_input('return to shutdown')
    man.shutdown()

client.py

## client.py -- this one works
import time
import multiprocessing.managers

class RemoteClient(multiprocessing.managers.SyncManager):
    def __init__(self, *args, **kwargs):
        multiprocessing.managers.SyncManager.__init__(self, *args, **kwargs)
        self.__type__ = 'RemoteClient'

def GetClient(host, port, authkey):
    RemoteClient.register('getdatetime')
    client = RemoteClient(address = (host, port), authkey = authkey)
    client.connect()
    return client

if __name__ == '__main__':
    # define our client connection parameters
    port = 55555
    host = 'localhost'
    authkey = 'auth1234'

    # start a manager
    client = GetClient(host, port, authkey)
    print 'connected', client
    print 'client.getdatetime()', client.getdatetime()
    # wait a couple of seconds, then do it again
    time.sleep(2)
    print 'client.getdatetime()', client.getdatetime()

    # exit...

clientWithGeventMonkeyPatch.py

## clientWithGeventMonkeyPatch.py -- breaks, depending on patch_all() parameters        
import time
import multiprocessing.managers


# this part is copied from grequests
# bear in mind that it doesn't actually do anything in this module.
try:
    import gevent
    from gevent import monkey as curious_george
    from gevent.pool import Pool
except ImportError:
    raise RuntimeError('Gevent is required for grequests.')

# this line causes breakage of the multiprocessing.manager connection auth method:
# Monkey-patch. 
# patch_all() parameters with default values:  socket=True, dns=True, time=True, select=True, thread=True, os=True, ssl=True, aggressive=True

curious_george.patch_all(thread=False, select=False) # breaks
#~ curious_george.patch_all(thread=False, select=False, socket = False) # works!
#~ curious_george.patch_all(thread=False, select=False, socket = True, aggressive = True, dns = True) # same as (thread=False, select=False); breaks
#~ curious_george.patch_all(thread=False, select=False, socket = True, aggressive = True, dns = False) # breaks
#~ curious_george.patch_all(thread=False, select=False, socket = True, aggressive = False, dns = True) # breaks
#~ curious_george.patch_all(thread=False, select=False, socket = True, aggressive = False, dns = False) # breaks







class RemoteClient(multiprocessing.managers.SyncManager):
    def __init__(self, *args, **kwargs):
        multiprocessing.managers.SyncManager.__init__(self, *args, **kwargs)
        self.__type__ = 'RemoteClient'

def GetClient(host, port, authkey):
    RemoteClient.register('getdatetime')
    client = RemoteClient(address = (host, port), authkey = authkey)
    client.connect()
    return client

if __name__ == '__main__':
    # define our client connection parameters
    port = 55555
    host = 'localhost'
    authkey = 'auth1234'

    # start a manager
    client = GetClient(host, port, authkey)
    print 'connected', client
    print 'client.getdatetime()', client.getdatetime()
    # wait a couple of seconds, then do it again
    time.sleep(2)
    print 'client.getdatetime()', client.getdatetime()

    # exit...

解决方法:

如果不修补套接字模块,gevent不能阻止网络操作的能力将无法使用,因此首先使用gevent的大部分好处将无法使用.

gevent和多处理并不是真的可以很好地相互配合 – gevent主要假设你通过它进行网络连接,而不是绕过*别的Python套接字接口(多处理工作).