race/deadlock when creating a multiprocessing.manager instance while importing a module ?

[Sebastien Binet]

hi there,

say I have this module

## farnsworth ##
__all__ = [
    'mgr',
    'maths',
    ]

from multiprocessing.managers import BaseManager

class MathsClass(object):
    def add(self, x, y):
        return x + y
    def mul(self, x, y):
        return x * y

class MyManager(BaseManager):
    pass

MyManager.register('Maths', MathsClass)

def _setup():
    print "creating a manager..."
    mgr = MyManager()
    print "starting the manager..."
    mgr.start()
    print "sciencing faster..."
    maths = mgr.Maths()
    print maths.add(4,3)
    print maths.mul(7,8)
    print "done with sciencing."
    return (mgr, maths)

# exec at module import
mgr, maths = _setup()

# prevent hysteresis + clean-up
del _setup
## EOF ##

if I use it like so:

$ python -m farnsworth
creating a manager...
starting the manager...
sciencing faster...
7
56
done with sciencing.

all is fine, but if I try to use it thru an import:
$ python
py> import farnsworth.mgr as mgr
creating a manager...
starting the manager...
sciencing faster...

[stuck for some time... hitting ^C]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "farnsworth.py", line 32, in <module>
    mgr, maths = _setup()
  File "farnsworth.py", line 25, in _setup
    maths = mgr.Maths()
  File "/usr/lib/python2.6/multiprocessing/managers.py", line 634, in
temp
    token, exp = self._create(typeid, *args, **kwds)
  File "/usr/lib/python2.6/multiprocessing/managers.py", line 532, in
_create
    conn = self._Client(self._address, authkey=self._authkey)
  File "/usr/lib/python2.6/multiprocessing/connection.py", line 140,
in Client
    answer_challenge(c, authkey)
  File "/usr/lib/python2.6/multiprocessing/connection.py", line 372,
in answer_challenge
    message = connection.recv_bytes(256)         # reject large
message
KeyboardInterrupt

is this a known limitation/feature of the multiprocessing module ?
is there a workaround (acquiring some import lock maybe) ?

cheers,
sebastien.

PS:
$ python
Python 2.6.4 (r264:75706, Oct 27 2009, 06:25:13)
[GCC 4.4.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.

$ python -c 'import sys; print sys.version_info'
(2, 6, 4, 'final', 0)

$ uname -a
Linux farnsworth 2.6.31-ARCH #1 SMP PREEMPT Tue Nov 10 19:01:40 CET
2009 x86_64 Intel(R) Core(TM)2 Duo CPU T9400 @ 2.53GHz GenuineIntel
GNU/Linux