_multiprocessing.Connection() allows to use any positive (or nul) 
number has socket handle. If you use an invalid file descriptor, 
poll() method may crash (especially for big positive integer). 
Example:

>>> import _multiprocessing
>>> obj = _multiprocessing.Connection(44977608)
>>> obj.poll()
Erreur de segmentation (core dumped)

Fix: use fstat() to make sure that the handle is valid. Attached patch 
implements this feature.

Another solution would be to reuse code from Modules/selectmodule.c.