interrupted system call w/ Queue.get

[Philip Winston]

We have a multiprocess Python program that uses Queue to communicate
between processes.  Recently we've seen some errors while blocked
waiting on Queue.get:

IOError: [Errno 4] Interrupted system call

What causes the exception?  Is it necessary to catch this exception
and manually retry the Queue operation?  Thanks.

We have some Python 2.5 and 2.6 machines that have run this program
for many 1,000 hours with no errors.  But we have one 2.5 machine and
one 2.7 machine that seem to get the error very often.