I have recently begun using multiprocessing for a variety of batch
jobs.  It's a great library, and it's been quite useful.  However, I have been bitten several times by situations where a worker process in a Pool will unexpectedly die, leaving multiprocessing hanging in a wait.  A simple example of this is produced by the following:
"""
#!/usr/bin/env python
import multiprocessing, sys
def foo(x):
  sys.exit(1)
multiprocessing.Pool(1).apply(foo, [1])
"""
The child will exit and the parent will hang forever.  A similar occurrence happens if one pushes C-c while a child process is running (this special case is noted in http://bugs.python.org/issue8296) or killed by a signal.

Attached is a patch to handle unexpected terminations of children
processes and prevent the parent process from hanging.  A test case is included.  (Developed and tested on 64-bit Ubuntu.)  Please let me know what you think.  Thanks!