Introduce the non-daemon process pool as an alternative to the original multiprocessing pool. This adds support for hierarchical multiprocessing (child classes can use multiprocessing again).

The code is based on the following StackOverflow answer:
http://stackoverflow.com/a/8963618/1183453

Author: Daniel Haehn

nipype/pipeline/plugins/multiproc.py

@@ -1,9 +1,13 @@
 # emacs: -*- mode: python; py-indent-offset: 4; indent-tabs-mode: nil -*-
 # vi: set ft=python sts=4 ts=4 sw=4 et:
 """Parallel workflow execution via multiprocessing
+
+Support for child processes running as non-daemons based on
+http://stackoverflow.com/a/8963618/1183453
 """
 
-from multiprocessing import Pool
+from multiprocessing import Process
+from multiprocessing.pool import Pool
 from traceback import format_exception
 import sys
 
@@ -19,6 +23,20 @@ def run_node(node, updatehash):
         result['result'] = node.result
     return result
 
+class NonDaemonProcess(Process):
+    """A non-daemon process to support internal multiprocessing.
+    """
+    def _get_daemon(self):
+        return False
+    def _set_daemon(self, value):
+        pass
+    daemon = property(_get_daemon, _set_daemon)
+
+class NonDaemonPool(Pool):
+    """A process pool with non-daemon processes.
+    """
+    Process = NonDaemonProcess
+
 class MultiProcPlugin(DistributedPluginBase):
     """Execute workflow with multiprocessing