I finally got to the bottom of why my script and threads were hanging. This glibc patch fixed the problem. Bug 906468 - Deadlock in glibc between fork and malloc:

https://bugzilla.redhat.com/show_bug.cgi?id=906468

In reply to Re^3: defunct process are WAY beyond my experienc by cristj1
in thread defunct process are WAY beyond my experienc by cristj1

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