I've been working on this same problem myself lately, and think I've found a work-around that looks like it works although I've not yet had time to try it.

The kill function can be used to check if a given process ID is available to receive signals (With some limitations on OS, see the perlport docs for details), so the way I'm planning on checking for a parent process' death is something like:

if (getppid==1 or !kill (0, getppid)) {
  # Parent is dead, long live the child!
} else {
  # Parent still alive.
}
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As I've said I've not had time to actually try this myself yet, but it's looking to be along the right lines and replace the Proc::ProcessTable hack I'm currently using for the job. Let me know if it does work for you.