Interface to Unix utility functions
val wrap_block_signals : (unit ‑> 'a) ‑> 'awrap_block_signals f blocks all signals before execution of f, and
restores them afterwards.
val get_ppids : Core.Pid.t ‑> Core.Pid.t list optionget_ppids pid returns the list of parent pids, up to init (1) for pid.