register_at_fork

Register callables to be called when forking a new process.

  before
    A callable to be called in the parent before the fork() syscall.
  after_in_child
    A callable to be called in the child after fork().
  after_in_parent
    A callable to be called in the parent after fork().

'before' callbacks are called in reverse order.
'after_in_child' and 'after_in_parent' callbacks are called in order.