code: def _RegisterProcess(self, process):
      
      if process is None:
        raise ValueError('Missing process.')
  
      if process.pid in self._processes_per_pid:
        raise KeyError(
            'Already managing process: {0!s} (PID: {1:d})'.format(
                process.name, process.pid))
  
      self._processes_per_pid[process.pid] = process
docs: Registers a process with the engine.
  
      Args:
        process (MultiProcessBaseProcess): process.
  
      Raises:
        KeyError: if the process is already registered with the engine.
        ValueError: if the process is missing.